diff --git a/services/java/com/android/server/ConnectivityService.java b/services/java/com/android/server/ConnectivityService.java
index a6ddcab..f735c4c 100644
--- a/services/java/com/android/server/ConnectivityService.java
+++ b/services/java/com/android/server/ConnectivityService.java
@@ -96,6 +96,7 @@
 import com.android.internal.telephony.PhoneConstants;
 import com.android.internal.util.IndentingPrintWriter;
 import com.android.server.am.BatteryStatsService;
+import com.android.server.connectivity.Nat464Xlat;
 import com.android.server.connectivity.Tethering;
 import com.android.server.connectivity.Vpn;
 import com.android.server.net.BaseNetworkObserver;
@@ -154,6 +155,8 @@
     private boolean mLockdownEnabled;
     private LockdownVpnTracker mLockdownTracker;
 
+    private Nat464Xlat mClat;
+
     /** Lock around {@link #mUidRules} and {@link #mMeteredIfaces}. */
     private Object mRulesLock = new Object();
     /** Currently active network rules by UID. */
@@ -544,9 +547,12 @@
         mVpn = new Vpn(mContext, mVpnCallback, mNetd);
         mVpn.startMonitoring(mContext, mTrackerHandler);
 
+        mClat = new Nat464Xlat(mContext, mNetd, this, mTrackerHandler);
+
         try {
             mNetd.registerObserver(mTethering);
             mNetd.registerObserver(mDataActivityObserver);
+            mNetd.registerObserver(mClat);
         } catch (RemoteException e) {
             loge("Error registering observer :" + e);
         }
@@ -2276,6 +2282,17 @@
             }
         }
 
+        // Update 464xlat state.
+        // TODO: Move to handleConnect()
+        NetworkStateTracker tracker = mNetTrackers[netType];
+        if (mClat.requiresClat(netType, tracker)) {
+            if (mNetTrackers[netType].getNetworkInfo().isConnected()) {
+                mClat.startClat(tracker);
+            } else {
+                mClat.stopClat();
+            }
+        }
+
         // TODO: Temporary notifying upstread change to Tethering.
         //       @see bug/4455071
         /** Notify TetheringService if interface name has been changed. */
diff --git a/services/java/com/android/server/connectivity/Nat464Xlat.java b/services/java/com/android/server/connectivity/Nat464Xlat.java
new file mode 100644
index 0000000..2884eaf
--- /dev/null
+++ b/services/java/com/android/server/connectivity/Nat464Xlat.java
@@ -0,0 +1,189 @@
+/*
+ * Copyright (C) 2012 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 com.android.server.connectivity;
+
+import static android.net.ConnectivityManager.TYPE_MOBILE;
+
+import java.net.Inet4Address;
+
+import android.content.Context;
+import android.net.IConnectivityManager;
+import android.net.InterfaceConfiguration;
+import android.net.LinkAddress;
+import android.net.LinkProperties;
+import android.net.NetworkStateTracker;
+import android.net.NetworkUtils;
+import android.net.RouteInfo;
+import android.os.Handler;
+import android.os.Message;
+import android.os.INetworkManagementService;
+import android.os.RemoteException;
+import android.util.Slog;
+
+import com.android.server.net.BaseNetworkObserver;
+
+/**
+ * @hide
+ *
+ * Class to manage a 464xlat CLAT daemon.
+ */
+public class Nat464Xlat extends BaseNetworkObserver {
+    private Context mContext;
+    private INetworkManagementService mNMService;
+    private IConnectivityManager mConnService;
+    private NetworkStateTracker mTracker;
+    private Handler mHandler;
+
+    // Whether we started clatd and expect it to be running.
+    private boolean mIsStarted;
+    // Whether the clatd interface exists (i.e., clatd is running).
+    private boolean mIsRunning;
+    // The LinkProperties of the clat interface.
+    private LinkProperties mLP;
+
+    // This must match the interface name in clatd.conf.
+    private static final String CLAT_INTERFACE_NAME = "clat4";
+
+    private static final String TAG = "Nat464Xlat";
+
+    public Nat464Xlat(Context context, INetworkManagementService nmService,
+                      IConnectivityManager connService, Handler handler) {
+        mContext = context;
+        mNMService = nmService;
+        mConnService = connService;
+        mHandler = handler;
+
+        mIsStarted = false;
+        mIsRunning = false;
+        mLP = new LinkProperties();
+    }
+
+    /**
+     * Determines whether an interface requires clat.
+     * @param netType the network type (one of the
+     *   android.net.ConnectivityManager.TYPE_* constants)
+     * @param tracker the NetworkStateTracker corresponding to the network type.
+     * @return true if the interface requires clat, false otherwise.
+     */
+    public boolean requiresClat(int netType, NetworkStateTracker tracker) {
+        LinkProperties lp = tracker.getLinkProperties();
+        // Only support clat on mobile for now.
+        Slog.d(TAG, "requiresClat: netType=" + netType + ", hasIPv4Address=" +
+               lp.hasIPv4Address());
+        return netType == TYPE_MOBILE && !lp.hasIPv4Address();
+    }
+
+    /**
+     * Starts the clat daemon.
+     * @param lp The link properties of the interface to start clatd on.
+     */
+    public void startClat(NetworkStateTracker tracker) {
+        if (mIsStarted) {
+            Slog.e(TAG, "startClat: already started");
+            return;
+        }
+        mTracker = tracker;
+        LinkProperties lp = mTracker.getLinkProperties();
+        String iface = lp.getInterfaceName();
+        Slog.i(TAG, "Starting clatd on " + iface + ", lp=" + lp);
+        try {
+            mNMService.startClatd(iface);
+        } catch(RemoteException e) {
+            Slog.e(TAG, "Error starting clat daemon: " + e);
+        }
+        mIsStarted = true;
+    }
+
+    /**
+     * Stops the clat daemon.
+     */
+    public void stopClat() {
+        if (mIsStarted) {
+            Slog.i(TAG, "Stopping clatd");
+            try {
+                mNMService.stopClatd();
+            } catch(RemoteException e) {
+                Slog.e(TAG, "Error stopping clat daemon: " + e);
+            }
+            mIsStarted = false;
+            mIsRunning = false;
+            mTracker = null;
+            mLP.clear();
+        } else {
+            Slog.e(TAG, "stopClat: already stopped");
+        }
+    }
+
+    public boolean isStarted() {
+        return mIsStarted;
+    }
+
+    public boolean isRunning() {
+        return mIsRunning;
+    }
+
+    @Override
+    public void interfaceAdded(String iface) {
+        if (iface.equals(CLAT_INTERFACE_NAME)) {
+            Slog.i(TAG, "interface " + CLAT_INTERFACE_NAME +
+                   " added, mIsRunning = " + mIsRunning + " -> true");
+            mIsRunning = true;
+
+            // Get the network configuration of the clat interface, store it
+            // in our link properties, and stack it on top of the interface
+            // it's running on.
+            try {
+                InterfaceConfiguration config = mNMService.getInterfaceConfig(iface);
+                mLP.clear();
+                mLP.setInterfaceName(iface);
+                RouteInfo ipv4Default = new RouteInfo(new LinkAddress(Inet4Address.ANY, 0), null,
+                                                      iface);
+                mLP.addRoute(ipv4Default);
+                mLP.addLinkAddress(config.getLinkAddress());
+                mTracker.addStackedLink(mLP);
+                Slog.i(TAG, "Adding stacked link. tracker LP: " +
+                       mTracker.getLinkProperties());
+            } catch(RemoteException e) {
+                Slog.e(TAG, "Error getting link properties: " + e);
+            }
+
+            // Inform ConnectivityService that things have changed.
+            Message msg = mHandler.obtainMessage(
+                NetworkStateTracker.EVENT_CONFIGURATION_CHANGED,
+                mTracker.getNetworkInfo());
+            Slog.i(TAG, "sending message to ConnectivityService: " + msg);
+            msg.sendToTarget();
+        }
+    }
+
+    @Override
+    public void interfaceRemoved(String iface) {
+        if (iface == CLAT_INTERFACE_NAME) {
+            if (mIsRunning) {
+                NetworkUtils.resetConnections(
+                    CLAT_INTERFACE_NAME,
+                    NetworkUtils.RESET_IPV4_ADDRESSES);
+            }
+            Slog.i(TAG, "interface " + CLAT_INTERFACE_NAME +
+                   " removed, mIsRunning = " + mIsRunning + " -> false");
+            mIsRunning = false;
+            mTracker.removeStackedLink(mLP);
+            mLP.clear();
+            Slog.i(TAG, "mLP = " + mLP);
+        }
+    }
+};
diff --git a/services/java/com/android/server/connectivity/Tethering.java b/services/java/com/android/server/connectivity/Tethering.java
index e4a7ead..32f39b7 100644
--- a/services/java/com/android/server/connectivity/Tethering.java
+++ b/services/java/com/android/server/connectivity/Tethering.java
@@ -35,6 +35,7 @@
 import android.net.LinkProperties;
 import android.net.NetworkInfo;
 import android.net.NetworkUtils;
+import android.net.RouteInfo;
 import android.os.Binder;
 import android.os.HandlerThread;
 import android.os.IBinder;
@@ -1345,7 +1346,21 @@
                         linkProperties = mConnService.getLinkProperties(upType);
                     } catch (RemoteException e) { }
                     if (linkProperties != null) {
-                        iface = linkProperties.getInterfaceName();
+                        // Find the interface with the default IPv4 route. It may be the
+                        // interface described by linkProperties, or one of the interfaces
+                        // stacked on top of it.
+                        Log.i(TAG, "Finding IPv4 upstream interface on: " + linkProperties);
+                        RouteInfo ipv4Default = RouteInfo.selectBestRoute(
+                            linkProperties.getAllRoutes(), Inet4Address.ANY);
+                        if (ipv4Default != null) {
+                            iface = ipv4Default.getInterface();
+                            Log.i(TAG, "Found interface " + ipv4Default.getInterface());
+                        } else {
+                            Log.i(TAG, "No IPv4 upstream interface, giving up.");
+                        }
+                    }
+
+                    if (iface != null) {
                         String[] dnsServers = mDefaultDnsServers;
                         Collection<InetAddress> dnses = linkProperties.getDnses();
                         if (dnses != null) {