diff --git a/Tethering/common/TetheringLib/src/android/net/ITetheringEventCallback.aidl b/Tethering/common/TetheringLib/src/android/net/ITetheringEventCallback.aidl
index a554193..b4e3ba4 100644
--- a/Tethering/common/TetheringLib/src/android/net/ITetheringEventCallback.aidl
+++ b/Tethering/common/TetheringLib/src/android/net/ITetheringEventCallback.aidl
@@ -35,4 +35,5 @@
     void onConfigurationChanged(in TetheringConfigurationParcel config);
     void onTetherStatesChanged(in TetherStatesParcel states);
     void onTetherClientsChanged(in List<TetheredClient> clients);
+    void onOffloadStatusChanged(int status);
 }
diff --git a/Tethering/common/TetheringLib/src/android/net/TetheringCallbackStartedParcel.aidl b/Tethering/common/TetheringLib/src/android/net/TetheringCallbackStartedParcel.aidl
index c064aa4..253eacb 100644
--- a/Tethering/common/TetheringLib/src/android/net/TetheringCallbackStartedParcel.aidl
+++ b/Tethering/common/TetheringLib/src/android/net/TetheringCallbackStartedParcel.aidl
@@ -31,4 +31,5 @@
     TetheringConfigurationParcel config;
     TetherStatesParcel states;
     List<TetheredClient> tetheredClients;
-}
\ No newline at end of file
+    int offloadStatus;
+}
diff --git a/Tethering/common/TetheringLib/src/android/net/TetheringManager.java b/Tethering/common/TetheringLib/src/android/net/TetheringManager.java
index fd9f713..7f831ce 100644
--- a/Tethering/common/TetheringLib/src/android/net/TetheringManager.java
+++ b/Tethering/common/TetheringLib/src/android/net/TetheringManager.java
@@ -18,6 +18,7 @@
 import static android.annotation.SystemApi.Client.MODULE_LIBRARIES;
 
 import android.Manifest;
+import android.annotation.IntDef;
 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.annotation.RequiresPermission;
@@ -34,6 +35,8 @@
 
 import com.android.internal.annotations.GuardedBy;
 
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -172,6 +175,23 @@
     public static final int TETHER_ERROR_NO_CHANGE_TETHERING_PERMISSION = 14;
     public static final int TETHER_ERROR_NO_ACCESS_TETHERING_PERMISSION = 15;
 
+    /** @hide */
+    @Retention(RetentionPolicy.SOURCE)
+    @IntDef(flag = false, value = {
+            TETHER_HARDWARE_OFFLOAD_STOPPED,
+            TETHER_HARDWARE_OFFLOAD_STARTED,
+            TETHER_HARDWARE_OFFLOAD_FAILED,
+    })
+    public @interface TetherOffloadStatus {
+    }
+
+    /** Tethering offload status is stopped. */
+    public static final int TETHER_HARDWARE_OFFLOAD_STOPPED = 0;
+    /** Tethering offload status is started. */
+    public static final int TETHER_HARDWARE_OFFLOAD_STARTED = 1;
+    /** Fail to start tethering offload. */
+    public static final int TETHER_HARDWARE_OFFLOAD_FAILED = 2;
+
     /**
      * Create a TetheringManager object for interacting with the tethering service.
      *
@@ -378,6 +398,9 @@
         @Override
         public void onTetherClientsChanged(List<TetheredClient> clients) { }
 
+        @Override
+        public void onOffloadStatusChanged(int status) { }
+
         public void waitForStarted() {
             mWaitForCallback.block(DEFAULT_TIMEOUT_MS);
             throwIfPermissionFailure(mError);
@@ -802,6 +825,14 @@
          * @param clients The new set of tethered clients; the collection is not ordered.
          */
         public void onClientsChanged(@NonNull Collection<TetheredClient> clients) {}
+
+        /**
+         * Called when tethering offload status changes.
+         *
+         * <p>This will be called immediately after the callback is registered.
+         * @param status The offload status.
+         */
+        public void onOffloadStatusChanged(@TetherOffloadStatus int status) {}
     }
 
     /**
@@ -925,6 +956,7 @@
                         maybeSendTetherableIfacesChangedCallback(parcel.states);
                         maybeSendTetheredIfacesChangedCallback(parcel.states);
                         callback.onClientsChanged(parcel.tetheredClients);
+                        callback.onOffloadStatusChanged(parcel.offloadStatus);
                     });
                 }
 
@@ -960,6 +992,11 @@
                 public void onTetherClientsChanged(final List<TetheredClient> clients) {
                     executor.execute(() -> callback.onClientsChanged(clients));
                 }
+
+                @Override
+                public void onOffloadStatusChanged(final int status) {
+                    executor.execute(() -> callback.onOffloadStatusChanged(status));
+                }
             };
             getConnector(c -> c.registerTetheringEventCallback(remoteCallback, callerPkg));
             mTetheringEventCallbacks.put(callback, remoteCallback);
@@ -1131,6 +1168,25 @@
     public boolean isTetheringSupported() {
         final String callerPkg = mContext.getOpPackageName();
 
+        return isTetheringSupported(callerPkg);
+    }
+
+    /**
+     * Check if the device allows for tethering. It may be disabled via {@code ro.tether.denied}
+     * system property, Settings.TETHER_SUPPORTED or due to device configuration. This is useful
+     * for system components that query this API on behalf of an app. In particular, Bluetooth
+     * has @UnsupportedAppUsage calls that will let apps turn on bluetooth tethering if they have
+     * the right permissions, but such an app needs to know whether it can (permissions as well
+     * as support from the device) turn on tethering in the first place to show the appropriate UI.
+     *
+     * @param callerPkg The caller package name, if it is not matching the calling uid,
+     *       SecurityException would be thrown.
+     * @return a boolean - {@code true} indicating Tethering is supported.
+     * @hide
+     */
+    @SystemApi(client = MODULE_LIBRARIES)
+    public boolean isTetheringSupported(@NonNull final String callerPkg) {
+
         final RequestDispatcher dispatcher = new RequestDispatcher();
         final int ret = dispatcher.waitForResult((connector, listener) -> {
             try {
diff --git a/Tethering/src/android/net/ip/IpServer.java b/Tethering/src/android/net/ip/IpServer.java
index 3acc766..38f8609 100644
--- a/Tethering/src/android/net/ip/IpServer.java
+++ b/Tethering/src/android/net/ip/IpServer.java
@@ -810,7 +810,7 @@
                     rule.dstMac.toByteArray());
             mIpv6ForwardingRules.put(rule.address, rule);
         } catch (RemoteException | ServiceSpecificException e) {
-            Log.e(TAG, "Could not add IPv6 downstream rule: " + e);
+            mLog.e("Could not add IPv6 downstream rule: ", e);
         }
     }
 
@@ -821,10 +821,17 @@
                 mIpv6ForwardingRules.remove(rule.address);
             }
         } catch (RemoteException | ServiceSpecificException e) {
-            Log.e(TAG, "Could not remove IPv6 downstream rule: " + e);
+            mLog.e("Could not remove IPv6 downstream rule: ", e);
         }
     }
 
+    private void clearIpv6ForwardingRules() {
+        for (Ipv6ForwardingRule rule : mIpv6ForwardingRules.values()) {
+            removeIpv6ForwardingRule(rule, false /*removeFromMap*/);
+        }
+        mIpv6ForwardingRules.clear();
+    }
+
     // Convenience method to replace a rule with the same rule on a new upstream interface.
     // Allows replacing the rules in one iteration pass without ConcurrentModificationExceptions.
     // Relies on the fact that rules are in a map indexed by IP address.
@@ -837,6 +844,12 @@
     // changes or if a neighbor event is received.
     private void updateIpv6ForwardingRules(int prevUpstreamIfindex, int upstreamIfindex,
             NeighborEvent e) {
+        // If we no longer have an upstream, clear forwarding rules and do nothing else.
+        if (upstreamIfindex == 0) {
+            clearIpv6ForwardingRules();
+            return;
+        }
+
         // If the upstream interface has changed, remove all rules and re-add them with the new
         // upstream interface.
         if (prevUpstreamIfindex != upstreamIfindex) {
@@ -846,13 +859,14 @@
         }
 
         // If we're here to process a NeighborEvent, do so now.
+        // mInterfaceParams must be non-null or the event would not have arrived.
         if (e == null) return;
         if (!(e.ip instanceof Inet6Address) || e.ip.isMulticastAddress()
                 || e.ip.isLoopbackAddress() || e.ip.isLinkLocalAddress()) {
             return;
         }
 
-        Ipv6ForwardingRule rule = new Ipv6ForwardingRule(mLastIPv6UpstreamIfindex,
+        Ipv6ForwardingRule rule = new Ipv6ForwardingRule(upstreamIfindex,
                 mInterfaceParams.index, (Inet6Address) e.ip, mInterfaceParams.macAddr,
                 e.macAddr);
         if (e.isValid()) {
@@ -1095,6 +1109,7 @@
 
             for (String ifname : mUpstreamIfaceSet.ifnames) cleanupUpstreamInterface(ifname);
             mUpstreamIfaceSet = null;
+            clearIpv6ForwardingRules();
         }
 
         private void cleanupUpstreamInterface(String upstreamIface) {
diff --git a/Tethering/src/com/android/server/connectivity/tethering/Tethering.java b/Tethering/src/com/android/server/connectivity/tethering/Tethering.java
index ca74430..f89da84 100644
--- a/Tethering/src/com/android/server/connectivity/tethering/Tethering.java
+++ b/Tethering/src/com/android/server/connectivity/tethering/Tethering.java
@@ -44,6 +44,9 @@
 import static android.net.TetheringManager.TETHER_ERROR_SERVICE_UNAVAIL;
 import static android.net.TetheringManager.TETHER_ERROR_UNAVAIL_IFACE;
 import static android.net.TetheringManager.TETHER_ERROR_UNKNOWN_IFACE;
+import static android.net.TetheringManager.TETHER_HARDWARE_OFFLOAD_FAILED;
+import static android.net.TetheringManager.TETHER_HARDWARE_OFFLOAD_STARTED;
+import static android.net.TetheringManager.TETHER_HARDWARE_OFFLOAD_STOPPED;
 import static android.net.util.TetheringMessageBase.BASE_MASTER;
 import static android.net.wifi.WifiManager.EXTRA_WIFI_AP_INTERFACE_NAME;
 import static android.net.wifi.WifiManager.EXTRA_WIFI_AP_MODE;
@@ -220,6 +223,7 @@
     private final UserRestrictionActionListener mTetheringRestriction;
     private final ActiveDataSubIdListener mActiveDataSubIdListener;
     private final ConnectedClientsTracker mConnectedClientsTracker;
+    private final TetheringThreadExecutor mExecutor;
     private int mActiveDataSubId = INVALID_SUBSCRIPTION_ID;
     // All the usage of mTetheringEventCallback should run in the same thread.
     private ITetheringEventCallback mTetheringEventCallback = null;
@@ -236,6 +240,7 @@
     private TetherStatesParcel mTetherStatesParcel;
     private boolean mDataSaverEnabled = false;
     private String mWifiP2pTetherInterface = null;
+    private int mOffloadStatus = TETHER_HARDWARE_OFFLOAD_STOPPED;
 
     @GuardedBy("mPublicSync")
     private EthernetManager.TetheredInterfaceRequest mEthernetIfaceRequest;
@@ -296,8 +301,8 @@
         final UserManager userManager = (UserManager) mContext.getSystemService(
                 Context.USER_SERVICE);
         mTetheringRestriction = new UserRestrictionActionListener(userManager, this);
-        final TetheringThreadExecutor executor = new TetheringThreadExecutor(mHandler);
-        mActiveDataSubIdListener = new ActiveDataSubIdListener(executor);
+        mExecutor = new TetheringThreadExecutor(mHandler);
+        mActiveDataSubIdListener = new ActiveDataSubIdListener(mExecutor);
 
         // Load tethering configuration.
         updateConfiguration();
@@ -315,9 +320,7 @@
 
         final WifiManager wifiManager = getWifiManager();
         if (wifiManager != null) {
-            wifiManager.registerSoftApCallback(
-                  mHandler::post /* executor */,
-                  new TetheringSoftApCallback());
+            wifiManager.registerSoftApCallback(mExecutor, new TetheringSoftApCallback());
         }
     }
 
@@ -606,14 +609,17 @@
                 Context.ETHERNET_SERVICE);
         synchronized (mPublicSync) {
             if (enable) {
+                if (mEthernetCallback != null) return TETHER_ERROR_NO_ERROR;
+
                 mEthernetCallback = new EthernetCallback();
-                mEthernetIfaceRequest = em.requestTetheredInterface(mEthernetCallback);
+                mEthernetIfaceRequest = em.requestTetheredInterface(mExecutor, mEthernetCallback);
             } else {
-                if (mConfiguredEthernetIface != null) {
-                    stopEthernetTetheringLocked();
+                stopEthernetTetheringLocked();
+                if (mEthernetCallback != null) {
                     mEthernetIfaceRequest.release();
+                    mEthernetCallback = null;
+                    mEthernetIfaceRequest = null;
                 }
-                mEthernetCallback = null;
             }
         }
         return TETHER_ERROR_NO_ERROR;
@@ -1899,12 +1905,15 @@
         // OffloadController implementation.
         class OffloadWrapper {
             public void start() {
-                mOffloadController.start();
+                final int status = mOffloadController.start() ? TETHER_HARDWARE_OFFLOAD_STARTED
+                        : TETHER_HARDWARE_OFFLOAD_FAILED;
+                updateOffloadStatus(status);
                 sendOffloadExemptPrefixes();
             }
 
             public void stop() {
                 mOffloadController.stop();
+                updateOffloadStatus(TETHER_HARDWARE_OFFLOAD_STOPPED);
             }
 
             public void updateUpstreamNetworkState(UpstreamNetworkState ns) {
@@ -1965,6 +1974,13 @@
 
                 mOffloadController.setLocalPrefixes(localPrefixes);
             }
+
+            private void updateOffloadStatus(final int newStatus) {
+                if (newStatus == mOffloadStatus) return;
+
+                mOffloadStatus = newStatus;
+                reportOffloadStatusChanged(mOffloadStatus);
+            }
         }
     }
 
@@ -1999,6 +2015,7 @@
             parcel.tetheredClients = hasListPermission
                     ? mConnectedClientsTracker.getLastTetheredClients()
                     : Collections.emptyList();
+            parcel.offloadStatus = mOffloadStatus;
             try {
                 callback.onCallbackStarted(parcel);
             } catch (RemoteException e) {
@@ -2093,6 +2110,21 @@
         }
     }
 
+    private void reportOffloadStatusChanged(final int status) {
+        final int length = mTetheringEventCallbacks.beginBroadcast();
+        try {
+            for (int i = 0; i < length; i++) {
+                try {
+                    mTetheringEventCallbacks.getBroadcastItem(i).onOffloadStatusChanged(status);
+                } catch (RemoteException e) {
+                    // Not really very much to do here.
+                }
+            }
+        } finally {
+            mTetheringEventCallbacks.finishBroadcast();
+        }
+    }
+
     void dump(@NonNull FileDescriptor fd, @NonNull PrintWriter writer, @Nullable String[] args) {
         // Binder.java closes the resource for us.
         @SuppressWarnings("resource")
diff --git a/Tethering/tests/unit/src/android/net/ip/IpServerTest.java b/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
index 33b3558..948266d 100644
--- a/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
+++ b/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
@@ -43,6 +43,7 @@
 import static org.junit.Assert.fail;
 import static org.mockito.ArgumentMatchers.argThat;
 import static org.mockito.Matchers.any;
+import static org.mockito.Matchers.anyInt;
 import static org.mockito.Matchers.anyString;
 import static org.mockito.Matchers.eq;
 import static org.mockito.Mockito.doAnswer;
@@ -546,9 +547,9 @@
         reset(mNetd);
 
         // Link-local and multicast neighbors are ignored.
-        recvNewNeigh(notMyIfindex, neighLL, NUD_REACHABLE, macA);
+        recvNewNeigh(myIfindex, neighLL, NUD_REACHABLE, macA);
         verifyNoMoreInteractions(mNetd);
-        recvNewNeigh(notMyIfindex, neighMC, NUD_REACHABLE, macA);
+        recvNewNeigh(myIfindex, neighMC, NUD_REACHABLE, macA);
         verifyNoMoreInteractions(mNetd);
 
         // A neighbor that is no longer valid causes the rule to be removed.
@@ -578,6 +579,52 @@
                 eq(neighB.getAddress()), eq(myMac.toByteArray()), eq(macB.toByteArray()));
         inOrder.verify(mNetd).tetherRuleRemoveDownstreamIpv6(eq(UPSTREAM_IFINDEX),
                 eq(neighB.getAddress()));
+        reset(mNetd);
+
+        // When the upstream is lost, rules are removed.
+        dispatchTetherConnectionChanged(null, null);
+        verify(mNetd).tetherRuleRemoveDownstreamIpv6(eq(UPSTREAM_IFINDEX2),
+                eq(neighA.getAddress()));
+        verify(mNetd).tetherRuleRemoveDownstreamIpv6(eq(UPSTREAM_IFINDEX2),
+                eq(neighB.getAddress()));
+        reset(mNetd);
+
+        // If the upstream is IPv4-only, no rules are added.
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE);
+        reset(mNetd);
+        recvNewNeigh(myIfindex, neighA, NUD_REACHABLE, macA);
+        verifyNoMoreInteractions(mNetd);
+
+        // Rules can be added again once upstream IPv6 connectivity is available.
+        lp.setInterfaceName(UPSTREAM_IFACE);
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE, lp);
+        recvNewNeigh(myIfindex, neighB, NUD_REACHABLE, macB);
+        verify(mNetd).tetherRuleAddDownstreamIpv6(eq(myIfindex), eq(UPSTREAM_IFINDEX),
+                eq(neighB.getAddress()), eq(myMac.toByteArray()), eq(macB.toByteArray()));
+        verify(mNetd, never()).tetherRuleAddDownstreamIpv6(anyInt(), anyInt(),
+                eq(neighA.getAddress()), any(), any());
+
+        // If upstream IPv6 connectivity is lost, rules are removed.
+        reset(mNetd);
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE, null);
+        verify(mNetd).tetherRuleRemoveDownstreamIpv6(eq(UPSTREAM_IFINDEX), eq(neighB.getAddress()));
+
+        // When the interface goes down, rules are removed.
+        lp.setInterfaceName(UPSTREAM_IFACE);
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE, lp);
+        recvNewNeigh(myIfindex, neighA, NUD_REACHABLE, macA);
+        recvNewNeigh(myIfindex, neighB, NUD_REACHABLE, macB);
+        verify(mNetd).tetherRuleAddDownstreamIpv6(eq(myIfindex), eq(UPSTREAM_IFINDEX),
+                eq(neighA.getAddress()), eq(myMac.toByteArray()), eq(macA.toByteArray()));
+        verify(mNetd).tetherRuleAddDownstreamIpv6(eq(myIfindex), eq(UPSTREAM_IFINDEX),
+                eq(neighB.getAddress()), eq(myMac.toByteArray()), eq(macB.toByteArray()));
+        reset(mNetd);
+
+        mIpServer.stop();
+        mLooper.dispatchAll();
+        verify(mNetd).tetherRuleRemoveDownstreamIpv6(eq(UPSTREAM_IFINDEX), eq(neighA.getAddress()));
+        verify(mNetd).tetherRuleRemoveDownstreamIpv6(eq(UPSTREAM_IFINDEX), eq(neighB.getAddress()));
+        reset(mNetd);
     }
 
     private void assertDhcpStarted(IpPrefix expectedPrefix) throws Exception {
@@ -624,16 +671,15 @@
      * @param v6lp IPv6 LinkProperties of the upstream interface, or null for an IPv4-only upstream.
      */
     private void dispatchTetherConnectionChanged(String upstreamIface, LinkProperties v6lp) {
-        mIpServer.sendMessage(IpServer.CMD_TETHER_CONNECTION_CHANGED,
-                new InterfaceSet(upstreamIface));
-        if (v6lp != null) {
-            mIpServer.sendMessage(IpServer.CMD_IPV6_TETHER_UPDATE, v6lp);
-        }
+        dispatchTetherConnectionChanged(upstreamIface);
+        mIpServer.sendMessage(IpServer.CMD_IPV6_TETHER_UPDATE, v6lp);
         mLooper.dispatchAll();
     }
 
     private void dispatchTetherConnectionChanged(String upstreamIface) {
-        dispatchTetherConnectionChanged(upstreamIface, null);
+        final InterfaceSet ifs = (upstreamIface != null) ? new InterfaceSet(upstreamIface) : null;
+        mIpServer.sendMessage(IpServer.CMD_TETHER_CONNECTION_CHANGED, ifs);
+        mLooper.dispatchAll();
     }
 
     private void assertIPv4AddressAndDirectlyConnectedRoute(LinkProperties lp) {
diff --git a/Tethering/tests/unit/src/com/android/server/connectivity/tethering/TetheringTest.java b/Tethering/tests/unit/src/com/android/server/connectivity/tethering/TetheringTest.java
index f2074bd..af7ad66 100644
--- a/Tethering/tests/unit/src/com/android/server/connectivity/tethering/TetheringTest.java
+++ b/Tethering/tests/unit/src/com/android/server/connectivity/tethering/TetheringTest.java
@@ -28,11 +28,15 @@
 import static android.net.TetheringManager.EXTRA_ACTIVE_LOCAL_ONLY;
 import static android.net.TetheringManager.EXTRA_ACTIVE_TETHER;
 import static android.net.TetheringManager.EXTRA_AVAILABLE_TETHER;
+import static android.net.TetheringManager.TETHERING_ETHERNET;
 import static android.net.TetheringManager.TETHERING_NCM;
 import static android.net.TetheringManager.TETHERING_USB;
 import static android.net.TetheringManager.TETHERING_WIFI;
 import static android.net.TetheringManager.TETHER_ERROR_NO_ERROR;
 import static android.net.TetheringManager.TETHER_ERROR_UNKNOWN_IFACE;
+import static android.net.TetheringManager.TETHER_HARDWARE_OFFLOAD_FAILED;
+import static android.net.TetheringManager.TETHER_HARDWARE_OFFLOAD_STARTED;
+import static android.net.TetheringManager.TETHER_HARDWARE_OFFLOAD_STOPPED;
 import static android.net.dhcp.IDhcpServer.STATUS_SUCCESS;
 import static android.net.wifi.WifiManager.EXTRA_WIFI_AP_INTERFACE_NAME;
 import static android.net.wifi.WifiManager.EXTRA_WIFI_AP_MODE;
@@ -75,6 +79,8 @@
 import android.content.res.Resources;
 import android.hardware.usb.UsbManager;
 import android.net.ConnectivityManager;
+import android.net.EthernetManager;
+import android.net.EthernetManager.TetheredInterfaceRequest;
 import android.net.INetd;
 import android.net.ITetheringEventCallback;
 import android.net.InetAddresses;
@@ -166,6 +172,7 @@
     @Mock private Context mContext;
     @Mock private NetworkStatsManager mStatsManager;
     @Mock private OffloadHardwareInterface mOffloadHardwareInterface;
+    @Mock private OffloadHardwareInterface.ForwardedStats mForwardedStats;
     @Mock private Resources mResources;
     @Mock private TelephonyManager mTelephonyManager;
     @Mock private UsbManager mUsbManager;
@@ -180,6 +187,7 @@
     @Mock private UserManager mUserManager;
     @Mock private NetworkRequest mNetworkRequest;
     @Mock private ConnectivityManager mCm;
+    @Mock private EthernetManager mEm;
 
     private final MockIpServerDependencies mIpServerDependencies =
             spy(new MockIpServerDependencies());
@@ -232,6 +240,7 @@
             if (Context.USER_SERVICE.equals(name)) return mUserManager;
             if (Context.NETWORK_STATS_SERVICE.equals(name)) return mStatsManager;
             if (Context.CONNECTIVITY_SERVICE.equals(name)) return mCm;
+            if (Context.ETHERNET_SERVICE.equals(name)) return mEm;
             return super.getSystemService(name);
         }
 
@@ -458,6 +467,9 @@
         mInterfaceConfiguration.flags = new String[0];
         when(mRouterAdvertisementDaemon.start())
                 .thenReturn(true);
+        initOffloadConfiguration(true /* offloadConfig */, true /* offloadControl */,
+                0 /* defaultDisabled */);
+        when(mOffloadHardwareInterface.getForwardedStats(any())).thenReturn(mForwardedStats);
 
         mServiceContext = new TestContext(mContext);
         when(mContext.getSystemService(Context.NOTIFICATION_SERVICE)).thenReturn(null);
@@ -1131,6 +1143,7 @@
         private final ArrayList<TetheringConfigurationParcel> mTetheringConfigs =
                 new ArrayList<>();
         private final ArrayList<TetherStatesParcel> mTetherStates = new ArrayList<>();
+        private final ArrayList<Integer> mOffloadStatus = new ArrayList<>();
 
         // This function will remove the recorded callbacks, so it must be called once for
         // each callback. If this is called after multiple callback, the order matters.
@@ -1166,6 +1179,11 @@
             assertNoConfigChangeCallback();
         }
 
+        public void expectOffloadStatusChanged(final int expectedStatus) {
+            assertOffloadStatusChangedCallback();
+            assertEquals(mOffloadStatus.remove(0), new Integer(expectedStatus));
+        }
+
         public TetherStatesParcel pollTetherStatesChanged() {
             assertStateChangeCallback();
             return mTetherStates.remove(0);
@@ -1192,10 +1210,16 @@
         }
 
         @Override
+        public void onOffloadStatusChanged(final int status) {
+            mOffloadStatus.add(status);
+        }
+
+        @Override
         public void onCallbackStarted(TetheringCallbackStartedParcel parcel) {
             mActualUpstreams.add(parcel.upstreamNetwork);
             mTetheringConfigs.add(parcel.config);
             mTetherStates.add(parcel.states);
+            mOffloadStatus.add(parcel.offloadStatus);
         }
 
         @Override
@@ -1217,6 +1241,10 @@
             assertFalse(mTetherStates.isEmpty());
         }
 
+        public void assertOffloadStatusChangedCallback() {
+            assertFalse(mOffloadStatus.isEmpty());
+        }
+
         public void assertNoCallback() {
             assertNoUpstreamChangeCallback();
             assertNoConfigChangeCallback();
@@ -1265,6 +1293,7 @@
                 mTethering.getTetheringConfiguration().toStableParcelable());
         TetherStatesParcel tetherState = callback.pollTetherStatesChanged();
         assertTetherStatesNotNullButEmpty(tetherState);
+        callback.expectOffloadStatusChanged(TETHER_HARDWARE_OFFLOAD_STOPPED);
         // 2. Enable wifi tethering.
         UpstreamNetworkState upstreamState = buildMobileDualStackUpstreamState();
         when(mUpstreamNetworkMonitor.getCurrentPreferredUpstream()).thenReturn(upstreamState);
@@ -1282,6 +1311,7 @@
         tetherState = callback.pollTetherStatesChanged();
         assertArrayEquals(tetherState.tetheredList, new String[] {TEST_WLAN_IFNAME});
         callback.expectUpstreamChanged(upstreamState.network);
+        callback.expectOffloadStatusChanged(TETHER_HARDWARE_OFFLOAD_STARTED);
 
         // 3. Register second callback.
         mTethering.registerTetheringEventCallback(callback2);
@@ -1291,6 +1321,7 @@
                 mTethering.getTetheringConfiguration().toStableParcelable());
         tetherState = callback2.pollTetherStatesChanged();
         assertEquals(tetherState.tetheredList, new String[] {TEST_WLAN_IFNAME});
+        callback2.expectOffloadStatusChanged(TETHER_HARDWARE_OFFLOAD_STARTED);
 
         // 4. Unregister first callback and disable wifi tethering
         mTethering.unregisterTetheringEventCallback(callback);
@@ -1302,10 +1333,59 @@
         assertArrayEquals(tetherState.availableList, new String[] {TEST_WLAN_IFNAME});
         mLooper.dispatchAll();
         callback2.expectUpstreamChanged(new Network[] {null});
+        callback2.expectOffloadStatusChanged(TETHER_HARDWARE_OFFLOAD_STOPPED);
         callback.assertNoCallback();
     }
 
     @Test
+    public void testReportFailCallbackIfOffloadNotSupported() throws Exception {
+        final UpstreamNetworkState upstreamState = buildMobileDualStackUpstreamState();
+        TestTetheringEventCallback callback = new TestTetheringEventCallback();
+        mTethering.registerTetheringEventCallback(callback);
+        mLooper.dispatchAll();
+        callback.expectOffloadStatusChanged(TETHER_HARDWARE_OFFLOAD_STOPPED);
+
+        // 1. Offload fail if no OffloadConfig.
+        initOffloadConfiguration(false /* offloadConfig */, true /* offloadControl */,
+                0 /* defaultDisabled */);
+        runUsbTethering(upstreamState);
+        callback.expectOffloadStatusChanged(TETHER_HARDWARE_OFFLOAD_FAILED);
+        runStopUSBTethering();
+        callback.expectOffloadStatusChanged(TETHER_HARDWARE_OFFLOAD_STOPPED);
+        reset(mUsbManager);
+        // 2. Offload fail if no OffloadControl.
+        initOffloadConfiguration(true /* offloadConfig */, false /* offloadControl */,
+                0 /* defaultDisabled */);
+        runUsbTethering(upstreamState);
+        callback.expectOffloadStatusChanged(TETHER_HARDWARE_OFFLOAD_FAILED);
+        runStopUSBTethering();
+        callback.expectOffloadStatusChanged(TETHER_HARDWARE_OFFLOAD_STOPPED);
+        reset(mUsbManager);
+        // 3. Offload fail if disabled by settings.
+        initOffloadConfiguration(true /* offloadConfig */, true /* offloadControl */,
+                1 /* defaultDisabled */);
+        runUsbTethering(upstreamState);
+        callback.expectOffloadStatusChanged(TETHER_HARDWARE_OFFLOAD_FAILED);
+        runStopUSBTethering();
+        callback.expectOffloadStatusChanged(TETHER_HARDWARE_OFFLOAD_STOPPED);
+    }
+
+    private void runStopUSBTethering() {
+        mTethering.stopTethering(TETHERING_USB);
+        mLooper.dispatchAll();
+        mTethering.interfaceRemoved(TEST_USB_IFNAME);
+        mLooper.dispatchAll();
+    }
+
+    private void initOffloadConfiguration(final boolean offloadConfig,
+            final boolean offloadControl, final int defaultDisabled) {
+        when(mOffloadHardwareInterface.initOffloadConfig()).thenReturn(offloadConfig);
+        when(mOffloadHardwareInterface.initOffloadControl(any())).thenReturn(offloadControl);
+        when(mOffloadHardwareInterface.getDefaultTetherOffloadDisabled()).thenReturn(
+                defaultDisabled);
+    }
+
+    @Test
     public void testMultiSimAware() throws Exception {
         final TetheringConfiguration initailConfig = mTethering.getTetheringConfiguration();
         assertEquals(INVALID_SUBSCRIPTION_ID, initailConfig.activeDataSubId);
@@ -1316,6 +1396,24 @@
         assertEquals(fakeSubId, newConfig.activeDataSubId);
     }
 
+    @Test
+    public void testNoDuplicatedEthernetRequest() throws Exception {
+        final TetheredInterfaceRequest mockRequest = mock(TetheredInterfaceRequest.class);
+        when(mEm.requestTetheredInterface(any(), any())).thenReturn(mockRequest);
+        mTethering.startTethering(createTetheringRquestParcel(TETHERING_ETHERNET), null);
+        mLooper.dispatchAll();
+        verify(mEm, times(1)).requestTetheredInterface(any(), any());
+        mTethering.startTethering(createTetheringRquestParcel(TETHERING_ETHERNET), null);
+        mLooper.dispatchAll();
+        verifyNoMoreInteractions(mEm);
+        mTethering.stopTethering(TETHERING_ETHERNET);
+        mLooper.dispatchAll();
+        verify(mockRequest, times(1)).release();
+        mTethering.stopTethering(TETHERING_ETHERNET);
+        mLooper.dispatchAll();
+        verifyNoMoreInteractions(mEm);
+    }
+
     private void workingWifiP2pGroupOwner(
             boolean emulateInterfaceStatusChanged) throws Exception {
         if (emulateInterfaceStatusChanged) {