diff --git a/Tethering/Android.bp b/Tethering/Android.bp
index 60c1f2b..495c9d7 100644
--- a/Tethering/Android.bp
+++ b/Tethering/Android.bp
@@ -41,6 +41,7 @@
         "net-utils-device-common",
         "net-utils-device-common-netlink",
         "netd-client",
+        "NetworkStackApiCurrentShims",
     ],
     libs: [
         "framework-connectivity",
diff --git a/Tethering/common/TetheringLib/Android.bp b/Tethering/common/TetheringLib/Android.bp
index f652772..6e64570 100644
--- a/Tethering/common/TetheringLib/Android.bp
+++ b/Tethering/common/TetheringLib/Android.bp
@@ -22,7 +22,19 @@
     defaults: ["framework-module-defaults"],
     impl_library_visibility: [
         "//packages/modules/Connectivity/Tethering:__subpackages__",
+
+        // Using for test only
+        "//cts/tests/netlegacy22.api",
+        "//external/sl4a:__subpackages__",
+        "//frameworks/base/packages/Connectivity/tests:__subpackages__",
+        "//frameworks/libs/net/common/testutils",
+        "//frameworks/libs/net/common/tests:__subpackages__",
+        "//frameworks/opt/telephony/tests/telephonytests",
+        "//packages/modules/CaptivePortalLogin/tests",
+        "//packages/modules/Connectivity/Tethering/tests:__subpackages__",
         "//packages/modules/Connectivity/tests:__subpackages__",
+        "//packages/modules/NetworkStack/tests:__subpackages__",
+        "//packages/modules/Wifi/service/tests/wifitests",
     ],
 
     srcs: [":framework-tethering-srcs"],
diff --git a/Tethering/common/TetheringLib/src/android/net/ITetheringConnector.aidl b/Tethering/common/TetheringLib/src/android/net/ITetheringConnector.aidl
index cf094aa..77e78bd 100644
--- a/Tethering/common/TetheringLib/src/android/net/ITetheringConnector.aidl
+++ b/Tethering/common/TetheringLib/src/android/net/ITetheringConnector.aidl
@@ -49,4 +49,6 @@
 
     void stopAllTethering(String callerPkg, String callingAttributionTag,
             IIntResultListener receiver);
+
+    void setPreferTestNetworks(boolean prefer, IIntResultListener listener);
 }
diff --git a/Tethering/common/TetheringLib/src/android/net/TetheringManager.java b/Tethering/common/TetheringLib/src/android/net/TetheringManager.java
index 73ab908..65b2650 100644
--- a/Tethering/common/TetheringLib/src/android/net/TetheringManager.java
+++ b/Tethering/common/TetheringLib/src/android/net/TetheringManager.java
@@ -1538,4 +1538,25 @@
                     }
                 }));
     }
+
+    /**
+     * Whether to treat networks that have TRANSPORT_TEST as Tethering upstreams. The effects of
+     * this method apply to any test networks that are already present on the system.
+     *
+     * @throws SecurityException If the caller doesn't have the NETWORK_SETTINGS permission.
+     * @hide
+     */
+    @RequiresPermission(android.Manifest.permission.NETWORK_SETTINGS)
+    public void setPreferTestNetworks(final boolean prefer) {
+        Log.i(TAG, "setPreferTestNetworks caller: " + mContext.getOpPackageName());
+
+        final RequestDispatcher dispatcher = new RequestDispatcher();
+        final int ret = dispatcher.waitForResult((connector, listener) -> {
+            try {
+                connector.setPreferTestNetworks(prefer, listener);
+            } catch (RemoteException e) {
+                throw new IllegalStateException(e);
+            }
+        });
+    }
 }
diff --git a/Tethering/src/com/android/networkstack/tethering/Tethering.java b/Tethering/src/com/android/networkstack/tethering/Tethering.java
index 08170f9..1559f3b 100644
--- a/Tethering/src/com/android/networkstack/tethering/Tethering.java
+++ b/Tethering/src/com/android/networkstack/tethering/Tethering.java
@@ -2601,4 +2601,13 @@
     private static String[] copy(String[] strarray) {
         return Arrays.copyOf(strarray, strarray.length);
     }
+
+    void setPreferTestNetworks(final boolean prefer, IIntResultListener listener) {
+        mHandler.post(() -> {
+            mUpstreamNetworkMonitor.setPreferTestNetworks(prefer);
+            try {
+                listener.onResult(TETHER_ERROR_NO_ERROR);
+            } catch (RemoteException e) { }
+        });
+    }
 }
diff --git a/Tethering/src/com/android/networkstack/tethering/TetheringInterfaceUtils.java b/Tethering/src/com/android/networkstack/tethering/TetheringInterfaceUtils.java
index ff38f71..d0a1ac3 100644
--- a/Tethering/src/com/android/networkstack/tethering/TetheringInterfaceUtils.java
+++ b/Tethering/src/com/android/networkstack/tethering/TetheringInterfaceUtils.java
@@ -16,6 +16,10 @@
 
 package com.android.networkstack.tethering;
 
+import static android.net.NetworkCapabilities.TRANSPORT_CELLULAR;
+import static android.net.NetworkCapabilities.TRANSPORT_TEST;
+
+import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.net.LinkProperties;
 import android.net.NetworkCapabilities;
@@ -78,13 +82,17 @@
                 // Minimal amount of IPv6 provisioning:
                 && ns.linkProperties.hasGlobalIpv6Address()
                 // Temporary approximation of "dedicated prefix":
-                && ns.networkCapabilities.hasTransport(NetworkCapabilities.TRANSPORT_CELLULAR);
+                && allowIpv6Tethering(ns.networkCapabilities);
 
         return canTether
                 ? getInterfaceForDestination(ns.linkProperties, IN6ADDR_ANY)
                 : null;
     }
 
+    private static boolean allowIpv6Tethering(@NonNull final NetworkCapabilities nc) {
+        return nc.hasTransport(TRANSPORT_CELLULAR) || nc.hasTransport(TRANSPORT_TEST);
+    }
+
     private static String getInterfaceForDestination(LinkProperties lp, InetAddress dst) {
         final RouteInfo ri = (lp != null)
                 ? NetUtils.selectBestRoute(lp.getAllRoutes(), dst)
diff --git a/Tethering/src/com/android/networkstack/tethering/TetheringService.java b/Tethering/src/com/android/networkstack/tethering/TetheringService.java
index 5ab3401..175b480 100644
--- a/Tethering/src/com/android/networkstack/tethering/TetheringService.java
+++ b/Tethering/src/com/android/networkstack/tethering/TetheringService.java
@@ -17,6 +17,7 @@
 package com.android.networkstack.tethering;
 
 import static android.Manifest.permission.ACCESS_NETWORK_STATE;
+import static android.Manifest.permission.NETWORK_SETTINGS;
 import static android.Manifest.permission.NETWORK_STACK;
 import static android.Manifest.permission.TETHER_PRIVILEGED;
 import static android.content.pm.PackageManager.PERMISSION_GRANTED;
@@ -46,13 +47,14 @@
 import android.os.Looper;
 import android.os.RemoteException;
 import android.os.ResultReceiver;
-import android.provider.Settings;
 import android.util.Log;
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 
 import com.android.internal.annotations.VisibleForTesting;
+import com.android.networkstack.apishim.SettingsShimImpl;
+import com.android.networkstack.apishim.common.SettingsShim;
 
 import java.io.FileDescriptor;
 import java.io.PrintWriter;
@@ -66,6 +68,7 @@
     private static final String TAG = TetheringService.class.getSimpleName();
 
     private TetheringConnector mConnector;
+    private SettingsShim mSettingsShim;
 
     @Override
     public void onCreate() {
@@ -73,6 +76,8 @@
         // The Tethering object needs a fully functional context to start, so this can't be done
         // in the constructor.
         mConnector = new TetheringConnector(makeTethering(deps), TetheringService.this);
+
+        mSettingsShim = SettingsShimImpl.newInstance();
     }
 
     /**
@@ -199,6 +204,17 @@
             } catch (RemoteException e) { }
         }
 
+        public void setPreferTestNetworks(boolean prefer, IIntResultListener listener) {
+            if (!checkCallingOrSelfPermission(NETWORK_SETTINGS)) {
+                try {
+                    listener.onResult(TETHER_ERROR_NO_CHANGE_TETHERING_PERMISSION);
+                } catch (RemoteException e) { }
+                return;
+            }
+
+            mTethering.setPreferTestNetworks(prefer, listener);
+        }
+
         @Override
         protected void dump(@NonNull FileDescriptor fd, @NonNull PrintWriter writer,
                     @Nullable String[] args) {
@@ -294,8 +310,8 @@
     boolean checkAndNoteWriteSettingsOperation(@NonNull Context context, int uid,
             @NonNull String callingPackage, @Nullable String callingAttributionTag,
             boolean throwException) {
-        return Settings.checkAndNoteWriteSettingsOperation(context, uid, callingPackage,
-                throwException);
+        return mSettingsShim.checkAndNoteWriteSettingsOperation(context, uid, callingPackage,
+                callingAttributionTag, throwException);
     }
 
     /**
diff --git a/Tethering/src/com/android/networkstack/tethering/UpstreamNetworkMonitor.java b/Tethering/src/com/android/networkstack/tethering/UpstreamNetworkMonitor.java
index 5584db2..5a86b84 100644
--- a/Tethering/src/com/android/networkstack/tethering/UpstreamNetworkMonitor.java
+++ b/Tethering/src/com/android/networkstack/tethering/UpstreamNetworkMonitor.java
@@ -135,6 +135,7 @@
     private Network mDefaultInternetNetwork;
     // The current upstream network used for tethering.
     private Network mTetheringUpstreamNetwork;
+    private boolean mPreferTestNetworks;
 
     public UpstreamNetworkMonitor(Context ctx, StateMachine tgt, SharedLog log, int what) {
         mContext = ctx;
@@ -325,6 +326,11 @@
         final UpstreamNetworkState dfltState = (mDefaultInternetNetwork != null)
                 ? mNetworkMap.get(mDefaultInternetNetwork)
                 : null;
+        if (mPreferTestNetworks) {
+            final UpstreamNetworkState testState = findFirstTestNetwork(mNetworkMap.values());
+            if (testState != null) return testState;
+        }
+
         if (isNetworkUsableAndNotCellular(dfltState)) return dfltState;
 
         if (!isCellularUpstreamPermitted()) return null;
@@ -656,6 +662,20 @@
         return null;
     }
 
+    static boolean isTestNetwork(UpstreamNetworkState ns) {
+        return ((ns != null) && (ns.networkCapabilities != null)
+                && ns.networkCapabilities.hasTransport(NetworkCapabilities.TRANSPORT_TEST));
+    }
+
+    private UpstreamNetworkState findFirstTestNetwork(
+            Iterable<UpstreamNetworkState> netStates) {
+        for (UpstreamNetworkState ns : netStates) {
+            if (isTestNetwork(ns)) return ns;
+        }
+
+        return null;
+    }
+
     /**
      * Given a legacy type (TYPE_WIFI, ...) returns the corresponding NetworkCapabilities instance.
      * This function is used for deprecated legacy type and be disabled by default.
@@ -681,4 +701,9 @@
         }
         return builder.build();
     }
+
+    /** Set test network as preferred upstream. */
+    public void setPreferTestNetworks(boolean prefer) {
+        mPreferTestNetworks = prefer;
+    }
 }
diff --git a/Tethering/tests/integration/Android.bp b/Tethering/tests/integration/Android.bp
index 2593b1b..c7f5527 100644
--- a/Tethering/tests/integration/Android.bp
+++ b/Tethering/tests/integration/Android.bp
@@ -19,6 +19,7 @@
 
 java_defaults {
     name: "TetheringIntegrationTestsDefaults",
+    defaults: ["framework-connectivity-test-defaults"],
     srcs: [
         "src/**/*.java",
         "src/**/*.kt",
diff --git a/Tethering/tests/integration/AndroidManifest.xml b/Tethering/tests/integration/AndroidManifest.xml
index fddfaad..c89c556 100644
--- a/Tethering/tests/integration/AndroidManifest.xml
+++ b/Tethering/tests/integration/AndroidManifest.xml
@@ -17,6 +17,11 @@
           package="com.android.networkstack.tethering.tests.integration">
 
     <uses-permission android:name="android.permission.INTERNET"/>
+    <!-- The test need CHANGE_NETWORK_STATE permission to use requestNetwork API to setup test
+         network. Since R shell application don't have such permission, grant permission to the test
+         here. TODO: Remove CHANGE_NETWORK_STATE permission here and use adopt shell perssion to
+         obtain CHANGE_NETWORK_STATE for testing once R device is no longer supported. -->
+    <uses-permission android:name="android.permission.CHANGE_NETWORK_STATE"/>
 
     <application android:debuggable="true">
         <uses-library android:name="android.test.runner" />
diff --git a/Tethering/tests/integration/src/android/net/EthernetTetheringTest.java b/Tethering/tests/integration/src/android/net/EthernetTetheringTest.java
index 26297a2..15f07f2 100644
--- a/Tethering/tests/integration/src/android/net/EthernetTetheringTest.java
+++ b/Tethering/tests/integration/src/android/net/EthernetTetheringTest.java
@@ -21,6 +21,7 @@
 import static android.Manifest.permission.MANAGE_TEST_NETWORKS;
 import static android.Manifest.permission.NETWORK_SETTINGS;
 import static android.Manifest.permission.TETHER_PRIVILEGED;
+import static android.net.InetAddresses.parseNumericAddress;
 import static android.net.TetheringManager.CONNECTIVITY_SCOPE_GLOBAL;
 import static android.net.TetheringManager.CONNECTIVITY_SCOPE_LOCAL;
 import static android.net.TetheringManager.TETHERING_ETHERNET;
@@ -29,6 +30,7 @@
 import static com.android.net.module.util.ConnectivityUtils.isIPv6ULA;
 import static com.android.net.module.util.NetworkStackConstants.ETHER_TYPE_IPV6;
 import static com.android.net.module.util.NetworkStackConstants.ICMPV6_ROUTER_ADVERTISEMENT;
+import static com.android.testutils.TestNetworkTrackerKt.initTestNetwork;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
@@ -45,14 +47,10 @@
 import android.net.TetheringManager.StartTetheringCallback;
 import android.net.TetheringManager.TetheringEventCallback;
 import android.net.TetheringManager.TetheringRequest;
-import android.net.dhcp.DhcpAckPacket;
-import android.net.dhcp.DhcpOfferPacket;
-import android.net.dhcp.DhcpPacket;
 import android.os.Handler;
 import android.os.HandlerThread;
 import android.os.SystemClock;
 import android.os.SystemProperties;
-import android.system.Os;
 import android.util.Log;
 
 import androidx.test.InstrumentationRegistry;
@@ -65,6 +63,7 @@
 import com.android.net.module.util.structs.Ipv6Header;
 import com.android.testutils.HandlerUtils;
 import com.android.testutils.TapPacketReader;
+import com.android.testutils.TestNetworkTracker;
 
 import org.junit.After;
 import org.junit.Before;
@@ -72,12 +71,12 @@
 import org.junit.runner.RunWith;
 
 import java.io.FileDescriptor;
-import java.net.Inet4Address;
 import java.net.InetAddress;
 import java.net.InterfaceAddress;
 import java.net.NetworkInterface;
 import java.net.SocketException;
 import java.nio.ByteBuffer;
+import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
 import java.util.Random;
@@ -93,24 +92,19 @@
 
     private static final String TAG = EthernetTetheringTest.class.getSimpleName();
     private static final int TIMEOUT_MS = 5000;
-    private static final int PACKET_READ_TIMEOUT_MS = 100;
-    private static final int DHCP_DISCOVER_ATTEMPTS = 10;
-    private static final byte[] DHCP_REQUESTED_PARAMS = new byte[] {
-            DhcpPacket.DHCP_SUBNET_MASK,
-            DhcpPacket.DHCP_ROUTER,
-            DhcpPacket.DHCP_DNS_SERVER,
-            DhcpPacket.DHCP_LEASE_TIME,
-    };
-    private static final String DHCP_HOSTNAME = "testhostname";
+    private static final LinkAddress TEST_IP4_ADDR = new LinkAddress("10.0.0.1/8");
+    private static final LinkAddress TEST_IP6_ADDR = new LinkAddress("2001:db8:1::101/64");
+    private static final InetAddress TEST_IP4_DNS = parseNumericAddress("8.8.8.8");
+    private static final InetAddress TEST_IP6_DNS = parseNumericAddress("2001:db8:1::888");
 
     private final Context mContext = InstrumentationRegistry.getContext();
     private final EthernetManager mEm = mContext.getSystemService(EthernetManager.class);
     private final TetheringManager mTm = mContext.getSystemService(TetheringManager.class);
 
-    private TestNetworkInterface mTestIface;
+    private TestNetworkInterface mDownstreamIface;
     private HandlerThread mHandlerThread;
     private Handler mHandler;
-    private TapPacketReader mTapPacketReader;
+    private TapPacketReader mDownstreamReader;
 
     private TetheredInterfaceRequester mTetheredInterfaceRequester;
     private MyTetheringEventCallback mTetheringEventCallback;
@@ -119,6 +113,8 @@
             InstrumentationRegistry.getInstrumentation().getUiAutomation();
     private boolean mRunTests;
 
+    private TestNetworkTracker mUpstreamTracker;
+
     @Before
     public void setUp() throws Exception {
         // Needed to create a TestNetworkInterface, to call requestTetheredInterface, and to receive
@@ -138,16 +134,23 @@
     }
 
     private void cleanUp() throws Exception {
+        mTm.setPreferTestNetworks(false);
+
+        if (mUpstreamTracker != null) {
+            mUpstreamTracker.teardown();
+            mUpstreamTracker = null;
+        }
+
         mTm.stopTethering(TETHERING_ETHERNET);
         if (mTetheringEventCallback != null) {
             mTetheringEventCallback.awaitInterfaceUntethered();
             mTetheringEventCallback.unregister();
             mTetheringEventCallback = null;
         }
-        if (mTapPacketReader != null) {
-            TapPacketReader reader = mTapPacketReader;
+        if (mDownstreamReader != null) {
+            TapPacketReader reader = mDownstreamReader;
             mHandler.post(() -> reader.stop());
-            mTapPacketReader = null;
+            mDownstreamReader = null;
         }
         mHandlerThread.quitSafely();
         mTetheredInterfaceRequester.release();
@@ -169,21 +172,21 @@
         // This test requires manipulating packets. Skip if there is a physical Ethernet connected.
         assumeFalse(mEm.isAvailable());
 
-        mTestIface = createTestInterface();
+        mDownstreamIface = createTestInterface();
         // This must be done now because as soon as setIncludeTestInterfaces(true) is called, the
         // interface will be placed in client mode, which will delete the link-local address.
         // At that point NetworkInterface.getByName() will cease to work on the interface, because
         // starting in R NetworkInterface can no longer see interfaces without IP addresses.
-        int mtu = getMTU(mTestIface);
+        int mtu = getMTU(mDownstreamIface);
 
         Log.d(TAG, "Including test interfaces");
         mEm.setIncludeTestInterfaces(true);
 
         final String iface = mTetheredInterfaceRequester.getInterface();
         assertEquals("TetheredInterfaceCallback for unexpected interface",
-                mTestIface.getInterfaceName(), iface);
+                mDownstreamIface.getInterfaceName(), iface);
 
-        checkVirtualEthernet(mTestIface, mtu);
+        checkVirtualEthernet(mDownstreamIface, mtu);
     }
 
     @Test
@@ -195,13 +198,13 @@
 
         mEm.setIncludeTestInterfaces(true);
 
-        mTestIface = createTestInterface();
+        mDownstreamIface = createTestInterface();
 
         final String iface = futureIface.get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
         assertEquals("TetheredInterfaceCallback for unexpected interface",
-                mTestIface.getInterfaceName(), iface);
+                mDownstreamIface.getInterfaceName(), iface);
 
-        checkVirtualEthernet(mTestIface, getMTU(mTestIface));
+        checkVirtualEthernet(mDownstreamIface, getMTU(mDownstreamIface));
     }
 
     @Test
@@ -210,11 +213,11 @@
 
         mEm.setIncludeTestInterfaces(true);
 
-        mTestIface = createTestInterface();
+        mDownstreamIface = createTestInterface();
 
         final String iface = mTetheredInterfaceRequester.getInterface();
         assertEquals("TetheredInterfaceCallback for unexpected interface",
-                mTestIface.getInterfaceName(), iface);
+                mDownstreamIface.getInterfaceName(), iface);
 
         assertInvalidStaticIpv4Request(iface, null, null);
         assertInvalidStaticIpv4Request(iface, "2001:db8::1/64", "2001:db8:2::/64");
@@ -235,13 +238,14 @@
         byte[] client1 = MacAddress.fromString("1:2:3:4:5:6").toByteArray();
         byte[] client2 = MacAddress.fromString("a:b:c:d:e:f").toByteArray();
 
-        FileDescriptor fd = mTestIface.getFileDescriptor().getFileDescriptor();
-        mTapPacketReader = makePacketReader(fd, getMTU(mTestIface));
-        DhcpResults dhcpResults = runDhcp(fd, client1);
+        FileDescriptor fd = mDownstreamIface.getFileDescriptor().getFileDescriptor();
+        mDownstreamReader = makePacketReader(fd, getMTU(mDownstreamIface));
+        TetheringTester tester = new TetheringTester(mDownstreamReader);
+        DhcpResults dhcpResults = tester.runDhcp(client1);
         assertEquals(new LinkAddress(clientAddr), dhcpResults.ipAddress);
 
         try {
-            runDhcp(fd, client2);
+            tester.runDhcp(client2);
             fail("Only one client should get an IP address");
         } catch (TimeoutException expected) { }
 
@@ -301,11 +305,11 @@
 
         mEm.setIncludeTestInterfaces(true);
 
-        mTestIface = createTestInterface();
+        mDownstreamIface = createTestInterface();
 
         final String iface = mTetheredInterfaceRequester.getInterface();
         assertEquals("TetheredInterfaceCallback for unexpected interface",
-                mTestIface.getInterfaceName(), iface);
+                mDownstreamIface.getInterfaceName(), iface);
 
         final TetheringRequest request = new TetheringRequest.Builder(TETHERING_ETHERNET)
                 .setConnectivityScope(CONNECTIVITY_SCOPE_LOCAL).build();
@@ -316,10 +320,9 @@
         // does not have an IP address, and unprivileged apps cannot see interfaces without IP
         // addresses. This shouldn't be flaky because the TAP interface will buffer all packets even
         // before the reader is started.
-        FileDescriptor fd = mTestIface.getFileDescriptor().getFileDescriptor();
-        mTapPacketReader = makePacketReader(fd, getMTU(mTestIface));
+        mDownstreamReader = makePacketReader(mDownstreamIface);
 
-        expectRouterAdvertisement(mTapPacketReader, iface, 2000 /* timeoutMs */);
+        expectRouterAdvertisement(mDownstreamReader, iface, 2000 /* timeoutMs */);
         expectLocalOnlyAddresses(iface);
     }
 
@@ -354,12 +357,14 @@
         private final CountDownLatch mLocalOnlyStartedLatch = new CountDownLatch(1);
         private final CountDownLatch mLocalOnlyStoppedLatch = new CountDownLatch(1);
         private final CountDownLatch mClientConnectedLatch = new CountDownLatch(1);
+        private final CountDownLatch mUpstreamConnectedLatch = new CountDownLatch(1);
         private final TetheringInterface mIface;
 
         private volatile boolean mInterfaceWasTethered = false;
         private volatile boolean mInterfaceWasLocalOnly = false;
         private volatile boolean mUnregistered = false;
         private volatile Collection<TetheredClient> mClients = null;
+        private volatile Network mUpstream = null;
 
         MyTetheringEventCallback(TetheringManager tm, String iface) {
             mTm = tm;
@@ -465,6 +470,22 @@
                     mClientConnectedLatch.await(TIMEOUT_MS, TimeUnit.MILLISECONDS));
             return mClients;
         }
+
+        @Override
+        public void onUpstreamChanged(Network network) {
+            // Ignore stale callbacks registered by previous test cases.
+            if (mUnregistered) return;
+
+            Log.d(TAG, "Got upstream changed: " + network);
+            mUpstream = network;
+            if (mUpstream != null) mUpstreamConnectedLatch.countDown();
+        }
+
+        public Network awaitFirstUpstreamConnected() throws Exception {
+            assertTrue("Did not receive upstream connected callback after " + TIMEOUT_MS + "ms",
+                    mUpstreamConnectedLatch.await(TIMEOUT_MS, TimeUnit.MILLISECONDS));
+            return mUpstream;
+        }
     }
 
     private MyTetheringEventCallback enableEthernetTethering(String iface,
@@ -508,6 +529,11 @@
         return nif.getMTU();
     }
 
+    private TapPacketReader makePacketReader(final TestNetworkInterface iface) throws Exception {
+        FileDescriptor fd = iface.getFileDescriptor().getFileDescriptor();
+        return makePacketReader(fd, getMTU(iface));
+    }
+
     private TapPacketReader makePacketReader(FileDescriptor fd, int mtu) {
         final TapPacketReader reader = new TapPacketReader(mHandler, fd, mtu);
         mHandler.post(() -> reader.start());
@@ -517,40 +543,18 @@
 
     private void checkVirtualEthernet(TestNetworkInterface iface, int mtu) throws Exception {
         FileDescriptor fd = iface.getFileDescriptor().getFileDescriptor();
-        mTapPacketReader = makePacketReader(fd, mtu);
+        mDownstreamReader = makePacketReader(fd, mtu);
         mTetheringEventCallback = enableEthernetTethering(iface.getInterfaceName());
-        checkTetheredClientCallbacks(fd);
+        checkTetheredClientCallbacks(mDownstreamReader);
     }
 
-    private DhcpResults runDhcp(FileDescriptor fd, byte[] clientMacAddr) throws Exception {
-        // We have to retransmit DHCP requests because IpServer declares itself to be ready before
-        // its DhcpServer is actually started. TODO: fix this race and remove this loop.
-        DhcpPacket offerPacket = null;
-        for (int i = 0; i < DHCP_DISCOVER_ATTEMPTS; i++) {
-            Log.d(TAG, "Sending DHCP discover");
-            sendDhcpDiscover(fd, clientMacAddr);
-            offerPacket = getNextDhcpPacket();
-            if (offerPacket instanceof DhcpOfferPacket) break;
-        }
-        if (!(offerPacket instanceof DhcpOfferPacket)) {
-            throw new TimeoutException("No DHCPOFFER received on interface within timeout");
-        }
-
-        sendDhcpRequest(fd, offerPacket, clientMacAddr);
-        DhcpPacket ackPacket = getNextDhcpPacket();
-        if (!(ackPacket instanceof DhcpAckPacket)) {
-            throw new TimeoutException("No DHCPACK received on interface within timeout");
-        }
-
-        return ackPacket.toDhcpResults();
-    }
-
-    private void checkTetheredClientCallbacks(FileDescriptor fd) throws Exception {
+    private void checkTetheredClientCallbacks(TapPacketReader packetReader) throws Exception {
         // Create a fake client.
         byte[] clientMacAddr = new byte[6];
         new Random().nextBytes(clientMacAddr);
 
-        DhcpResults dhcpResults = runDhcp(fd, clientMacAddr);
+        TetheringTester tester = new TetheringTester(packetReader);
+        DhcpResults dhcpResults = tester.runDhcp(clientMacAddr);
 
         final Collection<TetheredClient> clients = mTetheringEventCallback.awaitClientConnected();
         assertEquals(1, clients.size());
@@ -563,7 +567,7 @@
         // Check the hostname.
         assertEquals(1, client.getAddresses().size());
         TetheredClient.AddressInfo info = client.getAddresses().get(0);
-        assertEquals(DHCP_HOSTNAME, info.getHostname());
+        assertEquals(TetheringTester.DHCP_HOSTNAME, info.getHostname());
 
         // Check the address is the one that was handed out in the DHCP ACK.
         assertLinkAddressMatches(dhcpResults.ipAddress, info.getAddress());
@@ -576,18 +580,6 @@
         assertTrue(msg, Math.abs(dhcpResults.leaseDuration - actualLeaseDuration) < 10);
     }
 
-    private DhcpPacket getNextDhcpPacket() throws ParseException {
-        byte[] packet;
-        while ((packet = mTapPacketReader.popPacket(PACKET_READ_TIMEOUT_MS)) != null) {
-            try {
-                return DhcpPacket.decodeFullPacket(packet, packet.length, DhcpPacket.ENCAP_L2);
-            } catch (DhcpPacket.ParseException e) {
-                // Not a DHCP packet. Continue.
-            }
-        }
-        return null;
-    }
-
     private static final class TetheredInterfaceRequester implements TetheredInterfaceCallback {
         private final Handler mHandler;
         private final EthernetManager mEm;
@@ -631,31 +623,6 @@
         }
     }
 
-    private void sendDhcpDiscover(FileDescriptor fd, byte[] macAddress) throws Exception {
-        ByteBuffer packet = DhcpPacket.buildDiscoverPacket(DhcpPacket.ENCAP_L2,
-                new Random().nextInt() /* transactionId */, (short) 0 /* secs */,
-                macAddress,  false /* unicast */, DHCP_REQUESTED_PARAMS,
-                false /* rapid commit */,  DHCP_HOSTNAME);
-        sendPacket(fd, packet);
-    }
-
-    private void sendDhcpRequest(FileDescriptor fd, DhcpPacket offerPacket, byte[] macAddress)
-            throws Exception {
-        DhcpResults results = offerPacket.toDhcpResults();
-        Inet4Address clientIp = (Inet4Address) results.ipAddress.getAddress();
-        Inet4Address serverIdentifier = results.serverAddress;
-        ByteBuffer packet = DhcpPacket.buildRequestPacket(DhcpPacket.ENCAP_L2,
-                0 /* transactionId */, (short) 0 /* secs */, DhcpPacket.INADDR_ANY /* clientIp */,
-                false /* broadcast */, macAddress, clientIp /* requestedIpAddress */,
-                serverIdentifier, DHCP_REQUESTED_PARAMS, DHCP_HOSTNAME);
-        sendPacket(fd, packet);
-    }
-
-    private void sendPacket(FileDescriptor fd, ByteBuffer packet) throws Exception {
-        assertNotNull("Only tests on virtual interfaces can send packets", fd);
-        Os.write(fd, packet);
-    }
-
     public void assertLinkAddressMatches(LinkAddress l1, LinkAddress l2) {
         // Check all fields except the deprecation and expiry times.
         String msg = String.format("LinkAddresses do not match. expected: %s actual: %s", l1, l2);
@@ -701,10 +668,45 @@
     }
 
     private void maybeDeleteTestInterface() throws Exception {
-        if (mTestIface != null) {
-            mTestIface.getFileDescriptor().close();
-            Log.d(TAG, "Deleted test interface " + mTestIface.getInterfaceName());
-            mTestIface = null;
+        if (mDownstreamIface != null) {
+            mDownstreamIface.getFileDescriptor().close();
+            Log.d(TAG, "Deleted test interface " + mDownstreamIface.getInterfaceName());
+            mDownstreamIface = null;
         }
     }
+
+    private TestNetworkTracker createTestUpstream(final List<LinkAddress> addresses)
+            throws Exception {
+        mTm.setPreferTestNetworks(true);
+
+        return initTestNetwork(mContext, addresses, TIMEOUT_MS);
+    }
+
+    @Test
+    public void testTestNetworkUpstream() throws Exception {
+        assumeFalse(mEm.isAvailable());
+
+        // MyTetheringEventCallback currently only support await first available upstream. Tethering
+        // may select internet network as upstream if test network is not available and not be
+        // preferred yet. Create test upstream network before enable tethering.
+        mUpstreamTracker = createTestUpstream(toList(TEST_IP4_ADDR, TEST_IP6_ADDR));
+
+        mDownstreamIface = createTestInterface();
+        mEm.setIncludeTestInterfaces(true);
+
+        final String iface = mTetheredInterfaceRequester.getInterface();
+        assertEquals("TetheredInterfaceCallback for unexpected interface",
+                mDownstreamIface.getInterfaceName(), iface);
+
+        mTetheringEventCallback = enableEthernetTethering(mDownstreamIface.getInterfaceName());
+        assertEquals("onUpstreamChanged for unexpected network", mUpstreamTracker.getNetwork(),
+                mTetheringEventCallback.awaitFirstUpstreamConnected());
+
+        mDownstreamReader = makePacketReader(mDownstreamIface);
+        // TODO: do basic forwarding test here.
+    }
+
+    private <T> List<T> toList(T... array) {
+        return Arrays.asList(array);
+    }
 }
diff --git a/Tethering/tests/integration/src/android/net/TetheringTester.java b/Tethering/tests/integration/src/android/net/TetheringTester.java
new file mode 100644
index 0000000..38d74ad
--- /dev/null
+++ b/Tethering/tests/integration/src/android/net/TetheringTester.java
@@ -0,0 +1,155 @@
+/*
+ * 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 static org.junit.Assert.fail;
+
+import android.net.dhcp.DhcpAckPacket;
+import android.net.dhcp.DhcpOfferPacket;
+import android.net.dhcp.DhcpPacket;
+import android.util.ArrayMap;
+import android.util.Log;
+
+import com.android.testutils.TapPacketReader;
+
+import java.net.Inet4Address;
+import java.nio.ByteBuffer;
+import java.util.Random;
+import java.util.concurrent.TimeoutException;
+import java.util.function.Function;
+
+/**
+ * A class simulate tethered client. When caller create TetheringTester, it would connect to
+ * tethering module that do the dhcp and slaac to obtain ipv4 and ipv6 address. Then caller can
+ * send/receive packets by this class.
+ */
+public final class TetheringTester {
+    private static final String TAG = TetheringTester.class.getSimpleName();
+    private static final int PACKET_READ_TIMEOUT_MS = 100;
+    private static final int DHCP_DISCOVER_ATTEMPTS = 10;
+    private static final byte[] DHCP_REQUESTED_PARAMS = new byte[] {
+            DhcpPacket.DHCP_SUBNET_MASK,
+            DhcpPacket.DHCP_ROUTER,
+            DhcpPacket.DHCP_DNS_SERVER,
+            DhcpPacket.DHCP_LEASE_TIME,
+    };
+
+    public static final String DHCP_HOSTNAME = "testhostname";
+
+    private final ArrayMap<MacAddress, TetheredDevice> mTetheredDevices;
+    private final TapPacketReader mDownstreamReader;
+
+    public TetheringTester(TapPacketReader downstream) {
+        if (downstream == null) fail("Downstream reader could not be NULL");
+
+        mDownstreamReader = downstream;
+        mTetheredDevices = new ArrayMap<>();
+    }
+
+    public TetheredDevice createTetheredDevice(MacAddress macAddr) throws Exception {
+        if (mTetheredDevices.get(macAddr) != null) {
+            fail("Tethered device already created");
+        }
+
+        TetheredDevice tethered = new TetheredDevice(macAddr);
+        mTetheredDevices.put(macAddr, tethered);
+
+        return tethered;
+    }
+
+    public class TetheredDevice {
+        private final MacAddress mMacAddr;
+
+        public final Inet4Address mIpv4Addr;
+
+        private TetheredDevice(MacAddress mac) throws Exception {
+            mMacAddr = mac;
+
+            DhcpResults dhcpResults = runDhcp(mMacAddr.toByteArray());
+            mIpv4Addr = (Inet4Address) dhcpResults.ipAddress.getAddress();
+        }
+    }
+
+    /** Simulate dhcp client to obtain ipv4 address. */
+    public DhcpResults runDhcp(byte[] clientMacAddr)
+            throws Exception {
+        // We have to retransmit DHCP requests because IpServer declares itself to be ready before
+        // its DhcpServer is actually started. TODO: fix this race and remove this loop.
+        DhcpPacket offerPacket = null;
+        for (int i = 0; i < DHCP_DISCOVER_ATTEMPTS; i++) {
+            Log.d(TAG, "Sending DHCP discover");
+            sendDhcpDiscover(clientMacAddr);
+            offerPacket = getNextDhcpPacket();
+            if (offerPacket instanceof DhcpOfferPacket) break;
+        }
+        if (!(offerPacket instanceof DhcpOfferPacket)) {
+            throw new TimeoutException("No DHCPOFFER received on interface within timeout");
+        }
+
+        sendDhcpRequest(offerPacket, clientMacAddr);
+        DhcpPacket ackPacket = getNextDhcpPacket();
+        if (!(ackPacket instanceof DhcpAckPacket)) {
+            throw new TimeoutException("No DHCPACK received on interface within timeout");
+        }
+
+        return ackPacket.toDhcpResults();
+    }
+
+    private void sendDhcpDiscover(byte[] macAddress) throws Exception {
+        ByteBuffer packet = DhcpPacket.buildDiscoverPacket(DhcpPacket.ENCAP_L2,
+                new Random().nextInt() /* transactionId */, (short) 0 /* secs */,
+                macAddress,  false /* unicast */, DHCP_REQUESTED_PARAMS,
+                false /* rapid commit */,  DHCP_HOSTNAME);
+        mDownstreamReader.sendResponse(packet);
+    }
+
+    private void sendDhcpRequest(DhcpPacket offerPacket, byte[] macAddress)
+            throws Exception {
+        DhcpResults results = offerPacket.toDhcpResults();
+        Inet4Address clientIp = (Inet4Address) results.ipAddress.getAddress();
+        Inet4Address serverIdentifier = results.serverAddress;
+        ByteBuffer packet = DhcpPacket.buildRequestPacket(DhcpPacket.ENCAP_L2,
+                0 /* transactionId */, (short) 0 /* secs */, DhcpPacket.INADDR_ANY /* clientIp */,
+                false /* broadcast */, macAddress, clientIp /* requestedIpAddress */,
+                serverIdentifier, DHCP_REQUESTED_PARAMS, DHCP_HOSTNAME);
+        mDownstreamReader.sendResponse(packet);
+    }
+
+    private DhcpPacket getNextDhcpPacket() {
+        return getNextMatchedPacket((p) -> {
+            try {
+                return DhcpPacket.decodeFullPacket(p, p.length, DhcpPacket.ENCAP_L2);
+            } catch (DhcpPacket.ParseException e) {
+                // Not a DHCP packet. Continue.
+            }
+
+            return null;
+        });
+    }
+
+    private <R> R getNextMatchedPacket(Function<byte[], R> match) {
+        byte[] packet;
+        R result;
+        while ((packet = mDownstreamReader.popPacket(PACKET_READ_TIMEOUT_MS)) != null) {
+            result = match.apply(packet);
+
+            if (result != null) return result;
+        }
+
+        return null;
+    }
+}
diff --git a/framework/src/android/net/ConnectivityManager.java b/framework/src/android/net/ConnectivityManager.java
index 7294ec9..4f10abc 100644
--- a/framework/src/android/net/ConnectivityManager.java
+++ b/framework/src/android/net/ConnectivityManager.java
@@ -1163,10 +1163,11 @@
      * default data network.  In the event that the current active default data
      * network disconnects, the returned {@code Network} object will no longer
      * be usable.  This will return {@code null} when there is no default
-     * network.
+     * network, or when the default network is blocked.
      *
      * @return a {@link Network} object for the current default network or
-     *        {@code null} if no default network is currently active
+     *        {@code null} if no default network is currently active or if
+     *        the default network is blocked for the caller
      */
     @RequiresPermission(android.Manifest.permission.ACCESS_NETWORK_STATE)
     @Nullable
@@ -2326,6 +2327,7 @@
         void onNetworkActive();
     }
 
+    @GuardedBy("mNetworkActivityListeners")
     private final ArrayMap<OnNetworkActiveListener, INetworkActivityListener>
             mNetworkActivityListeners = new ArrayMap<>();
 
@@ -2342,18 +2344,20 @@
      * @param l The listener to be told when the network is active.
      */
     public void addDefaultNetworkActiveListener(final OnNetworkActiveListener l) {
-        INetworkActivityListener rl = new INetworkActivityListener.Stub() {
+        final INetworkActivityListener rl = new INetworkActivityListener.Stub() {
             @Override
             public void onNetworkActive() throws RemoteException {
                 l.onNetworkActive();
             }
         };
 
-        try {
-            mService.registerNetworkActivityListener(rl);
-            mNetworkActivityListeners.put(l, rl);
-        } catch (RemoteException e) {
-            throw e.rethrowFromSystemServer();
+        synchronized (mNetworkActivityListeners) {
+            try {
+                mService.registerNetworkActivityListener(rl);
+                mNetworkActivityListeners.put(l, rl);
+            } catch (RemoteException e) {
+                throw e.rethrowFromSystemServer();
+            }
         }
     }
 
@@ -2364,14 +2368,17 @@
      * @param l Previously registered listener.
      */
     public void removeDefaultNetworkActiveListener(@NonNull OnNetworkActiveListener l) {
-        INetworkActivityListener rl = mNetworkActivityListeners.get(l);
-        if (rl == null) {
-            throw new IllegalArgumentException("Listener was not registered.");
-        }
-        try {
-            mService.unregisterNetworkActivityListener(rl);
-        } catch (RemoteException e) {
-            throw e.rethrowFromSystemServer();
+        synchronized (mNetworkActivityListeners) {
+            final INetworkActivityListener rl = mNetworkActivityListeners.get(l);
+            if (rl == null) {
+                throw new IllegalArgumentException("Listener was not registered.");
+            }
+            try {
+                mService.unregisterNetworkActivityListener(rl);
+                mNetworkActivityListeners.remove(l);
+            } catch (RemoteException e) {
+                throw e.rethrowFromSystemServer();
+            }
         }
     }
 
diff --git a/service/src/com/android/server/ConnectivityService.java b/service/src/com/android/server/ConnectivityService.java
index c69af06..cf5f1c7 100644
--- a/service/src/com/android/server/ConnectivityService.java
+++ b/service/src/com/android/server/ConnectivityService.java
@@ -3014,9 +3014,9 @@
         }
         pw.println();
 
-        pw.print("Current per-app default networks: ");
+        pw.println("Current network preferences: ");
         pw.increaseIndent();
-        dumpPerAppNetworkPreferences(pw);
+        dumpNetworkPreferences(pw);
         pw.decreaseIndent();
         pw.println();
 
@@ -3144,37 +3144,55 @@
         }
     }
 
-    private void dumpPerAppNetworkPreferences(IndentingPrintWriter pw) {
-        pw.println("Per-App Network Preference:");
-        pw.increaseIndent();
-        if (0 == mOemNetworkPreferences.getNetworkPreferences().size()) {
-            pw.println("none");
-        } else {
-            pw.println(mOemNetworkPreferences.toString());
+    private void dumpNetworkPreferences(IndentingPrintWriter pw) {
+        if (!mProfileNetworkPreferences.isEmpty()) {
+            pw.println("Profile preferences:");
+            pw.increaseIndent();
+            pw.println(mProfileNetworkPreferences.preferences);
+            pw.decreaseIndent();
         }
-        pw.decreaseIndent();
+        if (!mOemNetworkPreferences.isEmpty()) {
+            pw.println("OEM preferences:");
+            pw.increaseIndent();
+            pw.println(mOemNetworkPreferences);
+            pw.decreaseIndent();
+        }
+        if (!mMobileDataPreferredUids.isEmpty()) {
+            pw.println("Mobile data preferred UIDs:");
+            pw.increaseIndent();
+            pw.println(mMobileDataPreferredUids);
+            pw.decreaseIndent();
+        }
 
+        pw.println("Default requests:");
+        pw.increaseIndent();
+        dumpPerAppDefaultRequests(pw);
+        pw.decreaseIndent();
+    }
+
+    private void dumpPerAppDefaultRequests(IndentingPrintWriter pw) {
         for (final NetworkRequestInfo defaultRequest : mDefaultNetworkRequests) {
             if (mDefaultRequest == defaultRequest) {
                 continue;
             }
 
-            final boolean isActive = null != defaultRequest.getSatisfier();
-            pw.println("Is per-app network active:");
-            pw.increaseIndent();
-            pw.println(isActive);
-            if (isActive) {
-                pw.println("Active network: " + defaultRequest.getSatisfier().network.netId);
-            }
-            pw.println("Tracked UIDs:");
-            pw.increaseIndent();
-            if (0 == defaultRequest.mRequests.size()) {
-                pw.println("none, this should never occur.");
+            final NetworkAgentInfo satisfier = defaultRequest.getSatisfier();
+            final String networkOutput;
+            if (null == satisfier) {
+                networkOutput = "null";
+            } else if (mNoServiceNetwork.equals(satisfier)) {
+                networkOutput = "no service network";
             } else {
-                pw.println(defaultRequest.mRequests.get(0).networkCapabilities.getUidRanges());
+                networkOutput = String.valueOf(satisfier.network.netId);
             }
-            pw.decreaseIndent();
-            pw.decreaseIndent();
+            final String asUidString = (defaultRequest.mAsUid == defaultRequest.mUid)
+                    ? "" : " asUid: " + defaultRequest.mAsUid;
+            final String requestInfo = "Request: [uid/pid:" + defaultRequest.mUid + "/"
+                    + defaultRequest.mPid + asUidString + "]";
+            final String satisfierOutput = "Satisfier: [" + networkOutput + "]"
+                    + " Preference order: " + defaultRequest.mPreferenceOrder
+                    + " Tracked UIDs: " + defaultRequest.getUids();
+            pw.println(requestInfo + " - " + satisfierOutput);
         }
     }
 
@@ -3848,9 +3866,7 @@
 
     private void handleNetworkAgentDisconnected(Message msg) {
         NetworkAgentInfo nai = (NetworkAgentInfo) msg.obj;
-        if (mNetworkAgentInfos.contains(nai)) {
-            disconnectAndDestroyNetwork(nai);
-        }
+        disconnectAndDestroyNetwork(nai);
     }
 
     // Destroys a network, remove references to it from the internal state managed by
@@ -3858,6 +3874,9 @@
     // Must be called on the Handler thread.
     private void disconnectAndDestroyNetwork(NetworkAgentInfo nai) {
         ensureRunningOnConnectivityServiceThread();
+
+        if (!mNetworkAgentInfos.contains(nai)) return;
+
         if (DBG) {
             log(nai.toShortString() + " disconnected, was satisfying " + nai.numNetworkRequests());
         }
@@ -3943,7 +3962,7 @@
         try {
             mNetd.networkSetPermissionForNetwork(nai.network.netId, INetd.PERMISSION_SYSTEM);
         } catch (RemoteException e) {
-            Log.d(TAG, "Error marking network restricted during teardown: " + e);
+            Log.d(TAG, "Error marking network restricted during teardown: ", e);
         }
         mHandler.postDelayed(() -> destroyNetwork(nai), nai.teardownDelayMs);
     }
@@ -6901,7 +6920,11 @@
         if (DBG) {
             log("unregister offer from providerId " + noi.offer.providerId + " : " + noi.offer);
         }
-        mNetworkOffers.remove(noi);
+
+        // If the provider removes the offer and dies immediately afterwards this
+        // function may be called twice in a row, but the array will no longer contain
+        // the offer.
+        if (!mNetworkOffers.remove(noi)) return;
         noi.offer.callback.asBinder().unlinkToDeath(noi, 0 /* flags */);
     }
 
diff --git a/service/src/com/android/server/connectivity/PermissionMonitor.java b/service/src/com/android/server/connectivity/PermissionMonitor.java
index f596c4a..4c6b669 100755
--- a/service/src/com/android/server/connectivity/PermissionMonitor.java
+++ b/service/src/com/android/server/connectivity/PermissionMonitor.java
@@ -222,6 +222,10 @@
                 mIntentReceiver, intentFilter, null /* broadcastPermission */,
                 null /* scheduler */);
 
+        // Listen to EXTERNAL_APPLICATIONS_AVAILABLE is that an app becoming available means it may
+        // need to gain a permission. But an app that becomes unavailable can neither gain nor lose
+        // permissions on that account, it just can no longer run. Thus, doesn't need to listen to
+        // EXTERNAL_APPLICATIONS_UNAVAILABLE.
         final IntentFilter externalIntentFilter =
                 new IntentFilter(Intent.ACTION_EXTERNAL_APPLICATIONS_AVAILABLE);
         userAllContext.registerReceiver(
diff --git a/tests/common/Android.bp b/tests/common/Android.bp
index e1fab09..9b136d5 100644
--- a/tests/common/Android.bp
+++ b/tests/common/Android.bp
@@ -115,6 +115,7 @@
         // meaning @hide APIs in framework-connectivity are resolved before @SystemApi
         // stubs in framework
         "framework-connectivity.impl",
+        "framework-tethering.impl",
         "framework",
 
         // if sdk_version="" this gets automatically included, but here we need to add manually.
diff --git a/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java b/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
index f5c43d6..199244f 100644
--- a/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
+++ b/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
@@ -75,6 +75,7 @@
 import static com.android.modules.utils.build.SdkLevel.isAtLeastS;
 import static com.android.networkstack.apishim.ConstantsShim.BLOCKED_REASON_LOCKDOWN_VPN;
 import static com.android.networkstack.apishim.ConstantsShim.BLOCKED_REASON_NONE;
+import static com.android.testutils.Cleanup.testAndCleanup;
 import static com.android.testutils.MiscAsserts.assertThrows;
 import static com.android.testutils.TestNetworkTrackerKt.initTestNetwork;
 import static com.android.testutils.TestPermissionUtil.runAsShell;
@@ -236,6 +237,7 @@
     private static final int MIN_KEEPALIVE_INTERVAL = 10;
 
     private static final int NETWORK_CALLBACK_TIMEOUT_MS = 30_000;
+    private static final int LISTEN_ACTIVITY_TIMEOUT_MS = 5_000;
     private static final int NO_CALLBACK_TIMEOUT_MS = 100;
     private static final int NUM_TRIES_MULTIPATH_PREF_CHECK = 20;
     private static final long INTERVAL_MULTIPATH_PREF_CHECK_MS = 500;
@@ -278,6 +280,7 @@
     private ConnectivityManagerShim mCmShim;
     private WifiManager mWifiManager;
     private PackageManager mPackageManager;
+    private TelephonyManager mTm;
     private final ArraySet<Integer> mNetworkTypes = new ArraySet<>();
     private UiAutomation mUiAutomation;
     private CtsNetUtils mCtsNetUtils;
@@ -297,6 +300,7 @@
         mWifiManager = (WifiManager) mContext.getSystemService(Context.WIFI_SERVICE);
         mPackageManager = mContext.getPackageManager();
         mCtsNetUtils = new CtsNetUtils(mContext);
+        mTm = mContext.getSystemService(TelephonyManager.class);
 
         if (DevSdkIgnoreRuleKt.isDevSdkInRange(null /* minExclusive */,
                 Build.VERSION_CODES.R /* maxInclusive */)) {
@@ -2793,6 +2797,36 @@
                 System.currentTimeMillis() + WIFI_CONNECT_TIMEOUT_MS);
     }
 
+    @AppModeFull(reason = "Need WiFi support to test the default active network")
+    @Test
+    public void testDefaultNetworkActiveListener() throws Exception {
+        final boolean supportWifi = mPackageManager.hasSystemFeature(FEATURE_WIFI);
+        final boolean supportTelephony = mPackageManager.hasSystemFeature(FEATURE_TELEPHONY);
+        assumeTrue("testDefaultNetworkActiveListener cannot execute"
+                + " unless device supports WiFi or telephony", (supportWifi || supportTelephony));
+
+        if (supportWifi) {
+            mCtsNetUtils.ensureWifiDisconnected(null /* wifiNetworkToCheck */);
+        } else {
+            mCtsNetUtils.disconnectFromCell();
+        }
+
+        final CompletableFuture<Boolean> future = new CompletableFuture<>();
+        final ConnectivityManager.OnNetworkActiveListener listener = () -> future.complete(true);
+        mCm.addDefaultNetworkActiveListener(listener);
+        testAndCleanup(() -> {
+            // New default network connected will trigger a network activity notification.
+            if (supportWifi) {
+                mCtsNetUtils.ensureWifiConnected();
+            } else {
+                mCtsNetUtils.connectToCell();
+            }
+            assertTrue(future.get(LISTEN_ACTIVITY_TIMEOUT_MS, TimeUnit.MILLISECONDS));
+        }, () -> {
+                mCm.removeDefaultNetworkActiveListener(listener);
+            });
+    }
+
     @AppModeFull(reason = "Cannot get WifiManager in instant app mode")
     @Test
     public void testMobileDataPreferredUids() throws Exception {
diff --git a/tests/cts/net/util/java/android/net/cts/util/CtsNetUtils.java b/tests/cts/net/util/java/android/net/cts/util/CtsNetUtils.java
index fd0cd18..7d9a24b 100644
--- a/tests/cts/net/util/java/android/net/cts/util/CtsNetUtils.java
+++ b/tests/cts/net/util/java/android/net/cts/util/CtsNetUtils.java
@@ -582,6 +582,9 @@
         }
 
         if (mOldPrivateDnsMode != ConnectivitySettingsUtils.PRIVATE_DNS_MODE_PROVIDER_HOSTNAME) {
+            // Also restore hostname even if the value is not used since private dns is not in
+            // the strict mode to prevent setting being changed after test.
+            ConnectivitySettingsUtils.setPrivateDnsHostname(mContext, mOldPrivateDnsSpecifier);
             ConnectivitySettingsUtils.setPrivateDnsMode(mContext, mOldPrivateDnsMode);
             return;
         }
diff --git a/tests/unit/Android.bp b/tests/unit/Android.bp
index 892da09..e2ea661 100644
--- a/tests/unit/Android.bp
+++ b/tests/unit/Android.bp
@@ -112,6 +112,7 @@
         "framework-protos",
         "mockito-target-minus-junit4",
         "net-tests-utils",
+        "platform-compat-test-rules",
         "platform-test-annotations",
         "service-connectivity-pre-jarjar",
         "services.core",
diff --git a/tests/unit/java/android/net/ConnectivityManagerTest.java b/tests/unit/java/android/net/ConnectivityManagerTest.java
index e7873af..c475419 100644
--- a/tests/unit/java/android/net/ConnectivityManagerTest.java
+++ b/tests/unit/java/android/net/ConnectivityManagerTest.java
@@ -37,6 +37,8 @@
 import static android.net.NetworkRequest.Type.TRACK_DEFAULT;
 import static android.net.NetworkRequest.Type.TRACK_SYSTEM_DEFAULT;
 
+import static com.android.testutils.MiscAsserts.assertThrows;
+
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
@@ -314,6 +316,21 @@
     }
 
     @Test
+    public void testDefaultNetworkActiveListener() throws Exception {
+        final ConnectivityManager manager = new ConnectivityManager(mCtx, mService);
+        final ConnectivityManager.OnNetworkActiveListener listener =
+                mock(ConnectivityManager.OnNetworkActiveListener.class);
+        assertThrows(IllegalArgumentException.class,
+                () -> manager.removeDefaultNetworkActiveListener(listener));
+        manager.addDefaultNetworkActiveListener(listener);
+        verify(mService, times(1)).registerNetworkActivityListener(any());
+        manager.removeDefaultNetworkActiveListener(listener);
+        verify(mService, times(1)).unregisterNetworkActivityListener(any());
+        assertThrows(IllegalArgumentException.class,
+                () -> manager.removeDefaultNetworkActiveListener(listener));
+    }
+
+    @Test
     public void testArgumentValidation() throws Exception {
         ConnectivityManager manager = new ConnectivityManager(mCtx, mService);
 
diff --git a/tests/unit/java/android/net/nsd/NsdManagerTest.java b/tests/unit/java/android/net/nsd/NsdManagerTest.java
index 31c8927..de77d23 100644
--- a/tests/unit/java/android/net/nsd/NsdManagerTest.java
+++ b/tests/unit/java/android/net/nsd/NsdManagerTest.java
@@ -16,6 +16,9 @@
 
 package android.net.nsd;
 
+import static libcore.junit.util.compat.CoreCompatChangeRule.DisableCompatChanges;
+import static libcore.junit.util.compat.CoreCompatChangeRule.EnableCompatChanges;
+
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.fail;
@@ -27,6 +30,7 @@
 import static org.mockito.Mockito.timeout;
 import static org.mockito.Mockito.verify;
 
+import android.compat.testing.PlatformCompatChangeRule;
 import android.content.Context;
 import android.os.Build;
 import android.os.Handler;
@@ -44,7 +48,9 @@
 
 import org.junit.After;
 import org.junit.Before;
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.TestRule;
 import org.junit.runner.RunWith;
 import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
@@ -56,6 +62,9 @@
 
     static final int PROTOCOL = NsdManager.PROTOCOL_DNS_SD;
 
+    @Rule
+    public TestRule compatChangeRule = new PlatformCompatChangeRule();
+
     @Mock Context mContext;
     @Mock INsdManager mService;
     MockServiceHandler mServiceHandler;
@@ -70,8 +79,6 @@
 
         mServiceHandler = spy(MockServiceHandler.create(mContext));
         doReturn(new Messenger(mServiceHandler)).when(mService).getMessenger();
-
-        mManager = makeManager();
     }
 
     @After
@@ -85,7 +92,76 @@
     }
 
     @Test
-    public void testResolveService() {
+    @EnableCompatChanges(NsdManager.RUN_NATIVE_NSD_ONLY_IF_LEGACY_APPS)
+    public void testResolveServiceS() {
+        mManager = makeNsdManagerS();
+        doTestResolveService();
+    }
+
+    @Test
+    @DisableCompatChanges(NsdManager.RUN_NATIVE_NSD_ONLY_IF_LEGACY_APPS)
+    public void testResolveServicePreS() {
+        mManager = makeNsdManagerPreS();
+        doTestResolveService();
+    }
+
+    @Test
+    @EnableCompatChanges(NsdManager.RUN_NATIVE_NSD_ONLY_IF_LEGACY_APPS)
+    public void testDiscoverServiceS() {
+        mManager = makeNsdManagerS();
+        doTestDiscoverService();
+    }
+
+    @Test
+    @DisableCompatChanges(NsdManager.RUN_NATIVE_NSD_ONLY_IF_LEGACY_APPS)
+    public void testDiscoverServicePreS() {
+        mManager = makeNsdManagerPreS();
+        doTestDiscoverService();
+    }
+
+    @Test
+    @EnableCompatChanges(NsdManager.RUN_NATIVE_NSD_ONLY_IF_LEGACY_APPS)
+    public void testParallelResolveServiceS() {
+        mManager = makeNsdManagerS();
+        doTestParallelResolveService();
+    }
+
+    @Test
+    @DisableCompatChanges(NsdManager.RUN_NATIVE_NSD_ONLY_IF_LEGACY_APPS)
+    public void testParallelResolveServicePreS() {
+        mManager = makeNsdManagerPreS();
+        doTestParallelResolveService();
+    }
+
+    @Test
+    @EnableCompatChanges(NsdManager.RUN_NATIVE_NSD_ONLY_IF_LEGACY_APPS)
+    public void testInvalidCallsS() {
+        mManager = makeNsdManagerS();
+        doTestInvalidCalls();
+    }
+
+    @Test
+    @DisableCompatChanges(NsdManager.RUN_NATIVE_NSD_ONLY_IF_LEGACY_APPS)
+    public void testInvalidCallsPreS() {
+        mManager = makeNsdManagerPreS();
+        doTestInvalidCalls();
+    }
+
+    @Test
+    @EnableCompatChanges(NsdManager.RUN_NATIVE_NSD_ONLY_IF_LEGACY_APPS)
+    public void testRegisterServiceS() {
+        mManager = makeNsdManagerS();
+        doTestRegisterService();
+    }
+
+    @Test
+    @DisableCompatChanges(NsdManager.RUN_NATIVE_NSD_ONLY_IF_LEGACY_APPS)
+    public void testRegisterServicePreS() {
+        mManager = makeNsdManagerPreS();
+        doTestRegisterService();
+    }
+
+    public void doTestResolveService() {
         NsdManager manager = mManager;
 
         NsdServiceInfo request = new NsdServiceInfo("a_name", "a_type");
@@ -104,8 +180,7 @@
         verify(listener, timeout(mTimeoutMs).times(1)).onServiceResolved(reply);
     }
 
-    @Test
-    public void testParallelResolveService() {
+    public void doTestParallelResolveService() {
         NsdManager manager = mManager;
 
         NsdServiceInfo request = new NsdServiceInfo("a_name", "a_type");
@@ -127,8 +202,7 @@
         verify(listener2, timeout(mTimeoutMs).times(1)).onServiceResolved(reply);
     }
 
-    @Test
-    public void testRegisterService() {
+    public void doTestRegisterService() {
         NsdManager manager = mManager;
 
         NsdServiceInfo request1 = new NsdServiceInfo("a_name", "a_type");
@@ -186,8 +260,7 @@
         //verify(listener2, timeout(mTimeoutMs).times(1)).onServiceUnregistered(request2);
     }
 
-    @Test
-    public void testDiscoverService() {
+    public void doTestDiscoverService() {
         NsdManager manager = mManager;
 
         NsdServiceInfo reply1 = new NsdServiceInfo("a_name", "a_type");
@@ -264,8 +337,7 @@
         verify(listener, timeout(mTimeoutMs).times(0)).onServiceFound(reply1);
     }
 
-    @Test
-    public void testInvalidCalls() {
+    public void doTestInvalidCalls() {
         NsdManager manager = mManager;
 
         NsdManager.RegistrationListener listener1 = mock(NsdManager.RegistrationListener.class);
@@ -326,10 +398,21 @@
         }
     }
 
-    NsdManager makeManager() {
+    NsdManager makeNsdManagerS() {
+        // Expect we'll get 2 AsyncChannel related msgs.
+        return makeManager(2);
+    }
+
+    NsdManager makeNsdManagerPreS() {
+        // Expect we'll get 3 msgs. 2 AsyncChannel related msgs + 1 additional daemon startup msg.
+        return makeManager(3);
+    }
+
+    NsdManager makeManager(int expectedMsgCount) {
         NsdManager manager = new NsdManager(mContext, mService);
         // Acknowledge first two messages connecting the AsyncChannel.
-        verify(mServiceHandler, timeout(mTimeoutMs).times(2)).handleMessage(any());
+        verify(mServiceHandler, timeout(mTimeoutMs).times(expectedMsgCount)).handleMessage(any());
+
         reset(mServiceHandler);
         assertNotNull(mServiceHandler.chan);
         return manager;
diff --git a/tests/unit/java/com/android/server/NsdServiceTest.java b/tests/unit/java/com/android/server/NsdServiceTest.java
index e80a938..4d2970a 100644
--- a/tests/unit/java/com/android/server/NsdServiceTest.java
+++ b/tests/unit/java/com/android/server/NsdServiceTest.java
@@ -16,6 +16,9 @@
 
 package com.android.server;
 
+import static libcore.junit.util.compat.CoreCompatChangeRule.DisableCompatChanges;
+import static libcore.junit.util.compat.CoreCompatChangeRule.EnableCompatChanges;
+
 import static org.junit.Assert.assertEquals;
 import static org.mockito.Mockito.any;
 import static org.mockito.Mockito.doReturn;
@@ -27,6 +30,7 @@
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
+import android.compat.testing.PlatformCompatChangeRule;
 import android.content.ContentResolver;
 import android.content.Context;
 import android.net.nsd.NsdManager;
@@ -48,7 +52,9 @@
 
 import org.junit.After;
 import org.junit.Before;
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.TestRule;
 import org.junit.runner.RunWith;
 import org.mockito.ArgumentCaptor;
 import org.mockito.Mock;
@@ -67,6 +73,8 @@
     private static final long CLEANUP_DELAY_MS = 500;
     private static final long TIMEOUT_MS = 500;
 
+    @Rule
+    public TestRule compatChangeRule = new PlatformCompatChangeRule();
     @Mock Context mContext;
     @Mock ContentResolver mResolver;
     @Mock NsdService.NsdSettings mSettings;
@@ -94,6 +102,34 @@
     }
 
     @Test
+    @DisableCompatChanges(NsdManager.RUN_NATIVE_NSD_ONLY_IF_LEGACY_APPS)
+    public void testPreSClients() {
+        when(mSettings.isEnabled()).thenReturn(true);
+        NsdService service = makeService();
+
+        // Pre S client connected, the daemon should be started.
+        NsdManager client1 = connectClient(service);
+        waitForIdle();
+        verify(mDaemon, times(1)).maybeStart();
+        verifyDaemonCommands("start-service");
+
+        NsdManager client2 = connectClient(service);
+        waitForIdle();
+        verify(mDaemon, times(1)).maybeStart();
+
+        client1.disconnect();
+        // Still 1 client remains, daemon shouldn't be stopped.
+        waitForIdle();
+        verify(mDaemon, never()).maybeStop();
+
+        client2.disconnect();
+        // All clients are disconnected, the daemon should be stopped.
+        verifyDelayMaybeStopDaemon(CLEANUP_DELAY_MS);
+        verifyDaemonCommands("stop-service");
+    }
+
+    @Test
+    @EnableCompatChanges(NsdManager.RUN_NATIVE_NSD_ONLY_IF_LEGACY_APPS)
     public void testNoDaemonStartedWhenClientsConnect() {
         when(mSettings.isEnabled()).thenReturn(true);
 
@@ -110,13 +146,12 @@
         waitForIdle();
         verify(mDaemon, never()).execute(any());
 
+        // If there is no active request, try to clean up the daemon
+        // every time the client disconnects.
         client1.disconnect();
-        // Still 1 client remains, daemon shouldn't be stopped.
-        waitForIdle();
-        verify(mDaemon, never()).maybeStop();
-
+        verifyDelayMaybeStopDaemon(CLEANUP_DELAY_MS);
+        reset(mDaemon);
         client2.disconnect();
-        // All clients are disconnected, stop the daemon after CLEANUP_DELAY_MS.
         verifyDelayMaybeStopDaemon(CLEANUP_DELAY_MS);
 
         client1.disconnect();
@@ -124,6 +159,7 @@
     }
 
     @Test
+    @EnableCompatChanges(NsdManager.RUN_NATIVE_NSD_ONLY_IF_LEGACY_APPS)
     public void testClientRequestsAreGCedAtDisconnection() {
         when(mSettings.isEnabled()).thenReturn(true);
 
@@ -169,6 +205,7 @@
     }
 
     @Test
+    @EnableCompatChanges(NsdManager.RUN_NATIVE_NSD_ONLY_IF_LEGACY_APPS)
     public void testCleanupDelayNoRequestActive() {
         when(mSettings.isEnabled()).thenReturn(true);