diff --git a/service/native/libs/libclat/Android.bp b/service/native/libs/libclat/Android.bp
new file mode 100644
index 0000000..a45ffa6
--- /dev/null
+++ b/service/native/libs/libclat/Android.bp
@@ -0,0 +1,42 @@
+// Copyright (C) 2022 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 {
+    default_applicable_licenses: ["Android-Apache-2.0"],
+}
+
+cc_library_static {
+    name: "libclat",
+    defaults: ["netd_defaults"],
+    srcs: ["clatutils.cpp"],
+    stl: "libc++_static",
+    static_libs: ["libip_checksum"],
+    export_include_dirs: ["include"],
+    min_sdk_version: "30",
+    apex_available: ["com.android.tethering"],
+}
+
+cc_test {
+    name: "libclat_test",
+    defaults: ["netd_defaults"],
+    test_suites: ["device-tests"],
+    srcs: [
+        "clatutils_test.cpp",
+    ],
+    static_libs: [
+        "libbase",
+        "libclat",
+        "libip_checksum",
+    ],
+}
\ No newline at end of file
diff --git a/service/native/libs/libclat/clatutils.cpp b/service/native/libs/libclat/clatutils.cpp
new file mode 100644
index 0000000..2a53ba8
--- /dev/null
+++ b/service/native/libs/libclat/clatutils.cpp
@@ -0,0 +1,51 @@
+// Copyright (C) 2022 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 "libclat/clatutils.h"
+
+#include <stdlib.h>
+
+extern "C" {
+#include "checksum.h"
+}
+
+namespace android {
+namespace net {
+namespace clat {
+
+// Alters the bits in the IPv6 address to make them checksum neutral with v4 and nat64Prefix.
+void makeChecksumNeutral(in6_addr* v6, const in_addr v4, const in6_addr& nat64Prefix) {
+    // Fill last 8 bytes of IPv6 address with random bits.
+    arc4random_buf(&v6->s6_addr[8], 8);
+
+    // Make the IID checksum-neutral. That is, make it so that:
+    //   checksum(Local IPv4 | Remote IPv4) = checksum(Local IPv6 | Remote IPv6)
+    // in other words (because remote IPv6 = NAT64 prefix | Remote IPv4):
+    //   checksum(Local IPv4) = checksum(Local IPv6 | NAT64 prefix)
+    // Do this by adjusting the two bytes in the middle of the IID.
+
+    uint16_t middlebytes = (v6->s6_addr[11] << 8) + v6->s6_addr[12];
+
+    uint32_t c1 = ip_checksum_add(0, &v4, sizeof(v4));
+    uint32_t c2 = ip_checksum_add(0, &nat64Prefix, sizeof(nat64Prefix)) +
+                  ip_checksum_add(0, v6, sizeof(*v6));
+
+    uint16_t delta = ip_checksum_adjust(middlebytes, c1, c2);
+    v6->s6_addr[11] = delta >> 8;
+    v6->s6_addr[12] = delta & 0xff;
+}
+
+}  // namespace clat
+}  // namespace net
+}  // namespace android
diff --git a/service/native/libs/libclat/clatutils_test.cpp b/service/native/libs/libclat/clatutils_test.cpp
new file mode 100644
index 0000000..1900abf
--- /dev/null
+++ b/service/native/libs/libclat/clatutils_test.cpp
@@ -0,0 +1,93 @@
+// Copyright (C) 2022 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 "libclat/clatutils.h"
+
+#include <android-base/stringprintf.h>
+#include <arpa/inet.h>
+#include <gtest/gtest.h>
+
+extern "C" {
+#include "checksum.h"
+}
+
+// Default translation parameters.
+static const char kIPv4LocalAddr[] = "192.0.0.4";
+
+namespace android {
+namespace net {
+namespace clat {
+
+using base::StringPrintf;
+
+class ClatUtils : public ::testing::Test {};
+
+TEST_F(ClatUtils, MakeChecksumNeutral) {
+    // We can't test generateIPv6Address here since it requires manipulating routing, which we can't
+    // do without talking to the real netd on the system.
+    uint32_t rand = arc4random_uniform(0xffffffff);
+    uint16_t rand1 = rand & 0xffff;
+    uint16_t rand2 = (rand >> 16) & 0xffff;
+    std::string v6PrefixStr = StringPrintf("2001:db8:%x:%x", rand1, rand2);
+    std::string v6InterfaceAddrStr = StringPrintf("%s::%x:%x", v6PrefixStr.c_str(), rand2, rand1);
+    std::string nat64PrefixStr = StringPrintf("2001:db8:%x:%x::", rand2, rand1);
+
+    in_addr v4 = {inet_addr(kIPv4LocalAddr)};
+    in6_addr v6InterfaceAddr;
+    ASSERT_TRUE(inet_pton(AF_INET6, v6InterfaceAddrStr.c_str(), &v6InterfaceAddr));
+    in6_addr nat64Prefix;
+    ASSERT_TRUE(inet_pton(AF_INET6, nat64PrefixStr.c_str(), &nat64Prefix));
+
+    // Generate a boatload of random IIDs.
+    int onebits = 0;
+    uint64_t prev_iid = 0;
+    for (int i = 0; i < 100000; i++) {
+        in6_addr v6 = v6InterfaceAddr;
+        makeChecksumNeutral(&v6, v4, nat64Prefix);
+
+        // Check the generated IP address is in the same prefix as the interface IPv6 address.
+        EXPECT_EQ(0, memcmp(&v6, &v6InterfaceAddr, 8));
+
+        // Check that consecutive IIDs are not the same.
+        uint64_t iid = *(uint64_t*)(&v6.s6_addr[8]);
+        ASSERT_TRUE(iid != prev_iid)
+                << "Two consecutive random IIDs are the same: " << std::showbase << std::hex << iid
+                << "\n";
+        prev_iid = iid;
+
+        // Check that the IID is checksum-neutral with the NAT64 prefix and the
+        // local prefix.
+        uint16_t c1 = ip_checksum_finish(ip_checksum_add(0, &v4, sizeof(v4)));
+        uint16_t c2 = ip_checksum_finish(ip_checksum_add(0, &nat64Prefix, sizeof(nat64Prefix)) +
+                                         ip_checksum_add(0, &v6, sizeof(v6)));
+
+        if (c1 != c2) {
+            char v6Str[INET6_ADDRSTRLEN];
+            inet_ntop(AF_INET6, &v6, v6Str, sizeof(v6Str));
+            FAIL() << "Bad IID: " << v6Str << " not checksum-neutral with " << kIPv4LocalAddr
+                   << " and " << nat64PrefixStr.c_str() << std::showbase << std::hex
+                   << "\n  IPv4 checksum: " << c1 << "\n  IPv6 checksum: " << c2 << "\n";
+        }
+
+        // Check that IIDs are roughly random and use all the bits by counting the
+        // total number of bits set to 1 in a random sample of 100000 generated IIDs.
+        onebits += __builtin_popcountll(*(uint64_t*)&iid);
+    }
+    EXPECT_LE(3190000, onebits);
+    EXPECT_GE(3210000, onebits);
+}
+
+}  // namespace clat
+}  // namespace net
+}  // namespace android
diff --git a/service/native/libs/libclat/include/libclat/clatutils.h b/service/native/libs/libclat/include/libclat/clatutils.h
new file mode 100644
index 0000000..05c99df
--- /dev/null
+++ b/service/native/libs/libclat/include/libclat/clatutils.h
@@ -0,0 +1,26 @@
+// Copyright (C) 2022 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 <netinet/in.h>
+#include <netinet/in6.h>
+
+namespace android {
+namespace net {
+namespace clat {
+
+void makeChecksumNeutral(in6_addr* v6, const in_addr v4, const in6_addr& nat64Prefix);
+}  // namespace clat
+}  // namespace net
+}  // namespace android