diff --git a/framework/api/module-lib-current.txt b/framework/api/module-lib-current.txt
index d2ed73e..5b64d52 100644
--- a/framework/api/module-lib-current.txt
+++ b/framework/api/module-lib-current.txt
@@ -8,7 +8,7 @@
   public class ConnectivityManager {
     method @NonNull @RequiresPermission(anyOf={android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK, android.Manifest.permission.NETWORK_STACK, android.Manifest.permission.NETWORK_SETTINGS}) public java.util.List<android.net.NetworkStateSnapshot> getAllNetworkStateSnapshot();
     method @RequiresPermission(anyOf={android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK, android.Manifest.permission.NETWORK_SETTINGS}) public void registerSystemDefaultNetworkCallback(@NonNull android.net.ConnectivityManager.NetworkCallback, @NonNull android.os.Handler);
-    method @RequiresPermission(anyOf={android.Manifest.permission.NETWORK_SETTINGS, android.Manifest.permission.NETWORK_STACK, android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK}) public void requestBackgroundNetwork(@NonNull android.net.NetworkRequest, @Nullable android.os.Handler, @NonNull android.net.ConnectivityManager.NetworkCallback);
+    method @RequiresPermission(anyOf={android.Manifest.permission.NETWORK_SETTINGS, android.Manifest.permission.NETWORK_STACK, android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK}) public void requestBackgroundNetwork(@NonNull android.net.NetworkRequest, @NonNull android.os.Handler, @NonNull android.net.ConnectivityManager.NetworkCallback);
     method @RequiresPermission(anyOf={android.Manifest.permission.MANAGE_TEST_NETWORKS, android.Manifest.permission.NETWORK_STACK}) public void simulateDataStall(int, long, @NonNull android.net.Network, @NonNull android.os.PersistableBundle);
   }
 
@@ -51,6 +51,14 @@
     field public static final String TEST_TAP_PREFIX = "testtap";
   }
 
+  public final class TestNetworkSpecifier extends android.net.NetworkSpecifier implements android.os.Parcelable {
+    ctor public TestNetworkSpecifier(@NonNull String);
+    method public int describeContents();
+    method @Nullable public String getInterfaceName();
+    method public void writeToParcel(@NonNull android.os.Parcel, int);
+    field @NonNull public static final android.os.Parcelable.Creator<android.net.TestNetworkSpecifier> CREATOR;
+  }
+
   public final class VpnTransportInfo implements android.os.Parcelable android.net.TransportInfo {
     ctor public VpnTransportInfo(int);
     method public int describeContents();
diff --git a/framework/src/android/net/ConnectivityManager.java b/framework/src/android/net/ConnectivityManager.java
index 45ed317..adf22da 100644
--- a/framework/src/android/net/ConnectivityManager.java
+++ b/framework/src/android/net/ConnectivityManager.java
@@ -20,6 +20,7 @@
 import static android.net.NetworkRequest.Type.BACKGROUND_REQUEST;
 import static android.net.NetworkRequest.Type.LISTEN;
 import static android.net.NetworkRequest.Type.REQUEST;
+import static android.net.NetworkRequest.Type.TRACK_BEST;
 import static android.net.NetworkRequest.Type.TRACK_DEFAULT;
 import static android.net.NetworkRequest.Type.TRACK_SYSTEM_DEFAULT;
 import static android.net.QosCallback.QosCallbackRegistrationException;
@@ -4190,6 +4191,18 @@
     }
 
     /**
+     * @hide
+     */
+    // TODO: Make it public api.
+    @SuppressLint("ExecutorRegistration")
+    public void registerBestMatchingNetworkCallback(@NonNull NetworkRequest request,
+            @NonNull NetworkCallback networkCallback, @NonNull Handler handler) {
+        final NetworkCapabilities nc = request.networkCapabilities;
+        final CallbackHandler cbHandler = new CallbackHandler(handler);
+        sendRequestForNetwork(nc, networkCallback, 0, TRACK_BEST, TYPE_NONE, cbHandler);
+    }
+
+    /**
      * Requests bandwidth update for a given {@link Network} and returns whether the update request
      * is accepted by ConnectivityService. Once accepted, ConnectivityService will poll underlying
      * network connection for updated bandwidth information. The caller will be notified via
@@ -4979,10 +4992,10 @@
             NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK
     })
     public void requestBackgroundNetwork(@NonNull NetworkRequest request,
-            @Nullable Handler handler, @NonNull NetworkCallback networkCallback) {
+            @NonNull Handler handler, @NonNull NetworkCallback networkCallback) {
         final NetworkCapabilities nc = request.networkCapabilities;
         sendRequestForNetwork(nc, networkCallback, 0, BACKGROUND_REQUEST,
-                TYPE_NONE, handler == null ? getDefaultHandler() : new CallbackHandler(handler));
+                TYPE_NONE, new CallbackHandler(handler));
     }
 
     /**
diff --git a/framework/src/android/net/NetworkRequest.java b/framework/src/android/net/NetworkRequest.java
index b4a651c..aa69756 100644
--- a/framework/src/android/net/NetworkRequest.java
+++ b/framework/src/android/net/NetworkRequest.java
@@ -31,6 +31,7 @@
 import static android.net.NetworkCapabilities.NET_CAPABILITY_TEMPORARILY_NOT_METERED;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_TRUSTED;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_VALIDATED;
+import static android.net.NetworkCapabilities.TRANSPORT_TEST;
 
 import android.annotation.NonNull;
 import android.annotation.Nullable;
@@ -113,6 +114,10 @@
      *       for the network (if any) that satisfies the default Internet
      *       request.
      *
+     *     - TRACK_BEST, which causes the framework to send callbacks about
+     *       the single, highest scoring current network (if any) that matches
+     *       the specified NetworkCapabilities.
+     *
      *     - BACKGROUND_REQUEST, like REQUEST but does not cause any networks
      *       to retain the NET_CAPABILITY_FOREGROUND capability. A network with
      *       no foreground requests is in the background. A network that has
@@ -135,6 +140,7 @@
         REQUEST,
         BACKGROUND_REQUEST,
         TRACK_SYSTEM_DEFAULT,
+        TRACK_BEST,
     };
 
     /**
@@ -382,11 +388,17 @@
                 return setNetworkSpecifier(new TelephonyNetworkSpecifier.Builder()
                         .setSubscriptionId(subId).build());
             } catch (NumberFormatException nfe) {
-                // A StringNetworkSpecifier does not accept null or empty ("") strings. When network
-                // specifiers were strings a null string and an empty string were considered
-                // equivalent. Hence no meaning is attached to a null or empty ("") string.
-                return setNetworkSpecifier(TextUtils.isEmpty(networkSpecifier) ? null
-                        : new StringNetworkSpecifier(networkSpecifier));
+                // An EthernetNetworkSpecifier or TestNetworkSpecifier does not accept null or empty
+                // ("") strings. When network specifiers were strings a null string and an empty
+                // string were considered equivalent. Hence no meaning is attached to a null or
+                // empty ("") string.
+                if (TextUtils.isEmpty(networkSpecifier)) {
+                    return setNetworkSpecifier((NetworkSpecifier) null);
+                } else if (mNetworkCapabilities.hasTransport(TRANSPORT_TEST)) {
+                    return setNetworkSpecifier(new TestNetworkSpecifier(networkSpecifier));
+                } else {
+                    return setNetworkSpecifier(new EthernetNetworkSpecifier(networkSpecifier));
+                }
             }
         }
 
diff --git a/framework/src/android/net/TestNetworkSpecifier.java b/framework/src/android/net/TestNetworkSpecifier.java
new file mode 100644
index 0000000..b7470a5
--- /dev/null
+++ b/framework/src/android/net/TestNetworkSpecifier.java
@@ -0,0 +1,97 @@
+/*
+ * 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.
+ */
+
+package android.net;
+
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+import android.annotation.SystemApi;
+import android.os.Parcel;
+import android.os.Parcelable;
+import android.text.TextUtils;
+
+import com.android.internal.util.Preconditions;
+
+import java.util.Objects;
+
+/**
+ * A {@link NetworkSpecifier} used to identify test interfaces.
+ *
+ * @see TestNetworkManager
+ * @hide
+ */
+@SystemApi(client = SystemApi.Client.MODULE_LIBRARIES)
+public final class TestNetworkSpecifier extends NetworkSpecifier implements Parcelable {
+
+    /**
+     * Name of the network interface.
+     */
+    @NonNull
+    private final String mInterfaceName;
+
+    public TestNetworkSpecifier(@NonNull String interfaceName) {
+        Preconditions.checkStringNotEmpty(interfaceName);
+        mInterfaceName = interfaceName;
+    }
+
+    // This may be null in the future to support specifiers based on data other than the interface
+    // name.
+    @Nullable
+    public String getInterfaceName() {
+        return mInterfaceName;
+    }
+
+    @Override
+    public boolean canBeSatisfiedBy(@Nullable NetworkSpecifier other) {
+        return equals(other);
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (!(o instanceof TestNetworkSpecifier)) return false;
+        return TextUtils.equals(mInterfaceName, ((TestNetworkSpecifier) o).mInterfaceName);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hashCode(mInterfaceName);
+    }
+
+    @Override
+    public String toString() {
+        return "TestNetworkSpecifier (" + mInterfaceName + ")";
+    }
+
+    @Override
+    public int describeContents() {
+        return 0;
+    }
+
+    @Override
+    public void writeToParcel(@NonNull Parcel dest, int flags) {
+        dest.writeString(mInterfaceName);
+    }
+
+    public static final @NonNull Creator<TestNetworkSpecifier> CREATOR =
+            new Creator<TestNetworkSpecifier>() {
+        public TestNetworkSpecifier createFromParcel(Parcel in) {
+            return new TestNetworkSpecifier(in.readString());
+        }
+        public TestNetworkSpecifier[] newArray(int size) {
+            return new TestNetworkSpecifier[size];
+        }
+    };
+}
diff --git a/services/core/java/com/android/server/ConnectivityService.java b/services/core/java/com/android/server/ConnectivityService.java
index d896130..c363478 100644
--- a/services/core/java/com/android/server/ConnectivityService.java
+++ b/services/core/java/com/android/server/ConnectivityService.java
@@ -175,6 +175,7 @@
 import android.os.UserHandle;
 import android.os.UserManager;
 import android.provider.Settings;
+import android.sysprop.NetworkProperties;
 import android.telephony.TelephonyManager;
 import android.text.TextUtils;
 import android.util.ArrayMap;
@@ -1067,10 +1068,14 @@
          */
         public void reportNetworkInterfaceForTransports(Context context, String iface,
                 int[] transportTypes) {
-            final BatteryStatsManager  batteryStats =
+            final BatteryStatsManager batteryStats =
                     context.getSystemService(BatteryStatsManager.class);
             batteryStats.reportNetworkInterfaceForTransports(iface, transportTypes);
         }
+
+        public boolean getCellular464XlatEnabled() {
+            return NetworkProperties.isCellular464XlatEnabled().orElse(true);
+        }
     }
 
     public ConnectivityService(Context context) {
@@ -1269,8 +1274,7 @@
                 new NetworkInfo(TYPE_NONE, 0, "", ""),
                 new LinkProperties(), new NetworkCapabilities(), 0, mContext,
                 null, new NetworkAgentConfig(), this, null,
-                null, 0, INVALID_UID,
-                mQosCallbackTracker);
+                null, 0, INVALID_UID, mQosCallbackTracker, mDeps);
     }
 
     private static NetworkCapabilities createDefaultNetworkCapabilitiesForUid(int uid) {
@@ -5501,6 +5505,8 @@
                 //  request if the app changes network state. http://b/29964605
                 enforceMeteredApnPolicy(networkCapabilities);
                 break;
+            case TRACK_BEST:
+                throw new UnsupportedOperationException("Not implemented yet");
             default:
                 throw new IllegalArgumentException("Unsupported request type " + reqType);
         }
@@ -6105,7 +6111,7 @@
         final NetworkAgentInfo nai = new NetworkAgentInfo(na,
                 new Network(mNetIdManager.reserveNetId()), new NetworkInfo(networkInfo), lp, nc,
                 currentScore, mContext, mTrackerHandler, new NetworkAgentConfig(networkAgentConfig),
-                this, mNetd, mDnsResolver, providerId, uid, mQosCallbackTracker);
+                this, mNetd, mDnsResolver, providerId, uid, mQosCallbackTracker, mDeps);
 
         // Make sure the LinkProperties and NetworkCapabilities reflect what the agent info says.
         processCapabilitiesFromAgent(nai, nc);
diff --git a/services/core/java/com/android/server/TestNetworkService.java b/services/core/java/com/android/server/TestNetworkService.java
index 55408ea..ee61067 100644
--- a/services/core/java/com/android/server/TestNetworkService.java
+++ b/services/core/java/com/android/server/TestNetworkService.java
@@ -33,8 +33,8 @@
 import android.net.NetworkCapabilities;
 import android.net.NetworkProvider;
 import android.net.RouteInfo;
-import android.net.StringNetworkSpecifier;
 import android.net.TestNetworkInterface;
+import android.net.TestNetworkSpecifier;
 import android.net.util.NetdService;
 import android.os.Binder;
 import android.os.Handler;
@@ -242,7 +242,7 @@
         nc.addCapability(NetworkCapabilities.NET_CAPABILITY_NOT_SUSPENDED);
         nc.addCapability(NetworkCapabilities.NET_CAPABILITY_NOT_RESTRICTED);
         nc.addCapability(NetworkCapabilities.NET_CAPABILITY_NOT_VCN_MANAGED);
-        nc.setNetworkSpecifier(new StringNetworkSpecifier(iface));
+        nc.setNetworkSpecifier(new TestNetworkSpecifier(iface));
         nc.setAdministratorUids(administratorUids);
         if (!isMetered) {
             nc.addCapability(NetworkCapabilities.NET_CAPABILITY_NOT_METERED);
diff --git a/services/core/java/com/android/server/connectivity/Nat464Xlat.java b/services/core/java/com/android/server/connectivity/Nat464Xlat.java
index fa80b25..c66a280 100644
--- a/services/core/java/com/android/server/connectivity/Nat464Xlat.java
+++ b/services/core/java/com/android/server/connectivity/Nat464Xlat.java
@@ -16,6 +16,8 @@
 
 package com.android.server.connectivity;
 
+import static android.net.NetworkCapabilities.TRANSPORT_CELLULAR;
+
 import static com.android.net.module.util.CollectionUtils.contains;
 
 import android.annotation.NonNull;
@@ -35,6 +37,7 @@
 
 import com.android.internal.annotations.VisibleForTesting;
 import com.android.net.module.util.NetworkStackConstants;
+import com.android.server.ConnectivityService;
 
 import java.net.Inet6Address;
 import java.util.Objects;
@@ -94,12 +97,15 @@
     private Inet6Address mIPv6Address;
     private State mState = State.IDLE;
 
+    private boolean mEnableClatOnCellular;
     private boolean mPrefixDiscoveryRunning;
 
-    public Nat464Xlat(NetworkAgentInfo nai, INetd netd, IDnsResolver dnsResolver) {
+    public Nat464Xlat(NetworkAgentInfo nai, INetd netd, IDnsResolver dnsResolver,
+            ConnectivityService.Dependencies deps) {
         mDnsResolver = dnsResolver;
         mNetd = netd;
         mNetwork = nai;
+        mEnableClatOnCellular = deps.getCellular464XlatEnabled();
     }
 
     /**
@@ -111,7 +117,7 @@
      * @return true if the network requires clat, false otherwise.
      */
     @VisibleForTesting
-    protected static boolean requiresClat(NetworkAgentInfo nai) {
+    protected boolean requiresClat(NetworkAgentInfo nai) {
         // TODO: migrate to NetworkCapabilities.TRANSPORT_*.
         final boolean supported = contains(NETWORK_TYPES, nai.networkInfo.getType());
         final boolean connected = contains(NETWORK_STATES, nai.networkInfo.getState());
@@ -126,7 +132,9 @@
         final boolean skip464xlat = (nai.netAgentConfig() != null)
                 && nai.netAgentConfig().skip464xlat;
 
-        return supported && connected && isIpv6OnlyNetwork && !skip464xlat;
+        return supported && connected && isIpv6OnlyNetwork && !skip464xlat
+            && (nai.networkCapabilities.hasTransport(TRANSPORT_CELLULAR)
+                ? isCellular464XlatEnabled() : true);
     }
 
     /**
@@ -137,7 +145,7 @@
      * @return true if the network should start clat, false otherwise.
      */
     @VisibleForTesting
-    protected static boolean shouldStartClat(NetworkAgentInfo nai) {
+    protected boolean shouldStartClat(NetworkAgentInfo nai) {
         LinkProperties lp = nai.linkProperties;
         return requiresClat(nai) && lp != null && lp.getNat64Prefix() != null;
     }
@@ -507,4 +515,9 @@
     protected int getNetId() {
         return mNetwork.network.getNetId();
     }
+
+    @VisibleForTesting
+    protected boolean isCellular464XlatEnabled() {
+        return mEnableClatOnCellular;
+    }
 }
diff --git a/services/core/java/com/android/server/connectivity/NetworkAgentInfo.java b/services/core/java/com/android/server/connectivity/NetworkAgentInfo.java
index 1d0e115..803cc9d 100644
--- a/services/core/java/com/android/server/connectivity/NetworkAgentInfo.java
+++ b/services/core/java/com/android/server/connectivity/NetworkAgentInfo.java
@@ -341,7 +341,7 @@
             @NonNull LinkProperties lp, @NonNull NetworkCapabilities nc, int score, Context context,
             Handler handler, NetworkAgentConfig config, ConnectivityService connService, INetd netd,
             IDnsResolver dnsResolver, int factorySerialNumber, int creatorUid,
-            QosCallbackTracker qosCallbackTracker) {
+            QosCallbackTracker qosCallbackTracker, ConnectivityService.Dependencies deps) {
         Objects.requireNonNull(net);
         Objects.requireNonNull(info);
         Objects.requireNonNull(lp);
@@ -355,7 +355,7 @@
         linkProperties = lp;
         networkCapabilities = nc;
         mScore = score;
-        clatd = new Nat464Xlat(this, netd, dnsResolver);
+        clatd = new Nat464Xlat(this, netd, dnsResolver, deps);
         mConnService = connService;
         mContext = context;
         mHandler = handler;
diff --git a/tests/net/common/java/android/net/NetworkCapabilitiesTest.java b/tests/net/common/java/android/net/NetworkCapabilitiesTest.java
index 5d0e016..e84b992 100644
--- a/tests/net/common/java/android/net/NetworkCapabilitiesTest.java
+++ b/tests/net/common/java/android/net/NetworkCapabilitiesTest.java
@@ -68,6 +68,7 @@
 import androidx.test.runner.AndroidJUnit4;
 
 import com.android.modules.utils.build.SdkLevel;
+import com.android.testutils.CompatUtil;
 import com.android.testutils.DevSdkIgnoreRule;
 import com.android.testutils.DevSdkIgnoreRule.IgnoreUpTo;
 
@@ -211,7 +212,7 @@
         nc1 = new NetworkCapabilities().addTransportType(TRANSPORT_WIFI);
         nc2 = new NetworkCapabilities()
                 .addTransportType(TRANSPORT_WIFI)
-                .setNetworkSpecifier(new StringNetworkSpecifier("specs"));
+                .setNetworkSpecifier(CompatUtil.makeEthernetNetworkSpecifier("eth42"));
         assertNotEquals("", nc1.describeImmutableDifferences(nc2));
         assertEquals("", nc1.describeImmutableDifferences(nc1));
     }
@@ -671,7 +672,7 @@
         NetworkCapabilities nc1 = new NetworkCapabilities();
         nc1.addTransportType(TRANSPORT_CELLULAR).addTransportType(TRANSPORT_WIFI);
         try {
-            nc1.setNetworkSpecifier(new StringNetworkSpecifier("specs"));
+            nc1.setNetworkSpecifier(CompatUtil.makeEthernetNetworkSpecifier("eth0"));
             fail("Cannot set NetworkSpecifier on a NetworkCapability with multiple transports!");
         } catch (IllegalStateException expected) {
             // empty
@@ -680,7 +681,7 @@
         // Sequence 2: Transport + NetworkSpecifier + Transport
         NetworkCapabilities nc2 = new NetworkCapabilities();
         nc2.addTransportType(TRANSPORT_CELLULAR).setNetworkSpecifier(
-                new StringNetworkSpecifier("specs"));
+                CompatUtil.makeEthernetNetworkSpecifier("testtap3"));
         try {
             nc2.addTransportType(TRANSPORT_WIFI);
             fail("Cannot set a second TransportType of a network which has a NetworkSpecifier!");
diff --git a/tests/net/common/java/android/net/NetworkProviderTest.kt b/tests/net/common/java/android/net/NetworkProviderTest.kt
index bcc9072..340e6f9 100644
--- a/tests/net/common/java/android/net/NetworkProviderTest.kt
+++ b/tests/net/common/java/android/net/NetworkProviderTest.kt
@@ -27,6 +27,7 @@
 import android.os.Looper
 import androidx.test.InstrumentationRegistry
 import com.android.net.module.util.ArrayTrackRecord
+import com.android.testutils.CompatUtil
 import com.android.testutils.DevSdkIgnoreRule.IgnoreUpTo
 import com.android.testutils.DevSdkIgnoreRunner
 import com.android.testutils.isDevSdkInRange
@@ -102,7 +103,8 @@
         mCm.registerNetworkProvider(provider)
         assertNotEquals(provider.getProviderId(), NetworkProvider.ID_NONE)
 
-        val specifier = StringNetworkSpecifier(UUID.randomUUID().toString())
+        val specifier = CompatUtil.makeTestNetworkSpecifier(
+                UUID.randomUUID().toString())
         val nr: NetworkRequest = NetworkRequest.Builder()
                 .addTransportType(TRANSPORT_TEST)
                 .setNetworkSpecifier(specifier)
@@ -183,7 +185,8 @@
 
         mCm.registerNetworkProvider(provider)
 
-        val specifier = StringNetworkSpecifier(UUID.randomUUID().toString())
+        val specifier = CompatUtil.makeTestNetworkSpecifier(
+                UUID.randomUUID().toString())
         val nr: NetworkRequest = NetworkRequest.Builder()
                 .addTransportType(TRANSPORT_TEST)
                 .setNetworkSpecifier(specifier)
diff --git a/tests/net/java/android/net/ConnectivityManagerTest.java b/tests/net/java/android/net/ConnectivityManagerTest.java
index 6a09b02..098b029 100644
--- a/tests/net/java/android/net/ConnectivityManagerTest.java
+++ b/tests/net/java/android/net/ConnectivityManagerTest.java
@@ -376,13 +376,13 @@
                 eq(testPkgName), eq(testAttributionTag));
         reset(mService);
 
-        manager.requestBackgroundNetwork(request, null, callback);
+        Handler handler = new Handler(ConnectivityThread.getInstanceLooper());
+        manager.requestBackgroundNetwork(request, handler, callback);
         verify(mService).requestNetwork(eq(request.networkCapabilities),
                 eq(BACKGROUND_REQUEST.ordinal()), any(), anyInt(), any(), eq(TYPE_NONE),
                 eq(testPkgName), eq(testAttributionTag));
         reset(mService);
 
-        Handler handler = new Handler(ConnectivityThread.getInstanceLooper());
         manager.registerSystemDefaultNetworkCallback(callback, handler);
         verify(mService).requestNetwork(eq(null),
                 eq(TRACK_SYSTEM_DEFAULT.ordinal()), any(), anyInt(), any(), eq(TYPE_NONE),
diff --git a/tests/net/java/com/android/server/ConnectivityServiceTest.java b/tests/net/java/com/android/server/ConnectivityServiceTest.java
index d2ea577..a6b20fb 100644
--- a/tests/net/java/com/android/server/ConnectivityServiceTest.java
+++ b/tests/net/java/com/android/server/ConnectivityServiceTest.java
@@ -1530,6 +1530,7 @@
                     inv.getArgument(0), inv.getArgument(1), inv.getArgument(2));
             return mPolicyTracker;
         }).when(deps).makeMultinetworkPolicyTracker(any(), any(), any());
+        doReturn(true).when(deps).getCellular464XlatEnabled();
 
         return deps;
     }
@@ -4026,7 +4027,8 @@
         grantUsingBackgroundNetworksPermissionForUid(Binder.getCallingUid());
         final TestNetworkCallback cellBgCallback = new TestNetworkCallback();
         mCm.requestBackgroundNetwork(new NetworkRequest.Builder()
-                .addTransportType(TRANSPORT_CELLULAR).build(), null, cellBgCallback);
+                .addTransportType(TRANSPORT_CELLULAR).build(),
+                mCsHandlerThread.getThreadHandler(), cellBgCallback);
 
         // Make callbacks for monitoring.
         final NetworkRequest request = new NetworkRequest.Builder().build();
@@ -8324,6 +8326,45 @@
     }
 
     @Test
+    public void testWith464XlatDisable() throws Exception {
+        doReturn(false).when(mDeps).getCellular464XlatEnabled();
+
+        final TestNetworkCallback callback = new TestNetworkCallback();
+        final TestNetworkCallback defaultCallback = new TestNetworkCallback();
+        final NetworkRequest networkRequest = new NetworkRequest.Builder()
+                .addCapability(NET_CAPABILITY_INTERNET)
+                .build();
+        mCm.registerNetworkCallback(networkRequest, callback);
+        mCm.registerDefaultNetworkCallback(defaultCallback);
+
+        // Bring up validated cell.
+        final LinkProperties cellLp = new LinkProperties();
+        cellLp.setInterfaceName(MOBILE_IFNAME);
+        cellLp.addLinkAddress(new LinkAddress("2001:db8:1::1/64"));
+        cellLp.addRoute(new RouteInfo(new IpPrefix("::/0"), null, MOBILE_IFNAME));
+        mCellNetworkAgent = new TestNetworkAgentWrapper(TRANSPORT_CELLULAR);
+
+        mCellNetworkAgent.sendLinkProperties(cellLp);
+        mCellNetworkAgent.connect(true);
+        callback.expectAvailableThenValidatedCallbacks(mCellNetworkAgent);
+        defaultCallback.expectAvailableThenValidatedCallbacks(mCellNetworkAgent);
+        final int cellNetId = mCellNetworkAgent.getNetwork().netId;
+        waitForIdle();
+
+        verify(mMockDnsResolver, never()).startPrefix64Discovery(cellNetId);
+        Nat464Xlat clat = getNat464Xlat(mCellNetworkAgent);
+        assertTrue("Nat464Xlat was not IDLE", !clat.isStarted());
+
+        // This cannot happen because prefix discovery cannot succeed if it is never started.
+        mService.mResolverUnsolEventCallback.onNat64PrefixEvent(
+                makeNat64PrefixEvent(cellNetId, PREFIX_OPERATION_ADDED, "64:ff9b::", 96));
+
+        // ... but still, check that even if it did, clatd would not be started.
+        verify(mMockNetd, never()).clatdStart(anyString(), anyString());
+        assertTrue("Nat464Xlat was not IDLE", !clat.isStarted());
+    }
+
+    @Test
     public void testDataActivityTracking() throws Exception {
         final TestNetworkCallback networkCallback = new TestNetworkCallback();
         final NetworkRequest networkRequest = new NetworkRequest.Builder()
@@ -9029,7 +9070,7 @@
                 TelephonyManager.getNetworkTypeName(TelephonyManager.NETWORK_TYPE_LTE));
         return new NetworkAgentInfo(null, new Network(NET_ID), info, new LinkProperties(),
                 nc, 0, mServiceContext, null, new NetworkAgentConfig(), mService, null, null, 0,
-                INVALID_UID, mQosCallbackTracker);
+                INVALID_UID, mQosCallbackTracker, new ConnectivityService.Dependencies());
     }
 
     @Test
@@ -10986,4 +11027,12 @@
         verifyNoNetwork();
         mCm.unregisterNetworkCallback(cellCb);
     }
+
+    @Test
+    public void testRegisterBestMatchingNetworkCallback() throws Exception {
+        final NetworkRequest request = new NetworkRequest.Builder().build();
+        assertThrows(UnsupportedOperationException.class,
+                () -> mCm.registerBestMatchingNetworkCallback(request, new NetworkCallback(),
+                        mCsHandlerThread.getThreadHandler()));
+    }
 }
diff --git a/tests/net/java/com/android/server/connectivity/LingerMonitorTest.java b/tests/net/java/com/android/server/connectivity/LingerMonitorTest.java
index a913673..1c0ba4f 100644
--- a/tests/net/java/com/android/server/connectivity/LingerMonitorTest.java
+++ b/tests/net/java/com/android/server/connectivity/LingerMonitorTest.java
@@ -357,7 +357,7 @@
         NetworkAgentInfo nai = new NetworkAgentInfo(null, new Network(netId), info,
                 new LinkProperties(), caps, 50, mCtx, null, new NetworkAgentConfig() /* config */,
                 mConnService, mNetd, mDnsResolver, NetworkProvider.ID_NONE, Binder.getCallingUid(),
-                mQosCallbackTracker);
+                mQosCallbackTracker, new ConnectivityService.Dependencies());
         nai.everValidated = true;
         return nai;
     }
diff --git a/tests/net/java/com/android/server/connectivity/MultipathPolicyTrackerTest.java b/tests/net/java/com/android/server/connectivity/MultipathPolicyTrackerTest.java
index 950d716..38f6d7f 100644
--- a/tests/net/java/com/android/server/connectivity/MultipathPolicyTrackerTest.java
+++ b/tests/net/java/com/android/server/connectivity/MultipathPolicyTrackerTest.java
@@ -46,12 +46,12 @@
 import android.content.pm.ApplicationInfo;
 import android.content.res.Resources;
 import android.net.ConnectivityManager;
+import android.net.EthernetNetworkSpecifier;
 import android.net.Network;
 import android.net.NetworkCapabilities;
 import android.net.NetworkPolicy;
 import android.net.NetworkPolicyManager;
 import android.net.NetworkTemplate;
-import android.net.StringNetworkSpecifier;
 import android.net.TelephonyNetworkSpecifier;
 import android.os.Handler;
 import android.os.UserHandle;
@@ -240,7 +240,7 @@
         NetworkCapabilities capabilities = new NetworkCapabilities()
                 .addCapability(NET_CAPABILITY_INTERNET)
                 .addTransportType(TRANSPORT_CELLULAR)
-                .setNetworkSpecifier(new StringNetworkSpecifier("234"));
+                .setNetworkSpecifier(new EthernetNetworkSpecifier("eth234"));
         if (!roaming) {
             capabilities.addCapability(NET_CAPABILITY_NOT_ROAMING);
         }
diff --git a/tests/net/java/com/android/server/connectivity/Nat464XlatTest.java b/tests/net/java/com/android/server/connectivity/Nat464XlatTest.java
index 5f56e25..9b2a638 100644
--- a/tests/net/java/com/android/server/connectivity/Nat464XlatTest.java
+++ b/tests/net/java/com/android/server/connectivity/Nat464XlatTest.java
@@ -16,11 +16,15 @@
 
 package com.android.server.connectivity;
 
+import static android.net.NetworkCapabilities.TRANSPORT_CELLULAR;
+
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.anyString;
 import static org.mockito.Mockito.eq;
 import static org.mockito.Mockito.inOrder;
+import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyNoMoreInteractions;
@@ -34,6 +38,7 @@
 import android.net.LinkAddress;
 import android.net.LinkProperties;
 import android.net.NetworkAgentConfig;
+import android.net.NetworkCapabilities;
 import android.net.NetworkInfo;
 import android.os.Handler;
 import android.os.test.TestLooper;
@@ -72,11 +77,15 @@
     Handler mHandler;
     NetworkAgentConfig mAgentConfig = new NetworkAgentConfig();
 
-    Nat464Xlat makeNat464Xlat() {
-        return new Nat464Xlat(mNai, mNetd, mDnsResolver) {
+    Nat464Xlat makeNat464Xlat(boolean isCellular464XlatEnabled) {
+        return new Nat464Xlat(mNai, mNetd, mDnsResolver, new ConnectivityService.Dependencies()) {
             @Override protected int getNetId() {
                 return NETID;
             }
+
+            @Override protected boolean isCellular464XlatEnabled() {
+                return isCellular464XlatEnabled;
+            }
         };
     }
 
@@ -99,6 +108,7 @@
         mNai.linkProperties.setInterfaceName(BASE_IFACE);
         mNai.networkInfo = new NetworkInfo(null);
         mNai.networkInfo.setType(ConnectivityManager.TYPE_WIFI);
+        mNai.networkCapabilities = new NetworkCapabilities();
         markNetworkConnected();
         when(mNai.connService()).thenReturn(mConnectivity);
         when(mNai.netAgentConfig()).thenReturn(mAgentConfig);
@@ -110,21 +120,23 @@
     }
 
     private void assertRequiresClat(boolean expected, NetworkAgentInfo nai) {
+        Nat464Xlat nat = makeNat464Xlat(true);
         String msg = String.format("requiresClat expected %b for type=%d state=%s skip=%b "
                 + "nat64Prefix=%s addresses=%s", expected, nai.networkInfo.getType(),
                 nai.networkInfo.getDetailedState(),
                 mAgentConfig.skip464xlat, nai.linkProperties.getNat64Prefix(),
                 nai.linkProperties.getLinkAddresses());
-        assertEquals(msg, expected, Nat464Xlat.requiresClat(nai));
+        assertEquals(msg, expected, nat.requiresClat(nai));
     }
 
     private void assertShouldStartClat(boolean expected, NetworkAgentInfo nai) {
+        Nat464Xlat nat = makeNat464Xlat(true);
         String msg = String.format("shouldStartClat expected %b for type=%d state=%s skip=%b "
                 + "nat64Prefix=%s addresses=%s", expected, nai.networkInfo.getType(),
                 nai.networkInfo.getDetailedState(),
                 mAgentConfig.skip464xlat, nai.linkProperties.getNat64Prefix(),
                 nai.linkProperties.getLinkAddresses());
-        assertEquals(msg, expected, Nat464Xlat.shouldStartClat(nai));
+        assertEquals(msg, expected, nat.shouldStartClat(nai));
     }
 
     @Test
@@ -194,7 +206,7 @@
     }
 
     private void checkNormalStartAndStop(boolean dueToDisconnect) throws Exception {
-        Nat464Xlat nat = makeNat464Xlat();
+        Nat464Xlat nat = makeNat464Xlat(true);
         ArgumentCaptor<LinkProperties> c = ArgumentCaptor.forClass(LinkProperties.class);
 
         mNai.linkProperties.addLinkAddress(V6ADDR);
@@ -245,7 +257,7 @@
     }
 
     private void checkStartStopStart(boolean interfaceRemovedFirst) throws Exception {
-        Nat464Xlat nat = makeNat464Xlat();
+        Nat464Xlat nat = makeNat464Xlat(true);
         ArgumentCaptor<LinkProperties> c = ArgumentCaptor.forClass(LinkProperties.class);
         InOrder inOrder = inOrder(mNetd, mConnectivity);
 
@@ -335,7 +347,7 @@
 
     @Test
     public void testClatdCrashWhileRunning() throws Exception {
-        Nat464Xlat nat = makeNat464Xlat();
+        Nat464Xlat nat = makeNat464Xlat(true);
         ArgumentCaptor<LinkProperties> c = ArgumentCaptor.forClass(LinkProperties.class);
 
         nat.setNat64PrefixFromDns(new IpPrefix(NAT64_PREFIX));
@@ -372,7 +384,7 @@
     }
 
     private void checkStopBeforeClatdStarts(boolean dueToDisconnect) throws Exception {
-        Nat464Xlat nat = makeNat464Xlat();
+        Nat464Xlat nat = makeNat464Xlat(true);
 
         mNai.linkProperties.addLinkAddress(new LinkAddress("2001:db8::1/64"));
 
@@ -414,7 +426,7 @@
     }
 
     private void checkStopAndClatdNeverStarts(boolean dueToDisconnect) throws Exception {
-        Nat464Xlat nat = makeNat464Xlat();
+        Nat464Xlat nat = makeNat464Xlat(true);
 
         mNai.linkProperties.addLinkAddress(new LinkAddress("2001:db8::1/64"));
 
@@ -450,7 +462,7 @@
         final IpPrefix prefixFromDns = new IpPrefix(NAT64_PREFIX);
         final IpPrefix prefixFromRa = new IpPrefix(OTHER_NAT64_PREFIX);
 
-        Nat464Xlat nat = makeNat464Xlat();
+        Nat464Xlat nat = makeNat464Xlat(true);
 
         final LinkProperties emptyLp = new LinkProperties();
         LinkProperties fixedupLp;
@@ -486,10 +498,57 @@
         assertEquals(null, fixedupLp.getNat64Prefix());
     }
 
+    private void checkClatDisabledOnCellular(boolean onCellular) throws Exception {
+        // Disable 464xlat on cellular networks.
+        Nat464Xlat nat = makeNat464Xlat(false);
+        mNai.linkProperties.addLinkAddress(V6ADDR);
+        mNai.networkCapabilities.setTransportType(TRANSPORT_CELLULAR, onCellular);
+        nat.update();
+
+        final IpPrefix nat64Prefix = new IpPrefix(NAT64_PREFIX);
+        if (onCellular) {
+            // Prefix discovery is never started.
+            verify(mDnsResolver, never()).startPrefix64Discovery(eq(NETID));
+            assertIdle(nat);
+
+            // If a NAT64 prefix comes in from an RA, clat is not started either.
+            mNai.linkProperties.setNat64Prefix(nat64Prefix);
+            nat.setNat64PrefixFromRa(nat64Prefix);
+            nat.update();
+            verify(mNetd, never()).clatdStart(anyString(), anyString());
+            assertIdle(nat);
+        } else {
+            // Prefix discovery is started.
+            verify(mDnsResolver).startPrefix64Discovery(eq(NETID));
+            assertIdle(nat);
+
+            // If a NAT64 prefix comes in from an RA, clat is started.
+            mNai.linkProperties.setNat64Prefix(nat64Prefix);
+            nat.setNat64PrefixFromRa(nat64Prefix);
+            nat.update();
+            verify(mNetd).clatdStart(BASE_IFACE, NAT64_PREFIX);
+            assertStarting(nat);
+        }
+    }
+
+    @Test
+    public void testClatDisabledOnCellular() throws Exception {
+        checkClatDisabledOnCellular(true);
+    }
+
+    @Test
+    public void testClatDisabledOnNonCellular() throws Exception {
+        checkClatDisabledOnCellular(false);
+    }
+
     static void assertIdle(Nat464Xlat nat) {
         assertTrue("Nat464Xlat was not IDLE", !nat.isStarted());
     }
 
+    static void assertStarting(Nat464Xlat nat) {
+        assertTrue("Nat464Xlat was not STARTING", nat.isStarting());
+    }
+
     static void assertRunning(Nat464Xlat nat) {
         assertTrue("Nat464Xlat was not RUNNING", nat.isRunning());
     }