diff --git a/Tethering/src/com/android/networkstack/tethering/BpfCoordinator.java b/Tethering/src/com/android/networkstack/tethering/BpfCoordinator.java
index ac0bbd4..05a2884 100644
--- a/Tethering/src/com/android/networkstack/tethering/BpfCoordinator.java
+++ b/Tethering/src/com/android/networkstack/tethering/BpfCoordinator.java
@@ -64,7 +64,7 @@
 import com.android.net.module.util.NetworkStackConstants;
 import com.android.net.module.util.SharedLog;
 import com.android.net.module.util.Struct;
-import com.android.net.module.util.Struct.U32;
+import com.android.net.module.util.Struct.S32;
 import com.android.net.module.util.bpf.Tether4Key;
 import com.android.net.module.util.bpf.Tether4Value;
 import com.android.net.module.util.bpf.TetherStatsKey;
@@ -575,7 +575,7 @@
             if (!mBpfCoordinatorShim.startUpstreamIpv6Forwarding(downstream, upstream, rule.srcMac,
                     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));
+                        + getIfName(downstream) + " to " + getIfName(upstream));
             }
         }
 
@@ -616,7 +616,7 @@
             if (!mBpfCoordinatorShim.stopUpstreamIpv6Forwarding(downstream, upstream,
                     rule.srcMac)) {
                 mLog.e("Failed to disable upstream IPv6 forwarding from "
-                        + mInterfaceNames.get(downstream) + " to " + mInterfaceNames.get(upstream));
+                        + getIfName(downstream) + " to " + getIfName(upstream));
             }
         }
 
@@ -960,8 +960,12 @@
     }
 
     // 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));
+    // This function should only be used for logging/dump purposes.
+    private String getIfName(int ifindex) {
+        // TODO: return something more useful on lookup failure
+        // likely use the 'iface_index_name_map' bpf map and/or if_nametoindex
+        // perhaps should even check that all 3 match if available.
+        return mInterfaceNames.get(ifindex, Integer.toString(ifindex));
     }
 
     /**
@@ -1038,8 +1042,8 @@
         for (int i = 0; i < mStats.size(); i++) {
             final int upstreamIfindex = mStats.keyAt(i);
             final ForwardedStats stats = mStats.get(upstreamIfindex);
-            pw.println(String.format("%d(%s) - %s", upstreamIfindex, mInterfaceNames.get(
-                    upstreamIfindex), stats.toString()));
+            pw.println(String.format("%d(%s) - %s", upstreamIfindex, getIfName(upstreamIfindex),
+                    stats.toString()));
         }
     }
     private void dumpBpfStats(@NonNull IndentingPrintWriter pw) {
@@ -1082,8 +1086,9 @@
             for (Ipv6ForwardingRule rule : rules.values()) {
                 final int upstreamIfindex = rule.upstreamIfindex;
                 pw.println(String.format("%d(%s) %d(%s) %s [%s] [%s]", upstreamIfindex,
-                        mInterfaceNames.get(upstreamIfindex), rule.downstreamIfindex,
-                        downstreamIface, rule.address.getHostAddress(), rule.srcMac, rule.dstMac));
+                        getIfName(upstreamIfindex), rule.downstreamIfindex,
+                        getIfName(rule.downstreamIfindex), rule.address.getHostAddress(),
+                        rule.srcMac, rule.dstMac));
             }
             pw.decreaseIndent();
         }
@@ -1278,18 +1283,18 @@
             pw.println("No counter support");
             return;
         }
-        try (BpfMap<U32, U32> map = new BpfMap<>(TETHER_ERROR_MAP_PATH, BpfMap.BPF_F_RDONLY,
-                U32.class, U32.class)) {
+        try (BpfMap<S32, S32> map = new BpfMap<>(TETHER_ERROR_MAP_PATH, BpfMap.BPF_F_RDONLY,
+                S32.class, S32.class)) {
 
             map.forEach((k, v) -> {
                 String counterName;
                 try {
-                    counterName = sBpfCounterNames[(int) k.val];
+                    counterName = sBpfCounterNames[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);
+                    counterName = Integer.toString(k.val);
                 }
                 if (v.val > 0) pw.println(String.format("%s: %d", counterName, v.val));
             });
@@ -1817,8 +1822,7 @@
         // TODO: Perhaps stop the coordinator.
         boolean success = updateDataLimit(upstreamIfindex);
         if (!success) {
-            final String iface = mInterfaceNames.get(upstreamIfindex);
-            mLog.e("Setting data limit for " + iface + " failed.");
+            mLog.e("Setting data limit for " + getIfName(upstreamIfindex) + " failed.");
         }
     }
 
diff --git a/Tethering/src/com/android/networkstack/tethering/TetherDevKey.java b/Tethering/src/com/android/networkstack/tethering/TetherDevKey.java
index 4283c1b..997080c 100644
--- a/Tethering/src/com/android/networkstack/tethering/TetherDevKey.java
+++ b/Tethering/src/com/android/networkstack/tethering/TetherDevKey.java
@@ -22,10 +22,10 @@
 
 /** The key of BpfMap which is used for mapping interface index. */
 public class TetherDevKey extends Struct {
-    @Field(order = 0, type = Type.U32)
-    public final long ifIndex;  // interface index
+    @Field(order = 0, type = Type.S32)
+    public final int ifIndex;  // interface index
 
-    public TetherDevKey(final long ifIndex) {
+    public TetherDevKey(final int ifIndex) {
         this.ifIndex = ifIndex;
     }
 }
diff --git a/Tethering/src/com/android/networkstack/tethering/TetherDevValue.java b/Tethering/src/com/android/networkstack/tethering/TetherDevValue.java
index 1cd99b5..b6e0c73 100644
--- a/Tethering/src/com/android/networkstack/tethering/TetherDevValue.java
+++ b/Tethering/src/com/android/networkstack/tethering/TetherDevValue.java
@@ -22,10 +22,10 @@
 
 /** The key of BpfMap which is used for mapping interface index. */
 public class TetherDevValue extends Struct {
-    @Field(order = 0, type = Type.U32)
-    public final long ifIndex;  // interface index
+    @Field(order = 0, type = Type.S32)
+    public final int ifIndex;  // interface index
 
-    public TetherDevValue(final long ifIndex) {
+    public TetherDevValue(final int ifIndex) {
         this.ifIndex = ifIndex;
     }
 }
diff --git a/Tethering/src/com/android/networkstack/tethering/TetherDownstream6Key.java b/Tethering/src/com/android/networkstack/tethering/TetherDownstream6Key.java
index a08ad4a..e34b3f1 100644
--- a/Tethering/src/com/android/networkstack/tethering/TetherDownstream6Key.java
+++ b/Tethering/src/com/android/networkstack/tethering/TetherDownstream6Key.java
@@ -32,8 +32,8 @@
 
 /** The key of BpfMap which is used for bpf offload. */
 public class TetherDownstream6Key extends Struct {
-    @Field(order = 0, type = Type.U32)
-    public final long iif; // The input interface index.
+    @Field(order = 0, type = Type.S32)
+    public final int iif; // The input interface index.
 
     @Field(order = 1, type = Type.EUI48, padding = 2)
     public final MacAddress dstMac; // Destination ethernet mac address (zeroed iff rawip ingress).
@@ -41,7 +41,7 @@
     @Field(order = 2, type = Type.ByteArray, arraysize = 16)
     public final byte[] neigh6; // The destination IPv6 address.
 
-    public TetherDownstream6Key(final long iif, @NonNull final MacAddress dstMac,
+    public TetherDownstream6Key(final int iif, @NonNull final MacAddress dstMac,
             final byte[] neigh6) {
         Objects.requireNonNull(dstMac);
 
diff --git a/Tethering/src/com/android/networkstack/tethering/TetherLimitKey.java b/Tethering/src/com/android/networkstack/tethering/TetherLimitKey.java
index bc9bb47..a7e8ccf 100644
--- a/Tethering/src/com/android/networkstack/tethering/TetherLimitKey.java
+++ b/Tethering/src/com/android/networkstack/tethering/TetherLimitKey.java
@@ -22,10 +22,10 @@
 
 /** The key of BpfMap which is used for tethering per-interface limit. */
 public class TetherLimitKey extends Struct {
-    @Field(order = 0, type = Type.U32)
-    public final long ifindex;  // upstream interface index
+    @Field(order = 0, type = Type.S32)
+    public final int ifindex;  // upstream interface index
 
-    public TetherLimitKey(final long ifindex) {
+    public TetherLimitKey(final int ifindex) {
         this.ifindex = ifindex;
     }
 
@@ -43,7 +43,7 @@
 
     @Override
     public int hashCode() {
-        return Long.hashCode(ifindex);
+        return Integer.hashCode(ifindex);
     }
 
     @Override
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 536ab2d..0e8b044 100644
--- a/Tethering/tests/privileged/src/com/android/networkstack/tethering/BpfMapTest.java
+++ b/Tethering/tests/privileged/src/com/android/networkstack/tethering/BpfMapTest.java
@@ -98,7 +98,7 @@
         assertTrue(mTestMap.isEmpty());
     }
 
-    private TetherDownstream6Key createTetherDownstream6Key(long iif, String mac,
+    private TetherDownstream6Key createTetherDownstream6Key(int iif, String mac,
             String address) throws Exception {
         final MacAddress dstMac = MacAddress.fromString(mac);
         final InetAddress ipv6Address = InetAddress.getByName(address);
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 63bb731..b100f58 100644
--- a/Tethering/tests/unit/src/com/android/networkstack/tethering/BpfCoordinatorTest.java
+++ b/Tethering/tests/unit/src/com/android/networkstack/tethering/BpfCoordinatorTest.java
@@ -222,7 +222,7 @@
 
     private static class TestUpstream4Key {
         public static class Builder {
-            private long mIif = DOWNSTREAM_IFINDEX;
+            private int mIif = DOWNSTREAM_IFINDEX;
             private MacAddress mDstMac = DOWNSTREAM_MAC;
             private short mL4proto = (short) IPPROTO_TCP;
             private byte[] mSrc4 = PRIVATE_ADDR.getAddress();
@@ -246,7 +246,7 @@
 
     private static class TestDownstream4Key {
         public static class Builder {
-            private long mIif = UPSTREAM_IFINDEX;
+            private int mIif = UPSTREAM_IFINDEX;
             private MacAddress mDstMac = MacAddress.ALL_ZEROS_ADDRESS /* dstMac (rawip) */;
             private short mL4proto = (short) IPPROTO_TCP;
             private byte[] mSrc4 = REMOTE_ADDR.getAddress();
@@ -270,7 +270,7 @@
 
     private static class TestUpstream4Value {
         public static class Builder {
-            private long mOif = UPSTREAM_IFINDEX;
+            private int mOif = UPSTREAM_IFINDEX;
             private MacAddress mEthDstMac = MacAddress.ALL_ZEROS_ADDRESS /* dstMac (rawip) */;
             private MacAddress mEthSrcMac = MacAddress.ALL_ZEROS_ADDRESS /* dstMac (rawip) */;
             private int mEthProto = ETH_P_IP;
@@ -290,7 +290,7 @@
 
     private static class TestDownstream4Value {
         public static class Builder {
-            private long mOif = DOWNSTREAM_IFINDEX;
+            private int mOif = DOWNSTREAM_IFINDEX;
             private MacAddress mEthDstMac = MAC_A /* client mac */;
             private MacAddress mEthSrcMac = DOWNSTREAM_MAC;
             private int mEthProto = ETH_P_IP;
@@ -941,11 +941,11 @@
 
     @Test
     public void testRuleMakeTetherDownstream6Key() throws Exception {
-        final Integer mobileIfIndex = 100;
+        final int mobileIfIndex = 100;
         final Ipv6ForwardingRule rule = buildTestForwardingRule(mobileIfIndex, NEIGH_A, MAC_A);
 
         final TetherDownstream6Key key = rule.makeTetherDownstream6Key();
-        assertEquals(key.iif, (long) mobileIfIndex);
+        assertEquals(key.iif, mobileIfIndex);
         assertEquals(key.dstMac, MacAddress.ALL_ZEROS_ADDRESS);  // rawip upstream
         assertTrue(Arrays.equals(key.neigh6, NEIGH_A.getAddress()));
         // iif (4) + dstMac(6) + padding(2) + neigh6 (16) = 28.
@@ -954,7 +954,7 @@
 
     @Test
     public void testRuleMakeTether6Value() throws Exception {
-        final Integer mobileIfIndex = 100;
+        final int mobileIfIndex = 100;
         final Ipv6ForwardingRule rule = buildTestForwardingRule(mobileIfIndex, NEIGH_A, MAC_A);
 
         final Tether6Value value = rule.makeTether6Value();
@@ -974,7 +974,7 @@
         final BpfCoordinator coordinator = makeBpfCoordinator();
 
         final String mobileIface = "rmnet_data0";
-        final Integer mobileIfIndex = 100;
+        final int mobileIfIndex = 100;
         coordinator.addUpstreamNameToLookupTable(mobileIfIndex, mobileIface);
 
         // [1] Default limit.
@@ -1018,7 +1018,7 @@
         final BpfCoordinator coordinator = makeBpfCoordinator();
 
         final String mobileIface = "rmnet_data0";
-        final Integer mobileIfIndex = 100;
+        final int mobileIfIndex = 100;
         coordinator.addUpstreamNameToLookupTable(mobileIfIndex, mobileIface);
 
         // Applying a data limit to the current upstream does not take any immediate action.
diff --git a/common/src/com/android/net/module/util/bpf/Tether4Key.java b/common/src/com/android/net/module/util/bpf/Tether4Key.java
index 638576f..8273e6a 100644
--- a/common/src/com/android/net/module/util/bpf/Tether4Key.java
+++ b/common/src/com/android/net/module/util/bpf/Tether4Key.java
@@ -30,8 +30,8 @@
 
 /** 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 = 0, type = Type.S32)
+    public final int iif;
 
     @Field(order = 1, type = Type.EUI48)
     public final MacAddress dstMac;
@@ -51,7 +51,7 @@
     @Field(order = 6, type = Type.UBE16)
     public final int dstPort;
 
-    public Tether4Key(final long iif, @NonNull final MacAddress dstMac, final short l4proto,
+    public Tether4Key(final int iif, @NonNull final MacAddress dstMac, final short l4proto,
             final byte[] src4, final byte[] dst4, final int srcPort,
             final int dstPort) {
         Objects.requireNonNull(dstMac);
diff --git a/common/src/com/android/net/module/util/bpf/Tether4Value.java b/common/src/com/android/net/module/util/bpf/Tether4Value.java
index de98766..74fdda2 100644
--- a/common/src/com/android/net/module/util/bpf/Tether4Value.java
+++ b/common/src/com/android/net/module/util/bpf/Tether4Value.java
@@ -30,8 +30,8 @@
 
 /** Value type for downstream & upstream IPv4 forwarding maps. */
 public class Tether4Value extends Struct {
-    @Field(order = 0, type = Type.U32)
-    public final long oif;
+    @Field(order = 0, type = Type.S32)
+    public final int oif;
 
     // The ethhdr struct which is defined in uapi/linux/if_ether.h
     @Field(order = 1, type = Type.EUI48)
@@ -60,7 +60,7 @@
     @Field(order = 9, type = Type.U63)
     public final long lastUsed;
 
-    public Tether4Value(final long oif, @NonNull final MacAddress ethDstMac,
+    public Tether4Value(final int 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) {