diff --git a/core/java/android/net/ConnectivityManager.java b/core/java/android/net/ConnectivityManager.java
index 826786b..99e368d 100644
--- a/core/java/android/net/ConnectivityManager.java
+++ b/core/java/android/net/ConnectivityManager.java
@@ -602,6 +602,27 @@
     }
 
     /**
+     * Returns a {@link Network} object corresponding to the currently active
+     * 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.
+     *
+     * @return a {@link Network} object for the current default network or
+     *        {@code null} if no default network is currently active
+     *
+     * <p>This method requires the caller to hold the permission
+     * {@link android.Manifest.permission#ACCESS_NETWORK_STATE}.
+     */
+    public Network getActiveNetwork() {
+        try {
+            return mService.getActiveNetwork();
+        } catch (RemoteException e) {
+            return null;
+        }
+    }
+
+    /**
      * Returns details about the currently active default data network
      * for a given uid.  This is for internal use only to avoid spying
      * other apps.
@@ -1927,12 +1948,18 @@
         } catch (RemoteException e) { }
     }
 
-    /** {@hide} */
-    public void registerNetworkAgent(Messenger messenger, NetworkInfo ni, LinkProperties lp,
+    /**
+     * @hide
+     * Register a NetworkAgent with ConnectivityService.
+     * @return NetID corresponding to NetworkAgent.
+     */
+    public int registerNetworkAgent(Messenger messenger, NetworkInfo ni, LinkProperties lp,
             NetworkCapabilities nc, int score, NetworkMisc misc) {
         try {
-            mService.registerNetworkAgent(messenger, ni, lp, nc, score, misc);
-        } catch (RemoteException e) { }
+            return mService.registerNetworkAgent(messenger, ni, lp, nc, score, misc);
+        } catch (RemoteException e) {
+            return NETID_UNSET;
+        }
     }
 
     /**
diff --git a/core/java/android/net/IConnectivityManager.aidl b/core/java/android/net/IConnectivityManager.aidl
index 31e60e7..171c7d4 100644
--- a/core/java/android/net/IConnectivityManager.aidl
+++ b/core/java/android/net/IConnectivityManager.aidl
@@ -42,6 +42,7 @@
 /** {@hide} */
 interface IConnectivityManager
 {
+    Network getActiveNetwork();
     NetworkInfo getActiveNetworkInfo();
     NetworkInfo getActiveNetworkInfoForUid(int uid);
     NetworkInfo getNetworkInfo(int networkType);
@@ -132,7 +133,7 @@
 
     void unregisterNetworkFactory(in Messenger messenger);
 
-    void registerNetworkAgent(in Messenger messenger, in NetworkInfo ni, in LinkProperties lp,
+    int registerNetworkAgent(in Messenger messenger, in NetworkInfo ni, in LinkProperties lp,
             in NetworkCapabilities nc, int score, in NetworkMisc misc);
 
     NetworkRequest requestNetwork(in NetworkCapabilities networkCapabilities,
diff --git a/core/java/android/net/NetworkAgent.java b/core/java/android/net/NetworkAgent.java
index 74d4ac2..ddaa808 100644
--- a/core/java/android/net/NetworkAgent.java
+++ b/core/java/android/net/NetworkAgent.java
@@ -42,6 +42,10 @@
  * @hide
  */
 public abstract class NetworkAgent extends Handler {
+    // Guaranteed to be valid (not NETID_UNSET), otherwise registerNetworkAgent() would have thrown
+    // an exception.
+    public final int netId;
+
     private volatile AsyncChannel mAsyncChannel;
     private final String LOG_TAG;
     private static final boolean DBG = true;
@@ -142,7 +146,7 @@
         if (VDBG) log("Registering NetworkAgent");
         ConnectivityManager cm = (ConnectivityManager)mContext.getSystemService(
                 Context.CONNECTIVITY_SERVICE);
-        cm.registerNetworkAgent(new Messenger(this), new NetworkInfo(ni),
+        netId = cm.registerNetworkAgent(new Messenger(this), new NetworkInfo(ni),
                 new LinkProperties(lp), new NetworkCapabilities(nc), score, misc);
     }
 
diff --git a/services/core/java/com/android/server/ConnectivityService.java b/services/core/java/com/android/server/ConnectivityService.java
index 3103592..ee44b09 100644
--- a/services/core/java/com/android/server/ConnectivityService.java
+++ b/services/core/java/com/android/server/ConnectivityService.java
@@ -20,6 +20,7 @@
 import static android.Manifest.permission.RECEIVE_DATA_ACTIVITY_CHANGE;
 import static android.net.ConnectivityManager.CONNECTIVITY_ACTION;
 import static android.net.ConnectivityManager.CONNECTIVITY_ACTION_IMMEDIATE;
+import static android.net.ConnectivityManager.NETID_UNSET;
 import static android.net.ConnectivityManager.TYPE_NONE;
 import static android.net.ConnectivityManager.TYPE_VPN;
 import static android.net.ConnectivityManager.getNetworkTypeName;
@@ -89,6 +90,7 @@
 import android.text.TextUtils;
 import android.util.Slog;
 import android.util.SparseArray;
+import android.util.SparseBooleanArray;
 import android.util.SparseIntArray;
 import android.util.Xml;
 
@@ -691,16 +693,15 @@
         return mNextNetworkRequestId++;
     }
 
-    private void assignNextNetId(NetworkAgentInfo nai) {
+    private int reserveNetId() {
         synchronized (mNetworkForNetId) {
             for (int i = MIN_NET_ID; i <= MAX_NET_ID; i++) {
                 int netId = mNextNetId;
                 if (++mNextNetId > MAX_NET_ID) mNextNetId = MIN_NET_ID;
                 // Make sure NetID unused.  http://b/16815182
-                if (mNetworkForNetId.get(netId) == null) {
-                    nai.network = new Network(netId);
-                    mNetworkForNetId.put(netId, nai);
-                    return;
+                if (!mNetIdInUse.get(netId)) {
+                    mNetIdInUse.put(netId, true);
+                    return netId;
                 }
             }
         }
@@ -859,6 +860,28 @@
         return getFilteredNetworkInfo(state.networkInfo, state.linkProperties, uid);
     }
 
+    @Override
+    public Network getActiveNetwork() {
+        enforceAccessPermission();
+        final int uid = Binder.getCallingUid();
+        final int user = UserHandle.getUserId(uid);
+        int vpnNetId = NETID_UNSET;
+        synchronized (mVpns) {
+            final Vpn vpn = mVpns.get(user);
+            if (vpn != null && vpn.appliesToUid(uid)) vpnNetId = vpn.getNetId();
+        }
+        NetworkAgentInfo nai;
+        if (vpnNetId != NETID_UNSET) {
+            synchronized (mNetworkForNetId) {
+                nai = mNetworkForNetId.get(vpnNetId);
+            }
+            if (nai != null) return nai.network;
+        }
+        nai = getDefaultNetwork();
+        if (nai != null && isNetworkWithLinkPropertiesBlocked(nai.linkProperties, uid)) nai = null;
+        return nai != null ? nai.network : null;
+    }
+
     /**
      * Find the first Provisioning network.
      *
@@ -1942,6 +1965,7 @@
                 if (nai != null) {
                     synchronized (mNetworkForNetId) {
                         mNetworkForNetId.remove(nai.network.netId);
+                        mNetIdInUse.delete(nai.network.netId);
                     }
                     // Just in case.
                     mLegacyTypeTracker.remove(nai);
@@ -1985,6 +2009,7 @@
             mLegacyTypeTracker.remove(nai);
             synchronized (mNetworkForNetId) {
                 mNetworkForNetId.remove(nai.network.netId);
+                mNetIdInUse.delete(nai.network.netId);
             }
             // Since we've lost the network, go through all the requests that
             // it was satisfying and see if any other factory can satisfy them.
@@ -3369,14 +3394,23 @@
      * and the are the highest scored network available.
      * the are keyed off the Requests requestId.
      */
+    // TODO: Yikes, this is accessed on multiple threads: add synchronization.
     private final SparseArray<NetworkAgentInfo> mNetworkForRequestId =
             new SparseArray<NetworkAgentInfo>();
 
+    // NOTE: Accessed on multiple threads, must be synchronized on itself.
+    @GuardedBy("mNetworkForNetId")
     private final SparseArray<NetworkAgentInfo> mNetworkForNetId =
             new SparseArray<NetworkAgentInfo>();
+    // NOTE: Accessed on multiple threads, synchronized with mNetworkForNetId.
+    // An entry is first added to mNetIdInUse, prior to mNetworkForNetId, so
+    // there may not be a strict 1:1 correlation between the two.
+    @GuardedBy("mNetworkForNetId")
+    private final SparseBooleanArray mNetIdInUse = new SparseBooleanArray();
 
     // NetworkAgentInfo keyed off its connecting messenger
     // TODO - eval if we can reduce the number of lists/hashmaps/sparsearrays
+    // NOTE: Only should be accessed on ConnectivityServiceThread, except dump().
     private final HashMap<Messenger, NetworkAgentInfo> mNetworkAgentInfos =
             new HashMap<Messenger, NetworkAgentInfo>();
 
@@ -3391,7 +3425,7 @@
         return nai == getDefaultNetwork();
     }
 
-    public void registerNetworkAgent(Messenger messenger, NetworkInfo networkInfo,
+    public int registerNetworkAgent(Messenger messenger, NetworkInfo networkInfo,
             LinkProperties linkProperties, NetworkCapabilities networkCapabilities,
             int currentScore, NetworkMisc networkMisc) {
         enforceConnectivityInternalPermission();
@@ -3399,20 +3433,23 @@
         // TODO: Instead of passing mDefaultRequest, provide an API to determine whether a Network
         // satisfies mDefaultRequest.
         NetworkAgentInfo nai = new NetworkAgentInfo(messenger, new AsyncChannel(),
-            new NetworkInfo(networkInfo), new LinkProperties(linkProperties),
-            new NetworkCapabilities(networkCapabilities), currentScore, mContext, mTrackerHandler,
-            new NetworkMisc(networkMisc), mDefaultRequest);
+                new Network(reserveNetId()), new NetworkInfo(networkInfo), new LinkProperties(
+                linkProperties), new NetworkCapabilities(networkCapabilities), currentScore,
+                mContext, mTrackerHandler, new NetworkMisc(networkMisc), mDefaultRequest);
         synchronized (this) {
             nai.networkMonitor.systemReady = mSystemReady;
         }
         if (DBG) log("registerNetworkAgent " + nai);
         mHandler.sendMessage(mHandler.obtainMessage(EVENT_REGISTER_NETWORK_AGENT, nai));
+        return nai.network.netId;
     }
 
     private void handleRegisterNetworkAgent(NetworkAgentInfo na) {
         if (VDBG) log("Got NetworkAgent Messenger");
         mNetworkAgentInfos.put(na.messenger, na);
-        assignNextNetId(na);
+        synchronized (mNetworkForNetId) {
+            mNetworkForNetId.put(na.network.netId, na);
+        }
         na.asyncChannel.connect(mContext, mTrackerHandler, na.messenger);
         NetworkInfo networkInfo = na.networkInfo;
         na.networkInfo = null;
diff --git a/services/core/java/com/android/server/connectivity/NetworkAgentInfo.java b/services/core/java/com/android/server/connectivity/NetworkAgentInfo.java
index f3e0bbc..2d1f939 100644
--- a/services/core/java/com/android/server/connectivity/NetworkAgentInfo.java
+++ b/services/core/java/com/android/server/connectivity/NetworkAgentInfo.java
@@ -40,7 +40,10 @@
  */
 public class NetworkAgentInfo {
     public NetworkInfo networkInfo;
-    public Network network;
+    // This Network object should always be used if possible, so as to encourage reuse of the
+    // enclosed socket factory and connection pool.  Avoid creating other Network objects.
+    // This Network object is always valid.
+    public final Network network;
     public LinkProperties linkProperties;
     public NetworkCapabilities networkCapabilities;
     public final NetworkMonitor networkMonitor;
@@ -83,12 +86,12 @@
     // Used by ConnectivityService to keep track of 464xlat.
     public Nat464Xlat clatd;
 
-    public NetworkAgentInfo(Messenger messenger, AsyncChannel ac, NetworkInfo info,
+    public NetworkAgentInfo(Messenger messenger, AsyncChannel ac, Network net, NetworkInfo info,
             LinkProperties lp, NetworkCapabilities nc, int score, Context context, Handler handler,
             NetworkMisc misc, NetworkRequest defaultRequest) {
         this.messenger = messenger;
         asyncChannel = ac;
-        network = null;
+        network = net;
         networkInfo = info;
         linkProperties = lp;
         networkCapabilities = nc;