diff --git a/OWNERS b/OWNERS
index 0e1e65d..22b5561 100644
--- a/OWNERS
+++ b/OWNERS
@@ -2,5 +2,6 @@
 jchalard@google.com
 junyulai@google.com
 lorenzo@google.com
+maze@google.com
 reminv@google.com
 satk@google.com
diff --git a/Tethering/Android.bp b/Tethering/Android.bp
index 7427481..73175580 100644
--- a/Tethering/Android.bp
+++ b/Tethering/Android.bp
@@ -62,7 +62,10 @@
         "com.android.tethering",
     ],
     min_sdk_version: "30",
-    header_libs: ["bpf_syscall_wrappers"],
+    header_libs: [
+        "bpf_syscall_wrappers",
+        "bpf_tethering_headers",
+    ],
     srcs: [
         "jni/*.cpp",
     ],
diff --git a/Tethering/apishim/30/com/android/networkstack/tethering/apishim/api30/BpfCoordinatorShimImpl.java b/Tethering/apishim/30/com/android/networkstack/tethering/apishim/api30/BpfCoordinatorShimImpl.java
index eafa3ea..4e615a1 100644
--- a/Tethering/apishim/30/com/android/networkstack/tethering/apishim/api30/BpfCoordinatorShimImpl.java
+++ b/Tethering/apishim/30/com/android/networkstack/tethering/apishim/api30/BpfCoordinatorShimImpl.java
@@ -17,6 +17,7 @@
 package com.android.networkstack.tethering.apishim.api30;
 
 import android.net.INetd;
+import android.net.MacAddress;
 import android.net.TetherStatsParcel;
 import android.net.util.SharedLog;
 import android.os.RemoteException;
@@ -28,6 +29,8 @@
 
 import com.android.networkstack.tethering.BpfCoordinator.Dependencies;
 import com.android.networkstack.tethering.BpfCoordinator.Ipv6ForwardingRule;
+import com.android.networkstack.tethering.Tether4Key;
+import com.android.networkstack.tethering.Tether4Value;
 import com.android.networkstack.tethering.TetherStatsValue;
 
 /**
@@ -76,6 +79,17 @@
     }
 
     @Override
+    public boolean startUpstreamIpv6Forwarding(int downstreamIfindex, int upstreamIfindex,
+            MacAddress srcMac, MacAddress dstMac, int mtu) {
+        return true;
+    }
+
+    @Override
+    public boolean stopUpstreamIpv6Forwarding(int downstreamIfindex, int upstreamIfindex) {
+        return true;
+    }
+
+    @Override
     @Nullable
     public SparseArray<TetherStatsValue> tetherOffloadGetStats() {
         final TetherStatsParcel[] tetherStatsList;
@@ -132,6 +146,19 @@
     }
 
     @Override
+    public boolean tetherOffloadRuleAdd(boolean downstream, @NonNull Tether4Key key,
+            @NonNull Tether4Value value) {
+        /* no op */
+        return true;
+    }
+
+    @Override
+    public boolean tetherOffloadRuleRemove(boolean downstream, @NonNull Tether4Key key) {
+        /* no op */
+        return true;
+    }
+
+    @Override
     public String toString() {
         return "Netd used";
     }
diff --git a/Tethering/apishim/31/com/android/networkstack/tethering/apishim/api31/BpfCoordinatorShimImpl.java b/Tethering/apishim/31/com/android/networkstack/tethering/apishim/api31/BpfCoordinatorShimImpl.java
index 4ebf914..4dc1c51 100644
--- a/Tethering/apishim/31/com/android/networkstack/tethering/apishim/api31/BpfCoordinatorShimImpl.java
+++ b/Tethering/apishim/31/com/android/networkstack/tethering/apishim/api31/BpfCoordinatorShimImpl.java
@@ -18,6 +18,7 @@
 
 import static android.net.netstats.provider.NetworkStatsProvider.QUOTA_UNLIMITED;
 
+import android.net.MacAddress;
 import android.net.util.SharedLog;
 import android.system.ErrnoException;
 import android.system.Os;
@@ -30,12 +31,15 @@
 import com.android.networkstack.tethering.BpfCoordinator.Dependencies;
 import com.android.networkstack.tethering.BpfCoordinator.Ipv6ForwardingRule;
 import com.android.networkstack.tethering.BpfMap;
-import com.android.networkstack.tethering.TetherIngressKey;
-import com.android.networkstack.tethering.TetherIngressValue;
+import com.android.networkstack.tethering.Tether4Key;
+import com.android.networkstack.tethering.Tether4Value;
+import com.android.networkstack.tethering.Tether6Value;
+import com.android.networkstack.tethering.TetherDownstream6Key;
 import com.android.networkstack.tethering.TetherLimitKey;
 import com.android.networkstack.tethering.TetherLimitValue;
 import com.android.networkstack.tethering.TetherStatsKey;
 import com.android.networkstack.tethering.TetherStatsValue;
+import com.android.networkstack.tethering.TetherUpstream6Key;
 
 import java.io.FileDescriptor;
 
@@ -54,10 +58,21 @@
     @NonNull
     private final SharedLog mLog;
 
-    // BPF map of ingress queueing discipline which pre-processes the packets by the IPv6
-    // forwarding rules.
+    // BPF map for downstream IPv4 forwarding.
     @Nullable
-    private final BpfMap<TetherIngressKey, TetherIngressValue> mBpfIngressMap;
+    private final BpfMap<Tether4Key, Tether4Value> mBpfDownstream4Map;
+
+    // BPF map for upstream IPv4 forwarding.
+    @Nullable
+    private final BpfMap<Tether4Key, Tether4Value> mBpfUpstream4Map;
+
+    // BPF map for downstream IPv6 forwarding.
+    @Nullable
+    private final BpfMap<TetherDownstream6Key, Tether6Value> mBpfDownstream6Map;
+
+    // BPF map for upstream IPv6 forwarding.
+    @Nullable
+    private final BpfMap<TetherUpstream6Key, Tether6Value> mBpfUpstream6Map;
 
     // BPF map of tethering statistics of the upstream interface since tethering startup.
     @Nullable
@@ -69,25 +84,29 @@
 
     public BpfCoordinatorShimImpl(@NonNull final Dependencies deps) {
         mLog = deps.getSharedLog().forSubComponent(TAG);
-        mBpfIngressMap = deps.getBpfIngressMap();
+        mBpfDownstream4Map = deps.getBpfDownstream4Map();
+        mBpfUpstream4Map = deps.getBpfUpstream4Map();
+        mBpfDownstream6Map = deps.getBpfDownstream6Map();
+        mBpfUpstream6Map = deps.getBpfUpstream6Map();
         mBpfStatsMap = deps.getBpfStatsMap();
         mBpfLimitMap = deps.getBpfLimitMap();
     }
 
     @Override
     public boolean isInitialized() {
-        return mBpfIngressMap != null && mBpfStatsMap != null  && mBpfLimitMap != null;
+        return mBpfDownstream4Map != null && mBpfUpstream4Map != null && mBpfDownstream6Map != null
+                && mBpfUpstream6Map != null && mBpfStatsMap != null && mBpfLimitMap != null;
     }
 
     @Override
     public boolean tetherOffloadRuleAdd(@NonNull final Ipv6ForwardingRule rule) {
         if (!isInitialized()) return false;
 
-        final TetherIngressKey key = rule.makeTetherIngressKey();
-        final TetherIngressValue value = rule.makeTetherIngressValue();
+        final TetherDownstream6Key key = rule.makeTetherDownstream6Key();
+        final Tether6Value value = rule.makeTether6Value();
 
         try {
-            mBpfIngressMap.updateEntry(key, value);
+            mBpfDownstream6Map.updateEntry(key, value);
         } catch (ErrnoException e) {
             mLog.e("Could not update entry: ", e);
             return false;
@@ -101,7 +120,7 @@
         if (!isInitialized()) return false;
 
         try {
-            mBpfIngressMap.deleteEntry(rule.makeTetherIngressKey());
+            mBpfDownstream6Map.deleteEntry(rule.makeTetherDownstream6Key());
         } catch (ErrnoException e) {
             // Silent if the rule did not exist.
             if (e.errno != OsConstants.ENOENT) {
@@ -113,6 +132,37 @@
     }
 
     @Override
+    public boolean startUpstreamIpv6Forwarding(int downstreamIfindex, int upstreamIfindex,
+            MacAddress srcMac, MacAddress dstMac, int mtu) {
+        if (!isInitialized()) return false;
+
+        final TetherUpstream6Key key = new TetherUpstream6Key(downstreamIfindex);
+        final Tether6Value value = new Tether6Value(upstreamIfindex, srcMac,
+                dstMac, OsConstants.ETH_P_IPV6, mtu);
+        try {
+            mBpfUpstream6Map.insertEntry(key, value);
+        } catch (ErrnoException | IllegalStateException e) {
+            mLog.e("Could not insert upstream6 entry: " + e);
+            return false;
+        }
+        return true;
+    }
+
+    @Override
+    public boolean stopUpstreamIpv6Forwarding(int downstreamIfindex, int upstreamIfindex) {
+        if (!isInitialized()) return false;
+
+        final TetherUpstream6Key key = new TetherUpstream6Key(downstreamIfindex);
+        try {
+            mBpfUpstream6Map.deleteEntry(key);
+        } catch (ErrnoException e) {
+            mLog.e("Could not delete upstream IPv6 entry: " + e);
+            return false;
+        }
+        return true;
+    }
+
+    @Override
     @Nullable
     public SparseArray<TetherStatsValue> tetherOffloadGetStats() {
         if (!isInitialized()) return null;
@@ -233,14 +283,61 @@
     }
 
     @Override
+    public boolean tetherOffloadRuleAdd(boolean downstream, @NonNull Tether4Key key,
+            @NonNull Tether4Value value) {
+        if (!isInitialized()) return false;
+
+        try {
+            // The last used time field of the value is updated by the bpf program. Adding the same
+            // map pair twice causes the unexpected refresh. Must be fixed before starting the
+            // conntrack timeout extension implementation.
+            // TODO: consider using insertEntry.
+            if (downstream) {
+                mBpfDownstream4Map.updateEntry(key, value);
+            } else {
+                mBpfUpstream4Map.updateEntry(key, value);
+            }
+        } catch (ErrnoException e) {
+            mLog.e("Could not update entry: ", e);
+            return false;
+        }
+        return true;
+    }
+
+    @Override
+    public boolean tetherOffloadRuleRemove(boolean downstream, @NonNull Tether4Key key) {
+        if (!isInitialized()) return false;
+
+        try {
+            if (downstream) {
+                mBpfDownstream4Map.deleteEntry(key);
+            } else {
+                mBpfUpstream4Map.deleteEntry(key);
+            }
+        } catch (ErrnoException e) {
+            // Silent if the rule did not exist.
+            if (e.errno != OsConstants.ENOENT) {
+                mLog.e("Could not delete entry: ", e);
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private String mapStatus(BpfMap m, String name) {
+        return name + "{" + (m != null ? "OK" : "ERROR") + "}";
+    }
+
+    @Override
     public String toString() {
-        return "mBpfIngressMap{"
-                + (mBpfIngressMap != null ? "initialized" : "not initialized") + "}, "
-                + "mBpfStatsMap{"
-                + (mBpfStatsMap != null ? "initialized" : "not initialized") + "}, "
-                + "mBpfLimitMap{"
-                + (mBpfLimitMap != null ? "initialized" : "not initialized") + "} "
-                + "}";
+        return String.join(", ", new String[] {
+                mapStatus(mBpfDownstream6Map, "mBpfDownstream6Map"),
+                mapStatus(mBpfUpstream6Map, "mBpfUpstream6Map"),
+                mapStatus(mBpfDownstream4Map, "mBpfDownstream4Map"),
+                mapStatus(mBpfUpstream4Map, "mBpfUpstream4Map"),
+                mapStatus(mBpfStatsMap, "mBpfStatsMap"),
+                mapStatus(mBpfLimitMap, "mBpfLimitMap")
+        });
     }
 
     /**
diff --git a/Tethering/apishim/common/com/android/networkstack/tethering/apishim/common/BpfCoordinatorShim.java b/Tethering/apishim/common/com/android/networkstack/tethering/apishim/common/BpfCoordinatorShim.java
index 61abfa3..c61c449 100644
--- a/Tethering/apishim/common/com/android/networkstack/tethering/apishim/common/BpfCoordinatorShim.java
+++ b/Tethering/apishim/common/com/android/networkstack/tethering/apishim/common/BpfCoordinatorShim.java
@@ -16,6 +16,7 @@
 
 package com.android.networkstack.tethering.apishim.common;
 
+import android.net.MacAddress;
 import android.util.SparseArray;
 
 import androidx.annotation.NonNull;
@@ -23,6 +24,8 @@
 
 import com.android.networkstack.tethering.BpfCoordinator.Dependencies;
 import com.android.networkstack.tethering.BpfCoordinator.Ipv6ForwardingRule;
+import com.android.networkstack.tethering.Tether4Key;
+import com.android.networkstack.tethering.Tether4Value;
 import com.android.networkstack.tethering.TetherStatsValue;
 
 /**
@@ -71,6 +74,27 @@
     public abstract boolean tetherOffloadRuleRemove(@NonNull Ipv6ForwardingRule rule);
 
     /**
+     * Starts IPv6 forwarding between the specified interfaces.
+
+     * @param downstreamIfindex the downstream interface index
+     * @param upstreamIfindex the upstream interface index
+     * @param srcMac the source MAC address to use for packets
+     * @oaram dstMac the destination MAC address to use for packets
+     * @return true if operation succeeded or was a no-op, false otherwise
+     */
+    public abstract boolean startUpstreamIpv6Forwarding(int downstreamIfindex, int upstreamIfindex,
+            MacAddress srcMac, MacAddress dstMac, int mtu);
+
+    /**
+     * Stops IPv6 forwarding between the specified interfaces.
+
+     * @param downstreamIfindex the downstream interface index
+     * @param upstreamIfindex the upstream interface index
+     * @return true if operation succeeded or was a no-op, false otherwise
+     */
+    public abstract boolean stopUpstreamIpv6Forwarding(int downstreamIfindex, int upstreamIfindex);
+
+    /**
      * Return BPF tethering offload statistics.
      *
      * @return an array of TetherStatsValue's, where each entry contains the upstream interface
@@ -108,5 +132,16 @@
      */
     @Nullable
     public abstract TetherStatsValue tetherOffloadGetAndClearStats(int ifIndex);
+
+    /**
+     * Adds a tethering IPv4 offload rule to appropriate BPF map.
+     */
+    public abstract boolean tetherOffloadRuleAdd(boolean downstream, @NonNull Tether4Key key,
+            @NonNull Tether4Value value);
+
+    /**
+     * Deletes a tethering IPv4 offload rule from the appropriate BPF map.
+     */
+    public abstract boolean tetherOffloadRuleRemove(boolean downstream, @NonNull Tether4Key key);
 }
 
diff --git a/Tethering/bpf_progs/Android.bp b/Tethering/bpf_progs/Android.bp
index d62e9a1..b06528b 100644
--- a/Tethering/bpf_progs/Android.bp
+++ b/Tethering/bpf_progs/Android.bp
@@ -15,6 +15,26 @@
 //
 
 //
+// struct definitions shared with JNI
+//
+cc_library_headers {
+    name: "bpf_tethering_headers",
+    vendor_available: false,
+    host_supported: false,
+    export_include_dirs: ["."],
+    cflags: [
+        "-Wall",
+        "-Werror",
+    ],
+    sdk_version: "30",
+    min_sdk_version: "30",
+    apex_available: ["com.android.tethering"],
+    visibility: [
+        "//packages/modules/Connectivity/Tethering",
+    ],
+}
+
+//
 // bpf kernel programs
 //
 bpf {
diff --git a/Tethering/bpf_progs/bpf_tethering.h b/Tethering/bpf_progs/bpf_tethering.h
new file mode 100644
index 0000000..10e6bb0
--- /dev/null
+++ b/Tethering/bpf_progs/bpf_tethering.h
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+// Common definitions for BPF code in the tethering mainline module.
+// These definitions are available to:
+// - The BPF programs in Tethering/bpf_progs/
+// - JNI code that depends on the bpf_tethering_headers library.
+
+#define BPF_TETHER_ERRORS    \
+    ERR(INVALID_IP_VERSION)  \
+    ERR(LOW_TTL)             \
+    ERR(INVALID_TCP_HEADER)  \
+    ERR(TCP_CONTROL_PACKET)  \
+    ERR(NON_GLOBAL_SRC)      \
+    ERR(NON_GLOBAL_DST)      \
+    ERR(LOCAL_SRC_DST)       \
+    ERR(NO_STATS_ENTRY)      \
+    ERR(NO_LIMIT_ENTRY)      \
+    ERR(BELOW_IPV4_MTU)      \
+    ERR(BELOW_IPV6_MTU)      \
+    ERR(LIMIT_REACHED)       \
+    ERR(CHANGE_HEAD_FAILED)  \
+    ERR(TOO_SHORT)           \
+    ERR(HAS_IP_OPTIONS)      \
+    ERR(IS_IP_FRAG)          \
+    ERR(CHECKSUM)            \
+    ERR(NON_TCP_UDP)         \
+    ERR(NON_TCP)             \
+    ERR(SHORT_TCP_HEADER)    \
+    ERR(SHORT_UDP_HEADER)    \
+    ERR(TRUNCATED_IPV4)      \
+    ERR(_MAX)
+
+#define ERR(x) BPF_TETHER_ERR_ ##x,
+enum {
+    BPF_TETHER_ERRORS
+};
+#undef ERR
+
+#define ERR(x) #x,
+static const char *bpf_tether_errors[] = {
+    BPF_TETHER_ERRORS
+};
+#undef ERR
diff --git a/Tethering/bpf_progs/offload.c b/Tethering/bpf_progs/offload.c
index cc5af31..d4b5246 100644
--- a/Tethering/bpf_progs/offload.c
+++ b/Tethering/bpf_progs/offload.c
@@ -20,27 +20,98 @@
 #include <linux/pkt_cls.h>
 #include <linux/tcp.h>
 
+// bionic kernel uapi linux/udp.h header is munged...
+#define __kernel_udphdr udphdr
+#include <linux/udp.h>
+
 #include "bpf_helpers.h"
 #include "bpf_net_helpers.h"
+#include "bpf_tethering.h"
 #include "netdbpf/bpf_shared.h"
 
-DEFINE_BPF_MAP_GRW(tether_ingress_map, HASH, TetherIngressKey, TetherIngressValue, 64,
-                   AID_NETWORK_STACK)
+// From kernel:include/net/ip.h
+#define IP_DF 0x4000  // Flag: "Don't Fragment"
+
+// ----- Helper functions for offsets to fields -----
+
+// They all assume simple IP packets:
+//   - no VLAN ethernet tags
+//   - no IPv4 options (see IPV4_HLEN/TCP4_OFFSET/UDP4_OFFSET)
+//   - no IPv6 extension headers
+//   - no TCP options (see TCP_HLEN)
+
+//#define ETH_HLEN sizeof(struct ethhdr)
+#define IP4_HLEN sizeof(struct iphdr)
+#define IP6_HLEN sizeof(struct ipv6hdr)
+#define TCP_HLEN sizeof(struct tcphdr)
+#define UDP_HLEN sizeof(struct udphdr)
+
+// Offsets from beginning of L4 (TCP/UDP) header
+#define TCP_OFFSET(field) offsetof(struct tcphdr, field)
+#define UDP_OFFSET(field) offsetof(struct udphdr, field)
+
+// Offsets from beginning of L3 (IPv4) header
+#define IP4_OFFSET(field) offsetof(struct iphdr, field)
+#define IP4_TCP_OFFSET(field) (IP4_HLEN + TCP_OFFSET(field))
+#define IP4_UDP_OFFSET(field) (IP4_HLEN + UDP_OFFSET(field))
+
+// Offsets from beginning of L3 (IPv6) header
+#define IP6_OFFSET(field) offsetof(struct ipv6hdr, field)
+#define IP6_TCP_OFFSET(field) (IP6_HLEN + TCP_OFFSET(field))
+#define IP6_UDP_OFFSET(field) (IP6_HLEN + UDP_OFFSET(field))
+
+// Offsets from beginning of L2 (ie. Ethernet) header (which must be present)
+#define ETH_IP4_OFFSET(field) (ETH_HLEN + IP4_OFFSET(field))
+#define ETH_IP4_TCP_OFFSET(field) (ETH_HLEN + IP4_TCP_OFFSET(field))
+#define ETH_IP4_UDP_OFFSET(field) (ETH_HLEN + IP4_UDP_OFFSET(field))
+#define ETH_IP6_OFFSET(field) (ETH_HLEN + IP6_OFFSET(field))
+#define ETH_IP6_TCP_OFFSET(field) (ETH_HLEN + IP6_TCP_OFFSET(field))
+#define ETH_IP6_UDP_OFFSET(field) (ETH_HLEN + IP6_UDP_OFFSET(field))
+
+// ----- Tethering stats and data limits -----
 
 // Tethering stats, indexed by upstream interface.
-DEFINE_BPF_MAP_GRW(tether_stats_map, HASH, uint32_t, TetherStatsValue, 16, AID_NETWORK_STACK)
+DEFINE_BPF_MAP_GRW(tether_stats_map, HASH, TetherStatsKey, TetherStatsValue, 16, AID_NETWORK_STACK)
 
 // Tethering data limit, indexed by upstream interface.
 // (tethering allowed when stats[iif].rxBytes + stats[iif].txBytes < limit[iif])
-DEFINE_BPF_MAP_GRW(tether_limit_map, HASH, uint32_t, uint64_t, 16, AID_NETWORK_STACK)
+DEFINE_BPF_MAP_GRW(tether_limit_map, HASH, TetherLimitKey, TetherLimitValue, 16, AID_NETWORK_STACK)
 
-static inline __always_inline int do_forward(struct __sk_buff* skb, bool is_ethernet) {
-    int l2_header_size = is_ethernet ? sizeof(struct ethhdr) : 0;
+// ----- IPv6 Support -----
+
+DEFINE_BPF_MAP_GRW(tether_downstream6_map, HASH, TetherDownstream6Key, Tether6Value, 64,
+                   AID_NETWORK_STACK)
+
+DEFINE_BPF_MAP_GRW(tether_downstream64_map, HASH, TetherDownstream64Key, TetherDownstream64Value,
+                   64, AID_NETWORK_STACK)
+
+DEFINE_BPF_MAP_GRW(tether_upstream6_map, HASH, TetherUpstream6Key, Tether6Value, 64,
+                   AID_NETWORK_STACK)
+
+DEFINE_BPF_MAP_GRW(tether_error_map, ARRAY, __u32, __u32, BPF_TETHER_ERR__MAX,
+                   AID_NETWORK_STACK)
+
+#define COUNT_AND_RETURN(counter, ret) do {                    \
+    __u32 code = BPF_TETHER_ERR_ ## counter;                 \
+    __u32 *count = bpf_tether_error_map_lookup_elem(&code);  \
+    if (count) __sync_fetch_and_add(count, 1);               \
+    return ret;                                              \
+} while(0)
+
+#define DROP(counter) COUNT_AND_RETURN(counter, TC_ACT_SHOT)
+#define PUNT(counter) COUNT_AND_RETURN(counter, TC_ACT_OK)
+
+static inline __always_inline int do_forward6(struct __sk_buff* skb, const bool is_ethernet,
+        const bool downstream) {
+    const int l2_header_size = is_ethernet ? sizeof(struct ethhdr) : 0;
     void* data = (void*)(long)skb->data;
     const void* data_end = (void*)(long)skb->data_end;
     struct ethhdr* eth = is_ethernet ? data : NULL;  // used iff is_ethernet
     struct ipv6hdr* ip6 = is_ethernet ? (void*)(eth + 1) : data;
 
+    // Require ethernet dst mac address to be our unicast address.
+    if (is_ethernet && (skb->pkt_type != PACKET_HOST)) return TC_ACT_OK;
+
     // Must be meta-ethernet IPv6 frame
     if (skb->protocol != htons(ETH_P_IPV6)) return TC_ACT_OK;
 
@@ -51,43 +122,70 @@
     if (is_ethernet && (eth->h_proto != htons(ETH_P_IPV6))) return TC_ACT_OK;
 
     // IP version must be 6
-    if (ip6->version != 6) return TC_ACT_OK;
+    if (ip6->version != 6) PUNT(INVALID_IP_VERSION);
 
     // Cannot decrement during forward if already zero or would be zero,
     // Let the kernel's stack handle these cases and generate appropriate ICMP errors.
-    if (ip6->hop_limit <= 1) return TC_ACT_OK;
+    if (ip6->hop_limit <= 1) PUNT(LOW_TTL);
+
+    // If hardware offload is running and programming flows based on conntrack entries,
+    // try not to interfere with it.
+    if (ip6->nexthdr == IPPROTO_TCP) {
+        struct tcphdr* tcph = (void*)(ip6 + 1);
+
+        // Make sure we can get at the tcp header
+        if (data + l2_header_size + sizeof(*ip6) + sizeof(*tcph) > data_end)
+            PUNT(INVALID_TCP_HEADER);
+
+        // Do not offload TCP packets with any one of the SYN/FIN/RST flags
+        if (tcph->syn || tcph->fin || tcph->rst) PUNT(TCP_CONTROL_PACKET);
+    }
 
     // Protect against forwarding packets sourced from ::1 or fe80::/64 or other weirdness.
     __be32 src32 = ip6->saddr.s6_addr32[0];
     if (src32 != htonl(0x0064ff9b) &&                        // 64:ff9b:/32 incl. XLAT464 WKP
         (src32 & htonl(0xe0000000)) != htonl(0x20000000))    // 2000::/3 Global Unicast
-        return TC_ACT_OK;
+        PUNT(NON_GLOBAL_SRC);
 
-    TetherIngressKey k = {
+    // Protect against forwarding packets destined to ::1 or fe80::/64 or other weirdness.
+    __be32 dst32 = ip6->daddr.s6_addr32[0];
+    if (dst32 != htonl(0x0064ff9b) &&                        // 64:ff9b:/32 incl. XLAT464 WKP
+        (dst32 & htonl(0xe0000000)) != htonl(0x20000000))    // 2000::/3 Global Unicast
+        PUNT(NON_GLOBAL_DST);
+
+    // In the upstream direction do not forward traffic within the same /64 subnet.
+    if (!downstream && (src32 == dst32) && (ip6->saddr.s6_addr32[1] == ip6->daddr.s6_addr32[1]))
+        PUNT(LOCAL_SRC_DST);
+
+    TetherDownstream6Key kd = {
             .iif = skb->ifindex,
             .neigh6 = ip6->daddr,
     };
 
-    TetherIngressValue* v = bpf_tether_ingress_map_lookup_elem(&k);
+    TetherUpstream6Key ku = {
+            .iif = skb->ifindex,
+    };
+
+    Tether6Value* v = downstream ? bpf_tether_downstream6_map_lookup_elem(&kd)
+                                 : bpf_tether_upstream6_map_lookup_elem(&ku);
 
     // If we don't find any offload information then simply let the core stack handle it...
     if (!v) return TC_ACT_OK;
 
-    uint32_t stat_and_limit_k = skb->ifindex;
+    uint32_t stat_and_limit_k = downstream ? skb->ifindex : v->oif;
 
     TetherStatsValue* stat_v = bpf_tether_stats_map_lookup_elem(&stat_and_limit_k);
 
     // If we don't have anywhere to put stats, then abort...
-    if (!stat_v) return TC_ACT_OK;
+    if (!stat_v) PUNT(NO_STATS_ENTRY);
 
     uint64_t* limit_v = bpf_tether_limit_map_lookup_elem(&stat_and_limit_k);
 
     // If we don't have a limit, then abort...
-    if (!limit_v) return TC_ACT_OK;
+    if (!limit_v) PUNT(NO_LIMIT_ENTRY);
 
     // Required IPv6 minimum mtu is 1280, below that not clear what we should do, abort...
-    const int pmtu = v->pmtu;
-    if (pmtu < IPV6_MIN_MTU) return TC_ACT_OK;
+    if (v->pmtu < IPV6_MIN_MTU) PUNT(BELOW_IPV6_MTU);
 
     // Approximate handling of TCP/IPv6 overhead for incoming LRO/GRO packets: default
     // outbound path mtu of 1500 is not necessarily correct, but worst case we simply
@@ -98,9 +196,9 @@
     // (This is also blindly assuming 12 bytes of tcp timestamp option in tcp header)
     uint64_t packets = 1;
     uint64_t bytes = skb->len;
-    if (bytes > pmtu) {
+    if (bytes > v->pmtu) {
         const int tcp_overhead = sizeof(struct ipv6hdr) + sizeof(struct tcphdr) + 12;
-        const int mss = pmtu - tcp_overhead;
+        const int mss = v->pmtu - tcp_overhead;
         const uint64_t payload = bytes - tcp_overhead;
         packets = (payload + mss - 1) / mss;
         bytes = tcp_overhead * packets + payload;
@@ -112,15 +210,15 @@
     // a packet we let the core stack deal with things.
     // (The core stack needs to handle limits correctly anyway,
     // since we don't offload all traffic in both directions)
-    if (stat_v->rxBytes + stat_v->txBytes + bytes > *limit_v) return TC_ACT_OK;
+    if (stat_v->rxBytes + stat_v->txBytes + bytes > *limit_v) PUNT(LIMIT_REACHED);
 
     if (!is_ethernet) {
-        is_ethernet = true;
-        l2_header_size = sizeof(struct ethhdr);
-        // Try to inject an ethernet header, and simply return if we fail
-        if (bpf_skb_change_head(skb, l2_header_size, /*flags*/ 0)) {
-            __sync_fetch_and_add(&stat_v->rxErrors, 1);
-            return TC_ACT_OK;
+        // Try to inject an ethernet header, and simply return if we fail.
+        // We do this even if TX interface is RAWIP and thus does not need an ethernet header,
+        // because this is easier and the kernel will strip extraneous ethernet header.
+        if (bpf_skb_change_head(skb, sizeof(struct ethhdr), /*flags*/ 0)) {
+            __sync_fetch_and_add(downstream ? &stat_v->rxErrors : &stat_v->txErrors, 1);
+            PUNT(CHANGE_HEAD_FAILED);
         }
 
         // bpf_skb_change_head() invalidates all pointers - reload them
@@ -130,12 +228,16 @@
         ip6 = (void*)(eth + 1);
 
         // I do not believe this can ever happen, but keep the verifier happy...
-        if (data + l2_header_size + sizeof(*ip6) > data_end) {
-            __sync_fetch_and_add(&stat_v->rxErrors, 1);
-            return TC_ACT_SHOT;
+        if (data + sizeof(struct ethhdr) + sizeof(*ip6) > data_end) {
+            __sync_fetch_and_add(downstream ? &stat_v->rxErrors : &stat_v->txErrors, 1);
+            DROP(TOO_SHORT);
         }
     };
 
+    // At this point we always have an ethernet header - which will get stripped by the
+    // kernel during transmit through a rawip interface.  ie. 'eth' pointer is valid.
+    // Additionally note that 'is_ethernet' and 'l2_header_size' are no longer correct.
+
     // CHECKSUM_COMPLETE is a 16-bit one's complement sum,
     // thus corrections for it need to be done in 16-byte chunks at even offsets.
     // IPv6 nexthdr is at offset 6, while hop limit is at offset 7
@@ -147,10 +249,11 @@
     // (-ENOTSUPP) if it isn't.
     bpf_csum_update(skb, 0xFFFF - ntohs(old_hl) + ntohs(new_hl));
 
-    __sync_fetch_and_add(&stat_v->rxPackets, packets);
-    __sync_fetch_and_add(&stat_v->rxBytes, bytes);
+    __sync_fetch_and_add(downstream ? &stat_v->rxPackets : &stat_v->txPackets, packets);
+    __sync_fetch_and_add(downstream ? &stat_v->rxBytes : &stat_v->txBytes, bytes);
 
     // Overwrite any mac header with the new one
+    // For a rawip tx interface it will simply be a bunch of zeroes and later stripped.
     *eth = v->macHeader;
 
     // Redirect to forwarded interface.
@@ -162,9 +265,16 @@
     return bpf_redirect(v->oif, 0 /* this is effectively BPF_F_EGRESS */);
 }
 
-SEC("schedcls/ingress/tether_ether")
-int sched_cls_ingress_tether_ether(struct __sk_buff* skb) {
-    return do_forward(skb, true);
+DEFINE_BPF_PROG("schedcls/tether_downstream6_ether", AID_ROOT, AID_NETWORK_STACK,
+                sched_cls_tether_downstream6_ether)
+(struct __sk_buff* skb) {
+    return do_forward6(skb, /* is_ethernet */ true, /* downstream */ true);
+}
+
+DEFINE_BPF_PROG("schedcls/tether_upstream6_ether", AID_ROOT, AID_NETWORK_STACK,
+                sched_cls_tether_upstream6_ether)
+(struct __sk_buff* skb) {
+    return do_forward6(skb, /* is_ethernet */ true, /* downstream */ false);
 }
 
 // Note: section names must be unique to prevent programs from appending to each other,
@@ -179,29 +289,409 @@
 // 5.4 kernel support was only added to Android Common Kernel in R,
 // and thus a 5.4 kernel always supports this.
 //
-// Hence, this mandatory (must load successfully) implementation for 5.4+ kernels:
-DEFINE_BPF_PROG_KVER("schedcls/ingress/tether_rawip$5_4", AID_ROOT, AID_ROOT,
-                     sched_cls_ingress_tether_rawip_5_4, KVER(5, 4, 0))
+// Hence, these mandatory (must load successfully) implementations for 5.4+ kernels:
+DEFINE_BPF_PROG_KVER("schedcls/tether_downstream6_rawip$5_4", AID_ROOT, AID_NETWORK_STACK,
+                     sched_cls_tether_downstream6_rawip_5_4, KVER(5, 4, 0))
 (struct __sk_buff* skb) {
-    return do_forward(skb, false);
+    return do_forward6(skb, /* is_ethernet */ false, /* downstream */ true);
 }
 
-// and this identical optional (may fail to load) implementation for [4.14..5.4) patched kernels:
-DEFINE_OPTIONAL_BPF_PROG_KVER_RANGE("schedcls/ingress/tether_rawip$4_14", AID_ROOT, AID_ROOT,
-                                    sched_cls_ingress_tether_rawip_4_14, KVER(4, 14, 0),
-                                    KVER(5, 4, 0))
+DEFINE_BPF_PROG_KVER("schedcls/tether_upstream6_rawip$5_4", AID_ROOT, AID_NETWORK_STACK,
+                     sched_cls_tether_upstream6_rawip_5_4, KVER(5, 4, 0))
 (struct __sk_buff* skb) {
-    return do_forward(skb, false);
+    return do_forward6(skb, /* is_ethernet */ false, /* downstream */ false);
 }
 
-// and define a no-op stub for [4.9,4.14) and unpatched [4.14,5.4) kernels.
+// and these identical optional (may fail to load) implementations for [4.14..5.4) patched kernels:
+DEFINE_OPTIONAL_BPF_PROG_KVER_RANGE("schedcls/tether_downstream6_rawip$4_14",
+                                    AID_ROOT, AID_NETWORK_STACK,
+                                    sched_cls_tether_downstream6_rawip_4_14,
+                                    KVER(4, 14, 0), KVER(5, 4, 0))
+(struct __sk_buff* skb) {
+    return do_forward6(skb, /* is_ethernet */ false, /* downstream */ true);
+}
+
+DEFINE_OPTIONAL_BPF_PROG_KVER_RANGE("schedcls/tether_upstream6_rawip$4_14",
+                                    AID_ROOT, AID_NETWORK_STACK,
+                                    sched_cls_tether_upstream6_rawip_4_14,
+                                    KVER(4, 14, 0), KVER(5, 4, 0))
+(struct __sk_buff* skb) {
+    return do_forward6(skb, /* is_ethernet */ false, /* downstream */ false);
+}
+
+// and define no-op stubs for [4.9,4.14) and unpatched [4.14,5.4) kernels.
 // (if the above real 4.14+ program loaded successfully, then bpfloader will have already pinned
 // it at the same location this one would be pinned at and will thus skip loading this stub)
-DEFINE_BPF_PROG_KVER_RANGE("schedcls/ingress/tether_rawip$stub", AID_ROOT, AID_ROOT,
-                           sched_cls_ingress_tether_rawip_stub, KVER_NONE, KVER(5, 4, 0))
+DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_downstream6_rawip$stub", AID_ROOT, AID_NETWORK_STACK,
+                           sched_cls_tether_downstream6_rawip_stub, KVER_NONE, KVER(5, 4, 0))
 (struct __sk_buff* skb) {
     return TC_ACT_OK;
 }
 
+DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_upstream6_rawip$stub", AID_ROOT, AID_NETWORK_STACK,
+                           sched_cls_tether_upstream6_rawip_stub, KVER_NONE, KVER(5, 4, 0))
+(struct __sk_buff* skb) {
+    return TC_ACT_OK;
+}
+
+// ----- IPv4 Support -----
+
+DEFINE_BPF_MAP_GRW(tether_downstream4_map, HASH, Tether4Key, Tether4Value, 64, AID_NETWORK_STACK)
+
+DEFINE_BPF_MAP_GRW(tether_upstream4_map, HASH, Tether4Key, Tether4Value, 64, AID_NETWORK_STACK)
+
+static inline __always_inline int do_forward4(struct __sk_buff* skb, const bool is_ethernet,
+        const bool downstream, const bool updatetime) {
+    const int l2_header_size = is_ethernet ? sizeof(struct ethhdr) : 0;
+    void* data = (void*)(long)skb->data;
+    const void* data_end = (void*)(long)skb->data_end;
+    struct ethhdr* eth = is_ethernet ? data : NULL;  // used iff is_ethernet
+    struct iphdr* ip = is_ethernet ? (void*)(eth + 1) : data;
+
+    // Require ethernet dst mac address to be our unicast address.
+    if (is_ethernet && (skb->pkt_type != PACKET_HOST)) return TC_ACT_OK;
+
+    // Must be meta-ethernet IPv4 frame
+    if (skb->protocol != htons(ETH_P_IP)) return TC_ACT_OK;
+
+    // Must have (ethernet and) ipv4 header
+    if (data + l2_header_size + sizeof(*ip) > data_end) return TC_ACT_OK;
+
+    // Ethertype - if present - must be IPv4
+    if (is_ethernet && (eth->h_proto != htons(ETH_P_IP))) return TC_ACT_OK;
+
+    // IP version must be 4
+    if (ip->version != 4) PUNT(INVALID_IP_VERSION);
+
+    // We cannot handle IP options, just standard 20 byte == 5 dword minimal IPv4 header
+    if (ip->ihl != 5) PUNT(HAS_IP_OPTIONS);
+
+    // Calculate the IPv4 one's complement checksum of the IPv4 header.
+    __wsum sum4 = 0;
+    for (int i = 0; i < sizeof(*ip) / sizeof(__u16); ++i) {
+        sum4 += ((__u16*)ip)[i];
+    }
+    // Note that sum4 is guaranteed to be non-zero by virtue of ip4->version == 4
+    sum4 = (sum4 & 0xFFFF) + (sum4 >> 16);  // collapse u32 into range 1 .. 0x1FFFE
+    sum4 = (sum4 & 0xFFFF) + (sum4 >> 16);  // collapse any potential carry into u16
+    // for a correct checksum we should get *a* zero, but sum4 must be positive, ie 0xFFFF
+    if (sum4 != 0xFFFF) PUNT(CHECKSUM);
+
+    // Minimum IPv4 total length is the size of the header
+    if (ntohs(ip->tot_len) < sizeof(*ip)) PUNT(TRUNCATED_IPV4);
+
+    // We are incapable of dealing with IPv4 fragments
+    if (ip->frag_off & ~htons(IP_DF)) PUNT(IS_IP_FRAG);
+
+    // Cannot decrement during forward if already zero or would be zero,
+    // Let the kernel's stack handle these cases and generate appropriate ICMP errors.
+    if (ip->ttl <= 1) PUNT(LOW_TTL);
+
+    // If we cannot update the 'last_used' field due to lack of bpf_ktime_get_boot_ns() helper,
+    // then it is not safe to offload UDP due to the small conntrack timeouts, as such,
+    // in such a situation we can only support TCP.  This also has the added nice benefit of
+    // using a separate error counter, and thus making it obvious which version of the program
+    // is loaded.
+    if (!updatetime && ip->protocol != IPPROTO_TCP) PUNT(NON_TCP);
+
+    // We do not support offloading anything besides IPv4 TCP and UDP, due to need for NAT,
+    // but no need to check this if !updatetime due to check immediately above.
+    if (updatetime && (ip->protocol != IPPROTO_TCP) && (ip->protocol != IPPROTO_UDP))
+        PUNT(NON_TCP_UDP);
+
+    // We want to make sure that the compiler will, in the !updatetime case, entirely optimize
+    // out all the non-tcp logic.  Also note that at this point is_udp === !is_tcp.
+    const bool is_tcp = !updatetime || (ip->protocol == IPPROTO_TCP);
+
+    struct tcphdr* tcph = is_tcp ? (void*)(ip + 1) : NULL;
+    struct udphdr* udph = is_tcp ? NULL : (void*)(ip + 1);
+
+    if (is_tcp) {
+        // Make sure we can get at the tcp header
+        if (data + l2_header_size + sizeof(*ip) + sizeof(*tcph) > data_end) PUNT(SHORT_TCP_HEADER);
+
+        // If hardware offload is running and programming flows based on conntrack entries, try not
+        // to interfere with it, so do not offload TCP packets with any one of the SYN/FIN/RST flags
+        if (tcph->syn || tcph->fin || tcph->rst) PUNT(TCP_CONTROL_PACKET);
+    } else { // UDP
+        // Make sure we can get at the udp header
+        if (data + l2_header_size + sizeof(*ip) + sizeof(*udph) > data_end) PUNT(SHORT_UDP_HEADER);
+    }
+
+    Tether4Key k = {
+            .iif = skb->ifindex,
+            .l4Proto = ip->protocol,
+            .src4.s_addr = ip->saddr,
+            .dst4.s_addr = ip->daddr,
+            .srcPort = is_tcp ? tcph->source : udph->source,
+            .dstPort = is_tcp ? tcph->dest : udph->dest,
+    };
+    if (is_ethernet) for (int i = 0; i < ETH_ALEN; ++i) k.dstMac[i] = eth->h_dest[i];
+
+    Tether4Value* v = downstream ? bpf_tether_downstream4_map_lookup_elem(&k)
+                                 : bpf_tether_upstream4_map_lookup_elem(&k);
+
+    // If we don't find any offload information then simply let the core stack handle it...
+    if (!v) return TC_ACT_OK;
+
+    uint32_t stat_and_limit_k = downstream ? skb->ifindex : v->oif;
+
+    TetherStatsValue* stat_v = bpf_tether_stats_map_lookup_elem(&stat_and_limit_k);
+
+    // If we don't have anywhere to put stats, then abort...
+    if (!stat_v) PUNT(NO_STATS_ENTRY);
+
+    uint64_t* limit_v = bpf_tether_limit_map_lookup_elem(&stat_and_limit_k);
+
+    // If we don't have a limit, then abort...
+    if (!limit_v) PUNT(NO_LIMIT_ENTRY);
+
+    // Required IPv4 minimum mtu is 68, below that not clear what we should do, abort...
+    if (v->pmtu < 68) PUNT(BELOW_IPV4_MTU);
+
+    // Approximate handling of TCP/IPv4 overhead for incoming LRO/GRO packets: default
+    // outbound path mtu of 1500 is not necessarily correct, but worst case we simply
+    // undercount, which is still better then not accounting for this overhead at all.
+    // Note: this really shouldn't be device/path mtu at all, but rather should be
+    // derived from this particular connection's mss (ie. from gro segment size).
+    // This would require a much newer kernel with newer ebpf accessors.
+    // (This is also blindly assuming 12 bytes of tcp timestamp option in tcp header)
+    uint64_t packets = 1;
+    uint64_t bytes = skb->len;
+    if (bytes > v->pmtu) {
+        const int tcp_overhead = sizeof(struct iphdr) + sizeof(struct tcphdr) + 12;
+        const int mss = v->pmtu - tcp_overhead;
+        const uint64_t payload = bytes - tcp_overhead;
+        packets = (payload + mss - 1) / mss;
+        bytes = tcp_overhead * packets + payload;
+    }
+
+    // Are we past the limit?  If so, then abort...
+    // Note: will not overflow since u64 is 936 years even at 5Gbps.
+    // Do not drop here.  Offload is just that, whenever we fail to handle
+    // a packet we let the core stack deal with things.
+    // (The core stack needs to handle limits correctly anyway,
+    // since we don't offload all traffic in both directions)
+    if (stat_v->rxBytes + stat_v->txBytes + bytes > *limit_v) PUNT(LIMIT_REACHED);
+
+    if (!is_tcp) PUNT(NON_TCP);  // TEMP HACK: will remove once UDP is supported.
+
+    if (!is_ethernet) {
+        // Try to inject an ethernet header, and simply return if we fail.
+        // We do this even if TX interface is RAWIP and thus does not need an ethernet header,
+        // because this is easier and the kernel will strip extraneous ethernet header.
+        if (bpf_skb_change_head(skb, sizeof(struct ethhdr), /*flags*/ 0)) {
+            __sync_fetch_and_add(downstream ? &stat_v->rxErrors : &stat_v->txErrors, 1);
+            PUNT(CHANGE_HEAD_FAILED);
+        }
+
+        // bpf_skb_change_head() invalidates all pointers - reload them
+        data = (void*)(long)skb->data;
+        data_end = (void*)(long)skb->data_end;
+        eth = data;
+        ip = (void*)(eth + 1);
+        tcph = is_tcp ? (void*)(ip + 1) : NULL;
+        udph = is_tcp ? NULL : (void*)(ip + 1);
+
+        // I do not believe this can ever happen, but keep the verifier happy...
+        if (data + sizeof(struct ethhdr) + sizeof(*ip) + (is_tcp ? sizeof(*tcph) : sizeof(*udph)) > data_end) {
+            __sync_fetch_and_add(downstream ? &stat_v->rxErrors : &stat_v->txErrors, 1);
+            DROP(TOO_SHORT);
+        }
+    };
+
+    // At this point we always have an ethernet header - which will get stripped by the
+    // kernel during transmit through a rawip interface.  ie. 'eth' pointer is valid.
+    // Additionally note that 'is_ethernet' and 'l2_header_size' are no longer correct.
+
+    // Overwrite any mac header with the new one
+    // For a rawip tx interface it will simply be a bunch of zeroes and later stripped.
+    *eth = v->macHeader;
+
+    const int sz4 = sizeof(__be32);
+    const __be32 old_daddr = k.dst4.s_addr;
+    const __be32 old_saddr = k.src4.s_addr;
+    const __be32 new_daddr = v->dst46.s6_addr32[3];
+    const __be32 new_saddr = v->src46.s6_addr32[3];
+
+    bpf_l4_csum_replace(skb, ETH_IP4_TCP_OFFSET(check), old_daddr, new_daddr, sz4 | BPF_F_PSEUDO_HDR);
+    bpf_l3_csum_replace(skb, ETH_IP4_OFFSET(check), old_daddr, new_daddr, sz4);
+    bpf_skb_store_bytes(skb, ETH_IP4_OFFSET(daddr), &new_daddr, sz4, 0);
+
+    bpf_l4_csum_replace(skb, ETH_IP4_TCP_OFFSET(check), old_saddr, new_saddr, sz4 | BPF_F_PSEUDO_HDR);
+    bpf_l3_csum_replace(skb, ETH_IP4_OFFSET(check), old_saddr, new_saddr, sz4);
+    bpf_skb_store_bytes(skb, ETH_IP4_OFFSET(saddr), &new_saddr, sz4, 0);
+
+    const int sz2 = sizeof(__be16);
+    bpf_l4_csum_replace(skb, ETH_IP4_TCP_OFFSET(check), k.srcPort, v->srcPort, sz2);
+    bpf_skb_store_bytes(skb, ETH_IP4_TCP_OFFSET(source), &v->srcPort, sz2, 0);
+
+    bpf_l4_csum_replace(skb, ETH_IP4_TCP_OFFSET(check), k.dstPort, v->dstPort, sz2);
+    bpf_skb_store_bytes(skb, ETH_IP4_TCP_OFFSET(dest), &v->dstPort, sz2, 0);
+
+    // TEMP HACK: lack of TTL decrement
+
+    // This requires the bpf_ktime_get_boot_ns() helper which was added in 5.8,
+    // and backported to all Android Common Kernel 4.14+ trees.
+    if (updatetime) v->last_used = bpf_ktime_get_boot_ns();
+
+    __sync_fetch_and_add(downstream ? &stat_v->rxPackets : &stat_v->txPackets, packets);
+    __sync_fetch_and_add(downstream ? &stat_v->rxBytes : &stat_v->txBytes, bytes);
+
+    // Redirect to forwarded interface.
+    //
+    // Note that bpf_redirect() cannot fail unless you pass invalid flags.
+    // The redirect actually happens after the ebpf program has already terminated,
+    // and can fail for example for mtu reasons at that point in time, but there's nothing
+    // we can do about it here.
+    return bpf_redirect(v->oif, 0 /* this is effectively BPF_F_EGRESS */);
+}
+
+// Full featured (required) implementations for 5.8+ kernels
+
+DEFINE_BPF_PROG_KVER("schedcls/tether_downstream4_ether$5_8", AID_ROOT, AID_NETWORK_STACK,
+                     sched_cls_tether_downstream4_ether_5_8, KVER(5, 8, 0))
+(struct __sk_buff* skb) {
+    return do_forward4(skb, /* is_ethernet */ true, /* downstream */ true, /* updatetime */ true);
+}
+
+DEFINE_BPF_PROG_KVER("schedcls/tether_downstream4_rawip$5_8", AID_ROOT, AID_NETWORK_STACK,
+                     sched_cls_tether_downstream4_rawip_5_8, KVER(5, 8, 0))
+(struct __sk_buff* skb) {
+    return do_forward4(skb, /* is_ethernet */ false, /* downstream */ true, /* updatetime */ true);
+}
+
+DEFINE_BPF_PROG_KVER("schedcls/tether_upstream4_ether$5_8", AID_ROOT, AID_NETWORK_STACK,
+                     sched_cls_tether_upstream4_ether_5_8, KVER(5, 8, 0))
+(struct __sk_buff* skb) {
+    return do_forward4(skb, /* is_ethernet */ true, /* downstream */ false, /* updatetime */ true);
+}
+
+DEFINE_BPF_PROG_KVER("schedcls/tether_upstream4_rawip$5_8", AID_ROOT, AID_NETWORK_STACK,
+                     sched_cls_tether_upstream4_rawip_5_8, KVER(5, 8, 0))
+(struct __sk_buff* skb) {
+    return do_forward4(skb, /* is_ethernet */ false, /* downstream */ false, /* updatetime */ true);
+}
+
+// Full featured (optional) implementations for [4.14..5.8) kernels
+
+DEFINE_OPTIONAL_BPF_PROG_KVER_RANGE("schedcls/tether_downstream4_ether$opt",
+                                    AID_ROOT, AID_NETWORK_STACK,
+                                    sched_cls_tether_downstream4_ether_opt,
+                                    KVER(4, 14, 0), KVER(5, 8, 0))
+(struct __sk_buff* skb) {
+    return do_forward4(skb, /* is_ethernet */ true, /* downstream */ true, /* updatetime */ true);
+}
+
+DEFINE_OPTIONAL_BPF_PROG_KVER_RANGE("schedcls/tether_downstream4_rawip$opt",
+                                    AID_ROOT, AID_NETWORK_STACK,
+                                    sched_cls_tether_downstream4_rawip_opt,
+                                    KVER(4, 14, 0), KVER(5, 8, 0))
+(struct __sk_buff* skb) {
+    return do_forward4(skb, /* is_ethernet */ false, /* downstream */ true, /* updatetime */ true);
+}
+
+DEFINE_OPTIONAL_BPF_PROG_KVER_RANGE("schedcls/tether_upstream4_ether$opt",
+                                    AID_ROOT, AID_NETWORK_STACK,
+                                    sched_cls_tether_upstream4_ether_opt,
+                                    KVER(4, 14, 0), KVER(5, 8, 0))
+(struct __sk_buff* skb) {
+    return do_forward4(skb, /* is_ethernet */ true, /* downstream */ false, /* updatetime */ true);
+}
+
+DEFINE_OPTIONAL_BPF_PROG_KVER_RANGE("schedcls/tether_upstream4_rawip$opt",
+                                    AID_ROOT, AID_NETWORK_STACK,
+                                    sched_cls_tether_upstream4_rawip_opt,
+                                    KVER(4, 14, 0), KVER(5, 8, 0))
+(struct __sk_buff* skb) {
+    return do_forward4(skb, /* is_ethernet */ false, /* downstream */ false, /* updatetime */ true);
+}
+
+// Partial (TCP-only: will not update 'last_used' field) implementations for 4.14+ kernels.
+// These will be loaded only if the above optional ones failed (loading of *these* must succeed).
+//
+// [Note: as a result TCP connections will not have their conntrack timeout refreshed, however,
+// since /proc/sys/net/netfilter/nf_conntrack_tcp_timeout_established defaults to 432000 (seconds),
+// this in practice means they'll break only after 5 days.  This seems an acceptable trade-off.
+//
+// Additionally kernel/tests change "net-test: add bpf_ktime_get_ns / bpf_ktime_get_boot_ns tests"
+// which enforces and documents the required kernel cherrypicks will make it pretty unlikely that
+// many devices upgrading to S will end up relying on these fallback programs.
+
+DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_downstream4_ether$4_14", AID_ROOT, AID_NETWORK_STACK,
+                           sched_cls_tether_downstream4_ether_4_14, KVER(4, 14, 0), KVER(5, 8, 0))
+(struct __sk_buff* skb) {
+    return do_forward4(skb, /* is_ethernet */ true, /* downstream */ true, /* updatetime */ false);
+}
+
+DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_downstream4_rawip$4_14", AID_ROOT, AID_NETWORK_STACK,
+                           sched_cls_tether_downstream4_rawip_4_14, KVER(4, 14, 0), KVER(5, 8, 0))
+(struct __sk_buff* skb) {
+    return do_forward4(skb, /* is_ethernet */ false, /* downstream */ true, /* updatetime */ false);
+}
+
+DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_upstream4_ether$4_14", AID_ROOT, AID_NETWORK_STACK,
+                           sched_cls_tether_upstream4_ether_4_14, KVER(4, 14, 0), KVER(5, 8, 0))
+(struct __sk_buff* skb) {
+    return do_forward4(skb, /* is_ethernet */ true, /* downstream */ false, /* updatetime */ false);
+}
+
+DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_upstream4_rawip$4_14", AID_ROOT, AID_NETWORK_STACK,
+                           sched_cls_tether_upstream4_rawip_4_14, KVER(4, 14, 0), KVER(5, 8, 0))
+(struct __sk_buff* skb) {
+    return do_forward4(skb, /* is_ethernet */ false, /* downstream */ false, /* updatetime */ false);
+}
+
+// Placeholder (no-op) implementations for older pre-4.14 kernels
+
+DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_downstream4_ether$stub", AID_ROOT, AID_NETWORK_STACK,
+                           sched_cls_tether_downstream4_ether_stub, KVER_NONE, KVER(4, 14, 0))
+(struct __sk_buff* skb) {
+    return TC_ACT_OK;
+}
+
+DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_downstream4_rawip$stub", AID_ROOT, AID_NETWORK_STACK,
+                           sched_cls_tether_downstream4_rawip_stub, KVER_NONE, KVER(4, 14, 0))
+(struct __sk_buff* skb) {
+    return TC_ACT_OK;
+}
+
+DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_upstream4_ether$stub", AID_ROOT, AID_NETWORK_STACK,
+                           sched_cls_tether_upstream4_ether_stub, KVER_NONE, KVER(4, 14, 0))
+(struct __sk_buff* skb) {
+    return TC_ACT_OK;
+}
+
+DEFINE_BPF_PROG_KVER_RANGE("schedcls/tether_upstream4_rawip$stub", AID_ROOT, AID_NETWORK_STACK,
+                           sched_cls_tether_upstream4_rawip_stub, KVER_NONE, KVER(4, 14, 0))
+(struct __sk_buff* skb) {
+    return TC_ACT_OK;
+}
+
+// ----- XDP Support -----
+
+#define DEFINE_XDP_PROG(str, func) \
+    DEFINE_BPF_PROG_KVER(str, AID_ROOT, AID_NETWORK_STACK, func, KVER(5, 9, 0))(struct xdp_md *ctx)
+
+DEFINE_XDP_PROG("xdp/tether_downstream_ether",
+                 xdp_tether_downstream_ether) {
+    return XDP_PASS;
+}
+
+DEFINE_XDP_PROG("xdp/tether_downstream_rawip",
+                 xdp_tether_downstream_rawip) {
+    return XDP_PASS;
+}
+
+DEFINE_XDP_PROG("xdp/tether_upstream_ether",
+                 xdp_tether_upstream_ether) {
+    return XDP_PASS;
+}
+
+DEFINE_XDP_PROG("xdp/tether_upstream_rawip",
+                 xdp_tether_upstream_rawip) {
+    return XDP_PASS;
+}
+
 LICENSE("Apache 2.0");
 CRITICAL("netd");
diff --git a/Tethering/bpf_progs/test.c b/Tethering/bpf_progs/test.c
index b5be33f..c4a8271 100644
--- a/Tethering/bpf_progs/test.c
+++ b/Tethering/bpf_progs/test.c
@@ -14,12 +14,34 @@
  * limitations under the License.
  */
 
+#include <linux/if_ether.h>
+#include <linux/in.h>
+#include <linux/ip.h>
+
 #include "bpf_helpers.h"
 #include "bpf_net_helpers.h"
 #include "netdbpf/bpf_shared.h"
 
 // Used only by TetheringPrivilegedTests, not by production code.
-DEFINE_BPF_MAP_GRW(tether_ingress_map, HASH, TetherIngressKey, TetherIngressValue, 16,
+DEFINE_BPF_MAP_GRW(tether_downstream6_map, HASH, TetherDownstream6Key, Tether6Value, 16,
                    AID_NETWORK_STACK)
 
+DEFINE_BPF_PROG_KVER("xdp/drop_ipv4_udp_ether", AID_ROOT, AID_NETWORK_STACK,
+                      xdp_test, KVER(5, 9, 0))
+(struct xdp_md *ctx) {
+    void *data = (void *)(long)ctx->data;
+    void *data_end = (void *)(long)ctx->data_end;
+
+    struct ethhdr *eth = data;
+    int hsize = sizeof(*eth);
+
+    struct iphdr *ip = data + hsize;
+    hsize += sizeof(struct iphdr);
+
+    if (data + hsize > data_end) return XDP_PASS;
+    if (eth->h_proto != htons(ETH_P_IP)) return XDP_PASS;
+    if (ip->protocol == IPPROTO_UDP) return XDP_DROP;
+    return XDP_PASS;
+}
+
 LICENSE("Apache 2.0");
diff --git a/Tethering/jni/com_android_networkstack_tethering_BpfCoordinator.cpp b/Tethering/jni/com_android_networkstack_tethering_BpfCoordinator.cpp
new file mode 100644
index 0000000..27357f8
--- /dev/null
+++ b/Tethering/jni/com_android_networkstack_tethering_BpfCoordinator.cpp
@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <jni.h>
+#include <nativehelper/JNIHelp.h>
+
+#include "bpf_tethering.h"
+
+namespace android {
+
+static jobjectArray getBpfCounterNames(JNIEnv *env) {
+    size_t size = BPF_TETHER_ERR__MAX;
+    jobjectArray ret = env->NewObjectArray(size, env->FindClass("java/lang/String"), nullptr);
+    for (int i = 0; i < size; i++) {
+        env->SetObjectArrayElement(ret, i, env->NewStringUTF(bpf_tether_errors[i]));
+    }
+    return ret;
+}
+
+/*
+ * JNI registration.
+ */
+static const JNINativeMethod gMethods[] = {
+    /* name, signature, funcPtr */
+    { "getBpfCounterNames", "()[Ljava/lang/String;", (void*) getBpfCounterNames },
+};
+
+int register_com_android_networkstack_tethering_BpfCoordinator(JNIEnv* env) {
+    return jniRegisterNativeMethods(env,
+            "com/android/networkstack/tethering/BpfCoordinator",
+            gMethods, NELEM(gMethods));
+}
+
+}; // namespace android
diff --git a/Tethering/jni/onload.cpp b/Tethering/jni/onload.cpp
index 3766de9..e31da60 100644
--- a/Tethering/jni/onload.cpp
+++ b/Tethering/jni/onload.cpp
@@ -24,6 +24,7 @@
 
 int register_android_net_util_TetheringUtils(JNIEnv* env);
 int register_com_android_networkstack_tethering_BpfMap(JNIEnv* env);
+int register_com_android_networkstack_tethering_BpfCoordinator(JNIEnv* env);
 
 extern "C" jint JNI_OnLoad(JavaVM* vm, void*) {
     JNIEnv *env;
@@ -36,6 +37,8 @@
 
     if (register_com_android_networkstack_tethering_BpfMap(env) < 0) return JNI_ERR;
 
+    if (register_com_android_networkstack_tethering_BpfCoordinator(env) < 0) return JNI_ERR;
+
     return JNI_VERSION_1_6;
 }
 
diff --git a/Tethering/src/android/net/ip/IpServer.java b/Tethering/src/android/net/ip/IpServer.java
index 52d59fc..194737a 100644
--- a/Tethering/src/android/net/ip/IpServer.java
+++ b/Tethering/src/android/net/ip/IpServer.java
@@ -67,13 +67,12 @@
 import com.android.internal.util.State;
 import com.android.internal.util.StateMachine;
 import com.android.networkstack.tethering.BpfCoordinator;
+import com.android.networkstack.tethering.BpfCoordinator.ClientInfo;
 import com.android.networkstack.tethering.BpfCoordinator.Ipv6ForwardingRule;
 import com.android.networkstack.tethering.PrivateAddressCoordinator;
 
-import java.io.IOException;
 import java.net.Inet4Address;
 import java.net.Inet6Address;
-import java.net.NetworkInterface;
 import java.net.UnknownHostException;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -186,16 +185,6 @@
             return InterfaceParams.getByName(ifName);
         }
 
-        /** Get |ifName|'s interface index. */
-        public int getIfindex(String ifName) {
-            try {
-                return NetworkInterface.getByName(ifName).getIndex();
-            } catch (IOException | NullPointerException e) {
-                Log.e(TAG, "Can't determine interface index for interface " + ifName);
-                return 0;
-            }
-        }
-
         /** Create a DhcpServer instance to be used by IpServer. */
         public abstract void makeDhcpServer(String ifName, DhcpServingParamsParcel params,
                 DhcpServerCallbacks cb);
@@ -941,11 +930,38 @@
         }
     }
 
+    // TODO: consider moving into BpfCoordinator.
+    private void updateClientInfoIpv4(NeighborEvent e) {
+        // TODO: Perhaps remove this protection check.
+        // See the related comment in #addIpv6ForwardingRule.
+        if (!mUsingBpfOffload) return;
+
+        if (e == null) return;
+        if (!(e.ip instanceof Inet4Address) || e.ip.isMulticastAddress()
+                || e.ip.isLoopbackAddress() || e.ip.isLinkLocalAddress()) {
+            return;
+        }
+
+        // When deleting clients, IpServer still need to pass a non-null MAC, even though it's
+        // ignored. Do this here instead of in the ClientInfo constructor to ensure that
+        // IpServer never add clients with a null MAC, only delete them.
+        final MacAddress clientMac = e.isValid() ? e.macAddr : NULL_MAC_ADDRESS;
+        final ClientInfo clientInfo = new ClientInfo(mInterfaceParams.index,
+                mInterfaceParams.macAddr, (Inet4Address) e.ip, clientMac);
+        if (e.isValid()) {
+            mBpfCoordinator.tetherOffloadClientAdd(this, clientInfo);
+        } else {
+            // TODO: Delete all related offload rules which are using this client.
+            mBpfCoordinator.tetherOffloadClientRemove(this, clientInfo);
+        }
+    }
+
     private void handleNeighborEvent(NeighborEvent e) {
         if (mInterfaceParams != null
                 && mInterfaceParams.index == e.ifindex
                 && mInterfaceParams.hasMacAddress) {
             updateIpv6ForwardingRules(mLastIPv6UpstreamIfindex, mLastIPv6UpstreamIfindex, e);
+            updateClientInfoIpv4(e);
         }
     }
 
@@ -1111,9 +1127,19 @@
         }
     }
 
+    private void startConntrackMonitoring() {
+        mBpfCoordinator.startMonitoring(this);
+    }
+
+    private void stopConntrackMonitoring() {
+        mBpfCoordinator.stopMonitoring(this);
+    }
+
     class BaseServingState extends State {
         @Override
         public void enter() {
+            startConntrackMonitoring();
+
             if (!startIPv4()) {
                 mLastError = TetheringManager.TETHER_ERROR_IFACE_CFG_ERROR;
                 return;
@@ -1149,6 +1175,7 @@
             }
 
             stopIPv4();
+            stopConntrackMonitoring();
 
             resetLinkProperties();
         }
diff --git a/Tethering/src/android/net/util/TetheringUtils.java b/Tethering/src/android/net/util/TetheringUtils.java
index 706d78c..9e7cc2f 100644
--- a/Tethering/src/android/net/util/TetheringUtils.java
+++ b/Tethering/src/android/net/util/TetheringUtils.java
@@ -36,6 +36,10 @@
  * {@hide}
  */
 public class TetheringUtils {
+    static {
+        System.loadLibrary("tetherutilsjni");
+    }
+
     public static final byte[] ALL_NODES = new byte[] {
         (byte) 0xff, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1
     };
diff --git a/Tethering/src/com/android/networkstack/tethering/BpfCoordinator.java b/Tethering/src/com/android/networkstack/tethering/BpfCoordinator.java
index 64ac37c..985328f 100644
--- a/Tethering/src/com/android/networkstack/tethering/BpfCoordinator.java
+++ b/Tethering/src/com/android/networkstack/tethering/BpfCoordinator.java
@@ -23,19 +23,26 @@
 import static android.net.NetworkStats.TAG_NONE;
 import static android.net.NetworkStats.UID_ALL;
 import static android.net.NetworkStats.UID_TETHERING;
+import static android.net.ip.ConntrackMonitor.ConntrackEvent;
 import static android.net.netstats.provider.NetworkStatsProvider.QUOTA_UNLIMITED;
+import static android.system.OsConstants.ETH_P_IP;
 import static android.system.OsConstants.ETH_P_IPV6;
 
 import static com.android.networkstack.tethering.TetheringConfiguration.DEFAULT_TETHER_OFFLOAD_POLL_INTERVAL_MS;
 
 import android.app.usage.NetworkStatsManager;
 import android.net.INetd;
+import android.net.LinkProperties;
 import android.net.MacAddress;
 import android.net.NetworkStats;
 import android.net.NetworkStats.Entry;
 import android.net.TetherOffloadRuleParcel;
+import android.net.ip.ConntrackMonitor;
+import android.net.ip.ConntrackMonitor.ConntrackEventConsumer;
 import android.net.ip.IpServer;
+import android.net.netlink.NetlinkConstants;
 import android.net.netstats.provider.NetworkStatsProvider;
+import android.net.util.InterfaceParams;
 import android.net.util.SharedLog;
 import android.net.util.TetheringUtils.ForwardedStats;
 import android.os.ConditionVariable;
@@ -52,14 +59,21 @@
 import com.android.internal.util.IndentingPrintWriter;
 import com.android.modules.utils.build.SdkLevel;
 import com.android.net.module.util.NetworkStackConstants;
+import com.android.net.module.util.Struct;
 import com.android.networkstack.tethering.apishim.common.BpfCoordinatorShim;
 
+import java.net.Inet4Address;
 import java.net.Inet6Address;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
 import java.util.ArrayList;
+import java.util.Collection;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Set;
 
 /**
  *  This coordinator is responsible for providing BPF offload relevant functionality.
@@ -71,14 +85,39 @@
  * @hide
  */
 public class BpfCoordinator {
+    // Ensure the JNI code is loaded. In production this will already have been loaded by
+    // TetherService, but for tests it needs to be either loaded here or loaded by every test.
+    // TODO: is there a better way?
+    static {
+        System.loadLibrary("tetherutilsjni");
+    }
+
+    static final boolean DOWNSTREAM = true;
+    static final boolean UPSTREAM = false;
+
     private static final String TAG = BpfCoordinator.class.getSimpleName();
     private static final int DUMP_TIMEOUT_MS = 10_000;
-    private static final String TETHER_INGRESS_FS_PATH =
-            "/sys/fs/bpf/map_offload_tether_ingress_map";
-    private static final String TETHER_STATS_MAP_PATH =
-            "/sys/fs/bpf/map_offload_tether_stats_map";
-    private static final String TETHER_LIMIT_MAP_PATH =
-            "/sys/fs/bpf/map_offload_tether_limit_map";
+    private static final MacAddress NULL_MAC_ADDRESS = MacAddress.fromString(
+            "00:00:00:00:00:00");
+    private static final String TETHER_DOWNSTREAM4_MAP_PATH = makeMapPath(DOWNSTREAM, 4);
+    private static final String TETHER_UPSTREAM4_MAP_PATH = makeMapPath(UPSTREAM, 4);
+    private static final String TETHER_DOWNSTREAM6_FS_PATH = makeMapPath(DOWNSTREAM, 6);
+    private static final String TETHER_UPSTREAM6_FS_PATH = makeMapPath(UPSTREAM, 6);
+    private static final String TETHER_STATS_MAP_PATH = makeMapPath("stats");
+    private static final String TETHER_LIMIT_MAP_PATH = makeMapPath("limit");
+    private static final String TETHER_ERROR_MAP_PATH = makeMapPath("error");
+
+    /** The names of all the BPF counters defined in bpf_tethering.h. */
+    public static final String[] sBpfCounterNames = getBpfCounterNames();
+
+    private static String makeMapPath(String which) {
+        return "/sys/fs/bpf/tethering/map_offload_tether_" + which + "_map";
+    }
+
+    private static String makeMapPath(boolean downstream, int ipVersion) {
+        return makeMapPath((downstream ? "downstream" : "upstream") + ipVersion);
+    }
+
 
     @VisibleForTesting
     enum StatsType {
@@ -94,6 +133,8 @@
     private final SharedLog mLog;
     @NonNull
     private final Dependencies mDeps;
+    @NonNull
+    private final ConntrackMonitor mConntrackMonitor;
     @Nullable
     private final BpfTetherStatsProvider mStatsProvider;
     @NonNull
@@ -156,6 +197,27 @@
     private final HashMap<IpServer, LinkedHashMap<Inet6Address, Ipv6ForwardingRule>>
             mIpv6ForwardingRules = new LinkedHashMap<>();
 
+    // Map of downstream client maps. Each of these maps represents the IPv4 clients for a given
+    // downstream. Needed to build IPv4 forwarding rules when conntrack events are received.
+    // Each map:
+    // - Is owned by the IpServer that is responsible for that downstream.
+    // - Must only be modified by that IpServer.
+    // - Is created when the IpServer adds its first client, and deleted when the IpServer deletes
+    //   its last client.
+    // Note that relying on the client address for finding downstream is okay for now because the
+    // client address is unique. See PrivateAddressCoordinator#requestDownstreamAddress.
+    // TODO: Refactor if any possible that the client address is not unique.
+    private final HashMap<IpServer, HashMap<Inet4Address, ClientInfo>>
+            mTetherClients = new HashMap<>();
+
+    // Set for which downstream is monitoring the conntrack netlink message.
+    private final Set<IpServer> mMonitoringIpServers = new HashSet<>();
+
+    // Map of upstream interface IPv4 address to interface index.
+    // TODO: consider making the key to be unique because the upstream address is not unique. It
+    // is okay for now because there have only one upstream generally.
+    private final HashMap<Inet4Address, Integer> mIpv4UpstreamIndices = new HashMap<>();
+
     // Runnable that used by scheduling next polling of stats.
     private final Runnable mScheduledPollingTask = () -> {
         updateForwardedStats();
@@ -179,6 +241,11 @@
         /** Get tethering configuration. */
         @Nullable public abstract TetheringConfiguration getTetherConfig();
 
+        /** Get conntrack monitor. */
+        @NonNull public ConntrackMonitor getConntrackMonitor(ConntrackEventConsumer consumer) {
+            return new ConntrackMonitor(getHandler(), getSharedLog(), consumer);
+        }
+
         /**
          * Check OS Build at least S.
          *
@@ -190,13 +257,46 @@
             return SdkLevel.isAtLeastS();
         }
 
-        /** Get ingress BPF map. */
-        @Nullable public BpfMap<TetherIngressKey, TetherIngressValue> getBpfIngressMap() {
+        /** Get downstream4 BPF map. */
+        @Nullable public BpfMap<Tether4Key, Tether4Value> getBpfDownstream4Map() {
             try {
-                return new BpfMap<>(TETHER_INGRESS_FS_PATH,
-                    BpfMap.BPF_F_RDWR, TetherIngressKey.class, TetherIngressValue.class);
+                return new BpfMap<>(TETHER_DOWNSTREAM4_MAP_PATH,
+                    BpfMap.BPF_F_RDWR, Tether4Key.class, Tether4Value.class);
             } catch (ErrnoException e) {
-                Log.e(TAG, "Cannot create ingress map: " + e);
+                Log.e(TAG, "Cannot create downstream4 map: " + e);
+                return null;
+            }
+        }
+
+        /** Get upstream4 BPF map. */
+        @Nullable public BpfMap<Tether4Key, Tether4Value> getBpfUpstream4Map() {
+            try {
+                return new BpfMap<>(TETHER_UPSTREAM4_MAP_PATH,
+                    BpfMap.BPF_F_RDWR, Tether4Key.class, Tether4Value.class);
+            } catch (ErrnoException e) {
+                Log.e(TAG, "Cannot create upstream4 map: " + e);
+                return null;
+            }
+        }
+
+        /** Get downstream6 BPF map. */
+        @Nullable public BpfMap<TetherDownstream6Key, Tether6Value> getBpfDownstream6Map() {
+            try {
+                return new BpfMap<>(TETHER_DOWNSTREAM6_FS_PATH,
+                    BpfMap.BPF_F_RDWR, TetherDownstream6Key.class, Tether6Value.class);
+            } catch (ErrnoException e) {
+                Log.e(TAG, "Cannot create downstream6 map: " + e);
+                return null;
+            }
+        }
+
+        /** Get upstream6 BPF map. */
+        @Nullable public BpfMap<TetherUpstream6Key, Tether6Value> getBpfUpstream6Map() {
+            try {
+                return new BpfMap<>(TETHER_UPSTREAM6_FS_PATH, BpfMap.BPF_F_RDWR,
+                        TetherUpstream6Key.class, Tether6Value.class);
+            } catch (ErrnoException e) {
+                Log.e(TAG, "Cannot create upstream6 map: " + e);
                 return null;
             }
         }
@@ -231,6 +331,7 @@
         mNetd = mDeps.getNetd();
         mLog = mDeps.getSharedLog().forSubComponent(TAG);
         mIsBpfEnabled = isBpfEnabled();
+        mConntrackMonitor = mDeps.getConntrackMonitor(new BpfConntrackEventConsumer());
         BpfTetherStatsProvider provider = new BpfTetherStatsProvider();
         try {
             mDeps.getNetworkStatsManager().registerNetworkStatsProvider(
@@ -295,6 +396,58 @@
     }
 
     /**
+     * Start conntrack message monitoring.
+     * Note that this can be only called on handler thread.
+     *
+     * TODO: figure out a better logging for non-interesting conntrack message.
+     * For example, the following logging is an IPCTNL_MSG_CT_GET message but looks scary.
+     * +---------------------------------------------------------------------------+
+     * | ERROR unparsable netlink msg: 1400000001010103000000000000000002000000    |
+     * +------------------+--------------------------------------------------------+
+     * |                  | struct nlmsghdr                                        |
+     * | 14000000         | length = 20                                            |
+     * | 0101             | type = NFNL_SUBSYS_CTNETLINK << 8 | IPCTNL_MSG_CT_GET  |
+     * | 0103             | flags                                                  |
+     * | 00000000         | seqno = 0                                              |
+     * | 00000000         | pid = 0                                                |
+     * |                  | struct nfgenmsg                                        |
+     * | 02               | nfgen_family  = AF_INET                                |
+     * | 00               | version = NFNETLINK_V0                                 |
+     * | 0000             | res_id                                                 |
+     * +------------------+--------------------------------------------------------+
+     * See NetlinkMonitor#handlePacket, NetlinkMessage#parseNfMessage.
+     */
+    public void startMonitoring(@NonNull final IpServer ipServer) {
+        if (!isUsingBpf()) return;
+
+        if (mMonitoringIpServers.contains(ipServer)) {
+            Log.wtf(TAG, "The same downstream " + ipServer.interfaceName()
+                    + " should not start monitoring twice.");
+            return;
+        }
+
+        if (mMonitoringIpServers.isEmpty()) {
+            mConntrackMonitor.start();
+            mLog.i("Monitoring started");
+        }
+
+        mMonitoringIpServers.add(ipServer);
+    }
+
+    /**
+     * Stop conntrack event monitoring.
+     * Note that this can be only called on handler thread.
+     */
+    public void stopMonitoring(@NonNull final IpServer ipServer) {
+        mMonitoringIpServers.remove(ipServer);
+
+        if (!mMonitoringIpServers.isEmpty()) return;
+
+        mConntrackMonitor.stop();
+        mLog.i("Monitoring stopped");
+    }
+
+    /**
      * Add forwarding rule. After adding the first rule on a given upstream, must add the data
      * limit on the given upstream.
      * Note that this can be only called on handler thread.
@@ -312,7 +465,7 @@
         }
         LinkedHashMap<Inet6Address, Ipv6ForwardingRule> rules = mIpv6ForwardingRules.get(ipServer);
 
-        // Setup the data limit on the given upstream if the first rule is added.
+        // When the first rule is added to an upstream, setup upstream forwarding and data limit.
         final int upstreamIfindex = rule.upstreamIfindex;
         if (!isAnyRuleOnUpstream(upstreamIfindex)) {
             // If failed to set a data limit, probably should not use this upstream, because
@@ -323,6 +476,19 @@
                 final String iface = mInterfaceNames.get(upstreamIfindex);
                 mLog.e("Setting data limit for " + iface + " failed.");
             }
+
+        }
+
+        if (!isAnyRuleFromDownstreamToUpstream(rule.downstreamIfindex, rule.upstreamIfindex)) {
+            final int downstream = rule.downstreamIfindex;
+            final int upstream = rule.upstreamIfindex;
+            // TODO: support upstream forwarding on non-point-to-point interfaces.
+            // TODO: get the MTU from LinkProperties and update the rules when it changes.
+            if (!mBpfCoordinatorShim.startUpstreamIpv6Forwarding(downstream, upstream,
+                    NULL_MAC_ADDRESS, NULL_MAC_ADDRESS, NetworkStackConstants.ETHER_MTU)) {
+                mLog.e("Failed to enable upstream IPv6 forwarding from "
+                        + mInterfaceNames.get(downstream) + " to " + mInterfaceNames.get(upstream));
+            }
         }
 
         // Must update the adding rule after calling #isAnyRuleOnUpstream because it needs to
@@ -355,6 +521,16 @@
             mIpv6ForwardingRules.remove(ipServer);
         }
 
+        // If no more rules between this upstream and downstream, stop upstream forwarding.
+        if (!isAnyRuleFromDownstreamToUpstream(rule.downstreamIfindex, rule.upstreamIfindex)) {
+            final int downstream = rule.downstreamIfindex;
+            final int upstream = rule.upstreamIfindex;
+            if (!mBpfCoordinatorShim.stopUpstreamIpv6Forwarding(downstream, upstream)) {
+                mLog.e("Failed to disable upstream IPv6 forwarding from "
+                        + mInterfaceNames.get(downstream) + " to " + mInterfaceNames.get(upstream));
+            }
+        }
+
         // Do cleanup functionality if there is no more rule on the given upstream.
         final int upstreamIfindex = rule.upstreamIfindex;
         if (!isAnyRuleOnUpstream(upstreamIfindex)) {
@@ -403,12 +579,22 @@
         if (rules == null) return;
 
         // Need to build a rule list because the rule map may be changed in the iteration.
-        for (final Ipv6ForwardingRule rule : new ArrayList<Ipv6ForwardingRule>(rules.values())) {
+        // First remove all the old rules, then add all the new rules. This is because the upstream
+        // forwarding code in tetherOffloadRuleAdd cannot support rules on two upstreams at the
+        // same time. Deleting the rules first ensures that upstream forwarding is disabled on the
+        // old upstream when the last rule is removed from it, and re-enabled on the new upstream
+        // when the first rule is added to it.
+        // TODO: Once the IPv6 client processing code has moved from IpServer to BpfCoordinator, do
+        // something smarter.
+        final ArrayList<Ipv6ForwardingRule> rulesCopy = new ArrayList<>(rules.values());
+        for (final Ipv6ForwardingRule rule : rulesCopy) {
             // Remove the old rule before adding the new one because the map uses the same key for
             // both rules. Reversing the processing order causes that the new rule is removed as
             // unexpected.
             // TODO: Add new rule first to reduce the latency which has no rule.
             tetherOffloadRuleRemove(ipServer, rule);
+        }
+        for (final Ipv6ForwardingRule rule : rulesCopy) {
             tetherOffloadRuleAdd(ipServer, rule.onNewUpstream(newUpstreamIfindex));
         }
     }
@@ -437,6 +623,80 @@
     }
 
     /**
+     * Add downstream client.
+     */
+    public void tetherOffloadClientAdd(@NonNull final IpServer ipServer,
+            @NonNull final ClientInfo client) {
+        if (!isUsingBpf()) return;
+
+        if (!mTetherClients.containsKey(ipServer)) {
+            mTetherClients.put(ipServer, new HashMap<Inet4Address, ClientInfo>());
+        }
+
+        HashMap<Inet4Address, ClientInfo> clients = mTetherClients.get(ipServer);
+        clients.put(client.clientAddress, client);
+    }
+
+    /**
+     * Remove downstream client.
+     */
+    public void tetherOffloadClientRemove(@NonNull final IpServer ipServer,
+            @NonNull final ClientInfo client) {
+        if (!isUsingBpf()) return;
+
+        HashMap<Inet4Address, ClientInfo> clients = mTetherClients.get(ipServer);
+        if (clients == null) return;
+
+        // If no rule is removed, return early. Avoid unnecessary work on a non-existent rule
+        // which may have never been added or removed already.
+        if (clients.remove(client.clientAddress) == null) return;
+
+        // Remove the downstream entry if it has no more rule.
+        if (clients.isEmpty()) {
+            mTetherClients.remove(ipServer);
+        }
+    }
+
+    /**
+     * Call when UpstreamNetworkState may be changed.
+     * If upstream has ipv4 for tethering, update this new UpstreamNetworkState to map. The
+     * upstream interface index and its address mapping is prepared for building IPv4
+     * offload rule.
+     *
+     * TODO: Delete the unused upstream interface mapping.
+     * TODO: Support ether ip upstream interface.
+     */
+    public void addUpstreamIfindexToMap(LinkProperties lp) {
+        if (!mPollingStarted) return;
+
+        // This will not work on a network that is using 464xlat because hasIpv4Address will not be
+        // true.
+        // TODO: need to consider 464xlat.
+        if (lp == null || !lp.hasIpv4Address()) return;
+
+        // Support raw ip upstream interface only.
+        final InterfaceParams params = InterfaceParams.getByName(lp.getInterfaceName());
+        if (params == null || params.hasMacAddress) return;
+
+        Collection<InetAddress> addresses = lp.getAddresses();
+        for (InetAddress addr: addresses) {
+            if (addr instanceof Inet4Address) {
+                Inet4Address i4addr = (Inet4Address) addr;
+                if (!i4addr.isAnyLocalAddress() && !i4addr.isLinkLocalAddress()
+                        && !i4addr.isLoopbackAddress() && !i4addr.isMulticastAddress()) {
+                    mIpv4UpstreamIndices.put(i4addr, params.index);
+                }
+            }
+        }
+    }
+
+
+    // TODO: make mInterfaceNames accessible to the shim and move this code to there.
+    private String getIfName(long ifindex) {
+        return mInterfaceNames.get((int) ifindex, Long.toString(ifindex));
+    }
+
+    /**
      * Dump information.
      * Block the function until all the data are dumped on the handler thread or timed-out. The
      * reason is that dumpsys invokes this function on the thread of caller and the data may only
@@ -464,11 +724,15 @@
 
             pw.println("Forwarding rules:");
             pw.increaseIndent();
-            if (mIpv6ForwardingRules.size() == 0) {
-                pw.println("<empty>");
-            } else {
-                dumpIpv6ForwardingRules(pw);
-            }
+            dumpIpv6UpstreamRules(pw);
+            dumpIpv6ForwardingRules(pw);
+            dumpIpv4ForwardingRules(pw);
+            pw.decreaseIndent();
+
+            pw.println();
+            pw.println("Forwarding counters:");
+            pw.increaseIndent();
+            dumpCounters(pw);
             pw.decreaseIndent();
 
             dumpDone.open();
@@ -488,6 +752,11 @@
     }
 
     private void dumpIpv6ForwardingRules(@NonNull IndentingPrintWriter pw) {
+        if (mIpv6ForwardingRules.size() == 0) {
+            pw.println("No IPv6 rules");
+            return;
+        }
+
         for (Map.Entry<IpServer, LinkedHashMap<Inet6Address, Ipv6ForwardingRule>> entry :
                 mIpv6ForwardingRules.entrySet()) {
             IpServer ipServer = entry.getKey();
@@ -508,11 +777,97 @@
         }
     }
 
+    private String ipv6UpstreamRuletoString(TetherUpstream6Key key, Tether6Value value) {
+        return String.format("%d(%s) -> %d(%s) %04x %s %s",
+                key.iif, getIfName(key.iif), value.oif, getIfName(value.oif),
+                value.ethProto, value.ethSrcMac, value.ethDstMac);
+    }
+
+    private void dumpIpv6UpstreamRules(IndentingPrintWriter pw) {
+        try (BpfMap<TetherUpstream6Key, Tether6Value> map = mDeps.getBpfUpstream6Map()) {
+            if (map == null) {
+                pw.println("No IPv6 upstream");
+                return;
+            }
+            if (map.isEmpty()) {
+                pw.println("No IPv6 upstream rules");
+                return;
+            }
+            map.forEach((k, v) -> pw.println(ipv6UpstreamRuletoString(k, v)));
+        } catch (ErrnoException e) {
+            pw.println("Error dumping IPv4 map: " + e);
+        }
+    }
+
+    private String ipv4RuleToString(Tether4Key key, Tether4Value value) {
+        final String private4, public4, dst4;
+        try {
+            private4 = InetAddress.getByAddress(key.src4).getHostAddress();
+            dst4 = InetAddress.getByAddress(key.dst4).getHostAddress();
+            public4 = InetAddress.getByAddress(value.src46).getHostAddress();
+        } catch (UnknownHostException impossible) {
+            throw new AssertionError("4-byte array not valid IPv4 address!");
+        }
+        return String.format("%d(%s) %d(%s) %s:%d -> %s:%d -> %s:%d",
+                key.iif, getIfName(key.iif), value.oif, getIfName(value.oif),
+                private4, key.srcPort, public4, value.srcPort, dst4, key.dstPort);
+    }
+
+    private void dumpIpv4ForwardingRules(IndentingPrintWriter pw) {
+        try (BpfMap<Tether4Key, Tether4Value> map = mDeps.getBpfUpstream4Map()) {
+            if (map == null) {
+                pw.println("No IPv4 support");
+                return;
+            }
+            if (map.isEmpty()) {
+                pw.println("No IPv4 rules");
+                return;
+            }
+            pw.println("[IPv4]: iif(iface) oif(iface) src nat dst");
+            pw.increaseIndent();
+            map.forEach((k, v) -> pw.println(ipv4RuleToString(k, v)));
+        } catch (ErrnoException e) {
+            pw.println("Error dumping IPv4 map: " + e);
+        }
+        pw.decreaseIndent();
+    }
+
+    /**
+     * Simple struct that only contains a u32. Must be public because Struct needs access to it.
+     * TODO: make this a public inner class of Struct so anyone can use it as, e.g., Struct.U32?
+     */
+    public static class U32Struct extends Struct {
+        @Struct.Field(order = 0, type = Struct.Type.U32)
+        public long val;
+    }
+
+    private void dumpCounters(@NonNull IndentingPrintWriter pw) {
+        try (BpfMap<U32Struct, U32Struct> map = new BpfMap<>(TETHER_ERROR_MAP_PATH,
+                BpfMap.BPF_F_RDONLY, U32Struct.class, U32Struct.class)) {
+
+            map.forEach((k, v) -> {
+                String counterName;
+                try {
+                    counterName = sBpfCounterNames[(int) k.val];
+                } catch (IndexOutOfBoundsException e) {
+                    // Should never happen because this code gets the counter name from the same
+                    // include file as the BPF program that increments the counter.
+                    Log.wtf(TAG, "Unknown tethering counter type " + k.val);
+                    counterName = Long.toString(k.val);
+                }
+                if (v.val > 0) pw.println(String.format("%s: %d", counterName, v.val));
+            });
+        } catch (ErrnoException e) {
+            pw.println("Error dumping counter map: " + e);
+        }
+    }
+
     /** IPv6 forwarding rule class. */
     public static class Ipv6ForwardingRule {
         public final int upstreamIfindex;
         public final int downstreamIfindex;
 
+        // TODO: store a ClientInfo object instead of storing address, srcMac, and dstMac directly.
         @NonNull
         public final Inet6Address address;
         @NonNull
@@ -554,19 +909,19 @@
         }
 
         /**
-         * Return a TetherIngressKey object built from the rule.
+         * Return a TetherDownstream6Key object built from the rule.
          */
         @NonNull
-        public TetherIngressKey makeTetherIngressKey() {
-            return new TetherIngressKey(upstreamIfindex, address.getAddress());
+        public TetherDownstream6Key makeTetherDownstream6Key() {
+            return new TetherDownstream6Key(upstreamIfindex, address.getAddress());
         }
 
         /**
-         * Return a TetherIngressValue object built from the rule.
+         * Return a Tether6Value object built from the rule.
          */
         @NonNull
-        public TetherIngressValue makeTetherIngressValue() {
-            return new TetherIngressValue(downstreamIfindex, dstMac, srcMac, ETH_P_IPV6,
+        public Tether6Value makeTether6Value() {
+            return new Tether6Value(downstreamIfindex, dstMac, srcMac, ETH_P_IPV6,
                     NetworkStackConstants.ETHER_MTU);
         }
 
@@ -589,6 +944,48 @@
         }
     }
 
+    /** Tethering client information class. */
+    public static class ClientInfo {
+        public final int downstreamIfindex;
+
+        @NonNull
+        public final MacAddress downstreamMac;
+        @NonNull
+        public final Inet4Address clientAddress;
+        @NonNull
+        public final MacAddress clientMac;
+
+        public ClientInfo(int downstreamIfindex,
+                @NonNull MacAddress downstreamMac, @NonNull Inet4Address clientAddress,
+                @NonNull MacAddress clientMac) {
+            this.downstreamIfindex = downstreamIfindex;
+            this.downstreamMac = downstreamMac;
+            this.clientAddress = clientAddress;
+            this.clientMac = clientMac;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (!(o instanceof ClientInfo)) return false;
+            ClientInfo that = (ClientInfo) o;
+            return this.downstreamIfindex == that.downstreamIfindex
+                    && Objects.equals(this.downstreamMac, that.downstreamMac)
+                    && Objects.equals(this.clientAddress, that.clientAddress)
+                    && Objects.equals(this.clientMac, that.clientMac);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(downstreamIfindex, downstreamMac, clientAddress, clientMac);
+        }
+
+        @Override
+        public String toString() {
+            return String.format("downstream: %d (%s), client: %s (%s)",
+                    downstreamIfindex, downstreamMac, clientAddress, clientMac);
+        }
+    }
+
     /**
      * A BPF tethering stats provider to provide network statistics to the system.
      * Note that this class' data may only be accessed on the handler thread.
@@ -655,6 +1052,99 @@
         }
     }
 
+    @Nullable
+    private ClientInfo getClientInfo(@NonNull Inet4Address clientAddress) {
+        for (HashMap<Inet4Address, ClientInfo> clients : mTetherClients.values()) {
+            for (ClientInfo client : clients.values()) {
+                if (clientAddress.equals(client.clientAddress)) {
+                    return client;
+                }
+            }
+        }
+        return null;
+    }
+
+    // Support raw ip only.
+    // TODO: add ether ip support.
+    private class BpfConntrackEventConsumer implements ConntrackEventConsumer {
+        @NonNull
+        private Tether4Key makeTetherUpstream4Key(
+                @NonNull ConntrackEvent e, @NonNull ClientInfo c) {
+            return new Tether4Key(c.downstreamIfindex, c.downstreamMac,
+                    e.tupleOrig.protoNum, e.tupleOrig.srcIp.getAddress(),
+                    e.tupleOrig.dstIp.getAddress(), e.tupleOrig.srcPort, e.tupleOrig.dstPort);
+        }
+
+        @NonNull
+        private Tether4Key makeTetherDownstream4Key(
+                @NonNull ConntrackEvent e, @NonNull ClientInfo c, int upstreamIndex) {
+            return new Tether4Key(upstreamIndex, NULL_MAC_ADDRESS /* dstMac (rawip) */,
+                    e.tupleReply.protoNum, e.tupleReply.srcIp.getAddress(),
+                    e.tupleReply.dstIp.getAddress(), e.tupleReply.srcPort, e.tupleReply.dstPort);
+        }
+
+        @NonNull
+        private Tether4Value makeTetherUpstream4Value(@NonNull ConntrackEvent e,
+                int upstreamIndex) {
+            return new Tether4Value(upstreamIndex,
+                    NULL_MAC_ADDRESS /* ethDstMac (rawip) */,
+                    NULL_MAC_ADDRESS /* ethSrcMac (rawip) */, ETH_P_IP,
+                    NetworkStackConstants.ETHER_MTU, toIpv4MappedAddressBytes(e.tupleReply.dstIp),
+                    toIpv4MappedAddressBytes(e.tupleReply.srcIp), e.tupleReply.dstPort,
+                    e.tupleReply.srcPort, 0 /* lastUsed, filled by bpf prog only */);
+        }
+
+        @NonNull
+        private Tether4Value makeTetherDownstream4Value(@NonNull ConntrackEvent e,
+                @NonNull ClientInfo c, int upstreamIndex) {
+            return new Tether4Value(c.downstreamIfindex,
+                    c.clientMac, c.downstreamMac, ETH_P_IP, NetworkStackConstants.ETHER_MTU,
+                    toIpv4MappedAddressBytes(e.tupleOrig.dstIp),
+                    toIpv4MappedAddressBytes(e.tupleOrig.srcIp),
+                    e.tupleOrig.dstPort, e.tupleOrig.srcPort,
+                    0 /* lastUsed, filled by bpf prog only */);
+        }
+
+        @NonNull
+        private byte[] toIpv4MappedAddressBytes(Inet4Address ia4) {
+            final byte[] addr4 = ia4.getAddress();
+            final byte[] addr6 = new byte[16];
+            addr6[10] = (byte) 0xff;
+            addr6[11] = (byte) 0xff;
+            addr6[12] = addr4[0];
+            addr6[13] = addr4[1];
+            addr6[14] = addr4[2];
+            addr6[15] = addr4[3];
+            return addr6;
+        }
+
+        public void accept(ConntrackEvent e) {
+            final ClientInfo tetherClient = getClientInfo(e.tupleOrig.srcIp);
+            if (tetherClient == null) return;
+
+            final Integer upstreamIndex = mIpv4UpstreamIndices.get(e.tupleReply.dstIp);
+            if (upstreamIndex == null) return;
+
+            final Tether4Key upstream4Key = makeTetherUpstream4Key(e, tetherClient);
+            final Tether4Key downstream4Key = makeTetherDownstream4Key(e, tetherClient,
+                    upstreamIndex);
+
+            if (e.msgType == (NetlinkConstants.NFNL_SUBSYS_CTNETLINK << 8
+                    | NetlinkConstants.IPCTNL_MSG_CT_DELETE)) {
+                mBpfCoordinatorShim.tetherOffloadRuleRemove(false, upstream4Key);
+                mBpfCoordinatorShim.tetherOffloadRuleRemove(true, downstream4Key);
+                return;
+            }
+
+            final Tether4Value upstream4Value = makeTetherUpstream4Value(e, upstreamIndex);
+            final Tether4Value downstream4Value = makeTetherDownstream4Value(e, tetherClient,
+                    upstreamIndex);
+
+            mBpfCoordinatorShim.tetherOffloadRuleAdd(false, upstream4Key, upstream4Value);
+            mBpfCoordinatorShim.tetherOffloadRuleAdd(true, downstream4Key, downstream4Value);
+        }
+    }
+
     private boolean isBpfEnabled() {
         final TetheringConfiguration config = mDeps.getTetherConfig();
         return (config != null) ? config.isBpfOffloadEnabled() : true /* default value */;
@@ -723,6 +1213,19 @@
         return false;
     }
 
+    private boolean isAnyRuleFromDownstreamToUpstream(int downstreamIfindex, int upstreamIfindex) {
+        for (LinkedHashMap<Inet6Address, Ipv6ForwardingRule> rules : mIpv6ForwardingRules
+                .values()) {
+            for (Ipv6ForwardingRule rule : rules.values()) {
+                if (downstreamIfindex == rule.downstreamIfindex
+                        && upstreamIfindex == rule.upstreamIfindex) {
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+
     @NonNull
     private NetworkStats buildNetworkStats(@NonNull StatsType type, int ifIndex,
             @NonNull final ForwardedStats diff) {
@@ -841,4 +1344,6 @@
     final SparseArray<String> getInterfaceNamesForTesting() {
         return mInterfaceNames;
     }
+
+    private static native String[] getBpfCounterNames();
 }
diff --git a/Tethering/src/com/android/networkstack/tethering/BpfMap.java b/Tethering/src/com/android/networkstack/tethering/BpfMap.java
index 78d212c..9a9376f 100644
--- a/Tethering/src/com/android/networkstack/tethering/BpfMap.java
+++ b/Tethering/src/com/android/networkstack/tethering/BpfMap.java
@@ -41,6 +41,10 @@
  * @param <V> the value of the map.
  */
 public class BpfMap<K extends Struct, V extends Struct> implements AutoCloseable {
+    static {
+        System.loadLibrary("tetherutilsjni");
+    }
+
     // Following definitions from kernel include/uapi/linux/bpf.h
     public static final int BPF_F_RDWR = 0;
     public static final int BPF_F_RDONLY = 1 << 3;
@@ -134,6 +138,11 @@
         return deleteMapEntry(mMapFd, key.writeToBytes());
     }
 
+    /** Returns {@code true} if this map contains no elements. */
+    public boolean isEmpty() throws ErrnoException {
+        return getFirstKey() == null;
+    }
+
     private K getNextKeyInternal(@Nullable K key) throws ErrnoException {
         final byte[] rawKey = getNextRawKey(
                 key == null ? null : key.writeToBytes());
@@ -213,7 +222,7 @@
     }
 
     @Override
-    public void close() throws Exception {
+    public void close() throws ErrnoException {
         closeMap(mMapFd);
     }
 
diff --git a/Tethering/src/com/android/networkstack/tethering/EntitlementManager.java b/Tethering/src/com/android/networkstack/tethering/EntitlementManager.java
index bb7322f..b1e3cfe 100644
--- a/Tethering/src/com/android/networkstack/tethering/EntitlementManager.java
+++ b/Tethering/src/com/android/networkstack/tethering/EntitlementManager.java
@@ -418,7 +418,8 @@
             if (period <= 0) return;
 
             Intent intent = new Intent(ACTION_PROVISIONING_ALARM);
-            mProvisioningRecheckAlarm = PendingIntent.getBroadcast(mContext, 0, intent, 0);
+            mProvisioningRecheckAlarm = PendingIntent.getBroadcast(mContext, 0, intent,
+                    PendingIntent.FLAG_IMMUTABLE);
             AlarmManager alarmManager = (AlarmManager) mContext.getSystemService(
                     Context.ALARM_SERVICE);
             long periodMs = period * MS_PER_HOUR;
diff --git a/Tethering/src/com/android/networkstack/tethering/Tether4Key.java b/Tethering/src/com/android/networkstack/tethering/Tether4Key.java
new file mode 100644
index 0000000..a01ea34
--- /dev/null
+++ b/Tethering/src/com/android/networkstack/tethering/Tether4Key.java
@@ -0,0 +1,81 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.networkstack.tethering;
+
+import android.net.MacAddress;
+
+import androidx.annotation.NonNull;
+
+import com.android.net.module.util.Struct;
+import com.android.net.module.util.Struct.Field;
+import com.android.net.module.util.Struct.Type;
+
+import java.net.Inet4Address;
+import java.net.UnknownHostException;
+import java.util.Objects;
+
+/** Key type for downstream & upstream IPv4 forwarding maps. */
+public class Tether4Key extends Struct {
+    @Field(order = 0, type = Type.U32)
+    public final long iif;
+
+    @Field(order = 1, type = Type.EUI48)
+    public final MacAddress dstMac;
+
+    @Field(order = 2, type = Type.U8, padding = 1)
+    public final short l4proto;
+
+    @Field(order = 3, type = Type.ByteArray, arraysize = 4)
+    public final byte[] src4;
+
+    @Field(order = 4, type = Type.ByteArray, arraysize = 4)
+    public final byte[] dst4;
+
+    @Field(order = 5, type = Type.UBE16)
+    public final int srcPort;
+
+    @Field(order = 6, type = Type.UBE16)
+    public final int dstPort;
+
+    public Tether4Key(final long iif, @NonNull final MacAddress dstMac, final short l4proto,
+            final byte[] src4, final byte[] dst4, final int srcPort,
+            final int dstPort) {
+        Objects.requireNonNull(dstMac);
+
+        this.iif = iif;
+        this.dstMac = dstMac;
+        this.l4proto = l4proto;
+        this.src4 = src4;
+        this.dst4 = dst4;
+        this.srcPort = srcPort;
+        this.dstPort = dstPort;
+    }
+
+    @Override
+    public String toString() {
+        try {
+            return String.format(
+                    "iif: %d, dstMac: %s, l4proto: %d, src4: %s, dst4: %s, "
+                            + "srcPort: %d, dstPort: %d",
+                    iif, dstMac, l4proto,
+                    Inet4Address.getByAddress(src4), Inet4Address.getByAddress(dst4),
+                    Short.toUnsignedInt((short) srcPort), Short.toUnsignedInt((short) dstPort));
+        } catch (UnknownHostException | IllegalArgumentException e) {
+            return String.format("Invalid IP address", e);
+        }
+    }
+}
diff --git a/Tethering/src/com/android/networkstack/tethering/Tether4Value.java b/Tethering/src/com/android/networkstack/tethering/Tether4Value.java
new file mode 100644
index 0000000..03a226c
--- /dev/null
+++ b/Tethering/src/com/android/networkstack/tethering/Tether4Value.java
@@ -0,0 +1,97 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.networkstack.tethering;
+
+import android.net.MacAddress;
+
+import androidx.annotation.NonNull;
+
+import com.android.net.module.util.Struct;
+import com.android.net.module.util.Struct.Field;
+import com.android.net.module.util.Struct.Type;
+
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.util.Objects;
+
+/** Value type for downstream & upstream IPv4 forwarding maps. */
+public class Tether4Value extends Struct {
+    @Field(order = 0, type = Type.U32)
+    public final long oif;
+
+    // The ethhdr struct which is defined in uapi/linux/if_ether.h
+    @Field(order = 1, type = Type.EUI48)
+    public final MacAddress ethDstMac;
+    @Field(order = 2, type = Type.EUI48)
+    public final MacAddress ethSrcMac;
+    @Field(order = 3, type = Type.UBE16)
+    public final int ethProto;  // Packet type ID field.
+
+    @Field(order = 4, type = Type.U16)
+    public final int pmtu;
+
+    @Field(order = 5, type = Type.ByteArray, arraysize = 16)
+    public final byte[] src46;
+
+    @Field(order = 6, type = Type.ByteArray, arraysize = 16)
+    public final byte[] dst46;
+
+    @Field(order = 7, type = Type.UBE16)
+    public final int srcPort;
+
+    @Field(order = 8, type = Type.UBE16)
+    public final int dstPort;
+
+    // TODO: consider using U64.
+    @Field(order = 9, type = Type.U63)
+    public final long lastUsed;
+
+    public Tether4Value(final long oif, @NonNull final MacAddress ethDstMac,
+            @NonNull final MacAddress ethSrcMac, final int ethProto, final int pmtu,
+            final byte[] src46, final byte[] dst46, final int srcPort,
+            final int dstPort, final long lastUsed) {
+        Objects.requireNonNull(ethDstMac);
+        Objects.requireNonNull(ethSrcMac);
+
+        this.oif = oif;
+        this.ethDstMac = ethDstMac;
+        this.ethSrcMac = ethSrcMac;
+        this.ethProto = ethProto;
+        this.pmtu = pmtu;
+        this.src46 = src46;
+        this.dst46 = dst46;
+        this.srcPort = srcPort;
+        this.dstPort = dstPort;
+        this.lastUsed = lastUsed;
+    }
+
+    @Override
+    public String toString() {
+        try {
+            return String.format(
+                    "oif: %d, ethDstMac: %s, ethSrcMac: %s, ethProto: %d, pmtu: %d, "
+                            + "src46: %s, dst46: %s, srcPort: %d, dstPort: %d, "
+                            + "lastUsed: %d",
+                    oif, ethDstMac, ethSrcMac, ethProto, pmtu,
+                    InetAddress.getByAddress(src46), InetAddress.getByAddress(dst46),
+                    Short.toUnsignedInt((short) srcPort), Short.toUnsignedInt((short) dstPort),
+                    lastUsed);
+        } catch (UnknownHostException | IllegalArgumentException e) {
+            return String.format("Invalid IP address", e);
+        }
+    }
+}
diff --git a/Tethering/src/com/android/networkstack/tethering/TetherIngressValue.java b/Tethering/src/com/android/networkstack/tethering/Tether6Value.java
similarity index 66%
rename from Tethering/src/com/android/networkstack/tethering/TetherIngressValue.java
rename to Tethering/src/com/android/networkstack/tethering/Tether6Value.java
index e2116fc..b3107fd 100644
--- a/Tethering/src/com/android/networkstack/tethering/TetherIngressValue.java
+++ b/Tethering/src/com/android/networkstack/tethering/Tether6Value.java
@@ -21,15 +21,13 @@
 import androidx.annotation.NonNull;
 
 import com.android.net.module.util.Struct;
-import com.android.net.module.util.Struct.Field;
-import com.android.net.module.util.Struct.Type;
 
 import java.util.Objects;
 
-/** The value of BpfMap which is used for bpf offload. */
-public class TetherIngressValue extends Struct {
-    @Field(order = 0, type = Type.U32)
-    public final long oif; // The output interface index.
+/** Value type for downstream and upstream IPv6 forwarding maps. */
+public class Tether6Value extends Struct {
+    @Field(order = 0, type = Type.S32)
+    public final int oif; // The output interface index.
 
     // The ethhdr struct which is defined in uapi/linux/if_ether.h
     @Field(order = 1, type = Type.EUI48)
@@ -42,7 +40,7 @@
     @Field(order = 4, type = Type.U16)
     public final int pmtu; // The maximum L3 output path/route mtu.
 
-    public TetherIngressValue(final long oif, @NonNull final MacAddress ethDstMac,
+    public Tether6Value(final int oif, @NonNull final MacAddress ethDstMac,
             @NonNull final MacAddress ethSrcMac, final int ethProto, final int pmtu) {
         Objects.requireNonNull(ethSrcMac);
         Objects.requireNonNull(ethDstMac);
@@ -55,24 +53,6 @@
     }
 
     @Override
-    public boolean equals(Object obj) {
-        if (this == obj) return true;
-
-        if (!(obj instanceof TetherIngressValue)) return false;
-
-        final TetherIngressValue that = (TetherIngressValue) obj;
-
-        return oif == that.oif && ethDstMac.equals(that.ethDstMac)
-                && ethSrcMac.equals(that.ethSrcMac) && ethProto == that.ethProto
-                && pmtu == that.pmtu;
-    }
-
-    @Override
-    public int hashCode() {
-        return Objects.hash(oif, ethDstMac, ethSrcMac, ethProto, pmtu);
-    }
-
-    @Override
     public String toString() {
         return String.format("oif: %d, dstMac: %s, srcMac: %s, proto: %d, pmtu: %d", oif,
                 ethDstMac, ethSrcMac, ethProto, pmtu);
diff --git a/Tethering/src/com/android/networkstack/tethering/TetherIngressKey.java b/Tethering/src/com/android/networkstack/tethering/TetherDownstream6Key.java
similarity index 86%
rename from Tethering/src/com/android/networkstack/tethering/TetherIngressKey.java
rename to Tethering/src/com/android/networkstack/tethering/TetherDownstream6Key.java
index 78683c5..3860cba 100644
--- a/Tethering/src/com/android/networkstack/tethering/TetherIngressKey.java
+++ b/Tethering/src/com/android/networkstack/tethering/TetherDownstream6Key.java
@@ -26,14 +26,14 @@
 import java.util.Arrays;
 
 /** The key of BpfMap which is used for bpf offload. */
-public class TetherIngressKey extends Struct {
+public class TetherDownstream6Key extends Struct {
     @Field(order = 0, type = Type.U32)
     public final long iif; // The input interface index.
 
     @Field(order = 1, type = Type.ByteArray, arraysize = 16)
     public final byte[] neigh6; // The destination IPv6 address.
 
-    public TetherIngressKey(final long iif, final byte[] neigh6) {
+    public TetherDownstream6Key(final long iif, final byte[] neigh6) {
         try {
             final Inet6Address unused = (Inet6Address) InetAddress.getByAddress(neigh6);
         } catch (ClassCastException | UnknownHostException e) {
@@ -48,9 +48,9 @@
     public boolean equals(Object obj) {
         if (this == obj) return true;
 
-        if (!(obj instanceof TetherIngressKey)) return false;
+        if (!(obj instanceof TetherDownstream6Key)) return false;
 
-        final TetherIngressKey that = (TetherIngressKey) obj;
+        final TetherDownstream6Key that = (TetherDownstream6Key) obj;
 
         return iif == that.iif && Arrays.equals(neigh6, that.neigh6);
     }
@@ -66,7 +66,7 @@
             return String.format("iif: %d, neigh: %s", iif, Inet6Address.getByAddress(neigh6));
         } catch (UnknownHostException e) {
             // Should not happen because construtor already verify neigh6.
-            throw new IllegalStateException("Invalid TetherIngressKey");
+            throw new IllegalStateException("Invalid TetherDownstream6Key");
         }
     }
 }
diff --git a/Tethering/src/com/android/networkstack/tethering/TetherUpstream6Key.java b/Tethering/src/com/android/networkstack/tethering/TetherUpstream6Key.java
new file mode 100644
index 0000000..c736f2a
--- /dev/null
+++ b/Tethering/src/com/android/networkstack/tethering/TetherUpstream6Key.java
@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.networkstack.tethering;
+
+import com.android.net.module.util.Struct;
+
+/** Key type for upstream IPv6 forwarding map. */
+public class TetherUpstream6Key extends Struct {
+    @Field(order = 0, type = Type.S32)
+    public final int iif; // The input interface index.
+
+    public TetherUpstream6Key(int iif) {
+        this.iif = iif;
+    }
+}
diff --git a/Tethering/src/com/android/networkstack/tethering/Tethering.java b/Tethering/src/com/android/networkstack/tethering/Tethering.java
index fdd1c40..385c691 100644
--- a/Tethering/src/com/android/networkstack/tethering/Tethering.java
+++ b/Tethering/src/com/android/networkstack/tethering/Tethering.java
@@ -1636,6 +1636,13 @@
         protected void handleNewUpstreamNetworkState(UpstreamNetworkState ns) {
             mIPv6TetheringCoordinator.updateUpstreamNetworkState(ns);
             mOffload.updateUpstreamNetworkState(ns);
+
+            // TODO: Delete all related offload rules which are using this upstream.
+            if (ns != null) {
+                // Add upstream index to the map. The upstream interface index is required while
+                // the conntrack event builds the offload rules.
+                mBpfCoordinator.addUpstreamIfindexToMap(ns.linkProperties);
+            }
         }
 
         private void handleInterfaceServingStateActive(int mode, IpServer who) {
@@ -2218,6 +2225,13 @@
                 && !isProvisioningNeededButUnavailable();
     }
 
+    private void dumpBpf(IndentingPrintWriter pw) {
+        pw.println("BPF offload:");
+        pw.increaseIndent();
+        mBpfCoordinator.dump(pw);
+        pw.decreaseIndent();
+    }
+
     void dump(@NonNull FileDescriptor fd, @NonNull PrintWriter writer, @Nullable String[] args) {
         // Binder.java closes the resource for us.
         @SuppressWarnings("resource")
@@ -2228,6 +2242,11 @@
             return;
         }
 
+        if (argsContain(args, "bpf")) {
+            dumpBpf(pw);
+            return;
+        }
+
         pw.println("Tethering:");
         pw.increaseIndent();
 
@@ -2279,10 +2298,7 @@
         mOffloadController.dump(pw);
         pw.decreaseIndent();
 
-        pw.println("BPF offload:");
-        pw.increaseIndent();
-        mBpfCoordinator.dump(pw);
-        pw.decreaseIndent();
+        dumpBpf(pw);
 
         pw.println("Private address coordinator:");
         pw.increaseIndent();
diff --git a/Tethering/src/com/android/networkstack/tethering/TetheringService.java b/Tethering/src/com/android/networkstack/tethering/TetheringService.java
index 613328d..c69dc49 100644
--- a/Tethering/src/com/android/networkstack/tethering/TetheringService.java
+++ b/Tethering/src/com/android/networkstack/tethering/TetheringService.java
@@ -82,7 +82,6 @@
      */
     @VisibleForTesting
     public Tethering makeTethering(TetheringDependencies deps) {
-        System.loadLibrary("tetherutilsjni");
         return new Tethering(deps);
     }
 
diff --git a/Tethering/tests/integration/Android.bp b/Tethering/tests/integration/Android.bp
index 42f83bf..f456273 100644
--- a/Tethering/tests/integration/Android.bp
+++ b/Tethering/tests/integration/Android.bp
@@ -70,6 +70,7 @@
     test_config: "AndroidTest_Coverage.xml",
     defaults: ["libnetworkstackutilsjni_deps"],
     static_libs: [
+        "NetdStaticLibTestsLib",
         "NetworkStaticLibTestsLib",
         "NetworkStackTestsLib",
         "TetheringTestsLib",
@@ -81,6 +82,7 @@
         "libstaticjvmtiagent",
         // For NetworkStackUtils included in NetworkStackBase
         "libnetworkstackutilsjni",
+        "libtetherutilsjni",
     ],
     jarjar_rules: ":TetheringTestsJarJarRules",
     compile_multilib: "both",
diff --git a/Tethering/tests/privileged/src/com/android/networkstack/tethering/BpfMapTest.java b/Tethering/tests/privileged/src/com/android/networkstack/tethering/BpfMapTest.java
index 04c1f00..cceaa8c 100644
--- a/Tethering/tests/privileged/src/com/android/networkstack/tethering/BpfMapTest.java
+++ b/Tethering/tests/privileged/src/com/android/networkstack/tethering/BpfMapTest.java
@@ -35,7 +35,6 @@
 
 import com.android.testutils.DevSdkIgnoreRule.IgnoreUpTo;
 
-import org.junit.After;
 import org.junit.Before;
 import org.junit.BeforeClass;
 import org.junit.Test;
@@ -51,10 +50,12 @@
 public final class BpfMapTest {
     // Sync from packages/modules/Connectivity/Tethering/bpf_progs/offload.c.
     private static final int TEST_MAP_SIZE = 16;
-    private static final String TETHER_INGRESS_FS_PATH =
-            "/sys/fs/bpf/map_test_tether_ingress_map";
+    private static final String TETHER_DOWNSTREAM6_FS_PATH =
+            "/sys/fs/bpf/tethering/map_test_tether_downstream6_map";
 
-    private ArrayMap<TetherIngressKey, TetherIngressValue> mTestData;
+    private ArrayMap<TetherDownstream6Key, Tether6Value> mTestData;
+
+    private BpfMap<TetherDownstream6Key, Tether6Value> mTestMap;
 
     @BeforeClass
     public static void setupOnce() {
@@ -63,66 +64,54 @@
 
     @Before
     public void setUp() throws Exception {
-        // TODO: Simply the test map creation and deletion.
-        // - Make the map a class member (mTestMap)
-        // - Open the test map RW in setUp
-        // - Close the test map in tearDown.
-        cleanTestMap();
-
         mTestData = new ArrayMap<>();
-        mTestData.put(createTetherIngressKey(101, "2001:db8::1"),
-                createTetherIngressValue(11, "00:00:00:00:00:0a", "11:11:11:00:00:0b", ETH_P_IPV6,
-                1280));
-        mTestData.put(createTetherIngressKey(102, "2001:db8::2"),
-                createTetherIngressValue(22, "00:00:00:00:00:0c", "22:22:22:00:00:0d", ETH_P_IPV6,
-                1400));
-        mTestData.put(createTetherIngressKey(103, "2001:db8::3"),
-                createTetherIngressValue(33, "00:00:00:00:00:0e", "33:33:33:00:00:0f", ETH_P_IPV6,
-                1500));
+        mTestData.put(createTetherDownstream6Key(101, "2001:db8::1"),
+                createTether6Value(11, "00:00:00:00:00:0a", "11:11:11:00:00:0b",
+                ETH_P_IPV6, 1280));
+        mTestData.put(createTetherDownstream6Key(102, "2001:db8::2"),
+                createTether6Value(22, "00:00:00:00:00:0c", "22:22:22:00:00:0d",
+                ETH_P_IPV6, 1400));
+        mTestData.put(createTetherDownstream6Key(103, "2001:db8::3"),
+                createTether6Value(33, "00:00:00:00:00:0e", "33:33:33:00:00:0f",
+                ETH_P_IPV6, 1500));
+
+        initTestMap();
     }
 
-    @After
-    public void tearDown() throws Exception {
-        cleanTestMap();
+    private void initTestMap() throws Exception {
+        mTestMap = new BpfMap<>(
+                TETHER_DOWNSTREAM6_FS_PATH, BpfMap.BPF_F_RDWR,
+                TetherDownstream6Key.class, Tether6Value.class);
+
+        mTestMap.forEach((key, value) -> {
+            try {
+                assertTrue(mTestMap.deleteEntry(key));
+            } catch (ErrnoException e) {
+                fail("Fail to delete the key " + key + ": " + e);
+            }
+        });
+        assertNull(mTestMap.getFirstKey());
+        assertTrue(mTestMap.isEmpty());
     }
 
-    private BpfMap<TetherIngressKey, TetherIngressValue> getTestMap() throws Exception {
-        return new BpfMap<>(
-                TETHER_INGRESS_FS_PATH, BpfMap.BPF_F_RDWR,
-                TetherIngressKey.class, TetherIngressValue.class);
-    }
-
-    private void cleanTestMap() throws Exception {
-        try (BpfMap<TetherIngressKey, TetherIngressValue> bpfMap = getTestMap()) {
-            bpfMap.forEach((key, value) -> {
-                try {
-                    assertTrue(bpfMap.deleteEntry(key));
-                } catch (ErrnoException e) {
-                    fail("Fail to delete the key " + key + ": " + e);
-                }
-            });
-            assertNull(bpfMap.getFirstKey());
-        }
-    }
-
-    private TetherIngressKey createTetherIngressKey(long iif, String address) throws Exception {
+    private TetherDownstream6Key createTetherDownstream6Key(long iif, String address)
+            throws Exception {
         final InetAddress ipv6Address = InetAddress.getByName(address);
 
-        return new TetherIngressKey(iif, ipv6Address.getAddress());
+        return new TetherDownstream6Key(iif, ipv6Address.getAddress());
     }
 
-    private TetherIngressValue createTetherIngressValue(long oif, String src, String dst, int proto,
-            int pmtu) throws Exception {
+    private Tether6Value createTether6Value(int oif, String src, String dst, int proto, int pmtu) {
         final MacAddress srcMac = MacAddress.fromString(src);
         final MacAddress dstMac = MacAddress.fromString(dst);
 
-        return new TetherIngressValue(oif, dstMac, srcMac, proto, pmtu);
+        return new Tether6Value(oif, dstMac, srcMac, proto, pmtu);
     }
 
     @Test
     public void testGetFd() throws Exception {
-        try (BpfMap readOnlyMap = new BpfMap<>(TETHER_INGRESS_FS_PATH, BpfMap.BPF_F_RDONLY,
-                TetherIngressKey.class, TetherIngressValue.class)) {
+        try (BpfMap readOnlyMap = new BpfMap<>(TETHER_DOWNSTREAM6_FS_PATH, BpfMap.BPF_F_RDONLY,
+                TetherDownstream6Key.class, Tether6Value.class)) {
             assertNotNull(readOnlyMap);
             try {
                 readOnlyMap.insertEntry(mTestData.keyAt(0), mTestData.valueAt(0));
@@ -131,8 +120,8 @@
                 assertEquals(OsConstants.EPERM, expected.errno);
             }
         }
-        try (BpfMap writeOnlyMap = new BpfMap<>(TETHER_INGRESS_FS_PATH, BpfMap.BPF_F_WRONLY,
-                TetherIngressKey.class, TetherIngressValue.class)) {
+        try (BpfMap writeOnlyMap = new BpfMap<>(TETHER_DOWNSTREAM6_FS_PATH, BpfMap.BPF_F_WRONLY,
+                TetherDownstream6Key.class, Tether6Value.class)) {
             assertNotNull(writeOnlyMap);
             try {
                 writeOnlyMap.getFirstKey();
@@ -141,214 +130,212 @@
                 assertEquals(OsConstants.EPERM, expected.errno);
             }
         }
-        try (BpfMap readWriteMap = new BpfMap<>(TETHER_INGRESS_FS_PATH, BpfMap.BPF_F_RDWR,
-                TetherIngressKey.class, TetherIngressValue.class)) {
+        try (BpfMap readWriteMap = new BpfMap<>(TETHER_DOWNSTREAM6_FS_PATH, BpfMap.BPF_F_RDWR,
+                TetherDownstream6Key.class, Tether6Value.class)) {
             assertNotNull(readWriteMap);
         }
     }
 
     @Test
-    public void testGetFirstKey() throws Exception {
-        try (BpfMap<TetherIngressKey, TetherIngressValue> bpfMap = getTestMap()) {
-            // getFirstKey on an empty map returns null.
-            assertFalse(bpfMap.containsKey(mTestData.keyAt(0)));
-            assertNull(bpfMap.getFirstKey());
-            assertNull(bpfMap.getValue(mTestData.keyAt(0)));
+    public void testIsEmpty() throws Exception {
+        assertNull(mTestMap.getFirstKey());
+        assertTrue(mTestMap.isEmpty());
 
-            // getFirstKey on a non-empty map returns the first key.
-            bpfMap.insertEntry(mTestData.keyAt(0), mTestData.valueAt(0));
-            assertEquals(mTestData.keyAt(0), bpfMap.getFirstKey());
-        }
+        mTestMap.insertEntry(mTestData.keyAt(0), mTestData.valueAt(0));
+        assertFalse(mTestMap.isEmpty());
+
+        mTestMap.deleteEntry((mTestData.keyAt(0)));
+        assertTrue(mTestMap.isEmpty());
+    }
+
+    @Test
+    public void testGetFirstKey() throws Exception {
+        // getFirstKey on an empty map returns null.
+        assertFalse(mTestMap.containsKey(mTestData.keyAt(0)));
+        assertNull(mTestMap.getFirstKey());
+        assertNull(mTestMap.getValue(mTestData.keyAt(0)));
+
+        // getFirstKey on a non-empty map returns the first key.
+        mTestMap.insertEntry(mTestData.keyAt(0), mTestData.valueAt(0));
+        assertEquals(mTestData.keyAt(0), mTestMap.getFirstKey());
     }
 
     @Test
     public void testGetNextKey() throws Exception {
-        try (BpfMap<TetherIngressKey, TetherIngressValue> bpfMap = getTestMap()) {
-            // [1] If the passed-in key is not found on empty map, return null.
-            final TetherIngressKey nonexistentKey = createTetherIngressKey(1234, "2001:db8::10");
-            assertNull(bpfMap.getNextKey(nonexistentKey));
+        // [1] If the passed-in key is not found on empty map, return null.
+        final TetherDownstream6Key nonexistentKey =
+                createTetherDownstream6Key(1234, "2001:db8::10");
+        assertNull(mTestMap.getNextKey(nonexistentKey));
 
-            // [2] If the passed-in key is null on empty map, throw NullPointerException.
-            try {
-                bpfMap.getNextKey(null);
-                fail("Getting next key with null key should throw NullPointerException");
-            } catch (NullPointerException expected) { }
+        // [2] If the passed-in key is null on empty map, throw NullPointerException.
+        try {
+            mTestMap.getNextKey(null);
+            fail("Getting next key with null key should throw NullPointerException");
+        } catch (NullPointerException expected) { }
 
-            // The BPF map has one entry now.
-            final ArrayMap<TetherIngressKey, TetherIngressValue> resultMap = new ArrayMap<>();
-            bpfMap.insertEntry(mTestData.keyAt(0), mTestData.valueAt(0));
-            resultMap.put(mTestData.keyAt(0), mTestData.valueAt(0));
+        // The BPF map has one entry now.
+        final ArrayMap<TetherDownstream6Key, Tether6Value> resultMap =
+                new ArrayMap<>();
+        mTestMap.insertEntry(mTestData.keyAt(0), mTestData.valueAt(0));
+        resultMap.put(mTestData.keyAt(0), mTestData.valueAt(0));
 
-            // [3] If the passed-in key is the last key, return null.
-            // Because there is only one entry in the map, the first key equals the last key.
-            final TetherIngressKey lastKey = bpfMap.getFirstKey();
-            assertNull(bpfMap.getNextKey(lastKey));
+        // [3] If the passed-in key is the last key, return null.
+        // Because there is only one entry in the map, the first key equals the last key.
+        final TetherDownstream6Key lastKey = mTestMap.getFirstKey();
+        assertNull(mTestMap.getNextKey(lastKey));
 
-            // The BPF map has two entries now.
-            bpfMap.insertEntry(mTestData.keyAt(1), mTestData.valueAt(1));
-            resultMap.put(mTestData.keyAt(1), mTestData.valueAt(1));
+        // The BPF map has two entries now.
+        mTestMap.insertEntry(mTestData.keyAt(1), mTestData.valueAt(1));
+        resultMap.put(mTestData.keyAt(1), mTestData.valueAt(1));
 
-            // [4] If the passed-in key is found, return the next key.
-            TetherIngressKey nextKey = bpfMap.getFirstKey();
-            while (nextKey != null) {
-                if (resultMap.remove(nextKey).equals(nextKey)) {
-                    fail("Unexpected result: " + nextKey);
-                }
-                nextKey = bpfMap.getNextKey(nextKey);
+        // [4] If the passed-in key is found, return the next key.
+        TetherDownstream6Key nextKey = mTestMap.getFirstKey();
+        while (nextKey != null) {
+            if (resultMap.remove(nextKey).equals(nextKey)) {
+                fail("Unexpected result: " + nextKey);
             }
-            assertTrue(resultMap.isEmpty());
-
-            // [5] If the passed-in key is not found on non-empty map, return the first key.
-            assertEquals(bpfMap.getFirstKey(), bpfMap.getNextKey(nonexistentKey));
-
-            // [6] If the passed-in key is null on non-empty map, throw NullPointerException.
-            try {
-                bpfMap.getNextKey(null);
-                fail("Getting next key with null key should throw NullPointerException");
-            } catch (NullPointerException expected) { }
+            nextKey = mTestMap.getNextKey(nextKey);
         }
+        assertTrue(resultMap.isEmpty());
+
+        // [5] If the passed-in key is not found on non-empty map, return the first key.
+        assertEquals(mTestMap.getFirstKey(), mTestMap.getNextKey(nonexistentKey));
+
+        // [6] If the passed-in key is null on non-empty map, throw NullPointerException.
+        try {
+            mTestMap.getNextKey(null);
+            fail("Getting next key with null key should throw NullPointerException");
+        } catch (NullPointerException expected) { }
     }
 
     @Test
     public void testUpdateBpfMap() throws Exception {
-        try (BpfMap<TetherIngressKey, TetherIngressValue> bpfMap = getTestMap()) {
+        final TetherDownstream6Key key = mTestData.keyAt(0);
+        final Tether6Value value = mTestData.valueAt(0);
+        final Tether6Value value2 = mTestData.valueAt(1);
+        assertFalse(mTestMap.deleteEntry(key));
 
-            final TetherIngressKey key = mTestData.keyAt(0);
-            final TetherIngressValue value = mTestData.valueAt(0);
-            final TetherIngressValue value2 = mTestData.valueAt(1);
-            assertFalse(bpfMap.deleteEntry(key));
+        // updateEntry will create an entry if it does not exist already.
+        mTestMap.updateEntry(key, value);
+        assertTrue(mTestMap.containsKey(key));
+        final Tether6Value result = mTestMap.getValue(key);
+        assertEquals(value, result);
 
-            // updateEntry will create an entry if it does not exist already.
-            bpfMap.updateEntry(key, value);
-            assertTrue(bpfMap.containsKey(key));
-            final TetherIngressValue result = bpfMap.getValue(key);
-            assertEquals(value, result);
+        // updateEntry will update an entry that already exists.
+        mTestMap.updateEntry(key, value2);
+        assertTrue(mTestMap.containsKey(key));
+        final Tether6Value result2 = mTestMap.getValue(key);
+        assertEquals(value2, result2);
 
-            // updateEntry will update an entry that already exists.
-            bpfMap.updateEntry(key, value2);
-            assertTrue(bpfMap.containsKey(key));
-            final TetherIngressValue result2 = bpfMap.getValue(key);
-            assertEquals(value2, result2);
-
-            assertTrue(bpfMap.deleteEntry(key));
-            assertFalse(bpfMap.containsKey(key));
-        }
+        assertTrue(mTestMap.deleteEntry(key));
+        assertFalse(mTestMap.containsKey(key));
     }
 
     @Test
     public void testInsertReplaceEntry() throws Exception {
-        try (BpfMap<TetherIngressKey, TetherIngressValue> bpfMap = getTestMap()) {
+        final TetherDownstream6Key key = mTestData.keyAt(0);
+        final Tether6Value value = mTestData.valueAt(0);
+        final Tether6Value value2 = mTestData.valueAt(1);
 
-            final TetherIngressKey key = mTestData.keyAt(0);
-            final TetherIngressValue value = mTestData.valueAt(0);
-            final TetherIngressValue value2 = mTestData.valueAt(1);
+        try {
+            mTestMap.replaceEntry(key, value);
+            fail("Replacing non-existent key " + key + " should throw NoSuchElementException");
+        } catch (NoSuchElementException expected) { }
+        assertFalse(mTestMap.containsKey(key));
 
-            try {
-                bpfMap.replaceEntry(key, value);
-                fail("Replacing non-existent key " + key + " should throw NoSuchElementException");
-            } catch (NoSuchElementException expected) { }
-            assertFalse(bpfMap.containsKey(key));
+        mTestMap.insertEntry(key, value);
+        assertTrue(mTestMap.containsKey(key));
+        final Tether6Value result = mTestMap.getValue(key);
+        assertEquals(value, result);
+        try {
+            mTestMap.insertEntry(key, value);
+            fail("Inserting existing key " + key + " should throw IllegalStateException");
+        } catch (IllegalStateException expected) { }
 
-            bpfMap.insertEntry(key, value);
-            assertTrue(bpfMap.containsKey(key));
-            final TetherIngressValue result = bpfMap.getValue(key);
-            assertEquals(value, result);
-            try {
-                bpfMap.insertEntry(key, value);
-                fail("Inserting existing key " + key + " should throw IllegalStateException");
-            } catch (IllegalStateException expected) { }
-
-            bpfMap.replaceEntry(key, value2);
-            assertTrue(bpfMap.containsKey(key));
-            final TetherIngressValue result2 = bpfMap.getValue(key);
-            assertEquals(value2, result2);
-        }
+        mTestMap.replaceEntry(key, value2);
+        assertTrue(mTestMap.containsKey(key));
+        final Tether6Value result2 = mTestMap.getValue(key);
+        assertEquals(value2, result2);
     }
 
     @Test
     public void testIterateBpfMap() throws Exception {
-        try (BpfMap<TetherIngressKey, TetherIngressValue> bpfMap = getTestMap()) {
-            final ArrayMap<TetherIngressKey, TetherIngressValue> resultMap =
-                    new ArrayMap<>(mTestData);
+        final ArrayMap<TetherDownstream6Key, Tether6Value> resultMap =
+                new ArrayMap<>(mTestData);
 
-            for (int i = 0; i < resultMap.size(); i++) {
-                bpfMap.insertEntry(resultMap.keyAt(i), resultMap.valueAt(i));
-            }
-
-            bpfMap.forEach((key, value) -> {
-                if (!value.equals(resultMap.remove(key))) {
-                    fail("Unexpected result: " + key + ", value: " + value);
-                }
-            });
-            assertTrue(resultMap.isEmpty());
+        for (int i = 0; i < resultMap.size(); i++) {
+            mTestMap.insertEntry(resultMap.keyAt(i), resultMap.valueAt(i));
         }
+
+        mTestMap.forEach((key, value) -> {
+            if (!value.equals(resultMap.remove(key))) {
+                fail("Unexpected result: " + key + ", value: " + value);
+            }
+        });
+        assertTrue(resultMap.isEmpty());
     }
 
     @Test
     public void testIterateEmptyMap() throws Exception {
-        try (BpfMap<TetherIngressKey, TetherIngressValue> bpfMap = getTestMap()) {
-            // Can't use an int because variables used in a lambda must be final.
-            final AtomicInteger count = new AtomicInteger();
-            bpfMap.forEach((key, value) -> count.incrementAndGet());
-            // Expect that the consumer was never called.
-            assertEquals(0, count.get());
-        }
+        // Can't use an int because variables used in a lambda must be final.
+        final AtomicInteger count = new AtomicInteger();
+        mTestMap.forEach((key, value) -> count.incrementAndGet());
+        // Expect that the consumer was never called.
+        assertEquals(0, count.get());
     }
 
     @Test
     public void testIterateDeletion() throws Exception {
-        try (BpfMap<TetherIngressKey, TetherIngressValue> bpfMap = getTestMap()) {
-            final ArrayMap<TetherIngressKey, TetherIngressValue> resultMap =
-                    new ArrayMap<>(mTestData);
+        final ArrayMap<TetherDownstream6Key, Tether6Value> resultMap =
+                new ArrayMap<>(mTestData);
 
-            for (int i = 0; i < resultMap.size(); i++) {
-                bpfMap.insertEntry(resultMap.keyAt(i), resultMap.valueAt(i));
-            }
-
-            // Can't use an int because variables used in a lambda must be final.
-            final AtomicInteger count = new AtomicInteger();
-            bpfMap.forEach((key, value) -> {
-                try {
-                    assertTrue(bpfMap.deleteEntry(key));
-                } catch (ErrnoException e) {
-                    fail("Fail to delete key " + key + ": " + e);
-                }
-                if (!value.equals(resultMap.remove(key))) {
-                    fail("Unexpected result: " + key + ", value: " + value);
-                }
-                count.incrementAndGet();
-            });
-            assertEquals(3, count.get());
-            assertTrue(resultMap.isEmpty());
-            assertNull(bpfMap.getFirstKey());
+        for (int i = 0; i < resultMap.size(); i++) {
+            mTestMap.insertEntry(resultMap.keyAt(i), resultMap.valueAt(i));
         }
+
+        // Can't use an int because variables used in a lambda must be final.
+        final AtomicInteger count = new AtomicInteger();
+        mTestMap.forEach((key, value) -> {
+            try {
+                assertTrue(mTestMap.deleteEntry(key));
+            } catch (ErrnoException e) {
+                fail("Fail to delete key " + key + ": " + e);
+            }
+            if (!value.equals(resultMap.remove(key))) {
+                fail("Unexpected result: " + key + ", value: " + value);
+            }
+            count.incrementAndGet();
+        });
+        assertEquals(3, count.get());
+        assertTrue(resultMap.isEmpty());
+        assertNull(mTestMap.getFirstKey());
     }
 
     @Test
     public void testInsertOverflow() throws Exception {
-        try (BpfMap<TetherIngressKey, TetherIngressValue> bpfMap = getTestMap()) {
-            final ArrayMap<TetherIngressKey, TetherIngressValue> testData = new ArrayMap<>();
+        final ArrayMap<TetherDownstream6Key, Tether6Value> testData =
+                new ArrayMap<>();
 
-            // Build test data for TEST_MAP_SIZE + 1 entries.
-            for (int i = 1; i <= TEST_MAP_SIZE + 1; i++) {
-                testData.put(createTetherIngressKey(i, "2001:db8::1"), createTetherIngressValue(
-                        100, "de:ad:be:ef:00:01", "de:ad:be:ef:00:02", ETH_P_IPV6, 1500));
-            }
+        // Build test data for TEST_MAP_SIZE + 1 entries.
+        for (int i = 1; i <= TEST_MAP_SIZE + 1; i++) {
+            testData.put(createTetherDownstream6Key(i, "2001:db8::1"),
+                    createTether6Value(100, "de:ad:be:ef:00:01", "de:ad:be:ef:00:02",
+                    ETH_P_IPV6, 1500));
+        }
 
-            // Insert #TEST_MAP_SIZE test entries to the map. The map has reached the limit.
-            for (int i = 0; i < TEST_MAP_SIZE; i++) {
-                bpfMap.insertEntry(testData.keyAt(i), testData.valueAt(i));
-            }
+        // Insert #TEST_MAP_SIZE test entries to the map. The map has reached the limit.
+        for (int i = 0; i < TEST_MAP_SIZE; i++) {
+            mTestMap.insertEntry(testData.keyAt(i), testData.valueAt(i));
+        }
 
-            // The map won't allow inserting any more entries.
-            try {
-                bpfMap.insertEntry(testData.keyAt(TEST_MAP_SIZE), testData.valueAt(TEST_MAP_SIZE));
-                fail("Writing too many entries should throw ErrnoException");
-            } catch (ErrnoException expected) {
-                // Expect that can't insert the entry anymore because the number of elements in the
-                // map reached the limit. See man-pages/bpf.
-                assertEquals(OsConstants.E2BIG, expected.errno);
-            }
+        // The map won't allow inserting any more entries.
+        try {
+            mTestMap.insertEntry(testData.keyAt(TEST_MAP_SIZE), testData.valueAt(TEST_MAP_SIZE));
+            fail("Writing too many entries should throw ErrnoException");
+        } catch (ErrnoException expected) {
+            // Expect that can't insert the entry anymore because the number of elements in the
+            // map reached the limit. See man-pages/bpf.
+            assertEquals(OsConstants.E2BIG, expected.errno);
         }
     }
 }
diff --git a/Tethering/tests/unit/Android.bp b/Tethering/tests/unit/Android.bp
index 5e4fe52..6c479a0 100644
--- a/Tethering/tests/unit/Android.bp
+++ b/Tethering/tests/unit/Android.bp
@@ -69,6 +69,7 @@
         // For mockito extended
         "libdexmakerjvmtiagent",
         "libstaticjvmtiagent",
+        "libtetherutilsjni",
     ],
 }
 
diff --git a/Tethering/tests/unit/src/android/net/ip/IpServerTest.java b/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
index 4763558..b45db7e 100644
--- a/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
+++ b/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
@@ -104,12 +104,15 @@
 import com.android.networkstack.tethering.BpfCoordinator.Ipv6ForwardingRule;
 import com.android.networkstack.tethering.BpfMap;
 import com.android.networkstack.tethering.PrivateAddressCoordinator;
-import com.android.networkstack.tethering.TetherIngressKey;
-import com.android.networkstack.tethering.TetherIngressValue;
+import com.android.networkstack.tethering.Tether4Key;
+import com.android.networkstack.tethering.Tether4Value;
+import com.android.networkstack.tethering.Tether6Value;
+import com.android.networkstack.tethering.TetherDownstream6Key;
 import com.android.networkstack.tethering.TetherLimitKey;
 import com.android.networkstack.tethering.TetherLimitValue;
 import com.android.networkstack.tethering.TetherStatsKey;
 import com.android.networkstack.tethering.TetherStatsValue;
+import com.android.networkstack.tethering.TetherUpstream6Key;
 import com.android.networkstack.tethering.TetheringConfiguration;
 import com.android.testutils.DevSdkIgnoreRule;
 import com.android.testutils.DevSdkIgnoreRule.IgnoreAfter;
@@ -172,7 +175,11 @@
     @Mock private PrivateAddressCoordinator mAddressCoordinator;
     @Mock private NetworkStatsManager mStatsManager;
     @Mock private TetheringConfiguration mTetherConfig;
-    @Mock private BpfMap<TetherIngressKey, TetherIngressValue> mBpfIngressMap;
+    @Mock private ConntrackMonitor mConntrackMonitor;
+    @Mock private BpfMap<Tether4Key, Tether4Value> mBpfDownstream4Map;
+    @Mock private BpfMap<Tether4Key, Tether4Value> mBpfUpstream4Map;
+    @Mock private BpfMap<TetherDownstream6Key, Tether6Value> mBpfDownstream6Map;
+    @Mock private BpfMap<TetherUpstream6Key, Tether6Value> mBpfUpstream6Map;
     @Mock private BpfMap<TetherStatsKey, TetherStatsValue> mBpfStatsMap;
     @Mock private BpfMap<TetherLimitKey, TetherLimitValue> mBpfLimitMap;
 
@@ -199,9 +206,6 @@
         when(mDependencies.getInterfaceParams(UPSTREAM_IFACE)).thenReturn(UPSTREAM_IFACE_PARAMS);
         when(mDependencies.getInterfaceParams(UPSTREAM_IFACE2)).thenReturn(UPSTREAM_IFACE_PARAMS2);
 
-        when(mDependencies.getIfindex(eq(UPSTREAM_IFACE))).thenReturn(UPSTREAM_IFINDEX);
-        when(mDependencies.getIfindex(eq(UPSTREAM_IFACE2))).thenReturn(UPSTREAM_IFINDEX2);
-
         mInterfaceConfiguration = new InterfaceConfigurationParcel();
         mInterfaceConfiguration.flags = new String[0];
         if (interfaceType == TETHERING_BLUETOOTH) {
@@ -295,9 +299,30 @@
                         return mTetherConfig;
                     }
 
+                    @NonNull
+                    public ConntrackMonitor getConntrackMonitor(
+                            ConntrackMonitor.ConntrackEventConsumer consumer) {
+                        return mConntrackMonitor;
+                    }
+
                     @Nullable
-                    public BpfMap<TetherIngressKey, TetherIngressValue> getBpfIngressMap() {
-                        return mBpfIngressMap;
+                    public BpfMap<Tether4Key, Tether4Value> getBpfDownstream4Map() {
+                        return mBpfDownstream4Map;
+                    }
+
+                    @Nullable
+                    public BpfMap<Tether4Key, Tether4Value> getBpfUpstream4Map() {
+                        return mBpfUpstream4Map;
+                    }
+
+                    @Nullable
+                    public BpfMap<TetherDownstream6Key, Tether6Value> getBpfDownstream6Map() {
+                        return mBpfDownstream6Map;
+                    }
+
+                    @Nullable
+                    public BpfMap<TetherUpstream6Key, Tether6Value> getBpfUpstream6Map() {
+                        return mBpfUpstream6Map;
                     }
 
                     @Nullable
@@ -770,15 +795,15 @@
     }
 
     @NonNull
-    private static TetherIngressKey makeIngressKey(int upstreamIfindex,
+    private static TetherDownstream6Key makeDownstream6Key(int upstreamIfindex,
             @NonNull final InetAddress dst) {
-        return new TetherIngressKey(upstreamIfindex, dst.getAddress());
+        return new TetherDownstream6Key(upstreamIfindex, dst.getAddress());
     }
 
     @NonNull
-    private static TetherIngressValue makeIngressValue(@NonNull final MacAddress dstMac) {
-        return new TetherIngressValue(TEST_IFACE_PARAMS.index, dstMac, TEST_IFACE_PARAMS.macAddr,
-                ETH_P_IPV6, NetworkStackConstants.ETHER_MTU);
+    private static Tether6Value makeDownstream6Value(@NonNull final MacAddress dstMac) {
+        return new Tether6Value(TEST_IFACE_PARAMS.index, dstMac,
+                TEST_IFACE_PARAMS.macAddr, ETH_P_IPV6, NetworkStackConstants.ETHER_MTU);
     }
 
     private <T> T verifyWithOrder(@Nullable InOrder inOrder, @NonNull T t) {
@@ -792,8 +817,8 @@
     private void verifyTetherOffloadRuleAdd(@Nullable InOrder inOrder, int upstreamIfindex,
             @NonNull final InetAddress dst, @NonNull final MacAddress dstMac) throws Exception {
         if (mBpfDeps.isAtLeastS()) {
-            verifyWithOrder(inOrder, mBpfIngressMap).updateEntry(
-                    makeIngressKey(upstreamIfindex, dst), makeIngressValue(dstMac));
+            verifyWithOrder(inOrder, mBpfDownstream6Map).updateEntry(
+                    makeDownstream6Key(upstreamIfindex, dst), makeDownstream6Value(dstMac));
         } else {
             verifyWithOrder(inOrder, mNetd).tetherOffloadRuleAdd(matches(upstreamIfindex, dst,
                     dstMac));
@@ -803,8 +828,9 @@
     private void verifyNeverTetherOffloadRuleAdd(int upstreamIfindex,
             @NonNull final InetAddress dst, @NonNull final MacAddress dstMac) throws Exception {
         if (mBpfDeps.isAtLeastS()) {
-            verify(mBpfIngressMap, never()).updateEntry(makeIngressKey(upstreamIfindex, dst),
-                    makeIngressValue(dstMac));
+            verify(mBpfDownstream6Map, never()).updateEntry(
+                    makeDownstream6Key(upstreamIfindex, dst),
+                    makeDownstream6Value(dstMac));
         } else {
             verify(mNetd, never()).tetherOffloadRuleAdd(matches(upstreamIfindex, dst, dstMac));
         }
@@ -812,7 +838,7 @@
 
     private void verifyNeverTetherOffloadRuleAdd() throws Exception {
         if (mBpfDeps.isAtLeastS()) {
-            verify(mBpfIngressMap, never()).updateEntry(any(), any());
+            verify(mBpfDownstream6Map, never()).updateEntry(any(), any());
         } else {
             verify(mNetd, never()).tetherOffloadRuleAdd(any());
         }
@@ -821,8 +847,8 @@
     private void verifyTetherOffloadRuleRemove(@Nullable InOrder inOrder, int upstreamIfindex,
             @NonNull final InetAddress dst, @NonNull final MacAddress dstMac) throws Exception {
         if (mBpfDeps.isAtLeastS()) {
-            verifyWithOrder(inOrder, mBpfIngressMap).deleteEntry(makeIngressKey(upstreamIfindex,
-                    dst));
+            verifyWithOrder(inOrder, mBpfDownstream6Map).deleteEntry(makeDownstream6Key(
+                    upstreamIfindex, dst));
         } else {
             // |dstMac| is not required for deleting rules. Used bacause tetherOffloadRuleRemove
             // uses a whole rule to be a argument.
@@ -834,12 +860,42 @@
 
     private void verifyNeverTetherOffloadRuleRemove() throws Exception {
         if (mBpfDeps.isAtLeastS()) {
-            verify(mBpfIngressMap, never()).deleteEntry(any());
+            verify(mBpfDownstream6Map, never()).deleteEntry(any());
         } else {
             verify(mNetd, never()).tetherOffloadRuleRemove(any());
         }
     }
 
+    private void verifyStartUpstreamIpv6Forwarding(@Nullable InOrder inOrder, int upstreamIfindex)
+            throws Exception {
+        if (!mBpfDeps.isAtLeastS()) return;
+        final TetherUpstream6Key key = new TetherUpstream6Key(TEST_IFACE_PARAMS.index);
+        final Tether6Value value = new Tether6Value(upstreamIfindex,
+                MacAddress.ALL_ZEROS_ADDRESS, MacAddress.ALL_ZEROS_ADDRESS,
+                ETH_P_IPV6, NetworkStackConstants.ETHER_MTU);
+        verifyWithOrder(inOrder, mBpfUpstream6Map).insertEntry(key, value);
+    }
+
+    private void verifyStopUpstreamIpv6Forwarding(@Nullable InOrder inOrder)
+            throws Exception {
+        if (!mBpfDeps.isAtLeastS()) return;
+        final TetherUpstream6Key key = new TetherUpstream6Key(TEST_IFACE_PARAMS.index);
+        verifyWithOrder(inOrder, mBpfUpstream6Map).deleteEntry(key);
+    }
+
+    private void verifyNoUpstreamIpv6ForwardingChange(@Nullable InOrder inOrder) throws Exception {
+        if (!mBpfDeps.isAtLeastS()) return;
+        if (inOrder != null) {
+            inOrder.verify(mBpfUpstream6Map, never()).deleteEntry(any());
+            inOrder.verify(mBpfUpstream6Map, never()).insertEntry(any(), any());
+            inOrder.verify(mBpfUpstream6Map, never()).updateEntry(any(), any());
+        } else {
+            verify(mBpfUpstream6Map, never()).deleteEntry(any());
+            verify(mBpfUpstream6Map, never()).insertEntry(any(), any());
+            verify(mBpfUpstream6Map, never()).updateEntry(any(), any());
+        }
+    }
+
     @NonNull
     private static TetherStatsParcel buildEmptyTetherStatsParcel(int ifIndex) {
         TetherStatsParcel parcel = new TetherStatsParcel();
@@ -848,12 +904,19 @@
     }
 
     private void resetNetdBpfMapAndCoordinator() throws Exception {
-        reset(mNetd, mBpfIngressMap, mBpfCoordinator);
+        reset(mNetd, mBpfDownstream6Map, mBpfUpstream6Map, mBpfCoordinator);
+        // When the last rule is removed, tetherOffloadGetAndClearStats will log a WTF (and
+        // potentially crash the test) if the stats map is empty.
         when(mNetd.tetherOffloadGetStats()).thenReturn(new TetherStatsParcel[0]);
         when(mNetd.tetherOffloadGetAndClearStats(UPSTREAM_IFINDEX))
                 .thenReturn(buildEmptyTetherStatsParcel(UPSTREAM_IFINDEX));
         when(mNetd.tetherOffloadGetAndClearStats(UPSTREAM_IFINDEX2))
                 .thenReturn(buildEmptyTetherStatsParcel(UPSTREAM_IFINDEX2));
+        // When the last rule is removed, tetherOffloadGetAndClearStats will log a WTF (and
+        // potentially crash the test) if the stats map is empty.
+        final TetherStatsValue allZeros = new TetherStatsValue(0, 0, 0, 0, 0, 0);
+        when(mBpfStatsMap.getValue(new TetherStatsKey(UPSTREAM_IFINDEX))).thenReturn(allZeros);
+        when(mBpfStatsMap.getValue(new TetherStatsKey(UPSTREAM_IFINDEX2))).thenReturn(allZeros);
     }
 
     @Test
@@ -864,7 +927,6 @@
         final int myIfindex = TEST_IFACE_PARAMS.index;
         final int notMyIfindex = myIfindex - 1;
 
-        final MacAddress myMac = TEST_IFACE_PARAMS.macAddr;
         final InetAddress neighA = InetAddresses.parseNumericAddress("2001:db8::1");
         final InetAddress neighB = InetAddresses.parseNumericAddress("2001:db8::2");
         final InetAddress neighLL = InetAddresses.parseNumericAddress("fe80::1");
@@ -874,33 +936,35 @@
         final MacAddress macB = MacAddress.fromString("11:22:33:00:00:0b");
 
         resetNetdBpfMapAndCoordinator();
-        verifyNoMoreInteractions(mBpfCoordinator, mNetd, mBpfIngressMap);
+        verifyNoMoreInteractions(mBpfCoordinator, mNetd, mBpfDownstream6Map, mBpfUpstream6Map);
 
         // TODO: Perhaps verify the interaction of tetherOffloadSetInterfaceQuota and
         // tetherOffloadGetAndClearStats in netd while the rules are changed.
 
         // Events on other interfaces are ignored.
         recvNewNeigh(notMyIfindex, neighA, NUD_REACHABLE, macA);
-        verifyNoMoreInteractions(mBpfCoordinator, mNetd, mBpfIngressMap);
+        verifyNoMoreInteractions(mBpfCoordinator, mNetd, mBpfDownstream6Map, mBpfUpstream6Map);
 
         // Events on this interface are received and sent to netd.
         recvNewNeigh(myIfindex, neighA, NUD_REACHABLE, macA);
         verify(mBpfCoordinator).tetherOffloadRuleAdd(
                 mIpServer, makeForwardingRule(UPSTREAM_IFINDEX, neighA, macA));
         verifyTetherOffloadRuleAdd(null, UPSTREAM_IFINDEX, neighA, macA);
+        verifyStartUpstreamIpv6Forwarding(null, UPSTREAM_IFINDEX);
         resetNetdBpfMapAndCoordinator();
 
         recvNewNeigh(myIfindex, neighB, NUD_REACHABLE, macB);
         verify(mBpfCoordinator).tetherOffloadRuleAdd(
                 mIpServer, makeForwardingRule(UPSTREAM_IFINDEX, neighB, macB));
         verifyTetherOffloadRuleAdd(null, UPSTREAM_IFINDEX, neighB, macB);
+        verifyNoUpstreamIpv6ForwardingChange(null);
         resetNetdBpfMapAndCoordinator();
 
         // Link-local and multicast neighbors are ignored.
         recvNewNeigh(myIfindex, neighLL, NUD_REACHABLE, macA);
-        verifyNoMoreInteractions(mBpfCoordinator, mNetd, mBpfIngressMap);
+        verifyNoMoreInteractions(mBpfCoordinator, mNetd, mBpfDownstream6Map, mBpfUpstream6Map);
         recvNewNeigh(myIfindex, neighMC, NUD_REACHABLE, macA);
-        verifyNoMoreInteractions(mBpfCoordinator, mNetd, mBpfIngressMap);
+        verifyNoMoreInteractions(mBpfCoordinator, mNetd, mBpfDownstream6Map, mBpfUpstream6Map);
 
         // A neighbor that is no longer valid causes the rule to be removed.
         // NUD_FAILED events do not have a MAC address.
@@ -908,6 +972,7 @@
         verify(mBpfCoordinator).tetherOffloadRuleRemove(
                 mIpServer, makeForwardingRule(UPSTREAM_IFINDEX, neighA, macNull));
         verifyTetherOffloadRuleRemove(null, UPSTREAM_IFINDEX, neighA, macNull);
+        verifyNoUpstreamIpv6ForwardingChange(null);
         resetNetdBpfMapAndCoordinator();
 
         // A neighbor that is deleted causes the rule to be removed.
@@ -915,22 +980,27 @@
         verify(mBpfCoordinator).tetherOffloadRuleRemove(
                 mIpServer,  makeForwardingRule(UPSTREAM_IFINDEX, neighB, macNull));
         verifyTetherOffloadRuleRemove(null, UPSTREAM_IFINDEX, neighB, macNull);
+        verifyStopUpstreamIpv6Forwarding(null);
         resetNetdBpfMapAndCoordinator();
 
         // Upstream changes result in updating the rules.
         recvNewNeigh(myIfindex, neighA, NUD_REACHABLE, macA);
+        verifyStartUpstreamIpv6Forwarding(null, UPSTREAM_IFINDEX);
         recvNewNeigh(myIfindex, neighB, NUD_REACHABLE, macB);
         resetNetdBpfMapAndCoordinator();
 
-        InOrder inOrder = inOrder(mNetd, mBpfIngressMap);
+        InOrder inOrder = inOrder(mNetd, mBpfDownstream6Map, mBpfUpstream6Map);
         LinkProperties lp = new LinkProperties();
         lp.setInterfaceName(UPSTREAM_IFACE2);
         dispatchTetherConnectionChanged(UPSTREAM_IFACE2, lp, -1);
         verify(mBpfCoordinator).tetherOffloadRuleUpdate(mIpServer, UPSTREAM_IFINDEX2);
         verifyTetherOffloadRuleRemove(inOrder, UPSTREAM_IFINDEX, neighA, macA);
-        verifyTetherOffloadRuleAdd(inOrder, UPSTREAM_IFINDEX2, neighA, macA);
         verifyTetherOffloadRuleRemove(inOrder, UPSTREAM_IFINDEX, neighB, macB);
+        verifyStopUpstreamIpv6Forwarding(inOrder);
+        verifyTetherOffloadRuleAdd(inOrder, UPSTREAM_IFINDEX2, neighA, macA);
+        verifyStartUpstreamIpv6Forwarding(inOrder, UPSTREAM_IFINDEX2);
         verifyTetherOffloadRuleAdd(inOrder, UPSTREAM_IFINDEX2, neighB, macB);
+        verifyNoUpstreamIpv6ForwardingChange(inOrder);
         resetNetdBpfMapAndCoordinator();
 
         // When the upstream is lost, rules are removed.
@@ -942,6 +1012,7 @@
         verify(mBpfCoordinator, times(2)).tetherOffloadRuleClear(mIpServer);
         verifyTetherOffloadRuleRemove(null, UPSTREAM_IFINDEX2, neighA, macA);
         verifyTetherOffloadRuleRemove(null, UPSTREAM_IFINDEX2, neighB, macB);
+        verifyStopUpstreamIpv6Forwarding(inOrder);
         resetNetdBpfMapAndCoordinator();
 
         // If the upstream is IPv4-only, no rules are added.
@@ -950,7 +1021,8 @@
         recvNewNeigh(myIfindex, neighA, NUD_REACHABLE, macA);
         // Clear function is called by #updateIpv6ForwardingRules for the IPv6 upstream is lost.
         verify(mBpfCoordinator).tetherOffloadRuleClear(mIpServer);
-        verifyNoMoreInteractions(mBpfCoordinator, mNetd, mBpfIngressMap);
+        verifyNoUpstreamIpv6ForwardingChange(null);
+        verifyNoMoreInteractions(mBpfCoordinator, mNetd, mBpfDownstream6Map, mBpfUpstream6Map);
 
         // Rules can be added again once upstream IPv6 connectivity is available.
         lp.setInterfaceName(UPSTREAM_IFACE);
@@ -959,6 +1031,7 @@
         verify(mBpfCoordinator).tetherOffloadRuleAdd(
                 mIpServer, makeForwardingRule(UPSTREAM_IFINDEX, neighB, macB));
         verifyTetherOffloadRuleAdd(null, UPSTREAM_IFINDEX, neighB, macB);
+        verifyStartUpstreamIpv6Forwarding(null, UPSTREAM_IFINDEX);
         verify(mBpfCoordinator, never()).tetherOffloadRuleAdd(
                 mIpServer, makeForwardingRule(UPSTREAM_IFINDEX, neighA, macA));
         verifyNeverTetherOffloadRuleAdd(UPSTREAM_IFINDEX, neighA, macA);
@@ -968,6 +1041,7 @@
         dispatchTetherConnectionChanged(UPSTREAM_IFACE, null, 0);
         verify(mBpfCoordinator).tetherOffloadRuleClear(mIpServer);
         verifyTetherOffloadRuleRemove(null, UPSTREAM_IFINDEX, neighB, macB);
+        verifyStopUpstreamIpv6Forwarding(null);
 
         // When the interface goes down, rules are removed.
         lp.setInterfaceName(UPSTREAM_IFACE);
@@ -977,6 +1051,7 @@
         verify(mBpfCoordinator).tetherOffloadRuleAdd(
                 mIpServer, makeForwardingRule(UPSTREAM_IFINDEX, neighA, macA));
         verifyTetherOffloadRuleAdd(null, UPSTREAM_IFINDEX, neighA, macA);
+        verifyStartUpstreamIpv6Forwarding(null, UPSTREAM_IFINDEX);
         verify(mBpfCoordinator).tetherOffloadRuleAdd(
                 mIpServer, makeForwardingRule(UPSTREAM_IFINDEX, neighB, macB));
         verifyTetherOffloadRuleAdd(null, UPSTREAM_IFINDEX, neighB, macB);
@@ -987,6 +1062,7 @@
         verify(mBpfCoordinator).tetherOffloadRuleClear(mIpServer);
         verifyTetherOffloadRuleRemove(null, UPSTREAM_IFINDEX, neighA, macA);
         verifyTetherOffloadRuleRemove(null, UPSTREAM_IFINDEX, neighB, macB);
+        verifyStopUpstreamIpv6Forwarding(null);
         verify(mIpNeighborMonitor).stop();
         resetNetdBpfMapAndCoordinator();
     }
@@ -1015,12 +1091,14 @@
         verify(mBpfCoordinator).tetherOffloadRuleAdd(
                 mIpServer, makeForwardingRule(UPSTREAM_IFINDEX, neigh, macA));
         verifyTetherOffloadRuleAdd(null, UPSTREAM_IFINDEX, neigh, macA);
+        verifyStartUpstreamIpv6Forwarding(null, UPSTREAM_IFINDEX);
         resetNetdBpfMapAndCoordinator();
 
         recvDelNeigh(myIfindex, neigh, NUD_STALE, macA);
         verify(mBpfCoordinator).tetherOffloadRuleRemove(
                 mIpServer, makeForwardingRule(UPSTREAM_IFINDEX, neigh, macNull));
         verifyTetherOffloadRuleRemove(null, UPSTREAM_IFINDEX, neigh, macNull);
+        verifyStopUpstreamIpv6Forwarding(null);
         resetNetdBpfMapAndCoordinator();
 
         // [2] Disable BPF offload.
@@ -1032,11 +1110,13 @@
         recvNewNeigh(myIfindex, neigh, NUD_REACHABLE, macA);
         verify(mBpfCoordinator, never()).tetherOffloadRuleAdd(any(), any());
         verifyNeverTetherOffloadRuleAdd();
+        verifyNoUpstreamIpv6ForwardingChange(null);
         resetNetdBpfMapAndCoordinator();
 
         recvDelNeigh(myIfindex, neigh, NUD_STALE, macA);
         verify(mBpfCoordinator, never()).tetherOffloadRuleRemove(any(), any());
         verifyNeverTetherOffloadRuleRemove();
+        verifyNoUpstreamIpv6ForwardingChange(null);
         resetNetdBpfMapAndCoordinator();
     }
 
diff --git a/Tethering/tests/unit/src/com/android/networkstack/tethering/BpfCoordinatorTest.java b/Tethering/tests/unit/src/com/android/networkstack/tethering/BpfCoordinatorTest.java
index 4abaf03..1270e50 100644
--- a/Tethering/tests/unit/src/com/android/networkstack/tethering/BpfCoordinatorTest.java
+++ b/Tethering/tests/unit/src/com/android/networkstack/tethering/BpfCoordinatorTest.java
@@ -56,6 +56,8 @@
 import android.net.NetworkStats;
 import android.net.TetherOffloadRuleParcel;
 import android.net.TetherStatsParcel;
+import android.net.ip.ConntrackMonitor;
+import android.net.ip.ConntrackMonitor.ConntrackEventConsumer;
 import android.net.ip.IpServer;
 import android.net.util.SharedLog;
 import android.os.Build;
@@ -153,8 +155,13 @@
     @Mock private NetworkStatsManager mStatsManager;
     @Mock private INetd mNetd;
     @Mock private IpServer mIpServer;
+    @Mock private IpServer mIpServer2;
     @Mock private TetheringConfiguration mTetherConfig;
-    @Mock private BpfMap<TetherIngressKey, TetherIngressValue> mBpfIngressMap;
+    @Mock private ConntrackMonitor mConntrackMonitor;
+    @Mock private BpfMap<Tether4Key, Tether4Value> mBpfDownstream4Map;
+    @Mock private BpfMap<Tether4Key, Tether4Value> mBpfUpstream4Map;
+    @Mock private BpfMap<TetherDownstream6Key, Tether6Value> mBpfDownstream6Map;
+    @Mock private BpfMap<TetherUpstream6Key, Tether6Value> mBpfUpstream6Map;
 
     // Late init since methods must be called by the thread that created this object.
     private TestableNetworkStatsProviderCbBinder mTetherStatsProviderCb;
@@ -193,9 +200,29 @@
                         return mTetherConfig;
                     }
 
+                    @NonNull
+                    public ConntrackMonitor getConntrackMonitor(ConntrackEventConsumer consumer) {
+                        return mConntrackMonitor;
+                    }
+
                     @Nullable
-                    public BpfMap<TetherIngressKey, TetherIngressValue> getBpfIngressMap() {
-                        return mBpfIngressMap;
+                    public BpfMap<Tether4Key, Tether4Value> getBpfDownstream4Map() {
+                        return mBpfDownstream4Map;
+                    }
+
+                    @Nullable
+                    public BpfMap<Tether4Key, Tether4Value> getBpfUpstream4Map() {
+                        return mBpfUpstream4Map;
+                    }
+
+                    @Nullable
+                    public BpfMap<TetherDownstream6Key, Tether6Value> getBpfDownstream6Map() {
+                        return mBpfDownstream6Map;
+                    }
+
+                    @Nullable
+                    public BpfMap<TetherUpstream6Key, Tether6Value> getBpfUpstream6Map() {
+                        return mBpfUpstream6Map;
                     }
 
                     @Nullable
@@ -338,11 +365,41 @@
         }
     }
 
+    private void verifyStartUpstreamIpv6Forwarding(@Nullable InOrder inOrder, int downstreamIfIndex,
+            int upstreamIfindex) throws Exception {
+        if (!mDeps.isAtLeastS()) return;
+        final TetherUpstream6Key key = new TetherUpstream6Key(downstreamIfIndex);
+        final Tether6Value value = new Tether6Value(upstreamIfindex,
+                MacAddress.ALL_ZEROS_ADDRESS, MacAddress.ALL_ZEROS_ADDRESS,
+                ETH_P_IPV6, NetworkStackConstants.ETHER_MTU);
+        verifyWithOrder(inOrder, mBpfUpstream6Map).insertEntry(key, value);
+    }
+
+    private void verifyStopUpstreamIpv6Forwarding(@Nullable InOrder inOrder, int downstreamIfIndex)
+            throws Exception {
+        if (!mDeps.isAtLeastS()) return;
+        final TetherUpstream6Key key = new TetherUpstream6Key(downstreamIfIndex);
+        verifyWithOrder(inOrder, mBpfUpstream6Map).deleteEntry(key);
+    }
+
+    private void verifyNoUpstreamIpv6ForwardingChange(@Nullable InOrder inOrder) throws Exception {
+        if (!mDeps.isAtLeastS()) return;
+        if (inOrder != null) {
+            inOrder.verify(mBpfUpstream6Map, never()).deleteEntry(any());
+            inOrder.verify(mBpfUpstream6Map, never()).insertEntry(any(), any());
+            inOrder.verify(mBpfUpstream6Map, never()).updateEntry(any(), any());
+        } else {
+            verify(mBpfUpstream6Map, never()).deleteEntry(any());
+            verify(mBpfUpstream6Map, never()).insertEntry(any(), any());
+            verify(mBpfUpstream6Map, never()).updateEntry(any(), any());
+        }
+    }
+
     private void verifyTetherOffloadRuleAdd(@Nullable InOrder inOrder,
             @NonNull Ipv6ForwardingRule rule) throws Exception {
         if (mDeps.isAtLeastS()) {
-            verifyWithOrder(inOrder, mBpfIngressMap).updateEntry(
-                    rule.makeTetherIngressKey(), rule.makeTetherIngressValue());
+            verifyWithOrder(inOrder, mBpfDownstream6Map).updateEntry(
+                    rule.makeTetherDownstream6Key(), rule.makeTether6Value());
         } else {
             verifyWithOrder(inOrder, mNetd).tetherOffloadRuleAdd(matches(rule));
         }
@@ -350,7 +407,7 @@
 
     private void verifyNeverTetherOffloadRuleAdd() throws Exception {
         if (mDeps.isAtLeastS()) {
-            verify(mBpfIngressMap, never()).updateEntry(any(), any());
+            verify(mBpfDownstream6Map, never()).updateEntry(any(), any());
         } else {
             verify(mNetd, never()).tetherOffloadRuleAdd(any());
         }
@@ -359,7 +416,8 @@
     private void verifyTetherOffloadRuleRemove(@Nullable InOrder inOrder,
             @NonNull final Ipv6ForwardingRule rule) throws Exception {
         if (mDeps.isAtLeastS()) {
-            verifyWithOrder(inOrder, mBpfIngressMap).deleteEntry(rule.makeTetherIngressKey());
+            verifyWithOrder(inOrder, mBpfDownstream6Map).deleteEntry(
+                    rule.makeTetherDownstream6Key());
         } else {
             verifyWithOrder(inOrder, mNetd).tetherOffloadRuleRemove(matches(rule));
         }
@@ -367,7 +425,7 @@
 
     private void verifyNeverTetherOffloadRuleRemove() throws Exception {
         if (mDeps.isAtLeastS()) {
-            verify(mBpfIngressMap, never()).deleteEntry(any());
+            verify(mBpfDownstream6Map, never()).deleteEntry(any());
         } else {
             verify(mNetd, never()).tetherOffloadRuleRemove(any());
         }
@@ -435,7 +493,7 @@
         // BpfCoordinator#tetherOffloadRuleAdd and BpfCoordinator#tetherOffloadGetAndClearStats.
         // The #verifyTetherOffloadGetAndClearStats can't distinguish who has ever called
         // mBpfStatsMap#getValue and get a wrong calling count which counts all.
-        final InOrder inOrder = inOrder(mNetd, mBpfIngressMap, mBpfLimitMap, mBpfStatsMap);
+        final InOrder inOrder = inOrder(mNetd, mBpfDownstream6Map, mBpfLimitMap, mBpfStatsMap);
         final Ipv6ForwardingRule rule = buildTestForwardingRule(mobileIfIndex, NEIGH_A, MAC_A);
         coordinator.tetherOffloadRuleAdd(mIpServer, rule);
         verifyTetherOffloadRuleAdd(inOrder, rule);
@@ -651,11 +709,11 @@
     }
 
     @Test
-    public void testRuleMakeTetherIngressKey() throws Exception {
+    public void testRuleMakeTetherDownstream6Key() throws Exception {
         final Integer mobileIfIndex = 100;
         final Ipv6ForwardingRule rule = buildTestForwardingRule(mobileIfIndex, NEIGH_A, MAC_A);
 
-        final TetherIngressKey key = rule.makeTetherIngressKey();
+        final TetherDownstream6Key key = rule.makeTetherDownstream6Key();
         assertEquals(key.iif, (long) mobileIfIndex);
         assertTrue(Arrays.equals(key.neigh6, NEIGH_A.getAddress()));
         // iif (4) + neigh6 (16) = 20.
@@ -663,11 +721,11 @@
     }
 
     @Test
-    public void testRuleMakeTetherIngressValue() throws Exception {
+    public void testRuleMakeTether6Value() throws Exception {
         final Integer mobileIfIndex = 100;
         final Ipv6ForwardingRule rule = buildTestForwardingRule(mobileIfIndex, NEIGH_A, MAC_A);
 
-        final TetherIngressValue value = rule.makeTetherIngressValue();
+        final Tether6Value value = rule.makeTether6Value();
         assertEquals(value.oif, DOWNSTREAM_IFINDEX);
         assertEquals(value.ethDstMac, MAC_A);
         assertEquals(value.ethSrcMac, DOWNSTREAM_MAC);
@@ -691,7 +749,7 @@
         // Set the unlimited quota as default if the service has never applied a data limit for a
         // given upstream. Note that the data limit only be applied on an upstream which has rules.
         final Ipv6ForwardingRule rule = buildTestForwardingRule(mobileIfIndex, NEIGH_A, MAC_A);
-        final InOrder inOrder = inOrder(mNetd, mBpfIngressMap, mBpfLimitMap, mBpfStatsMap);
+        final InOrder inOrder = inOrder(mNetd, mBpfDownstream6Map, mBpfLimitMap, mBpfStatsMap);
         coordinator.tetherOffloadRuleAdd(mIpServer, rule);
         verifyTetherOffloadRuleAdd(inOrder, rule);
         verifyTetherOffloadSetInterfaceQuota(inOrder, mobileIfIndex, QUOTA_UNLIMITED,
@@ -734,7 +792,7 @@
         // Applying a data limit to the current upstream does not take any immediate action.
         // The data limit could be only set on an upstream which has rules.
         final long limit = 12345;
-        final InOrder inOrder = inOrder(mNetd, mBpfIngressMap, mBpfLimitMap, mBpfStatsMap);
+        final InOrder inOrder = inOrder(mNetd, mBpfDownstream6Map, mBpfLimitMap, mBpfStatsMap);
         mTetherStatsProvider.onSetLimit(mobileIface, limit);
         waitForIdle();
         verifyNeverTetherOffloadSetInterfaceQuota(inOrder);
@@ -779,7 +837,8 @@
         coordinator.addUpstreamNameToLookupTable(ethIfIndex, ethIface);
         coordinator.addUpstreamNameToLookupTable(mobileIfIndex, mobileIface);
 
-        final InOrder inOrder = inOrder(mNetd, mBpfIngressMap, mBpfLimitMap, mBpfStatsMap);
+        final InOrder inOrder = inOrder(mNetd, mBpfDownstream6Map, mBpfUpstream6Map, mBpfLimitMap,
+                mBpfStatsMap);
 
         // Before the rule test, here are the additional actions while the rules are changed.
         // - After adding the first rule on a given upstream, the coordinator adds a data limit.
@@ -799,7 +858,7 @@
         verifyTetherOffloadRuleAdd(inOrder, ethernetRuleA);
         verifyTetherOffloadSetInterfaceQuota(inOrder, ethIfIndex, QUOTA_UNLIMITED,
                 true /* isInit */);
-
+        verifyStartUpstreamIpv6Forwarding(inOrder, DOWNSTREAM_IFINDEX, ethIfIndex);
         coordinator.tetherOffloadRuleAdd(mIpServer, ethernetRuleB);
         verifyTetherOffloadRuleAdd(inOrder, ethernetRuleB);
 
@@ -815,11 +874,13 @@
         // by one for updating upstream interface index by #tetherOffloadRuleUpdate.
         coordinator.tetherOffloadRuleUpdate(mIpServer, mobileIfIndex);
         verifyTetherOffloadRuleRemove(inOrder, ethernetRuleA);
+        verifyTetherOffloadRuleRemove(inOrder, ethernetRuleB);
+        verifyStopUpstreamIpv6Forwarding(inOrder, DOWNSTREAM_IFINDEX);
+        verifyTetherOffloadGetAndClearStats(inOrder, ethIfIndex);
         verifyTetherOffloadRuleAdd(inOrder, mobileRuleA);
         verifyTetherOffloadSetInterfaceQuota(inOrder, mobileIfIndex, QUOTA_UNLIMITED,
                 true /* isInit */);
-        verifyTetherOffloadRuleRemove(inOrder, ethernetRuleB);
-        verifyTetherOffloadGetAndClearStats(inOrder, ethIfIndex);
+        verifyStartUpstreamIpv6Forwarding(inOrder, DOWNSTREAM_IFINDEX, mobileIfIndex);
         verifyTetherOffloadRuleAdd(inOrder, mobileRuleB);
 
         // [3] Clear all rules for a given IpServer.
@@ -828,6 +889,7 @@
         coordinator.tetherOffloadRuleClear(mIpServer);
         verifyTetherOffloadRuleRemove(inOrder, mobileRuleA);
         verifyTetherOffloadRuleRemove(inOrder, mobileRuleB);
+        verifyStopUpstreamIpv6Forwarding(inOrder, DOWNSTREAM_IFINDEX);
         verifyTetherOffloadGetAndClearStats(inOrder, mobileIfIndex);
 
         // [4] Force pushing stats update to verify that the last diff of stats is reported on all
@@ -845,7 +907,7 @@
     private void checkBpfDisabled() throws Exception {
         // The caller may mock the global dependencies |mDeps| which is used in
         // #makeBpfCoordinator for testing.
-        // See #testBpfDisabledbyNoBpfIngressMap.
+        // See #testBpfDisabledbyNoBpfDownstream6Map.
         final BpfCoordinator coordinator = makeBpfCoordinator();
         coordinator.startPolling();
 
@@ -908,9 +970,18 @@
 
     @Test
     @IgnoreUpTo(Build.VERSION_CODES.R)
-    public void testBpfDisabledbyNoBpfIngressMap() throws Exception {
+    public void testBpfDisabledbyNoBpfDownstream6Map() throws Exception {
         setupFunctioningNetdInterface();
-        doReturn(null).when(mDeps).getBpfIngressMap();
+        doReturn(null).when(mDeps).getBpfDownstream6Map();
+
+        checkBpfDisabled();
+    }
+
+    @Test
+    @IgnoreUpTo(Build.VERSION_CODES.R)
+    public void testBpfDisabledbyNoBpfUpstream6Map() throws Exception {
+        setupFunctioningNetdInterface();
+        doReturn(null).when(mDeps).getBpfUpstream6Map();
 
         checkBpfDisabled();
     }
@@ -981,4 +1052,48 @@
         waitForIdle();
         verifyTetherOffloadGetStats();
     }
+
+    @Test
+    public void testStartStopConntrackMonitoring() throws Exception {
+        setupFunctioningNetdInterface();
+
+        final BpfCoordinator coordinator = makeBpfCoordinator();
+
+        // [1] Don't stop monitoring if it has never started.
+        coordinator.stopMonitoring(mIpServer);
+        verify(mConntrackMonitor, never()).start();
+
+        // [2] Start monitoring.
+        coordinator.startMonitoring(mIpServer);
+        verify(mConntrackMonitor).start();
+        clearInvocations(mConntrackMonitor);
+
+        // [3] Stop monitoring.
+        coordinator.stopMonitoring(mIpServer);
+        verify(mConntrackMonitor).stop();
+    }
+
+    @Test
+    public void testStartStopConntrackMonitoringWithTwoDownstreamIfaces() throws Exception {
+        setupFunctioningNetdInterface();
+
+        final BpfCoordinator coordinator = makeBpfCoordinator();
+
+        // [1] Start monitoring at the first IpServer adding.
+        coordinator.startMonitoring(mIpServer);
+        verify(mConntrackMonitor).start();
+        clearInvocations(mConntrackMonitor);
+
+        // [2] Don't start monitoring at the second IpServer adding.
+        coordinator.startMonitoring(mIpServer2);
+        verify(mConntrackMonitor, never()).start();
+
+        // [3] Don't stop monitoring if any downstream interface exists.
+        coordinator.stopMonitoring(mIpServer2);
+        verify(mConntrackMonitor, never()).stop();
+
+        // [4] Stop monitoring if no downstream exists.
+        coordinator.stopMonitoring(mIpServer);
+        verify(mConntrackMonitor).stop();
+    }
 }
diff --git a/framework/Android.bp b/framework/Android.bp
deleted file mode 100644
index 8db8d76..0000000
--- a/framework/Android.bp
+++ /dev/null
@@ -1,29 +0,0 @@
-//
-// Copyright (C) 2020 The Android Open Source Project
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//      http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-//
-
-// TODO: use a java_library in the bootclasspath instead
-filegroup {
-    name: "framework-connectivity-sources",
-    srcs: [
-        "src/**/*.java",
-        "src/**/*.aidl",
-    ],
-    path: "src",
-    visibility: [
-        "//frameworks/base",
-        "//packages/modules/Connectivity:__subpackages__",
-    ],
-}
\ No newline at end of file
diff --git a/framework/src/com/android/connectivity/aidl/INetworkAgent.aidl b/framework/src/com/android/connectivity/aidl/INetworkAgent.aidl
deleted file mode 100644
index 1af9e76..0000000
--- a/framework/src/com/android/connectivity/aidl/INetworkAgent.aidl
+++ /dev/null
@@ -1,46 +0,0 @@
-/**
- * Copyright (c) 2020, The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing perNmissions and
- * limitations under the License.
- */
-package com.android.connectivity.aidl;
-
-import android.net.NattKeepalivePacketData;
-import android.net.TcpKeepalivePacketData;
-
-import com.android.connectivity.aidl.INetworkAgentRegistry;
-
-/**
- * Interface to notify NetworkAgent of connectivity events.
- * @hide
- */
-oneway interface INetworkAgent {
-    void onRegistered(in INetworkAgentRegistry registry);
-    void onDisconnected();
-    void onBandwidthUpdateRequested();
-    void onValidationStatusChanged(int validationStatus,
-            in @nullable String captivePortalUrl);
-    void onSaveAcceptUnvalidated(boolean acceptUnvalidated);
-    void onStartNattSocketKeepalive(int slot, int intervalDurationMs,
-        in NattKeepalivePacketData packetData);
-    void onStartTcpSocketKeepalive(int slot, int intervalDurationMs,
-        in TcpKeepalivePacketData packetData);
-    void onStopSocketKeepalive(int slot);
-    void onSignalStrengthThresholdsUpdated(in int[] thresholds);
-    void onPreventAutomaticReconnect();
-    void onAddNattKeepalivePacketFilter(int slot,
-        in NattKeepalivePacketData packetData);
-    void onAddTcpKeepalivePacketFilter(int slot,
-        in TcpKeepalivePacketData packetData);
-    void onRemoveKeepalivePacketFilter(int slot);
-}
diff --git a/framework/src/com/android/connectivity/aidl/INetworkAgentRegistry.aidl b/framework/src/com/android/connectivity/aidl/INetworkAgentRegistry.aidl
deleted file mode 100644
index d42a340..0000000
--- a/framework/src/com/android/connectivity/aidl/INetworkAgentRegistry.aidl
+++ /dev/null
@@ -1,36 +0,0 @@
-/**
- * Copyright (c) 2020, The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing perNmissions and
- * limitations under the License.
- */
-package com.android.connectivity.aidl;
-
-import android.net.LinkProperties;
-import android.net.Network;
-import android.net.NetworkCapabilities;
-import android.net.NetworkInfo;
-
-/**
- * Interface for NetworkAgents to send network network properties.
- * @hide
- */
-oneway interface INetworkAgentRegistry {
-    void sendNetworkCapabilities(in NetworkCapabilities nc);
-    void sendLinkProperties(in LinkProperties lp);
-    // TODO: consider replacing this by "markConnected()" and removing
-    void sendNetworkInfo(in NetworkInfo info);
-    void sendScore(int score);
-    void sendExplicitlySelected(boolean explicitlySelected, boolean acceptPartial);
-    void sendSocketKeepaliveEvent(int slot, int reason);
-    void sendUnderlyingNetworks(in @nullable List<Network> networks);
-}
diff --git a/tests/cts/hostside/app/src/com/android/cts/net/hostside/MeterednessConfigurationRule.java b/tests/cts/hostside/app/src/com/android/cts/net/hostside/MeterednessConfigurationRule.java
index 8fadf9e..5c99c67 100644
--- a/tests/cts/hostside/app/src/com/android/cts/net/hostside/MeterednessConfigurationRule.java
+++ b/tests/cts/hostside/app/src/com/android/cts/net/hostside/MeterednessConfigurationRule.java
@@ -15,21 +15,20 @@
  */
 package com.android.cts.net.hostside;
 
-import static com.android.cts.net.hostside.NetworkPolicyTestUtils.resetMeteredNetwork;
-import static com.android.cts.net.hostside.NetworkPolicyTestUtils.setupMeteredNetwork;
+import static com.android.cts.net.hostside.NetworkPolicyTestUtils.setupActiveNetworkMeteredness;
 import static com.android.cts.net.hostside.Property.METERED_NETWORK;
 import static com.android.cts.net.hostside.Property.NON_METERED_NETWORK;
 
 import android.util.ArraySet;
-import android.util.Pair;
 
 import com.android.compatibility.common.util.BeforeAfterRule;
+import com.android.compatibility.common.util.ThrowingRunnable;
 
 import org.junit.runner.Description;
 import org.junit.runners.model.Statement;
 
 public class MeterednessConfigurationRule extends BeforeAfterRule {
-    private Pair<String, Boolean> mSsidAndInitialMeteredness;
+    private ThrowingRunnable mMeterednessResetter;
 
     @Override
     public void onBefore(Statement base, Description description) throws Throwable {
@@ -48,13 +47,13 @@
     }
 
     public void configureNetworkMeteredness(boolean metered) throws Exception {
-        mSsidAndInitialMeteredness = setupMeteredNetwork(metered);
+        mMeterednessResetter = setupActiveNetworkMeteredness(metered);
     }
 
     public void resetNetworkMeteredness() throws Exception {
-        if (mSsidAndInitialMeteredness != null) {
-            resetMeteredNetwork(mSsidAndInitialMeteredness.first,
-                    mSsidAndInitialMeteredness.second);
+        if (mMeterednessResetter != null) {
+            mMeterednessResetter.run();
+            mMeterednessResetter = null;
         }
     }
 }
diff --git a/tests/cts/hostside/app/src/com/android/cts/net/hostside/NetworkCallbackTest.java b/tests/cts/hostside/app/src/com/android/cts/net/hostside/NetworkCallbackTest.java
index 2ac29e7..955317b 100644
--- a/tests/cts/hostside/app/src/com/android/cts/net/hostside/NetworkCallbackTest.java
+++ b/tests/cts/hostside/app/src/com/android/cts/net/hostside/NetworkCallbackTest.java
@@ -17,16 +17,13 @@
 package com.android.cts.net.hostside;
 
 import static android.net.NetworkCapabilities.NET_CAPABILITY_NOT_METERED;
+
 import static com.android.cts.net.hostside.NetworkPolicyTestUtils.canChangeActiveNetworkMeteredness;
 import static com.android.cts.net.hostside.NetworkPolicyTestUtils.setRestrictBackground;
-import static com.android.cts.net.hostside.NetworkPolicyTestUtils.isActiveNetworkMetered;
 import static com.android.cts.net.hostside.Property.BATTERY_SAVER_MODE;
 import static com.android.cts.net.hostside.Property.DATA_SAVER_MODE;
 
 import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertNull;
-import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 import static org.junit.Assume.assumeTrue;
 
@@ -186,7 +183,7 @@
     public void setUp() throws Exception {
         super.setUp();
 
-        assumeTrue(isActiveNetworkMetered(true) || canChangeActiveNetworkMeteredness());
+        assumeTrue(canChangeActiveNetworkMeteredness());
 
         registerBroadcastReceiver();
 
@@ -198,13 +195,13 @@
         setBatterySaverMode(false);
         setRestrictBackground(false);
 
-        // Make wifi a metered network.
+        // Mark network as metered.
         mMeterednessConfiguration.configureNetworkMeteredness(true);
 
         // Register callback
         registerNetworkCallback((INetworkCallback.Stub) mTestNetworkCallback);
-        // Once the wifi is marked as metered, the wifi will reconnect. Wait for onAvailable()
-        // callback to ensure wifi is connected before the test and store the default network.
+        // Wait for onAvailable() callback to ensure network is available before the test
+        // and store the default network.
         mNetwork = mTestNetworkCallback.expectAvailableCallbackAndGetNetwork();
         // Check that the network is metered.
         mTestNetworkCallback.expectCapabilitiesCallbackEventually(mNetwork,
diff --git a/tests/cts/hostside/app/src/com/android/cts/net/hostside/NetworkPolicyTestUtils.java b/tests/cts/hostside/app/src/com/android/cts/net/hostside/NetworkPolicyTestUtils.java
index 3041dfa..b61535b 100644
--- a/tests/cts/hostside/app/src/com/android/cts/net/hostside/NetworkPolicyTestUtils.java
+++ b/tests/cts/hostside/app/src/com/android/cts/net/hostside/NetworkPolicyTestUtils.java
@@ -20,6 +20,7 @@
 import static android.net.ConnectivityManager.RESTRICT_BACKGROUND_STATUS_ENABLED;
 import static android.net.ConnectivityManager.RESTRICT_BACKGROUND_STATUS_WHITELISTED;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_NOT_METERED;
+import static android.net.NetworkCapabilities.TRANSPORT_CELLULAR;
 import static android.net.NetworkCapabilities.TRANSPORT_WIFI;
 
 import static com.android.compatibility.common.util.SystemUtil.runShellCommand;
@@ -28,6 +29,7 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
@@ -40,25 +42,36 @@
 import android.net.Network;
 import android.net.NetworkCapabilities;
 import android.net.wifi.WifiManager;
+import android.os.PersistableBundle;
 import android.os.Process;
+import android.telephony.CarrierConfigManager;
+import android.telephony.SubscriptionManager;
+import android.telephony.data.ApnSetting;
 import android.text.TextUtils;
 import android.util.Log;
-import android.util.Pair;
+
+import androidx.test.platform.app.InstrumentationRegistry;
 
 import com.android.compatibility.common.util.AppStandbyUtils;
 import com.android.compatibility.common.util.BatteryUtils;
+import com.android.compatibility.common.util.ShellIdentityUtils;
+import com.android.compatibility.common.util.ThrowingRunnable;
 
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 
-import androidx.test.platform.app.InstrumentationRegistry;
-
 public class NetworkPolicyTestUtils {
 
+    // android.telephony.CarrierConfigManager.KEY_CARRIER_METERED_APN_TYPES_STRINGS
+    // TODO: Expose it as a @TestApi instead of copying the constant
+    private static final String KEY_CARRIER_METERED_APN_TYPES_STRINGS =
+            "carrier_metered_apn_types_strings";
+
     private static final int TIMEOUT_CHANGE_METEREDNESS_MS = 10_000;
 
     private static ConnectivityManager mCm;
     private static WifiManager mWm;
+    private static CarrierConfigManager mCarrierConfigManager;
 
     private static Boolean mBatterySaverSupported;
     private static Boolean mDataSaverSupported;
@@ -135,16 +148,40 @@
     }
 
     public static boolean canChangeActiveNetworkMeteredness() {
-        final Network activeNetwork = getConnectivityManager().getActiveNetwork();
-        final NetworkCapabilities networkCapabilities
-                = getConnectivityManager().getNetworkCapabilities(activeNetwork);
-        return networkCapabilities.hasTransport(TRANSPORT_WIFI);
+        final NetworkCapabilities networkCapabilities = getActiveNetworkCapabilities();
+        return networkCapabilities.hasTransport(TRANSPORT_WIFI)
+                || networkCapabilities.hasTransport(TRANSPORT_CELLULAR);
     }
 
-    public static Pair<String, Boolean> setupMeteredNetwork(boolean metered) throws Exception {
+    /**
+     * Updates the meteredness of the active network. Right now we can only change meteredness
+     * of either Wifi or cellular network, so if the active network is not either of these, this
+     * will throw an exception.
+     *
+     * @return a {@link ThrowingRunnable} object that can used to reset the meteredness change
+     *         made by this method.
+     */
+    public static ThrowingRunnable setupActiveNetworkMeteredness(boolean metered) throws Exception {
         if (isActiveNetworkMetered(metered)) {
             return null;
         }
+        final NetworkCapabilities networkCapabilities = getActiveNetworkCapabilities();
+        if (networkCapabilities.hasTransport(TRANSPORT_WIFI)) {
+            final String ssid = getWifiSsid();
+            setWifiMeteredStatus(ssid, metered);
+            return () -> setWifiMeteredStatus(ssid, !metered);
+        } else if (networkCapabilities.hasTransport(TRANSPORT_CELLULAR)) {
+            final int subId = SubscriptionManager.getActiveDataSubscriptionId();
+            setCellularMeteredStatus(subId, metered);
+            return () -> setCellularMeteredStatus(subId, !metered);
+        } else {
+            // Right now, we don't have a way to change meteredness of networks other
+            // than Wi-Fi or Cellular, so just throw an exception.
+            throw new IllegalStateException("Can't change meteredness of current active network");
+        }
+    }
+
+    private static String getWifiSsid() {
         final boolean isLocationEnabled = isLocationEnabled();
         try {
             if (!isLocationEnabled) {
@@ -152,8 +189,7 @@
             }
             final String ssid = unquoteSSID(getWifiManager().getConnectionInfo().getSSID());
             assertNotEquals(WifiManager.UNKNOWN_SSID, ssid);
-            setWifiMeteredStatus(ssid, metered);
-            return Pair.create(ssid, !metered);
+            return ssid;
         } finally {
             // Reset the location enabled state
             if (!isLocationEnabled) {
@@ -162,11 +198,13 @@
         }
     }
 
-    public static void resetMeteredNetwork(String ssid, boolean metered) throws Exception {
-        setWifiMeteredStatus(ssid, metered);
+    private static NetworkCapabilities getActiveNetworkCapabilities() {
+        final Network activeNetwork = getConnectivityManager().getActiveNetwork();
+        assertNotNull("No active network available", activeNetwork);
+        return getConnectivityManager().getNetworkCapabilities(activeNetwork);
     }
 
-    public static void setWifiMeteredStatus(String ssid, boolean metered) throws Exception {
+    private static void setWifiMeteredStatus(String ssid, boolean metered) throws Exception {
         assertFalse("SSID should not be empty", TextUtils.isEmpty(ssid));
         final String cmd = "cmd netpolicy set metered-network " + ssid + " " + metered;
         executeShellCommand(cmd);
@@ -174,15 +212,24 @@
         assertActiveNetworkMetered(metered);
     }
 
-    public static void assertWifiMeteredStatus(String ssid, boolean expectedMeteredStatus) {
+    private static void assertWifiMeteredStatus(String ssid, boolean expectedMeteredStatus) {
         final String result = executeShellCommand("cmd netpolicy list wifi-networks");
         final String expectedLine = ssid + ";" + expectedMeteredStatus;
         assertTrue("Expected line: " + expectedLine + "; Actual result: " + result,
                 result.contains(expectedLine));
     }
 
+    private static void setCellularMeteredStatus(int subId, boolean metered) throws Exception {
+        final PersistableBundle bundle = new PersistableBundle();
+        bundle.putStringArray(KEY_CARRIER_METERED_APN_TYPES_STRINGS,
+                new String[] {ApnSetting.TYPE_MMS_STRING});
+        ShellIdentityUtils.invokeMethodWithShellPermissionsNoReturn(getCarrierConfigManager(),
+                (cm) -> cm.overrideConfig(subId, metered ? null : bundle));
+        assertActiveNetworkMetered(metered);
+    }
+
     // Copied from cts/tests/tests/net/src/android/net/cts/ConnectivityManagerTest.java
-    public static void assertActiveNetworkMetered(boolean expectedMeteredStatus) throws Exception {
+    private static void assertActiveNetworkMetered(boolean expectedMeteredStatus) throws Exception {
         final CountDownLatch latch = new CountDownLatch(1);
         final NetworkCallback networkCallback = new NetworkCallback() {
             @Override
@@ -197,12 +244,15 @@
         // with the current setting. Therefore, if the setting has already been changed,
         // this method will return right away, and if not it will wait for the setting to change.
         getConnectivityManager().registerDefaultNetworkCallback(networkCallback);
-        if (!latch.await(TIMEOUT_CHANGE_METEREDNESS_MS, TimeUnit.MILLISECONDS)) {
-            fail("Timed out waiting for active network metered status to change to "
-                    + expectedMeteredStatus + " ; network = "
-                    + getConnectivityManager().getActiveNetwork());
+        try {
+            if (!latch.await(TIMEOUT_CHANGE_METEREDNESS_MS, TimeUnit.MILLISECONDS)) {
+                fail("Timed out waiting for active network metered status to change to "
+                        + expectedMeteredStatus + "; network = "
+                        + getConnectivityManager().getActiveNetwork());
+            }
+        } finally {
+            getConnectivityManager().unregisterNetworkCallback(networkCallback);
         }
-        getConnectivityManager().unregisterNetworkCallback(networkCallback);
     }
 
     public static void setRestrictBackground(boolean enabled) {
@@ -274,6 +324,14 @@
         return mWm;
     }
 
+    public static CarrierConfigManager getCarrierConfigManager() {
+        if (mCarrierConfigManager == null) {
+            mCarrierConfigManager = (CarrierConfigManager) getContext().getSystemService(
+                    Context.CARRIER_CONFIG_SERVICE);
+        }
+        return mCarrierConfigManager;
+    }
+
     public static Context getContext() {
         return getInstrumentation().getContext();
     }
diff --git a/tests/cts/hostside/app/src/com/android/cts/net/hostside/VpnTest.java b/tests/cts/hostside/app/src/com/android/cts/net/hostside/VpnTest.java
index 81a431c..a663cd6 100755
--- a/tests/cts/hostside/app/src/com/android/cts/net/hostside/VpnTest.java
+++ b/tests/cts/hostside/app/src/com/android/cts/net/hostside/VpnTest.java
@@ -16,6 +16,8 @@
 
 package com.android.cts.net.hostside;
 
+import static android.Manifest.permission.NETWORK_SETTINGS;
+import static android.net.NetworkCapabilities.TRANSPORT_VPN;
 import static android.os.Process.INVALID_UID;
 import static android.system.OsConstants.AF_INET;
 import static android.system.OsConstants.AF_INET6;
@@ -25,6 +27,9 @@
 import static android.system.OsConstants.IPPROTO_TCP;
 import static android.system.OsConstants.POLLIN;
 import static android.system.OsConstants.SOCK_DGRAM;
+import static android.test.MoreAsserts.assertNotEqual;
+
+import static com.android.compatibility.common.util.SystemUtil.runWithShellPermissionIdentity;
 
 import android.annotation.Nullable;
 import android.app.DownloadManager;
@@ -45,9 +50,14 @@
 import android.net.NetworkRequest;
 import android.net.Proxy;
 import android.net.ProxyInfo;
+import android.net.TransportInfo;
 import android.net.Uri;
+import android.net.VpnManager;
 import android.net.VpnService;
+import android.net.VpnTransportInfo;
 import android.net.wifi.WifiManager;
+import android.os.Handler;
+import android.os.Looper;
 import android.os.ParcelFileDescriptor;
 import android.os.Process;
 import android.os.SystemProperties;
@@ -687,6 +697,34 @@
         setAndVerifyPrivateDns(initialMode);
     }
 
+    private class NeverChangeNetworkCallback extends NetworkCallback {
+        private CountDownLatch mLatch = new CountDownLatch(1);
+        private volatile Network mFirstNetwork;
+        private volatile Network mOtherNetwork;
+
+        public void onAvailable(Network n) {
+            // Don't assert here, as it crashes the test with a hard to debug message.
+            if (mFirstNetwork == null) {
+                mFirstNetwork = n;
+                mLatch.countDown();
+            } else if (mOtherNetwork == null) {
+                mOtherNetwork = n;
+            }
+        }
+
+        public Network getFirstNetwork() throws Exception {
+            assertTrue(
+                    "System default callback got no network after " + TIMEOUT_MS + "ms. "
+                    + "Please ensure the device has a working Internet connection.",
+                    mLatch.await(TIMEOUT_MS, TimeUnit.MILLISECONDS));
+            return mFirstNetwork;
+        }
+
+        public void assertNeverChanged() {
+            assertNull(mOtherNetwork);
+        }
+    }
+
     public void testDefault() throws Exception {
         if (!supportedHardware()) return;
         // If adb TCP port opened, this test may running by adb over network.
@@ -702,6 +740,14 @@
                 getInstrumentation().getTargetContext(), MyVpnService.ACTION_ESTABLISHED);
         receiver.register();
 
+
+        // Expect the system default network not to change.
+        final NeverChangeNetworkCallback neverChangeCallback = new NeverChangeNetworkCallback();
+        final Network defaultNetwork = mCM.getActiveNetwork();
+        runWithShellPermissionIdentity(() ->
+                mCM.registerSystemDefaultNetworkCallback(neverChangeCallback,
+                        new Handler(Looper.getMainLooper())), NETWORK_SETTINGS);
+
         FileDescriptor fd = openSocketFdInOtherApp(TEST_HOST, 80, TIMEOUT_MS);
 
         startVpn(new String[] {"192.0.2.2/32", "2001:db8:1:2::ffe/128"},
@@ -719,6 +765,20 @@
 
         checkTrafficOnVpn();
 
+        expectVpnTransportInfo(mCM.getActiveNetwork());
+
+        // Check that system default network callback has not seen any network changes, even though
+        // the app's default network changed. This needs to be done before testing private
+        // DNS because checkStrictModePrivateDns will set the private DNS server to a nonexistent
+        // name, which will cause validation to fail and cause the default network to switch (e.g.,
+        // from wifi to cellular).
+        assertEquals(defaultNetwork, neverChangeCallback.getFirstNetwork());
+        assertNotEqual(defaultNetwork, mCM.getActiveNetwork());
+        neverChangeCallback.assertNeverChanged();
+        runWithShellPermissionIdentity(
+                () ->  mCM.unregisterNetworkCallback(neverChangeCallback),
+                NETWORK_SETTINGS);
+
         checkStrictModePrivateDns();
 
         receiver.unregisterQuietly();
@@ -739,6 +799,8 @@
 
         checkTrafficOnVpn();
 
+        expectVpnTransportInfo(mCM.getActiveNetwork());
+
         checkStrictModePrivateDns();
     }
 
@@ -764,6 +826,10 @@
         assertSocketStillOpen(remoteFd, TEST_HOST);
 
         checkNoTrafficOnVpn();
+
+        final Network network = mCM.getActiveNetwork();
+        final NetworkCapabilities nc = mCM.getNetworkCapabilities(network);
+        assertFalse(nc.hasTransport(TRANSPORT_VPN));
     }
 
     public void testGetConnectionOwnerUidSecurity() throws Exception {
@@ -778,8 +844,11 @@
         InetSocketAddress rem = new InetSocketAddress(s.getInetAddress(), s.getPort());
         try {
             int uid = mCM.getConnectionOwnerUid(OsConstants.IPPROTO_TCP, loc, rem);
-            fail("Only an active VPN app may call this API.");
-        } catch (SecurityException expected) {
+            assertEquals("Only an active VPN app should see connection information",
+                    INVALID_UID, uid);
+        } catch (SecurityException acceptable) {
+            // R and below throw SecurityException if a non-active VPN calls this method.
+            // As long as we can't actually get socket information, either behaviour is fine.
             return;
         }
     }
@@ -918,6 +987,8 @@
         // VPN with no underlying networks should be metered by default.
         assertTrue(isNetworkMetered(mNetwork));
         assertTrue(mCM.isActiveNetworkMetered());
+
+        expectVpnTransportInfo(mCM.getActiveNetwork());
     }
 
     public void testVpnMeterednessWithNullUnderlyingNetwork() throws Exception {
@@ -944,6 +1015,8 @@
         assertEquals(isNetworkMetered(underlyingNetwork), isNetworkMetered(mNetwork));
         // Meteredness based on VPN capabilities and CM#isActiveNetworkMetered should be in sync.
         assertEquals(isNetworkMetered(mNetwork), mCM.isActiveNetworkMetered());
+
+        expectVpnTransportInfo(mCM.getActiveNetwork());
     }
 
     public void testVpnMeterednessWithNonNullUnderlyingNetwork() throws Exception {
@@ -971,6 +1044,8 @@
         assertEquals(isNetworkMetered(underlyingNetwork), isNetworkMetered(mNetwork));
         // Meteredness based on VPN capabilities and CM#isActiveNetworkMetered should be in sync.
         assertEquals(isNetworkMetered(mNetwork), mCM.isActiveNetworkMetered());
+
+        expectVpnTransportInfo(mCM.getActiveNetwork());
     }
 
     public void testAlwaysMeteredVpnWithNullUnderlyingNetwork() throws Exception {
@@ -995,6 +1070,8 @@
         // VPN's meteredness does not depend on underlying network since it is always metered.
         assertTrue(isNetworkMetered(mNetwork));
         assertTrue(mCM.isActiveNetworkMetered());
+
+        expectVpnTransportInfo(mCM.getActiveNetwork());
     }
 
     public void testAlwaysMeteredVpnWithNonNullUnderlyingNetwork() throws Exception {
@@ -1020,6 +1097,8 @@
         // VPN's meteredness does not depend on underlying network since it is always metered.
         assertTrue(isNetworkMetered(mNetwork));
         assertTrue(mCM.isActiveNetworkMetered());
+
+        expectVpnTransportInfo(mCM.getActiveNetwork());
     }
 
     public void testB141603906() throws Exception {
@@ -1069,6 +1148,14 @@
         }
     }
 
+    private void expectVpnTransportInfo(Network network) {
+        final NetworkCapabilities vpnNc = mCM.getNetworkCapabilities(network);
+        assertTrue(vpnNc.hasTransport(TRANSPORT_VPN));
+        final TransportInfo ti = vpnNc.getTransportInfo();
+        assertTrue(ti instanceof VpnTransportInfo);
+        assertEquals(VpnManager.TYPE_VPN_SERVICE, ((VpnTransportInfo) ti).type);
+    }
+
     private void assertDefaultProxy(ProxyInfo expected) {
         assertEquals("Incorrect proxy config.", expected, mCM.getDefaultProxy());
         String expectedHost = expected == null ? null : expected.getHost();
diff --git a/tests/cts/hostside/app2/src/com/android/cts/net/hostside/app2/MyService.java b/tests/cts/hostside/app2/src/com/android/cts/net/hostside/app2/MyService.java
index 590e17e..1c9ff05 100644
--- a/tests/cts/hostside/app2/src/com/android/cts/net/hostside/app2/MyService.java
+++ b/tests/cts/hostside/app2/src/com/android/cts/net/hostside/app2/MyService.java
@@ -138,7 +138,7 @@
                     }
                 }
             };
-            mCm.registerNetworkCallback(makeWifiNetworkRequest(), mNetworkCallback);
+            mCm.registerNetworkCallback(makeNetworkRequest(), mNetworkCallback);
             try {
                 cb.asBinder().linkToDeath(() -> unregisterNetworkCallback(), 0);
             } catch (RemoteException e) {
@@ -156,9 +156,8 @@
         }
       };
 
-    private NetworkRequest makeWifiNetworkRequest() {
+    private NetworkRequest makeNetworkRequest() {
         return new NetworkRequest.Builder()
-                .addTransportType(NetworkCapabilities.TRANSPORT_WIFI)
                 .addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)
                 .build();
     }
diff --git a/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java b/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
index cbf43e7..831810c 100644
--- a/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
+++ b/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
@@ -25,10 +25,12 @@
 import static android.content.pm.PackageManager.FEATURE_WIFI;
 import static android.content.pm.PackageManager.GET_PERMISSIONS;
 import static android.content.pm.PackageManager.PERMISSION_GRANTED;
+import static android.net.NetworkCapabilities.NET_CAPABILITY_FOREGROUND;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_IMS;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_INTERNET;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_NOT_METERED;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_NOT_RESTRICTED;
+import static android.net.NetworkCapabilities.TRANSPORT_TEST;
 import static android.net.NetworkCapabilities.TRANSPORT_WIFI;
 import static android.net.cts.util.CtsNetUtils.ConnectivityActionReceiver;
 import static android.net.cts.util.CtsNetUtils.HTTP_PORT;
@@ -43,6 +45,7 @@
 
 import static com.android.compatibility.common.util.SystemUtil.runShellCommand;
 import static com.android.compatibility.common.util.SystemUtil.runWithShellPermissionIdentity;
+import static com.android.testutils.MiscAsserts.assertThrows;
 import static com.android.testutils.TestPermissionUtil.runAsShell;
 
 import static org.junit.Assert.assertEquals;
@@ -68,8 +71,10 @@
 import android.content.res.Resources;
 import android.net.ConnectivityManager;
 import android.net.ConnectivityManager.NetworkCallback;
+import android.net.InetAddresses;
 import android.net.IpSecManager;
 import android.net.IpSecManager.UdpEncapsulationSocket;
+import android.net.LinkAddress;
 import android.net.LinkProperties;
 import android.net.Network;
 import android.net.NetworkCapabilities;
@@ -80,11 +85,15 @@
 import android.net.NetworkRequest;
 import android.net.NetworkUtils;
 import android.net.SocketKeepalive;
+import android.net.StringNetworkSpecifier;
+import android.net.TestNetworkInterface;
+import android.net.TestNetworkManager;
 import android.net.cts.util.CtsNetUtils;
 import android.net.util.KeepaliveUtils;
 import android.net.wifi.WifiManager;
 import android.os.Binder;
 import android.os.Build;
+import android.os.Handler;
 import android.os.Looper;
 import android.os.MessageQueue;
 import android.os.SystemClock;
@@ -104,10 +113,10 @@
 import com.android.testutils.SkipPresubmit;
 import com.android.testutils.TestableNetworkCallback;
 
-import libcore.io.Streams;
-
 import junit.framework.AssertionFailedError;
 
+import libcore.io.Streams;
+
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -176,6 +185,9 @@
     private static final String KEEPALIVE_RESERVED_PER_SLOT_RES_NAME =
             "config_reservedPrivilegedKeepaliveSlots";
 
+    private static final LinkAddress TEST_LINKADDR = new LinkAddress(
+            InetAddresses.parseNumericAddress("2001:db8::8"), 64);
+
     private Context mContext;
     private Instrumentation mInstrumentation;
     private ConnectivityManager mCm;
@@ -183,7 +195,6 @@
     private PackageManager mPackageManager;
     private final HashMap<Integer, NetworkConfig> mNetworks =
             new HashMap<Integer, NetworkConfig>();
-    boolean mWifiWasDisabled;
     private UiAutomation mUiAutomation;
     private CtsNetUtils mCtsNetUtils;
 
@@ -195,7 +206,6 @@
         mWifiManager = (WifiManager) mContext.getSystemService(Context.WIFI_SERVICE);
         mPackageManager = mContext.getPackageManager();
         mCtsNetUtils = new CtsNetUtils(mContext);
-        mWifiWasDisabled = false;
 
         // Get com.android.internal.R.array.networkAttributes
         int resId = mContext.getResources().getIdentifier("networkAttributes", "array", "android");
@@ -218,10 +228,7 @@
 
     @After
     public void tearDown() throws Exception {
-        // Return WiFi to its original disabled state after tests that explicitly connect.
-        if (mWifiWasDisabled) {
-            mCtsNetUtils.disconnectFromWifi(null);
-        }
+        // Release any NetworkRequests filed to connect mobile data.
         if (mCtsNetUtils.cellConnectAttempted()) {
             mCtsNetUtils.disconnectFromCell();
         }
@@ -237,17 +244,6 @@
         }
     }
 
-    /**
-     * Make sure WiFi is connected to an access point if it is not already. If
-     * WiFi is enabled as a result of this function, it will be disabled
-     * automatically in tearDown().
-     */
-    private Network ensureWifiConnected() {
-        mWifiWasDisabled = !mWifiManager.isWifiEnabled();
-        // Even if wifi is enabled, the network may not be connected or ready yet
-        return mCtsNetUtils.connectToWifi();
-    }
-
     @Test
     public void testIsNetworkTypeValid() {
         assertTrue(ConnectivityManager.isNetworkTypeValid(ConnectivityManager.TYPE_MOBILE));
@@ -521,25 +517,38 @@
         final TestNetworkCallback defaultTrackingCallback = new TestNetworkCallback();
         mCm.registerDefaultNetworkCallback(defaultTrackingCallback);
 
+        final TestNetworkCallback systemDefaultTrackingCallback = new TestNetworkCallback();
+        runWithShellPermissionIdentity(() ->
+                mCm.registerSystemDefaultNetworkCallback(systemDefaultTrackingCallback,
+                        new Handler(Looper.getMainLooper())),
+                NETWORK_SETTINGS);
+
+
         Network wifiNetwork = null;
 
         try {
-            ensureWifiConnected();
+            mCtsNetUtils.ensureWifiConnected();
 
             // Now we should expect to get a network callback about availability of the wifi
             // network even if it was already connected as a state-based action when the callback
             // is registered.
             wifiNetwork = callback.waitForAvailable();
-            assertNotNull("Did not receive NetworkCallback.onAvailable for TRANSPORT_WIFI",
+            assertNotNull("Did not receive onAvailable for TRANSPORT_WIFI request",
                     wifiNetwork);
 
-            assertNotNull("Did not receive NetworkCallback.onAvailable for any default network",
+            assertNotNull("Did not receive onAvailable on default network callback",
                     defaultTrackingCallback.waitForAvailable());
+
+            assertNotNull("Did not receive onAvailable on system default network callback",
+                    systemDefaultTrackingCallback.waitForAvailable());
         } catch (InterruptedException e) {
             fail("Broadcast receiver or NetworkCallback wait was interrupted.");
         } finally {
             mCm.unregisterNetworkCallback(callback);
             mCm.unregisterNetworkCallback(defaultTrackingCallback);
+            runWithShellPermissionIdentity(
+                    () -> mCm.unregisterNetworkCallback(systemDefaultTrackingCallback),
+                    NETWORK_SETTINGS);
         }
     }
 
@@ -574,7 +583,7 @@
         mCm.registerNetworkCallback(makeWifiNetworkRequest(), pendingIntent);
 
         try {
-            ensureWifiConnected();
+            mCtsNetUtils.ensureWifiConnected();
 
             // Now we expect to get the Intent delivered notifying of the availability of the wifi
             // network even if it was already connected as a state-based action when the callback
@@ -655,6 +664,17 @@
         return null;
     }
 
+    /**
+     * Checks that enabling/disabling wifi causes CONNECTIVITY_ACTION broadcasts.
+     */
+    @AppModeFull(reason = "Cannot get WifiManager in instant app mode")
+    @Test
+    public void testToggleWifiConnectivityAction() {
+        // toggleWifi calls connectToWifi and disconnectFromWifi, which both wait for
+        // CONNECTIVITY_ACTION broadcasts.
+        mCtsNetUtils.toggleWifi();
+    }
+
     /** Verify restricted networks cannot be requested. */
     @AppModeFull(reason = "CHANGE_NETWORK_STATE permission can't be granted to instant apps")
     @Test
@@ -782,7 +802,7 @@
     @Test
     public void testGetMultipathPreference() throws Exception {
         final ContentResolver resolver = mContext.getContentResolver();
-        ensureWifiConnected();
+        mCtsNetUtils.ensureWifiConnected();
         final String ssid = unquoteSSID(mWifiManager.getConnectionInfo().getSSID());
         final String oldMeteredSetting = getWifiMeteredStatus(ssid);
         final String oldMeteredMultipathPreference = Settings.Global.getString(
@@ -796,7 +816,7 @@
             waitForActiveNetworkMetered(TRANSPORT_WIFI, true);
             // Wifi meterness changes from unmetered to metered will disconnect and reconnect since
             // R.
-            final Network network = ensureWifiConnected();
+            final Network network = mCtsNetUtils.ensureWifiConnected();
             assertEquals(ssid, unquoteSSID(mWifiManager.getConnectionInfo().getSSID()));
             assertEquals(mCm.getNetworkCapabilities(network).hasCapability(
                     NET_CAPABILITY_NOT_METERED), false);
@@ -1010,7 +1030,7 @@
             return;
         }
 
-        final Network network = ensureWifiConnected();
+        final Network network = mCtsNetUtils.ensureWifiConnected();
         if (getSupportedKeepalivesForNet(network) != 0) return;
         final InetAddress srcAddr = getFirstV4Address(network);
         assumeTrue("This test requires native IPv4", srcAddr != null);
@@ -1030,7 +1050,7 @@
             return;
         }
 
-        final Network network = ensureWifiConnected();
+        final Network network = mCtsNetUtils.ensureWifiConnected();
         if (getSupportedKeepalivesForNet(network) == 0) return;
         final InetAddress srcAddr = getFirstV4Address(network);
         assumeTrue("This test requires native IPv4", srcAddr != null);
@@ -1241,7 +1261,7 @@
             return;
         }
 
-        final Network network = ensureWifiConnected();
+        final Network network = mCtsNetUtils.ensureWifiConnected();
         final int supported = getSupportedKeepalivesForNet(network);
         if (supported == 0) {
             return;
@@ -1338,7 +1358,7 @@
             return;
         }
 
-        final Network network = ensureWifiConnected();
+        final Network network = mCtsNetUtils.ensureWifiConnected();
         final int supported = getSupportedKeepalivesForNet(network);
         if (supported == 0) {
             return;
@@ -1386,7 +1406,7 @@
 
         // Ensure that NetworkUtils.queryUserAccess always returns false since this package should
         // not have netd system permission to call this function.
-        final Network wifiNetwork = ensureWifiConnected();
+        final Network wifiNetwork = mCtsNetUtils.ensureWifiConnected();
         assertFalse(NetworkUtils.queryUserAccess(Binder.getCallingUid(), wifiNetwork.netId));
 
         // Ensure that this package cannot bind to any restricted network that's currently
@@ -1531,4 +1551,72 @@
             throw new AssertionFailedError("Captive portal server URL is invalid: " + e);
         }
     }
+
+    /**
+     * Verify background request can only be requested when acquiring
+     * {@link android.Manifest.permission.NETWORK_SETTINGS}.
+     */
+    @SkipPresubmit(reason = "Flaky: b/179554972; add to presubmit after fixing")
+    @Test
+    public void testRequestBackgroundNetwork() throws Exception {
+        // Create a tun interface. Use the returned interface name as the specifier to create
+        // a test network request.
+        final TestNetworkInterface testNetworkInterface = runWithShellPermissionIdentity(() -> {
+            final TestNetworkManager tnm =
+                    mContext.getSystemService(TestNetworkManager.class);
+            return tnm.createTunInterface(new LinkAddress[]{TEST_LINKADDR});
+        }, android.Manifest.permission.MANAGE_TEST_NETWORKS,
+                android.Manifest.permission.NETWORK_SETTINGS);
+        assertNotNull(testNetworkInterface);
+
+        final NetworkRequest testRequest = new NetworkRequest.Builder()
+                .addTransportType(TRANSPORT_TEST)
+                // Test networks do not have NOT_VPN or TRUSTED capabilities by default
+                .removeCapability(NetworkCapabilities.NET_CAPABILITY_NOT_VPN)
+                .removeCapability(NetworkCapabilities.NET_CAPABILITY_TRUSTED)
+                .setNetworkSpecifier(
+                        new StringNetworkSpecifier(testNetworkInterface.getInterfaceName()))
+                .build();
+
+        // Verify background network cannot be requested without NETWORK_SETTINGS permission.
+        final TestableNetworkCallback callback = new TestableNetworkCallback();
+        assertThrows(SecurityException.class,
+                () -> mCm.requestBackgroundNetwork(testRequest, null, callback));
+
+        try {
+            // Request background test network via Shell identity which has NETWORK_SETTINGS
+            // permission granted.
+            runWithShellPermissionIdentity(
+                    () -> mCm.requestBackgroundNetwork(testRequest, null, callback),
+                    android.Manifest.permission.NETWORK_SETTINGS);
+
+            // Register the test network agent which has no foreground request associated to it.
+            // And verify it can satisfy the background network request just fired.
+            final Binder binder = new Binder();
+            runWithShellPermissionIdentity(() -> {
+                final TestNetworkManager tnm =
+                        mContext.getSystemService(TestNetworkManager.class);
+                tnm.setupTestNetwork(testNetworkInterface.getInterfaceName(), binder);
+            }, android.Manifest.permission.MANAGE_TEST_NETWORKS,
+                    android.Manifest.permission.NETWORK_SETTINGS);
+            waitForAvailable(callback);
+            final Network testNetwork = callback.getLastAvailableNetwork();
+            assertNotNull(testNetwork);
+
+            // The test network that has just connected is a foreground network,
+            // non-listen requests will get available callback before it can be put into
+            // background if no foreground request can be satisfied. Thus, wait for a short
+            // period is needed to let foreground capability go away.
+            callback.eventuallyExpect(CallbackEntry.NETWORK_CAPS_UPDATED,
+                    callback.getDefaultTimeoutMs(),
+                    c -> c instanceof CallbackEntry.CapabilitiesChanged
+                            && !((CallbackEntry.CapabilitiesChanged) c).getCaps()
+                            .hasCapability(NET_CAPABILITY_FOREGROUND));
+            final NetworkCapabilities nc = mCm.getNetworkCapabilities(testNetwork);
+            assertFalse("expected background network, but got " + nc,
+                    nc.hasCapability(NET_CAPABILITY_FOREGROUND));
+        } finally {
+            mCm.unregisterNetworkCallback(callback);
+        }
+    }
 }
diff --git a/tests/cts/net/src/android/net/cts/Ikev2VpnTest.java b/tests/cts/net/src/android/net/cts/Ikev2VpnTest.java
index 9eab024..8f2d93d 100644
--- a/tests/cts/net/src/android/net/cts/Ikev2VpnTest.java
+++ b/tests/cts/net/src/android/net/cts/Ikev2VpnTest.java
@@ -55,7 +55,7 @@
 import androidx.test.InstrumentationRegistry;
 
 import com.android.internal.util.HexDump;
-import com.android.org.bouncycastle.x509.X509V1CertificateGenerator;
+import com.android.internal.org.bouncycastle.x509.X509V1CertificateGenerator;
 import com.android.testutils.DevSdkIgnoreRule.IgnoreUpTo;
 import com.android.testutils.DevSdkIgnoreRunner;
 
diff --git a/tests/cts/net/src/android/net/cts/NetworkAgentTest.kt b/tests/cts/net/src/android/net/cts/NetworkAgentTest.kt
index a429faa..aea33ca 100644
--- a/tests/cts/net/src/android/net/cts/NetworkAgentTest.kt
+++ b/tests/cts/net/src/android/net/cts/NetworkAgentTest.kt
@@ -47,6 +47,8 @@
 import android.net.SocketKeepalive
 import android.net.StringNetworkSpecifier
 import android.net.Uri
+import android.net.VpnManager
+import android.net.VpnTransportInfo
 import android.net.cts.NetworkAgentTest.TestableNetworkAgent.CallbackEntry.OnAddKeepalivePacketFilter
 import android.net.cts.NetworkAgentTest.TestableNetworkAgent.CallbackEntry.OnAutomaticReconnectDisabled
 import android.net.cts.NetworkAgentTest.TestableNetworkAgent.CallbackEntry.OnBandwidthUpdateRequested
@@ -541,7 +543,7 @@
 
     @Test
     @IgnoreUpTo(Build.VERSION_CODES.R)
-    fun testSetUnderlyingNetworks() {
+    fun testSetUnderlyingNetworksAndVpnSpecifier() {
         val request = NetworkRequest.Builder()
                 .addTransportType(TRANSPORT_TEST)
                 .addTransportType(TRANSPORT_VPN)
@@ -555,6 +557,7 @@
             addTransportType(TRANSPORT_TEST)
             addTransportType(TRANSPORT_VPN)
             removeCapability(NET_CAPABILITY_NOT_VPN)
+            setTransportInfo(VpnTransportInfo(VpnManager.TYPE_VPN_SERVICE))
         }
         val defaultNetwork = mCM.activeNetwork
         assertNotNull(defaultNetwork)
@@ -569,6 +572,8 @@
         // Check that the default network's transport is propagated to the VPN.
         var vpnNc = mCM.getNetworkCapabilities(agent.network)
         assertNotNull(vpnNc)
+        assertEquals(VpnManager.TYPE_VPN_SERVICE,
+                (vpnNc.transportInfo as VpnTransportInfo).type)
 
         val testAndVpn = intArrayOf(TRANSPORT_TEST, TRANSPORT_VPN)
         assertTrue(hasAllTransports(vpnNc, testAndVpn))
diff --git a/tests/cts/net/util/java/android/net/cts/util/CtsNetUtils.java b/tests/cts/net/util/java/android/net/cts/util/CtsNetUtils.java
index 0527011..88172d7 100644
--- a/tests/cts/net/util/java/android/net/cts/util/CtsNetUtils.java
+++ b/tests/cts/net/util/java/android/net/cts/util/CtsNetUtils.java
@@ -212,7 +212,7 @@
         mContext.registerReceiver(receiver, filter);
 
         boolean connected = false;
-        final String err = "Wifi must be configured to connect to an access point for this test.";
+        final String err = "Wifi must be configured to connect to an access point for this test";
         try {
             clearWifiBlacklist();
             SystemUtil.runShellCommand("svc wifi enable");
@@ -235,7 +235,7 @@
             }
             // Ensure we get an onAvailable callback and possibly a CONNECTIVITY_ACTION.
             wifiNetwork = callback.waitForAvailable();
-            assertNotNull(err, wifiNetwork);
+            assertNotNull(err + ": onAvailable callback not received", wifiNetwork);
             connected = !expectLegacyBroadcast || receiver.waitForState();
         } catch (InterruptedException ex) {
             fail("connectToWifi was interrupted");
@@ -244,7 +244,7 @@
             mContext.unregisterReceiver(receiver);
         }
 
-        assertTrue(err, connected);
+        assertTrue(err + ": CONNECTIVITY_ACTION not received", connected);
         return wifiNetwork;
     }