diff --git a/Tethering/apex/Android.bp b/Tethering/apex/Android.bp
index 4c64e98..72c83fa 100644
--- a/Tethering/apex/Android.bp
+++ b/Tethering/apex/Android.bp
@@ -63,6 +63,7 @@
     ],
     canned_fs_config: "canned_fs_config",
     bpfs: [
+        "clatd.o_mainline",
         "netd.o_mainline",
         "offload.o",
         "test.o",
diff --git a/bpf_progs/Android.bp b/bpf_progs/Android.bp
index 4fa288b..bb9f5ead6 100644
--- a/bpf_progs/Android.bp
+++ b/bpf_progs/Android.bp
@@ -73,6 +73,19 @@
 }
 
 bpf {
+    name: "clatd.o_mainline",
+    srcs: ["clatd.c"],
+    cflags: [
+        "-Wall",
+        "-Werror",
+    ],
+    include_dirs: [
+        "frameworks/libs/net/common/netd/libnetdutils/include",
+    ],
+    sub_dir: "net_shared",
+}
+
+bpf {
     name: "netd.o_mainline",
     srcs: ["netd.c"],
     cflags: [
diff --git a/bpf_progs/clatd.c b/bpf_progs/clatd.c
new file mode 100644
index 0000000..dc646c3
--- /dev/null
+++ b/bpf_progs/clatd.c
@@ -0,0 +1,322 @@
+/*
+ * 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.
+ */
+
+#include <linux/bpf.h>
+#include <linux/if.h>
+#include <linux/if_ether.h>
+#include <linux/in.h>
+#include <linux/in6.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <linux/pkt_cls.h>
+#include <linux/swab.h>
+#include <stdbool.h>
+#include <stdint.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_shared.h"
+
+// From kernel:include/net/ip.h
+#define IP_DF 0x4000  // Flag: "Don't Fragment"
+
+DEFINE_BPF_MAP_GRW(clat_ingress6_map, HASH, ClatIngress6Key, ClatIngress6Value, 16, AID_SYSTEM)
+
+static inline __always_inline int nat64(struct __sk_buff* skb, bool is_ethernet) {
+    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;
+    const struct ethhdr* const eth = is_ethernet ? data : NULL;  // used iff is_ethernet
+    const struct ipv6hdr* const 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_PIPE;
+
+    // Must be meta-ethernet IPv6 frame
+    if (skb->protocol != htons(ETH_P_IPV6)) return TC_ACT_PIPE;
+
+    // Must have (ethernet and) ipv6 header
+    if (data + l2_header_size + sizeof(*ip6) > data_end) return TC_ACT_PIPE;
+
+    // Ethertype - if present - must be IPv6
+    if (is_ethernet && (eth->h_proto != htons(ETH_P_IPV6))) return TC_ACT_PIPE;
+
+    // IP version must be 6
+    if (ip6->version != 6) return TC_ACT_PIPE;
+
+    // Maximum IPv6 payload length that can be translated to IPv4
+    if (ntohs(ip6->payload_len) > 0xFFFF - sizeof(struct iphdr)) return TC_ACT_PIPE;
+
+    switch (ip6->nexthdr) {
+        case IPPROTO_TCP:  // For TCP & UDP the checksum neutrality of the chosen IPv6
+        case IPPROTO_UDP:  // address means there is no need to update their checksums.
+        case IPPROTO_GRE:  // We do not need to bother looking at GRE/ESP headers,
+        case IPPROTO_ESP:  // since there is never a checksum to update.
+            break;
+
+        default:  // do not know how to handle anything else
+            return TC_ACT_PIPE;
+    }
+
+    ClatIngress6Key k = {
+            .iif = skb->ifindex,
+            .pfx96.in6_u.u6_addr32 =
+                    {
+                            ip6->saddr.in6_u.u6_addr32[0],
+                            ip6->saddr.in6_u.u6_addr32[1],
+                            ip6->saddr.in6_u.u6_addr32[2],
+                    },
+            .local6 = ip6->daddr,
+    };
+
+    ClatIngress6Value* v = bpf_clat_ingress6_map_lookup_elem(&k);
+
+    if (!v) return TC_ACT_PIPE;
+
+    struct ethhdr eth2;  // used iff is_ethernet
+    if (is_ethernet) {
+        eth2 = *eth;                     // Copy over the ethernet header (src/dst mac)
+        eth2.h_proto = htons(ETH_P_IP);  // But replace the ethertype
+    }
+
+    struct iphdr ip = {
+            .version = 4,                                                      // u4
+            .ihl = sizeof(struct iphdr) / sizeof(__u32),                       // u4
+            .tos = (ip6->priority << 4) + (ip6->flow_lbl[0] >> 4),             // u8
+            .tot_len = htons(ntohs(ip6->payload_len) + sizeof(struct iphdr)),  // u16
+            .id = 0,                                                           // u16
+            .frag_off = htons(IP_DF),                                          // u16
+            .ttl = ip6->hop_limit,                                             // u8
+            .protocol = ip6->nexthdr,                                          // u8
+            .check = 0,                                                        // u16
+            .saddr = ip6->saddr.in6_u.u6_addr32[3],                            // u32
+            .daddr = v->local4.s_addr,                                         // u32
+    };
+
+    // 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 ip.version == 4
+    sum4 = (sum4 & 0xFFFF) + (sum4 >> 16);  // collapse u32 into range 1 .. 0x1FFFE
+    sum4 = (sum4 & 0xFFFF) + (sum4 >> 16);  // collapse any potential carry into u16
+    ip.check = (__u16)~sum4;                // sum4 cannot be zero, so this is never 0xFFFF
+
+    // Calculate the *negative* IPv6 16-bit one's complement checksum of the IPv6 header.
+    __wsum sum6 = 0;
+    // We'll end up with a non-zero sum due to ip6->version == 6 (which has '0' bits)
+    for (int i = 0; i < sizeof(*ip6) / sizeof(__u16); ++i) {
+        sum6 += ~((__u16*)ip6)[i];  // note the bitwise negation
+    }
+
+    // Note that there is no L4 checksum update: we are relying on the checksum neutrality
+    // of the ipv6 address chosen by netd's ClatdController.
+
+    // Packet mutations begin - point of no return, but if this first modification fails
+    // the packet is probably still pristine, so let clatd handle it.
+    if (bpf_skb_change_proto(skb, htons(ETH_P_IP), 0)) return TC_ACT_PIPE;
+
+    // This takes care of updating the skb->csum field for a CHECKSUM_COMPLETE packet.
+    //
+    // In such a case, skb->csum is a 16-bit one's complement sum of the entire payload,
+    // thus we need to subtract out the ipv6 header's sum, and add in the ipv4 header's sum.
+    // However, by construction of ip.check above the checksum of an ipv4 header is zero.
+    // Thus we only need to subtract the ipv6 header's sum, which is the same as adding
+    // in the sum of the bitwise negation of the ipv6 header.
+    //
+    // bpf_csum_update() always succeeds if the skb is CHECKSUM_COMPLETE and returns an error
+    // (-ENOTSUPP) if it isn't.  So we just ignore the return code.
+    //
+    // if (skb->ip_summed == CHECKSUM_COMPLETE)
+    //   return (skb->csum = csum_add(skb->csum, csum));
+    // else
+    //   return -ENOTSUPP;
+    bpf_csum_update(skb, sum6);
+
+    // bpf_skb_change_proto() invalidates all pointers - reload them.
+    data = (void*)(long)skb->data;
+    data_end = (void*)(long)skb->data_end;
+
+    // I cannot think of any valid way for this error condition to trigger, however I do
+    // believe the explicit check is required to keep the in kernel ebpf verifier happy.
+    if (data + l2_header_size + sizeof(struct iphdr) > data_end) return TC_ACT_SHOT;
+
+    if (is_ethernet) {
+        struct ethhdr* new_eth = data;
+
+        // Copy over the updated ethernet header
+        *new_eth = eth2;
+
+        // Copy over the new ipv4 header.
+        *(struct iphdr*)(new_eth + 1) = ip;
+    } else {
+        // Copy over the new ipv4 header without an ethernet header.
+        *(struct iphdr*)data = ip;
+    }
+
+    // Redirect, possibly back to same interface, so tcpdump sees packet twice.
+    if (v->oif) return bpf_redirect(v->oif, BPF_F_INGRESS);
+
+    // Just let it through, tcpdump will not see IPv4 packet.
+    return TC_ACT_PIPE;
+}
+
+DEFINE_BPF_PROG("schedcls/ingress6/clat_ether", AID_ROOT, AID_SYSTEM, sched_cls_ingress6_clat_ether)
+(struct __sk_buff* skb) {
+    return nat64(skb, true);
+}
+
+DEFINE_BPF_PROG("schedcls/ingress6/clat_rawip", AID_ROOT, AID_SYSTEM, sched_cls_ingress6_clat_rawip)
+(struct __sk_buff* skb) {
+    return nat64(skb, false);
+}
+
+DEFINE_BPF_MAP_GRW(clat_egress4_map, HASH, ClatEgress4Key, ClatEgress4Value, 16, AID_SYSTEM)
+
+DEFINE_BPF_PROG("schedcls/egress4/clat_ether", AID_ROOT, AID_SYSTEM, sched_cls_egress4_clat_ether)
+(struct __sk_buff* skb) {
+    return TC_ACT_PIPE;
+}
+
+DEFINE_BPF_PROG("schedcls/egress4/clat_rawip", AID_ROOT, AID_SYSTEM, sched_cls_egress4_clat_rawip)
+(struct __sk_buff* skb) {
+    void* data = (void*)(long)skb->data;
+    const void* data_end = (void*)(long)skb->data_end;
+    const struct iphdr* const ip4 = data;
+
+    // Must be meta-ethernet IPv4 frame
+    if (skb->protocol != htons(ETH_P_IP)) return TC_ACT_PIPE;
+
+    // Must have ipv4 header
+    if (data + sizeof(*ip4) > data_end) return TC_ACT_PIPE;
+
+    // IP version must be 4
+    if (ip4->version != 4) return TC_ACT_PIPE;
+
+    // We cannot handle IP options, just standard 20 byte == 5 dword minimal IPv4 header
+    if (ip4->ihl != 5) return TC_ACT_PIPE;
+
+    // Calculate the IPv4 one's complement checksum of the IPv4 header.
+    __wsum sum4 = 0;
+    for (int i = 0; i < sizeof(*ip4) / sizeof(__u16); ++i) {
+        sum4 += ((__u16*)ip4)[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) return TC_ACT_PIPE;
+
+    // Minimum IPv4 total length is the size of the header
+    if (ntohs(ip4->tot_len) < sizeof(*ip4)) return TC_ACT_PIPE;
+
+    // We are incapable of dealing with IPv4 fragments
+    if (ip4->frag_off & ~htons(IP_DF)) return TC_ACT_PIPE;
+
+    switch (ip4->protocol) {
+        case IPPROTO_TCP:  // For TCP & UDP the checksum neutrality of the chosen IPv6
+        case IPPROTO_GRE:  // address means there is no need to update their checksums.
+        case IPPROTO_ESP:  // We do not need to bother looking at GRE/ESP headers,
+            break;         // since there is never a checksum to update.
+
+        case IPPROTO_UDP:  // See above comment, but must also have UDP header...
+            if (data + sizeof(*ip4) + sizeof(struct udphdr) > data_end) return TC_ACT_PIPE;
+            const struct udphdr* uh = (const struct udphdr*)(ip4 + 1);
+            // If IPv4/UDP checksum is 0 then fallback to clatd so it can calculate the
+            // checksum.  Otherwise the network or more likely the NAT64 gateway might
+            // drop the packet because in most cases IPv6/UDP packets with a zero checksum
+            // are invalid. See RFC 6935.  TODO: calculate checksum via bpf_csum_diff()
+            if (!uh->check) return TC_ACT_PIPE;
+            break;
+
+        default:  // do not know how to handle anything else
+            return TC_ACT_PIPE;
+    }
+
+    ClatEgress4Key k = {
+            .iif = skb->ifindex,
+            .local4.s_addr = ip4->saddr,
+    };
+
+    ClatEgress4Value* v = bpf_clat_egress4_map_lookup_elem(&k);
+
+    if (!v) return TC_ACT_PIPE;
+
+    // Translating without redirecting doesn't make sense.
+    if (!v->oif) return TC_ACT_PIPE;
+
+    // This implementation is currently limited to rawip.
+    if (v->oifIsEthernet) return TC_ACT_PIPE;
+
+    struct ipv6hdr ip6 = {
+            .version = 6,                                    // __u8:4
+            .priority = ip4->tos >> 4,                       // __u8:4
+            .flow_lbl = {(ip4->tos & 0xF) << 4, 0, 0},       // __u8[3]
+            .payload_len = htons(ntohs(ip4->tot_len) - 20),  // __be16
+            .nexthdr = ip4->protocol,                        // __u8
+            .hop_limit = ip4->ttl,                           // __u8
+            .saddr = v->local6,                              // struct in6_addr
+            .daddr = v->pfx96,                               // struct in6_addr
+    };
+    ip6.daddr.in6_u.u6_addr32[3] = ip4->daddr;
+
+    // Calculate the IPv6 16-bit one's complement checksum of the IPv6 header.
+    __wsum sum6 = 0;
+    // We'll end up with a non-zero sum due to ip6.version == 6
+    for (int i = 0; i < sizeof(ip6) / sizeof(__u16); ++i) {
+        sum6 += ((__u16*)&ip6)[i];
+    }
+
+    // Note that there is no L4 checksum update: we are relying on the checksum neutrality
+    // of the ipv6 address chosen by netd's ClatdController.
+
+    // Packet mutations begin - point of no return, but if this first modification fails
+    // the packet is probably still pristine, so let clatd handle it.
+    if (bpf_skb_change_proto(skb, htons(ETH_P_IPV6), 0)) return TC_ACT_PIPE;
+
+    // This takes care of updating the skb->csum field for a CHECKSUM_COMPLETE packet.
+    //
+    // In such a case, skb->csum is a 16-bit one's complement sum of the entire payload,
+    // thus we need to subtract out the ipv4 header's sum, and add in the ipv6 header's sum.
+    // However, we've already verified the ipv4 checksum is correct and thus 0.
+    // Thus we only need to add the ipv6 header's sum.
+    //
+    // bpf_csum_update() always succeeds if the skb is CHECKSUM_COMPLETE and returns an error
+    // (-ENOTSUPP) if it isn't.  So we just ignore the return code (see above for more details).
+    bpf_csum_update(skb, sum6);
+
+    // bpf_skb_change_proto() invalidates all pointers - reload them.
+    data = (void*)(long)skb->data;
+    data_end = (void*)(long)skb->data_end;
+
+    // I cannot think of any valid way for this error condition to trigger, however I do
+    // believe the explicit check is required to keep the in kernel ebpf verifier happy.
+    if (data + sizeof(ip6) > data_end) return TC_ACT_SHOT;
+
+    // Copy over the new ipv6 header without an ethernet header.
+    *(struct ipv6hdr*)data = ip6;
+
+    // Redirect to non v4-* interface.  Tcpdump only sees packet after this redirect.
+    return bpf_redirect(v->oif, 0 /* this is effectively BPF_F_EGRESS */);
+}
+
+LICENSE("Apache 2.0");
+CRITICAL("netd");