diff --git a/bpf_progs/Android.bp b/bpf_progs/Android.bp
index e228df0..a3ca90c 100644
--- a/bpf_progs/Android.bp
+++ b/bpf_progs/Android.bp
@@ -42,6 +42,7 @@
         // TODO: remove it when NetworkStatsService is moved into the mainline module and no more
         // calls to JNI in libservices.core.
         "//frameworks/base/services/core/jni",
+        "//packages/modules/Connectivity/service/native/libs/libclat",
         "//packages/modules/Connectivity/Tethering",
         "//packages/modules/Connectivity/service/native",
         "//packages/modules/Connectivity/tests/unit/jni",
diff --git a/service/Android.bp b/service/Android.bp
index e376ff7..d1a9004 100644
--- a/service/Android.bp
+++ b/service/Android.bp
@@ -65,6 +65,7 @@
         "libbase_headers",
     ],
     static_libs: [
+        "libbase",
         "libclat",
         "libip_checksum",
         "libnetjniutils",
diff --git a/service/jni/com_android_server_connectivity_ClatCoordinator.cpp b/service/jni/com_android_server_connectivity_ClatCoordinator.cpp
index a9d7946..9603139 100644
--- a/service/jni/com_android_server_connectivity_ClatCoordinator.cpp
+++ b/service/jni/com_android_server_connectivity_ClatCoordinator.cpp
@@ -19,17 +19,22 @@
 #include <fcntl.h>
 #include <linux/if_tun.h>
 #include <linux/ioctl.h>
+#include <log/log.h>
 #include <nativehelper/JNIHelp.h>
 #include <net/if.h>
+#include <string>
 
 #include <netjniutils/netjniutils.h>
 
+#include "libclat/bpfhelper.h"
 #include "libclat/clatutils.h"
 #include "nativehelper/scoped_utf_chars.h"
 
 // Sync from system/netd/include/netid_client.h
 #define MARK_UNSET 0u
 
+#define DEVICEPREFIX "v4-"
+
 namespace android {
 static void throwIOException(JNIEnv* env, const char* msg, int error) {
     jniThrowExceptionFmt(env, "java/io/IOException", "%s: %s", msg, strerror(error));
@@ -237,6 +242,86 @@
     }
 }
 
+int initTracker(const std::string& iface, const std::string& pfx96, const std::string& v4,
+        const std::string& v6, net::clat::ClatdTracker* output) {
+    strlcpy(output->iface, iface.c_str(), sizeof(output->iface));
+    output->ifIndex = if_nametoindex(iface.c_str());
+    if (output->ifIndex == 0) {
+        ALOGE("interface %s not found", output->iface);
+        return -1;
+    }
+
+    unsigned len = snprintf(output->v4iface, sizeof(output->v4iface),
+            "%s%s", DEVICEPREFIX, iface.c_str());
+    if (len >= sizeof(output->v4iface)) {
+        ALOGE("interface name too long '%s'", output->v4iface);
+        return -1;
+    }
+
+    output->v4ifIndex = if_nametoindex(output->v4iface);
+    if (output->v4ifIndex == 0) {
+        ALOGE("v4-interface %s not found", output->v4iface);
+        return -1;
+    }
+
+    if (!inet_pton(AF_INET6, pfx96.c_str(), &output->pfx96)) {
+        ALOGE("invalid IPv6 address specified for plat prefix: %s", pfx96.c_str());
+        return -1;
+    }
+
+    if (!inet_pton(AF_INET, v4.c_str(), &output->v4)) {
+        ALOGE("Invalid IPv4 address %s", v4.c_str());
+        return -1;
+    }
+
+    if (!inet_pton(AF_INET6, v6.c_str(), &output->v6)) {
+        ALOGE("Invalid source address %s", v6.c_str());
+        return -1;
+    }
+
+    return 0;
+}
+
+// TODO: fork clatd and rename to .._startClatd.
+static jint com_android_server_connectivity_ClatCoordinator_maybeStartBpf(
+        JNIEnv* env, jobject clazz, jobject tunJavaFd, jobject readSockJavaFd,
+        jobject writeSockJavaFd, jstring iface, jstring pfx96, jstring v4, jstring v6) {
+    ScopedUtfChars ifaceStr(env, iface);
+    ScopedUtfChars pfx96Str(env, pfx96);
+    ScopedUtfChars v4Str(env, v4);
+    ScopedUtfChars v6Str(env, v6);
+
+    // Start BPF if any
+    if (!net::clat::initMaps()) {
+        net::clat::ClatdTracker tracker = {};
+        if (!initTracker(ifaceStr.c_str(), pfx96Str.c_str(), v4Str.c_str(), v6Str.c_str(),
+                &tracker)) {
+            net::clat::maybeStartBpf(tracker);
+        }
+    }
+
+    return 0; // TODO: return forked clatd pid.
+}
+
+// TODO: stop clatd and rename to .._stopClatd.
+static void com_android_server_connectivity_ClatCoordinator_maybeStopBpf(JNIEnv* env, jobject clazz,
+                                                                       jstring iface, jstring pfx96,
+                                                                       jstring v4, jstring v6,
+                                                                       jint pid /* unused */) {
+    ScopedUtfChars ifaceStr(env, iface);
+    ScopedUtfChars pfx96Str(env, pfx96);
+    ScopedUtfChars v4Str(env, v4);
+    ScopedUtfChars v6Str(env, v6);
+
+    if (!net::clat::initMaps()) {
+        net::clat::ClatdTracker tracker = {};
+        if (!initTracker(ifaceStr.c_str(), pfx96Str.c_str(), v4Str.c_str(), v6Str.c_str(),
+                &tracker)) {
+            net::clat::maybeStopBpf(tracker);
+        }
+    }
+}
+
 /*
  * JNI registration.
  */
@@ -259,6 +344,13 @@
          (void*)com_android_server_connectivity_ClatCoordinator_addAnycastSetsockopt},
         {"native_configurePacketSocket", "(Ljava/io/FileDescriptor;Ljava/lang/String;I)V",
          (void*)com_android_server_connectivity_ClatCoordinator_configurePacketSocket},
+        {"native_maybeStartBpf",
+         "(Ljava/io/FileDescriptor;Ljava/io/FileDescriptor;Ljava/io/FileDescriptor;Ljava/lang/"
+         "String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)I",
+         (void*)com_android_server_connectivity_ClatCoordinator_maybeStartBpf},
+        {"native_maybeStopBpf",
+         "(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;I)V",
+          (void*)com_android_server_connectivity_ClatCoordinator_maybeStopBpf},
 };
 
 int register_android_server_connectivity_ClatCoordinator(JNIEnv* env) {
diff --git a/service/native/libs/libclat/Android.bp b/service/native/libs/libclat/Android.bp
index 8540787..5e208d8 100644
--- a/service/native/libs/libclat/Android.bp
+++ b/service/native/libs/libclat/Android.bp
@@ -19,9 +19,22 @@
 cc_library_static {
     name: "libclat",
     defaults: ["netd_defaults"],
-    srcs: ["clatutils.cpp"],
+    header_libs: [
+        "bpf_connectivity_headers",
+        "bpf_headers",
+        "bpf_syscall_wrappers",
+    ],
+    srcs: [
+        "TcUtils.cpp",  // TODO: move to frameworks/libs/net
+        "bpfhelper.cpp",
+        "clatutils.cpp",
+    ],
     stl: "libc++_static",
-    static_libs: ["libip_checksum"],
+    static_libs: [
+        "libbase",
+        "libip_checksum",
+        "libnetdutils",  // for netdutils/UidConstants.h in bpf_shared.h
+    ],
     shared_libs: ["liblog"],
     export_include_dirs: ["include"],
     min_sdk_version: "30",
@@ -32,7 +45,13 @@
     name: "libclat_test",
     defaults: ["netd_defaults"],
     test_suites: ["device-tests"],
+    header_libs: [
+        "bpf_connectivity_headers",
+        "bpf_headers",
+        "bpf_syscall_wrappers",
+    ],
     srcs: [
+        "TcUtilsTest.cpp",
         "clatutils_test.cpp",
     ],
     static_libs: [
@@ -40,10 +59,12 @@
         "libclat",
         "libip_checksum",
         "libnetd_test_tun_interface",
+        "libnetdutils",  // for netdutils/UidConstants.h in bpf_shared.h
+        "libtcutils",
     ],
     shared_libs: [
         "liblog",
         "libnetutils",
     ],
     require_root: true,
-}
\ No newline at end of file
+}
diff --git a/service/native/libs/libclat/TcUtils.cpp b/service/native/libs/libclat/TcUtils.cpp
new file mode 100644
index 0000000..cdfb763
--- /dev/null
+++ b/service/native/libs/libclat/TcUtils.cpp
@@ -0,0 +1,390 @@
+/*
+ * Copyright (C) 2019 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.
+ */
+
+#define LOG_TAG "TcUtils"
+
+#include "libclat/TcUtils.h"
+
+#include <arpa/inet.h>
+#include <linux/if.h>
+#include <linux/if_arp.h>
+#include <linux/netlink.h>
+#include <linux/pkt_cls.h>
+#include <linux/pkt_sched.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <log/log.h>
+
+#include "android-base/unique_fd.h"
+
+namespace android {
+namespace net {
+
+using std::max;
+
+// Sync from system/netd/server/NetlinkCommands.h
+const sockaddr_nl KERNEL_NLADDR = {AF_NETLINK, 0, 0, 0};
+const uint16_t NETLINK_REQUEST_FLAGS = NLM_F_REQUEST | NLM_F_ACK;
+
+static int doSIOCGIF(const std::string& interface, int opt) {
+    base::unique_fd ufd(socket(AF_INET6, SOCK_DGRAM | SOCK_CLOEXEC, 0));
+
+    if (ufd < 0) {
+        const int err = errno;
+        ALOGE("socket(AF_INET6, SOCK_DGRAM | SOCK_CLOEXEC, 0)");
+        return -err;
+    };
+
+    struct ifreq ifr = {};
+    // We use strncpy() instead of strlcpy() since kernel has to be able
+    // to handle non-zero terminated junk passed in by userspace anyway,
+    // and this way too long interface names (more than IFNAMSIZ-1 = 15
+    // characters plus terminating NULL) will not get truncated to 15
+    // characters and zero-terminated and thus potentially erroneously
+    // match a truncated interface if one were to exist.
+    strncpy(ifr.ifr_name, interface.c_str(), sizeof(ifr.ifr_name));
+
+    if (ioctl(ufd, opt, &ifr, sizeof(ifr))) return -errno;
+
+    if (opt == SIOCGIFHWADDR) return ifr.ifr_hwaddr.sa_family;
+    if (opt == SIOCGIFMTU) return ifr.ifr_mtu;
+    return -EINVAL;
+}
+
+int hardwareAddressType(const std::string& interface) {
+    return doSIOCGIF(interface, SIOCGIFHWADDR);
+}
+
+int deviceMTU(const std::string& interface) {
+    return doSIOCGIF(interface, SIOCGIFMTU);
+}
+
+base::Result<bool> isEthernet(const std::string& interface) {
+    int rv = hardwareAddressType(interface);
+    if (rv < 0) {
+        errno = -rv;
+        return ErrnoErrorf("Get hardware address type of interface {} failed", interface);
+    }
+
+    switch (rv) {
+        case ARPHRD_ETHER:
+            return true;
+        case ARPHRD_NONE:
+        case ARPHRD_RAWIP:  // in Linux 4.14+ rmnet support was upstreamed and this is 519
+        case 530:           // this is ARPHRD_RAWIP on some Android 4.9 kernels with rmnet
+            return false;
+        default:
+            errno = EAFNOSUPPORT;  // Address family not supported
+            return ErrnoErrorf("Unknown hardware address type {} on interface {}", rv, interface);
+    }
+}
+
+// TODO: use //system/netd/server/NetlinkCommands.cpp:openNetlinkSocket(protocol)
+// and //system/netd/server/SockDiag.cpp:checkError(fd)
+static int sendAndProcessNetlinkResponse(const void* req, int len) {
+    base::unique_fd fd(socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE));
+    if (fd == -1) {
+        const int err = errno;
+        ALOGE("socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE)");
+        return -err;
+    }
+
+    static constexpr int on = 1;
+    int rv = setsockopt(fd, SOL_NETLINK, NETLINK_CAP_ACK, &on, sizeof(on));
+    if (rv) ALOGE("setsockopt(fd, SOL_NETLINK, NETLINK_CAP_ACK, %d)", on);
+
+    // this is needed to get sane strace netlink parsing, it allocates the pid
+    rv = bind(fd, (const struct sockaddr*)&KERNEL_NLADDR, sizeof(KERNEL_NLADDR));
+    if (rv) {
+        const int err = errno;
+        ALOGE("bind(fd, {AF_NETLINK, 0, 0})");
+        return -err;
+    }
+
+    // we do not want to receive messages from anyone besides the kernel
+    rv = connect(fd, (const struct sockaddr*)&KERNEL_NLADDR, sizeof(KERNEL_NLADDR));
+    if (rv) {
+        const int err = errno;
+        ALOGE("connect(fd, {AF_NETLINK, 0, 0})");
+        return -err;
+    }
+
+    rv = send(fd, req, len, 0);
+    if (rv == -1) return -errno;
+    if (rv != len) return -EMSGSIZE;
+
+    struct {
+        nlmsghdr h;
+        nlmsgerr e;
+        char buf[256];
+    } resp = {};
+
+    rv = recv(fd, &resp, sizeof(resp), MSG_TRUNC);
+
+    if (rv == -1) {
+        const int err = errno;
+        ALOGE("recv() failed");
+        return -err;
+    }
+
+    if (rv < (int)NLMSG_SPACE(sizeof(struct nlmsgerr))) {
+        ALOGE("recv() returned short packet: %d", rv);
+        return -EMSGSIZE;
+    }
+
+    if (resp.h.nlmsg_len != (unsigned)rv) {
+        ALOGE("recv() returned invalid header length: %d != %d", resp.h.nlmsg_len, rv);
+        return -EBADMSG;
+    }
+
+    if (resp.h.nlmsg_type != NLMSG_ERROR) {
+        ALOGE("recv() did not return NLMSG_ERROR message: %d", resp.h.nlmsg_type);
+        return -EBADMSG;
+    }
+
+    return resp.e.error;  // returns 0 on success
+}
+
+// ADD:     nlMsgType=RTM_NEWQDISC nlMsgFlags=NLM_F_EXCL|NLM_F_CREATE
+// REPLACE: nlMsgType=RTM_NEWQDISC nlMsgFlags=NLM_F_CREATE|NLM_F_REPLACE
+// DEL:     nlMsgType=RTM_DELQDISC nlMsgFlags=0
+int doTcQdiscClsact(int ifIndex, uint16_t nlMsgType, uint16_t nlMsgFlags) {
+    // This is the name of the qdisc we are attaching.
+    // Some hoop jumping to make this compile time constant with known size,
+    // so that the structure declaration is well defined at compile time.
+#define CLSACT "clsact"
+    // sizeof() includes the terminating NULL
+    static constexpr size_t ASCIIZ_LEN_CLSACT = sizeof(CLSACT);
+
+    const struct {
+        nlmsghdr n;
+        tcmsg t;
+        struct {
+            nlattr attr;
+            char str[NLMSG_ALIGN(ASCIIZ_LEN_CLSACT)];
+        } kind;
+    } req = {
+            .n =
+                    {
+                            .nlmsg_len = sizeof(req),
+                            .nlmsg_type = nlMsgType,
+                            .nlmsg_flags = static_cast<__u16>(NETLINK_REQUEST_FLAGS | nlMsgFlags),
+                    },
+            .t =
+                    {
+                            .tcm_family = AF_UNSPEC,
+                            .tcm_ifindex = ifIndex,
+                            .tcm_handle = TC_H_MAKE(TC_H_CLSACT, 0),
+                            .tcm_parent = TC_H_CLSACT,
+                    },
+            .kind =
+                    {
+                            .attr =
+                                    {
+                                            .nla_len = NLA_HDRLEN + ASCIIZ_LEN_CLSACT,
+                                            .nla_type = TCA_KIND,
+                                    },
+                            .str = CLSACT,
+                    },
+    };
+#undef CLSACT
+
+    return sendAndProcessNetlinkResponse(&req, sizeof(req));
+}
+
+// tc filter add dev .. in/egress prio 4 protocol ipv6/ip bpf object-pinned /sys/fs/bpf/...
+// direct-action
+int tcFilterAddDevBpf(int ifIndex, bool ingress, uint16_t proto, int bpfFd, bool ethernet) {
+    // This is the name of the filter we're attaching (ie. this is the 'bpf'
+    // packet classifier enabled by kernel config option CONFIG_NET_CLS_BPF.
+    //
+    // We go through some hoops in order to make this compile time constants
+    // so that we can define the struct further down the function with the
+    // field for this sized correctly already during the build.
+#define BPF "bpf"
+    // sizeof() includes the terminating NULL
+    static constexpr size_t ASCIIZ_LEN_BPF = sizeof(BPF);
+
+    // This is to replicate program name suffix used by 'tc' Linux cli
+    // when it attaches programs.
+#define FSOBJ_SUFFIX ":[*fsobj]"
+
+    // This macro expands (from header files) to:
+    //   prog_clatd_schedcls_ingress6_clat_rawip:[*fsobj]
+    // and is the name of the pinned ingress ebpf program for ARPHRD_RAWIP interfaces.
+    // (also compatible with anything that has 0 size L2 header)
+    static constexpr char name_clat_rx_rawip[] = CLAT_INGRESS6_PROG_RAWIP_NAME FSOBJ_SUFFIX;
+
+    // This macro expands (from header files) to:
+    //   prog_clatd_schedcls_ingress6_clat_ether:[*fsobj]
+    // and is the name of the pinned ingress ebpf program for ARPHRD_ETHER interfaces.
+    // (also compatible with anything that has standard ethernet header)
+    static constexpr char name_clat_rx_ether[] = CLAT_INGRESS6_PROG_ETHER_NAME FSOBJ_SUFFIX;
+
+    // This macro expands (from header files) to:
+    //   prog_clatd_schedcls_egress4_clat_rawip:[*fsobj]
+    // and is the name of the pinned egress ebpf program for ARPHRD_RAWIP interfaces.
+    // (also compatible with anything that has 0 size L2 header)
+    static constexpr char name_clat_tx_rawip[] = CLAT_EGRESS4_PROG_RAWIP_NAME FSOBJ_SUFFIX;
+
+    // This macro expands (from header files) to:
+    //   prog_clatd_schedcls_egress4_clat_ether:[*fsobj]
+    // and is the name of the pinned egress ebpf program for ARPHRD_ETHER interfaces.
+    // (also compatible with anything that has standard ethernet header)
+    static constexpr char name_clat_tx_ether[] = CLAT_EGRESS4_PROG_ETHER_NAME FSOBJ_SUFFIX;
+
+#undef FSOBJ_SUFFIX
+
+    // The actual name we'll use is determined at run time via 'ethernet' and 'ingress'
+    // booleans.  We need to compile time allocate enough space in the struct
+    // hence this macro magic to make sure we have enough space for either
+    // possibility.  In practice some of these are actually the same size.
+    static constexpr size_t ASCIIZ_MAXLEN_NAME = max({
+            sizeof(name_clat_rx_rawip),
+            sizeof(name_clat_rx_ether),
+            sizeof(name_clat_tx_rawip),
+            sizeof(name_clat_tx_ether),
+    });
+
+    // These are not compile time constants: 'name' is used in strncpy below
+    const char* const name_clat_rx = ethernet ? name_clat_rx_ether : name_clat_rx_rawip;
+    const char* const name_clat_tx = ethernet ? name_clat_tx_ether : name_clat_tx_rawip;
+    const char* const name = ingress ? name_clat_rx : name_clat_tx;
+
+    struct {
+        nlmsghdr n;
+        tcmsg t;
+        struct {
+            nlattr attr;
+            char str[NLMSG_ALIGN(ASCIIZ_LEN_BPF)];
+        } kind;
+        struct {
+            nlattr attr;
+            struct {
+                nlattr attr;
+                __u32 u32;
+            } fd;
+            struct {
+                nlattr attr;
+                char str[NLMSG_ALIGN(ASCIIZ_MAXLEN_NAME)];
+            } name;
+            struct {
+                nlattr attr;
+                __u32 u32;
+            } flags;
+        } options;
+    } req = {
+            .n =
+                    {
+                            .nlmsg_len = sizeof(req),
+                            .nlmsg_type = RTM_NEWTFILTER,
+                            .nlmsg_flags = NETLINK_REQUEST_FLAGS | NLM_F_EXCL | NLM_F_CREATE,
+                    },
+            .t =
+                    {
+                            .tcm_family = AF_UNSPEC,
+                            .tcm_ifindex = ifIndex,
+                            .tcm_handle = TC_H_UNSPEC,
+                            .tcm_parent = TC_H_MAKE(TC_H_CLSACT,
+                                                    ingress ? TC_H_MIN_INGRESS : TC_H_MIN_EGRESS),
+                            .tcm_info = static_cast<__u32>((PRIO_CLAT << 16) | htons(proto)),
+                    },
+            .kind =
+                    {
+                            .attr =
+                                    {
+                                            .nla_len = sizeof(req.kind),
+                                            .nla_type = TCA_KIND,
+                                    },
+                            .str = BPF,
+                    },
+            .options =
+                    {
+                            .attr =
+                                    {
+                                            .nla_len = sizeof(req.options),
+                                            .nla_type = NLA_F_NESTED | TCA_OPTIONS,
+                                    },
+                            .fd =
+                                    {
+                                            .attr =
+                                                    {
+                                                            .nla_len = sizeof(req.options.fd),
+                                                            .nla_type = TCA_BPF_FD,
+                                                    },
+                                            .u32 = static_cast<__u32>(bpfFd),
+                                    },
+                            .name =
+                                    {
+                                            .attr =
+                                                    {
+                                                            .nla_len = sizeof(req.options.name),
+                                                            .nla_type = TCA_BPF_NAME,
+                                                    },
+                                            // Visible via 'tc filter show', but
+                                            // is overwritten by strncpy below
+                                            .str = "placeholder",
+                                    },
+                            .flags =
+                                    {
+                                            .attr =
+                                                    {
+                                                            .nla_len = sizeof(req.options.flags),
+                                                            .nla_type = TCA_BPF_FLAGS,
+                                                    },
+                                            .u32 = TCA_BPF_FLAG_ACT_DIRECT,
+                                    },
+                    },
+    };
+#undef BPF
+
+    strncpy(req.options.name.str, name, sizeof(req.options.name.str));
+
+    return sendAndProcessNetlinkResponse(&req, sizeof(req));
+}
+
+// tc filter del dev .. in/egress prio 4 protocol ..
+int tcFilterDelDev(int ifIndex, bool ingress, uint16_t prio, uint16_t proto) {
+    const struct {
+        nlmsghdr n;
+        tcmsg t;
+    } req = {
+            .n =
+                    {
+                            .nlmsg_len = sizeof(req),
+                            .nlmsg_type = RTM_DELTFILTER,
+                            .nlmsg_flags = NETLINK_REQUEST_FLAGS,
+                    },
+            .t =
+                    {
+                            .tcm_family = AF_UNSPEC,
+                            .tcm_ifindex = ifIndex,
+                            .tcm_handle = TC_H_UNSPEC,
+                            .tcm_parent = TC_H_MAKE(TC_H_CLSACT,
+                                                    ingress ? TC_H_MIN_INGRESS : TC_H_MIN_EGRESS),
+                            .tcm_info = (static_cast<uint32_t>(prio) << 16) |
+                                        static_cast<uint32_t>(htons(proto)),
+                    },
+    };
+
+    return sendAndProcessNetlinkResponse(&req, sizeof(req));
+}
+
+}  // namespace net
+}  // namespace android
diff --git a/service/native/libs/libclat/TcUtilsTest.cpp b/service/native/libs/libclat/TcUtilsTest.cpp
new file mode 100644
index 0000000..08f3042
--- /dev/null
+++ b/service/native/libs/libclat/TcUtilsTest.cpp
@@ -0,0 +1,212 @@
+/*
+ * Copyright 2019 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.
+ *
+ * TcUtilsTest.cpp - unit tests for TcUtils.cpp
+ */
+
+#include <gtest/gtest.h>
+
+#include "libclat/TcUtils.h"
+
+#include <linux/if_arp.h>
+#include <stdlib.h>
+#include <sys/wait.h>
+
+#include "bpf/BpfUtils.h"
+#include "bpf_shared.h"
+
+namespace android {
+namespace net {
+
+class TcUtilsTest : public ::testing::Test {
+  public:
+    void SetUp() {}
+};
+
+TEST_F(TcUtilsTest, HardwareAddressTypeOfNonExistingIf) {
+    ASSERT_EQ(-ENODEV, hardwareAddressType("not_existing_if"));
+}
+
+TEST_F(TcUtilsTest, HardwareAddressTypeOfLoopback) {
+    ASSERT_EQ(ARPHRD_LOOPBACK, hardwareAddressType("lo"));
+}
+
+// If wireless 'wlan0' interface exists it should be Ethernet.
+TEST_F(TcUtilsTest, HardwareAddressTypeOfWireless) {
+    int type = hardwareAddressType("wlan0");
+    if (type == -ENODEV) return;
+
+    ASSERT_EQ(ARPHRD_ETHER, type);
+}
+
+// If cellular 'rmnet_data0' interface exists it should
+// *probably* not be Ethernet and instead be RawIp.
+TEST_F(TcUtilsTest, HardwareAddressTypeOfCellular) {
+    int type = hardwareAddressType("rmnet_data0");
+    if (type == -ENODEV) return;
+
+    ASSERT_NE(ARPHRD_ETHER, type);
+
+    // ARPHRD_RAWIP is 530 on some pre-4.14 Qualcomm devices.
+    if (type == 530) return;
+
+    ASSERT_EQ(ARPHRD_RAWIP, type);
+}
+
+TEST_F(TcUtilsTest, IsEthernetOfNonExistingIf) {
+    auto res = isEthernet("not_existing_if");
+    ASSERT_FALSE(res.ok());
+    ASSERT_EQ(ENODEV, res.error().code());
+}
+
+TEST_F(TcUtilsTest, IsEthernetOfLoopback) {
+    auto res = isEthernet("lo");
+    ASSERT_FALSE(res.ok());
+    ASSERT_EQ(EAFNOSUPPORT, res.error().code());
+}
+
+// If wireless 'wlan0' interface exists it should be Ethernet.
+// See also HardwareAddressTypeOfWireless.
+TEST_F(TcUtilsTest, IsEthernetOfWireless) {
+    auto res = isEthernet("wlan0");
+    if (!res.ok() && res.error().code() == ENODEV) return;
+
+    ASSERT_RESULT_OK(res);
+    ASSERT_TRUE(res.value());
+}
+
+// If cellular 'rmnet_data0' interface exists it should
+// *probably* not be Ethernet and instead be RawIp.
+// See also HardwareAddressTypeOfCellular.
+TEST_F(TcUtilsTest, IsEthernetOfCellular) {
+    auto res = isEthernet("rmnet_data0");
+    if (!res.ok() && res.error().code() == ENODEV) return;
+
+    ASSERT_RESULT_OK(res);
+    ASSERT_FALSE(res.value());
+}
+
+TEST_F(TcUtilsTest, DeviceMTUOfNonExistingIf) {
+    ASSERT_EQ(-ENODEV, deviceMTU("not_existing_if"));
+}
+
+TEST_F(TcUtilsTest, DeviceMTUofLoopback) {
+    ASSERT_EQ(65536, deviceMTU("lo"));
+}
+
+TEST_F(TcUtilsTest, GetClatEgress4MapFd) {
+    int fd = getClatEgress4MapFd();
+    ASSERT_GE(fd, 3);  // 0,1,2 - stdin/out/err, thus fd >= 3
+    EXPECT_EQ(FD_CLOEXEC, fcntl(fd, F_GETFD));
+    close(fd);
+}
+
+TEST_F(TcUtilsTest, GetClatEgress4RawIpProgFd) {
+    int fd = getClatEgress4ProgFd(RAWIP);
+    ASSERT_GE(fd, 3);
+    EXPECT_EQ(FD_CLOEXEC, fcntl(fd, F_GETFD));
+    close(fd);
+}
+
+TEST_F(TcUtilsTest, GetClatEgress4EtherProgFd) {
+    int fd = getClatEgress4ProgFd(ETHER);
+    ASSERT_GE(fd, 3);
+    EXPECT_EQ(FD_CLOEXEC, fcntl(fd, F_GETFD));
+    close(fd);
+}
+
+TEST_F(TcUtilsTest, GetClatIngress6MapFd) {
+    int fd = getClatIngress6MapFd();
+    ASSERT_GE(fd, 3);  // 0,1,2 - stdin/out/err, thus fd >= 3
+    EXPECT_EQ(FD_CLOEXEC, fcntl(fd, F_GETFD));
+    close(fd);
+}
+
+TEST_F(TcUtilsTest, GetClatIngress6RawIpProgFd) {
+    int fd = getClatIngress6ProgFd(RAWIP);
+    ASSERT_GE(fd, 3);
+    EXPECT_EQ(FD_CLOEXEC, fcntl(fd, F_GETFD));
+    close(fd);
+}
+
+TEST_F(TcUtilsTest, GetClatIngress6EtherProgFd) {
+    int fd = getClatIngress6ProgFd(ETHER);
+    ASSERT_GE(fd, 3);
+    EXPECT_EQ(FD_CLOEXEC, fcntl(fd, F_GETFD));
+    close(fd);
+}
+
+// See Linux kernel source in include/net/flow.h
+#define LOOPBACK_IFINDEX 1
+
+TEST_F(TcUtilsTest, AttachReplaceDetachClsactLo) {
+    // This attaches and detaches a configuration-less and thus no-op clsact
+    // qdisc to loopback interface (and it takes fractions of a second)
+    EXPECT_EQ(0, tcQdiscAddDevClsact(LOOPBACK_IFINDEX));
+    EXPECT_EQ(0, tcQdiscReplaceDevClsact(LOOPBACK_IFINDEX));
+    EXPECT_EQ(0, tcQdiscDelDevClsact(LOOPBACK_IFINDEX));
+    EXPECT_EQ(-EINVAL, tcQdiscDelDevClsact(LOOPBACK_IFINDEX));
+}
+
+static void checkAttachDetachBpfFilterClsactLo(const bool ingress, const bool ethernet) {
+    // Older kernels return EINVAL instead of ENOENT due to lacking proper error propagation...
+    const int errNOENT = android::bpf::isAtLeastKernelVersion(4, 19, 0) ? ENOENT : EINVAL;
+
+    int clatBpfFd = ingress ? getClatIngress6ProgFd(ethernet) : getClatEgress4ProgFd(ethernet);
+    ASSERT_GE(clatBpfFd, 3);
+
+    // This attaches and detaches a clsact plus ebpf program to loopback
+    // interface, but it should not affect traffic by virtue of us not
+    // actually populating the ebpf control map.
+    // Furthermore: it only takes fractions of a second.
+    EXPECT_EQ(-EINVAL, tcFilterDelDevIngressClatIpv6(LOOPBACK_IFINDEX));
+    EXPECT_EQ(-EINVAL, tcFilterDelDevEgressClatIpv4(LOOPBACK_IFINDEX));
+    EXPECT_EQ(0, tcQdiscAddDevClsact(LOOPBACK_IFINDEX));
+    EXPECT_EQ(-errNOENT, tcFilterDelDevIngressClatIpv6(LOOPBACK_IFINDEX));
+    EXPECT_EQ(-errNOENT, tcFilterDelDevEgressClatIpv4(LOOPBACK_IFINDEX));
+    if (ingress) {
+        EXPECT_EQ(0, tcFilterAddDevIngressClatIpv6(LOOPBACK_IFINDEX, clatBpfFd, ethernet));
+        EXPECT_EQ(0, tcFilterDelDevIngressClatIpv6(LOOPBACK_IFINDEX));
+    } else {
+        EXPECT_EQ(0, tcFilterAddDevEgressClatIpv4(LOOPBACK_IFINDEX, clatBpfFd, ethernet));
+        EXPECT_EQ(0, tcFilterDelDevEgressClatIpv4(LOOPBACK_IFINDEX));
+    }
+    EXPECT_EQ(-errNOENT, tcFilterDelDevIngressClatIpv6(LOOPBACK_IFINDEX));
+    EXPECT_EQ(-errNOENT, tcFilterDelDevEgressClatIpv4(LOOPBACK_IFINDEX));
+    EXPECT_EQ(0, tcQdiscDelDevClsact(LOOPBACK_IFINDEX));
+    EXPECT_EQ(-EINVAL, tcFilterDelDevIngressClatIpv6(LOOPBACK_IFINDEX));
+    EXPECT_EQ(-EINVAL, tcFilterDelDevEgressClatIpv4(LOOPBACK_IFINDEX));
+
+    close(clatBpfFd);
+}
+
+TEST_F(TcUtilsTest, CheckAttachBpfFilterRawIpClsactEgressLo) {
+    checkAttachDetachBpfFilterClsactLo(EGRESS, RAWIP);
+}
+
+TEST_F(TcUtilsTest, CheckAttachBpfFilterEthernetClsactEgressLo) {
+    checkAttachDetachBpfFilterClsactLo(EGRESS, ETHER);
+}
+
+TEST_F(TcUtilsTest, CheckAttachBpfFilterRawIpClsactIngressLo) {
+    checkAttachDetachBpfFilterClsactLo(INGRESS, RAWIP);
+}
+
+TEST_F(TcUtilsTest, CheckAttachBpfFilterEthernetClsactIngressLo) {
+    checkAttachDetachBpfFilterClsactLo(INGRESS, ETHER);
+}
+
+}  // namespace net
+}  // namespace android
diff --git a/service/native/libs/libclat/bpfhelper.cpp b/service/native/libs/libclat/bpfhelper.cpp
new file mode 100644
index 0000000..6e230d0
--- /dev/null
+++ b/service/native/libs/libclat/bpfhelper.cpp
@@ -0,0 +1,231 @@
+/*
+ * Copyright 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.
+ *
+ * main.c - main function
+ */
+#define LOG_TAG "bpfhelper"
+
+#include "libclat/bpfhelper.h"
+
+#include <android-base/unique_fd.h>
+#include <log/log.h>
+
+#include "bpf/BpfMap.h"
+#include "libclat/TcUtils.h"
+
+#define DEVICEPREFIX "v4-"
+
+using android::base::unique_fd;
+using android::net::RAWIP;
+using android::net::getClatEgress4MapFd;
+using android::net::getClatIngress6MapFd;
+using android::net::getClatEgress4ProgFd;
+using android::net::getClatIngress6ProgFd;
+using android::net::tcQdiscAddDevClsact;
+using android::net::tcFilterAddDevEgressClatIpv4;
+using android::net::tcFilterAddDevIngressClatIpv6;
+using android::net::tcFilterDelDevEgressClatIpv4;
+using android::net::tcFilterDelDevIngressClatIpv6;
+using android::bpf::BpfMap;
+
+BpfMap<ClatEgress4Key, ClatEgress4Value> mClatEgress4Map;
+BpfMap<ClatIngress6Key, ClatIngress6Value> mClatIngress6Map;
+
+namespace android {
+namespace net {
+namespace clat {
+
+// TODO: have a clearMap function to remove all stubs while system server crash.
+// For long term, move bpf access into java and map initialization should live
+// ClatCoordinator constructor.
+int initMaps(void) {
+    int rv = getClatEgress4MapFd();
+    if (rv < 0) {
+        ALOGE("getClatEgress4MapFd() failure: %s", strerror(-rv));
+        return -rv;
+    }
+    mClatEgress4Map.reset(rv);
+
+    rv = getClatIngress6MapFd();
+    if (rv < 0) {
+        ALOGE("getClatIngress6MapFd() failure: %s", strerror(-rv));
+        mClatEgress4Map.reset(-1);
+        return -rv;
+    }
+    mClatIngress6Map.reset(rv);
+
+    return 0;
+}
+
+void maybeStartBpf(const ClatdTracker& tracker) {
+    auto isEthernet = android::net::isEthernet(tracker.iface);
+    if (!isEthernet.ok()) {
+        ALOGE("isEthernet(%s[%d]) failure: %s", tracker.iface, tracker.ifIndex,
+              isEthernet.error().message().c_str());
+        return;
+    }
+
+    // This program will be attached to the v4-* interface which is a TUN and thus always rawip.
+    int rv = getClatEgress4ProgFd(RAWIP);
+    if (rv < 0) {
+        ALOGE("getClatEgress4ProgFd(RAWIP) failure: %s", strerror(-rv));
+        return;
+    }
+    unique_fd txRawIpProgFd(rv);
+
+    rv = getClatIngress6ProgFd(isEthernet.value());
+    if (rv < 0) {
+        ALOGE("getClatIngress6ProgFd(%d) failure: %s", isEthernet.value(), strerror(-rv));
+        return;
+    }
+    unique_fd rxProgFd(rv);
+
+    ClatEgress4Key txKey = {
+            .iif = tracker.v4ifIndex,
+            .local4 = tracker.v4,
+    };
+    ClatEgress4Value txValue = {
+            .oif = tracker.ifIndex,
+            .local6 = tracker.v6,
+            .pfx96 = tracker.pfx96,
+            .oifIsEthernet = isEthernet.value(),
+    };
+
+    auto ret = mClatEgress4Map.writeValue(txKey, txValue, BPF_ANY);
+    if (!ret.ok()) {
+        ALOGE("mClatEgress4Map.writeValue failure: %s", strerror(ret.error().code()));
+        return;
+    }
+
+    ClatIngress6Key rxKey = {
+            .iif = tracker.ifIndex,
+            .pfx96 = tracker.pfx96,
+            .local6 = tracker.v6,
+    };
+    ClatIngress6Value rxValue = {
+            // TODO: move all the clat code to eBPF and remove the tun interface entirely.
+            .oif = tracker.v4ifIndex,
+            .local4 = tracker.v4,
+    };
+
+    ret = mClatIngress6Map.writeValue(rxKey, rxValue, BPF_ANY);
+    if (!ret.ok()) {
+        ALOGE("mClatIngress6Map.writeValue failure: %s", strerror(ret.error().code()));
+        ret = mClatEgress4Map.deleteValue(txKey);
+        if (!ret.ok())
+            ALOGE("mClatEgress4Map.deleteValue failure: %s", strerror(ret.error().code()));
+        return;
+    }
+
+    // We do tc setup *after* populating the maps, so scanning through them
+    // can always be used to tell us what needs cleanup.
+
+    // Usually the clsact will be added in RouteController::addInterfaceToPhysicalNetwork.
+    // But clat is started before the v4- interface is added to the network. The clat startup have
+    // to add clsact of v4- tun interface first for adding bpf filter in maybeStartBpf.
+    // TODO: move "qdisc add clsact" of v4- tun interface out from ClatdController.
+    rv = tcQdiscAddDevClsact(tracker.v4ifIndex);
+    if (rv) {
+        ALOGE("tcQdiscAddDevClsact(%d[%s]) failure: %s", tracker.v4ifIndex, tracker.v4iface,
+              strerror(-rv));
+        ret = mClatEgress4Map.deleteValue(txKey);
+        if (!ret.ok())
+            ALOGE("mClatEgress4Map.deleteValue failure: %s", strerror(ret.error().code()));
+        ret = mClatIngress6Map.deleteValue(rxKey);
+        if (!ret.ok())
+            ALOGE("mClatIngress6Map.deleteValue failure: %s", strerror(ret.error().code()));
+        return;
+    }
+
+    rv = tcFilterAddDevEgressClatIpv4(tracker.v4ifIndex, txRawIpProgFd, RAWIP);
+    if (rv) {
+        ALOGE("tcFilterAddDevEgressClatIpv4(%d[%s], RAWIP) failure: %s", tracker.v4ifIndex,
+              tracker.v4iface, strerror(-rv));
+
+        // The v4- interface clsact is not deleted for unwinding error because once it is created
+        // with interface addition, the lifetime is till interface deletion. Moreover, the clsact
+        // has no clat filter now. It should not break anything.
+
+        ret = mClatEgress4Map.deleteValue(txKey);
+        if (!ret.ok())
+            ALOGE("mClatEgress4Map.deleteValue failure: %s", strerror(ret.error().code()));
+        ret = mClatIngress6Map.deleteValue(rxKey);
+        if (!ret.ok())
+            ALOGE("mClatIngress6Map.deleteValue failure: %s", strerror(ret.error().code()));
+        return;
+    }
+
+    rv = tcFilterAddDevIngressClatIpv6(tracker.ifIndex, rxProgFd, isEthernet.value());
+    if (rv) {
+        ALOGE("tcFilterAddDevIngressClatIpv6(%d[%s], %d) failure: %s", tracker.ifIndex,
+              tracker.iface, isEthernet.value(), strerror(-rv));
+        rv = tcFilterDelDevEgressClatIpv4(tracker.v4ifIndex);
+        if (rv) {
+            ALOGE("tcFilterDelDevEgressClatIpv4(%d[%s]) failure: %s", tracker.v4ifIndex,
+                  tracker.v4iface, strerror(-rv));
+        }
+
+        // The v4- interface clsact is not deleted. See the reason in the error unwinding code of
+        // the egress filter attaching of v4- tun interface.
+
+        ret = mClatEgress4Map.deleteValue(txKey);
+        if (!ret.ok())
+            ALOGE("mClatEgress4Map.deleteValue failure: %s", strerror(ret.error().code()));
+        ret = mClatIngress6Map.deleteValue(rxKey);
+        if (!ret.ok())
+            ALOGE("mClatIngress6Map.deleteValue failure: %s", strerror(ret.error().code()));
+        return;
+    }
+
+    // success
+}
+
+void maybeStopBpf(const ClatdTracker& tracker) {
+    int rv = tcFilterDelDevIngressClatIpv6(tracker.ifIndex);
+    if (rv < 0) {
+        ALOGE("tcFilterDelDevIngressClatIpv6(%d[%s]) failure: %s", tracker.ifIndex, tracker.iface,
+              strerror(-rv));
+    }
+
+    rv = tcFilterDelDevEgressClatIpv4(tracker.v4ifIndex);
+    if (rv < 0) {
+        ALOGE("tcFilterDelDevEgressClatIpv4(%d[%s]) failure: %s", tracker.v4ifIndex,
+              tracker.v4iface, strerror(-rv));
+    }
+
+    // We cleanup the maps last, so scanning through them can be used to
+    // determine what still needs cleanup.
+
+    ClatEgress4Key txKey = {
+            .iif = tracker.v4ifIndex,
+            .local4 = tracker.v4,
+    };
+
+    auto ret = mClatEgress4Map.deleteValue(txKey);
+    if (!ret.ok()) ALOGE("mClatEgress4Map.deleteValue failure: %s", strerror(ret.error().code()));
+
+    ClatIngress6Key rxKey = {
+            .iif = tracker.ifIndex,
+            .pfx96 = tracker.pfx96,
+            .local6 = tracker.v6,
+    };
+
+    ret = mClatIngress6Map.deleteValue(rxKey);
+    if (!ret.ok()) ALOGE("mClatIngress6Map.deleteValue failure: %s", strerror(ret.error().code()));
+}
+
+}  // namespace clat
+}  // namespace net
+}  // namespace android
diff --git a/service/native/libs/libclat/include/libclat/TcUtils.h b/service/native/libs/libclat/include/libclat/TcUtils.h
new file mode 100644
index 0000000..212838e
--- /dev/null
+++ b/service/native/libs/libclat/include/libclat/TcUtils.h
@@ -0,0 +1,117 @@
+/*
+ * Copyright (C) 2019 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
+
+#include <android-base/result.h>
+#include <errno.h>
+#include <linux/if_ether.h>
+#include <linux/if_link.h>
+#include <linux/rtnetlink.h>
+
+#include <string>
+
+#include "bpf/BpfUtils.h"
+#include "bpf_shared.h"
+
+namespace android {
+namespace net {
+
+// For better code clarity - do not change values - used for booleans like
+// with_ethernet_header or isEthernet.
+constexpr bool RAWIP = false;
+constexpr bool ETHER = true;
+
+// For better code clarity when used for 'bool ingress' parameter.
+constexpr bool EGRESS = false;
+constexpr bool INGRESS = true;
+
+// The priority of clat hook - must be after tethering.
+constexpr uint16_t PRIO_CLAT = 4;
+
+// this returns an ARPHRD_* constant or a -errno
+int hardwareAddressType(const std::string& interface);
+
+// return MTU or -errno
+int deviceMTU(const std::string& interface);
+
+base::Result<bool> isEthernet(const std::string& interface);
+
+inline int getClatEgress4MapFd(void) {
+    const int fd = bpf::mapRetrieveRW(CLAT_EGRESS4_MAP_PATH);
+    return (fd == -1) ? -errno : fd;
+}
+
+inline int getClatEgress4ProgFd(bool with_ethernet_header) {
+    const int fd = bpf::retrieveProgram(with_ethernet_header ? CLAT_EGRESS4_PROG_ETHER_PATH
+                                                             : CLAT_EGRESS4_PROG_RAWIP_PATH);
+    return (fd == -1) ? -errno : fd;
+}
+
+inline int getClatIngress6MapFd(void) {
+    const int fd = bpf::mapRetrieveRW(CLAT_INGRESS6_MAP_PATH);
+    return (fd == -1) ? -errno : fd;
+}
+
+inline int getClatIngress6ProgFd(bool with_ethernet_header) {
+    const int fd = bpf::retrieveProgram(with_ethernet_header ? CLAT_INGRESS6_PROG_ETHER_PATH
+                                                             : CLAT_INGRESS6_PROG_RAWIP_PATH);
+    return (fd == -1) ? -errno : fd;
+}
+
+int doTcQdiscClsact(int ifIndex, uint16_t nlMsgType, uint16_t nlMsgFlags);
+
+inline int tcQdiscAddDevClsact(int ifIndex) {
+    return doTcQdiscClsact(ifIndex, RTM_NEWQDISC, NLM_F_EXCL | NLM_F_CREATE);
+}
+
+inline int tcQdiscReplaceDevClsact(int ifIndex) {
+    return doTcQdiscClsact(ifIndex, RTM_NEWQDISC, NLM_F_CREATE | NLM_F_REPLACE);
+}
+
+inline int tcQdiscDelDevClsact(int ifIndex) {
+    return doTcQdiscClsact(ifIndex, RTM_DELQDISC, 0);
+}
+
+// tc filter add dev .. in/egress prio 4 protocol ipv6/ip bpf object-pinned /sys/fs/bpf/...
+// direct-action
+int tcFilterAddDevBpf(int ifIndex, bool ingress, uint16_t proto, int bpfFd, bool ethernet);
+
+// tc filter add dev .. ingress prio 4 protocol ipv6 bpf object-pinned /sys/fs/bpf/... direct-action
+inline int tcFilterAddDevIngressClatIpv6(int ifIndex, int bpfFd, bool ethernet) {
+    return tcFilterAddDevBpf(ifIndex, INGRESS, ETH_P_IPV6, bpfFd, ethernet);
+}
+
+// tc filter add dev .. egress prio 4 protocol ip bpf object-pinned /sys/fs/bpf/... direct-action
+inline int tcFilterAddDevEgressClatIpv4(int ifIndex, int bpfFd, bool ethernet) {
+    return tcFilterAddDevBpf(ifIndex, EGRESS, ETH_P_IP, bpfFd, ethernet);
+}
+
+// tc filter del dev .. in/egress prio .. protocol ..
+int tcFilterDelDev(int ifIndex, bool ingress, uint16_t prio, uint16_t proto);
+
+// tc filter del dev .. ingress prio 4 protocol ipv6
+inline int tcFilterDelDevIngressClatIpv6(int ifIndex) {
+    return tcFilterDelDev(ifIndex, INGRESS, PRIO_CLAT, ETH_P_IPV6);
+}
+
+// tc filter del dev .. egress prio 4 protocol ip
+inline int tcFilterDelDevEgressClatIpv4(int ifIndex) {
+    return tcFilterDelDev(ifIndex, EGRESS, PRIO_CLAT, ETH_P_IP);
+}
+
+}  // namespace net
+}  // namespace android
diff --git a/service/native/libs/libclat/include/libclat/bpfhelper.h b/service/native/libs/libclat/include/libclat/bpfhelper.h
new file mode 100644
index 0000000..c0328c0
--- /dev/null
+++ b/service/native/libs/libclat/include/libclat/bpfhelper.h
@@ -0,0 +1,40 @@
+// 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
+
+#include <arpa/inet.h>
+#include <linux/if.h>
+
+namespace android {
+namespace net {
+namespace clat {
+
+struct ClatdTracker {
+    unsigned ifIndex;
+    char iface[IFNAMSIZ];
+    unsigned v4ifIndex;
+    char v4iface[IFNAMSIZ];
+    in_addr v4;
+    in6_addr v6;
+    in6_addr pfx96;
+};
+
+int initMaps(void);
+void maybeStartBpf(const ClatdTracker& tracker);
+void maybeStopBpf(const ClatdTracker& tracker);
+
+}  // namespace clat
+}  // namespace net
+}  // namespace android
diff --git a/service/src/com/android/server/connectivity/ClatCoordinator.java b/service/src/com/android/server/connectivity/ClatCoordinator.java
index 4d243c4..5a5e24a 100644
--- a/service/src/com/android/server/connectivity/ClatCoordinator.java
+++ b/service/src/com/android/server/connectivity/ClatCoordinator.java
@@ -74,6 +74,12 @@
     private final Dependencies mDeps;
     @Nullable
     private String mIface = null;
+    @Nullable
+    private String mNat64Prefix = null;
+    @Nullable
+    private String mXlatLocalAddress4 = null;
+    @Nullable
+    private String mXlatLocalAddress6 = null;
     private int mPid = INVALID_PID;
 
     @VisibleForTesting
@@ -162,6 +168,23 @@
                 throws IOException {
             native_configurePacketSocket(sock, v6, ifindex);
         }
+
+        /**
+         * Maybe start bpf.
+         */
+        public int maybeStartBpf(@NonNull FileDescriptor tunfd, @NonNull FileDescriptor readsock6,
+                @NonNull FileDescriptor writesock6, @NonNull String iface, @NonNull String pfx96,
+                @NonNull String v4, @NonNull String v6) throws IOException {
+            return native_maybeStartBpf(tunfd, readsock6, writesock6, iface, pfx96, v4, v6);
+        }
+
+        /**
+         * Maybe stop bpf.
+         */
+        public void maybeStopBpf(String iface, String pfx96, String v4, String v6, int pid)
+                throws IOException {
+            native_maybeStopBpf(iface, pfx96, v4, v6, pid);
+        }
     }
 
     @VisibleForTesting
@@ -304,10 +327,38 @@
             throw new IOException("configure packet socket failed: " + e);
         }
 
+        // [5] Maybe start bpf.
+        try {
+            mDeps.maybeStartBpf(tunFd.getFileDescriptor(), readSock6.getFileDescriptor(),
+                    writeSock6.getFileDescriptor(), iface, pfx96, v4, v6);
+            mIface = iface;
+            mNat64Prefix = pfx96;
+            mXlatLocalAddress4 = v4;
+            mXlatLocalAddress6 = v6;
+        } catch (IOException e) {
+            throw new IOException("Error start bpf on " + iface + ": " + e);
+        }
+
         // TODO: start clatd and returns local xlat464 v6 address.
         return null;
     }
 
+    /**
+     * Stop clatd
+     */
+    public void clatStop() throws IOException {
+        mDeps.maybeStopBpf(mIface, mNat64Prefix, mXlatLocalAddress4, mXlatLocalAddress6,
+                mPid /* unused */);
+        // TODO: remove setIptablesDropRule
+
+        Log.i(TAG, "clatd on " + mIface + " stopped");
+
+        mIface = null;
+        mNat64Prefix = null;
+        mXlatLocalAddress4 = null;
+        mXlatLocalAddress6 = null;
+    }
+
     private static native String native_selectIpv4Address(String v4addr, int prefixlen)
             throws IOException;
     private static native String native_generateIpv6Address(String iface, String v4,
@@ -321,4 +372,9 @@
             int ifindex) throws IOException;
     private static native void native_configurePacketSocket(FileDescriptor sock, String v6,
             int ifindex) throws IOException;
+    private static native int native_maybeStartBpf(FileDescriptor tunfd, FileDescriptor readsock6,
+            FileDescriptor writesock6, String iface, String pfx96, String v4, String v6)
+            throws IOException;
+    private static native void native_maybeStopBpf(String iface, String pfx96, String v4,
+            String v6, int pid) throws IOException;
 }