diff --git a/framework/src/android/net/NetworkCapabilities.java b/framework/src/android/net/NetworkCapabilities.java
index e9bcd95..51c5585 100644
--- a/framework/src/android/net/NetworkCapabilities.java
+++ b/framework/src/android/net/NetworkCapabilities.java
@@ -2129,14 +2129,17 @@
             sb.append(" SubscriptionIds: ").append(mSubIds);
         }
 
-        if (mUnderlyingNetworks != null && mUnderlyingNetworks.size() > 0) {
-            sb.append(" Underlying networks: [");
+        sb.append(" UnderlyingNetworks: ");
+        if (mUnderlyingNetworks != null) {
+            sb.append("[");
             final StringJoiner joiner = new StringJoiner(",");
             for (int i = 0; i < mUnderlyingNetworks.size(); i++) {
                 joiner.add(mUnderlyingNetworks.get(i).toString());
             }
             sb.append(joiner.toString());
             sb.append("]");
+        } else {
+            sb.append("Null");
         }
 
         sb.append("]");
diff --git a/service/src/com/android/server/ConnectivityService.java b/service/src/com/android/server/ConnectivityService.java
index 408dba3..88cd876 100644
--- a/service/src/com/android/server/ConnectivityService.java
+++ b/service/src/com/android/server/ConnectivityService.java
@@ -2032,6 +2032,7 @@
         if (!checkSettingsPermission(callerPid, callerUid)) {
             newNc.setUids(null);
             newNc.setSSID(null);
+            newNc.setUnderlyingNetworks(null);
         }
         if (newNc.getNetworkSpecifier() != null) {
             newNc.setNetworkSpecifier(newNc.getNetworkSpecifier().redact());
@@ -7305,7 +7306,9 @@
         boolean suspended = true; // suspended if all underlying are suspended
 
         boolean hadUnderlyingNetworks = false;
+        ArrayList<Network> newUnderlyingNetworks = null;
         if (null != underlyingNetworks) {
+            newUnderlyingNetworks = new ArrayList<>();
             for (Network underlyingNetwork : underlyingNetworks) {
                 final NetworkAgentInfo underlying =
                         getNetworkAgentInfoForNetwork(underlyingNetwork);
@@ -7335,6 +7338,7 @@
                 // If this network is not suspended, the VPN is not suspended (the VPN
                 // is able to transfer some data).
                 suspended &= !underlyingCaps.hasCapability(NET_CAPABILITY_NOT_SUSPENDED);
+                newUnderlyingNetworks.add(underlyingNetwork);
             }
         }
         if (!hadUnderlyingNetworks) {
@@ -7352,6 +7356,7 @@
         newNc.setCapability(NET_CAPABILITY_NOT_ROAMING, !roaming);
         newNc.setCapability(NET_CAPABILITY_NOT_CONGESTED, !congested);
         newNc.setCapability(NET_CAPABILITY_NOT_SUSPENDED, !suspended);
+        newNc.setUnderlyingNetworks(newUnderlyingNetworks);
     }
 
     /**
diff --git a/service/src/com/android/server/connectivity/NetworkAgentInfo.java b/service/src/com/android/server/connectivity/NetworkAgentInfo.java
index 6426f86..b7f3ed9 100644
--- a/service/src/com/android/server/connectivity/NetworkAgentInfo.java
+++ b/service/src/com/android/server/connectivity/NetworkAgentInfo.java
@@ -377,6 +377,9 @@
         this.creatorUid = creatorUid;
         mLingerDurationMs = lingerDurationMs;
         mQosCallbackTracker = qosCallbackTracker;
+        declaredUnderlyingNetworks = (nc.getUnderlyingNetworks() != null)
+                ? nc.getUnderlyingNetworks().toArray(new Network[0])
+                : null;
     }
 
     private class AgentDeathMonitor implements IBinder.DeathRecipient {
diff --git a/tests/unit/java/com/android/server/ConnectivityServiceTest.java b/tests/unit/java/com/android/server/ConnectivityServiceTest.java
index 352a468..c54a11e 100644
--- a/tests/unit/java/com/android/server/ConnectivityServiceTest.java
+++ b/tests/unit/java/com/android/server/ConnectivityServiceTest.java
@@ -151,6 +151,7 @@
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
+import static org.junit.Assume.assumeTrue;
 import static org.mockito.AdditionalMatchers.aryEq;
 import static org.mockito.ArgumentMatchers.anyBoolean;
 import static org.mockito.ArgumentMatchers.anyLong;
@@ -319,6 +320,7 @@
 import com.android.internal.util.WakeupMessage;
 import com.android.internal.util.test.BroadcastInterceptingContext;
 import com.android.internal.util.test.FakeSettingsProvider;
+import com.android.modules.utils.build.SdkLevel;
 import com.android.net.module.util.ArrayTrackRecord;
 import com.android.net.module.util.CollectionUtils;
 import com.android.net.module.util.LocationPermissionChecker;
@@ -7252,6 +7254,15 @@
         initialCaps.addTransportType(TRANSPORT_VPN);
         initialCaps.addCapability(NET_CAPABILITY_INTERNET);
         initialCaps.removeCapability(NET_CAPABILITY_NOT_VPN);
+        final ArrayList<Network> emptyUnderlyingNetworks = new ArrayList<Network>();
+        final ArrayList<Network> underlyingNetworksContainMobile = new ArrayList<Network>();
+        underlyingNetworksContainMobile.add(mobile);
+        final ArrayList<Network> underlyingNetworksContainWifi = new ArrayList<Network>();
+        underlyingNetworksContainWifi.add(wifi);
+        final ArrayList<Network> underlyingNetworksContainMobileAndMobile =
+                new ArrayList<Network>();
+        underlyingNetworksContainMobileAndMobile.add(mobile);
+        underlyingNetworksContainMobileAndMobile.add(wifi);
 
         final NetworkCapabilities withNoUnderlying = new NetworkCapabilities();
         withNoUnderlying.addCapability(NET_CAPABILITY_INTERNET);
@@ -7260,17 +7271,20 @@
         withNoUnderlying.addCapability(NET_CAPABILITY_NOT_SUSPENDED);
         withNoUnderlying.addTransportType(TRANSPORT_VPN);
         withNoUnderlying.removeCapability(NET_CAPABILITY_NOT_VPN);
+        withNoUnderlying.setUnderlyingNetworks(emptyUnderlyingNetworks);
 
         final NetworkCapabilities withMobileUnderlying = new NetworkCapabilities(withNoUnderlying);
         withMobileUnderlying.addTransportType(TRANSPORT_CELLULAR);
         withMobileUnderlying.removeCapability(NET_CAPABILITY_NOT_ROAMING);
         withMobileUnderlying.removeCapability(NET_CAPABILITY_NOT_SUSPENDED);
         withMobileUnderlying.setLinkDownstreamBandwidthKbps(10);
+        withMobileUnderlying.setUnderlyingNetworks(underlyingNetworksContainMobile);
 
         final NetworkCapabilities withWifiUnderlying = new NetworkCapabilities(withNoUnderlying);
         withWifiUnderlying.addTransportType(TRANSPORT_WIFI);
         withWifiUnderlying.addCapability(NET_CAPABILITY_NOT_METERED);
         withWifiUnderlying.setLinkUpstreamBandwidthKbps(20);
+        withWifiUnderlying.setUnderlyingNetworks(underlyingNetworksContainWifi);
 
         final NetworkCapabilities withWifiAndMobileUnderlying =
                 new NetworkCapabilities(withNoUnderlying);
@@ -7280,6 +7294,7 @@
         withWifiAndMobileUnderlying.removeCapability(NET_CAPABILITY_NOT_ROAMING);
         withWifiAndMobileUnderlying.setLinkDownstreamBandwidthKbps(10);
         withWifiAndMobileUnderlying.setLinkUpstreamBandwidthKbps(20);
+        withWifiAndMobileUnderlying.setUnderlyingNetworks(underlyingNetworksContainMobileAndMobile);
 
         final NetworkCapabilities initialCapsNotMetered = new NetworkCapabilities(initialCaps);
         initialCapsNotMetered.addCapability(NET_CAPABILITY_NOT_METERED);
@@ -7287,40 +7302,61 @@
         NetworkCapabilities caps = new NetworkCapabilities(initialCaps);
         mService.applyUnderlyingCapabilities(new Network[]{}, initialCapsNotMetered, caps);
         assertEquals(withNoUnderlying, caps);
+        assertEquals(0, new ArrayList<>(caps.getUnderlyingNetworks()).size());
 
         caps = new NetworkCapabilities(initialCaps);
         mService.applyUnderlyingCapabilities(new Network[]{null}, initialCapsNotMetered, caps);
         assertEquals(withNoUnderlying, caps);
+        assertEquals(0, new ArrayList<>(caps.getUnderlyingNetworks()).size());
 
         caps = new NetworkCapabilities(initialCaps);
         mService.applyUnderlyingCapabilities(new Network[]{mobile}, initialCapsNotMetered, caps);
         assertEquals(withMobileUnderlying, caps);
+        assertEquals(1, new ArrayList<>(caps.getUnderlyingNetworks()).size());
+        assertEquals(mobile, new ArrayList<>(caps.getUnderlyingNetworks()).get(0));
 
+        caps = new NetworkCapabilities(initialCaps);
         mService.applyUnderlyingCapabilities(new Network[]{wifi}, initialCapsNotMetered, caps);
         assertEquals(withWifiUnderlying, caps);
+        assertEquals(1, new ArrayList<>(caps.getUnderlyingNetworks()).size());
+        assertEquals(wifi, new ArrayList<>(caps.getUnderlyingNetworks()).get(0));
 
         withWifiUnderlying.removeCapability(NET_CAPABILITY_NOT_METERED);
         caps = new NetworkCapabilities(initialCaps);
         mService.applyUnderlyingCapabilities(new Network[]{wifi}, initialCaps, caps);
         assertEquals(withWifiUnderlying, caps);
+        assertEquals(1, new ArrayList<>(caps.getUnderlyingNetworks()).size());
+        assertEquals(wifi, new ArrayList<>(caps.getUnderlyingNetworks()).get(0));
 
         caps = new NetworkCapabilities(initialCaps);
         mService.applyUnderlyingCapabilities(new Network[]{mobile, wifi}, initialCaps, caps);
         assertEquals(withWifiAndMobileUnderlying, caps);
+        assertEquals(2, new ArrayList<>(caps.getUnderlyingNetworks()).size());
+        assertEquals(mobile, new ArrayList<>(caps.getUnderlyingNetworks()).get(0));
+        assertEquals(wifi, new ArrayList<>(caps.getUnderlyingNetworks()).get(1));
 
         withWifiUnderlying.addCapability(NET_CAPABILITY_NOT_METERED);
         caps = new NetworkCapabilities(initialCaps);
         mService.applyUnderlyingCapabilities(new Network[]{null, mobile, null, wifi},
                 initialCapsNotMetered, caps);
         assertEquals(withWifiAndMobileUnderlying, caps);
+        assertEquals(2, new ArrayList<>(caps.getUnderlyingNetworks()).size());
+        assertEquals(mobile, new ArrayList<>(caps.getUnderlyingNetworks()).get(0));
+        assertEquals(wifi, new ArrayList<>(caps.getUnderlyingNetworks()).get(1));
 
         caps = new NetworkCapabilities(initialCaps);
         mService.applyUnderlyingCapabilities(new Network[]{null, mobile, null, wifi},
                 initialCapsNotMetered, caps);
         assertEquals(withWifiAndMobileUnderlying, caps);
+        assertEquals(2, new ArrayList<>(caps.getUnderlyingNetworks()).size());
+        assertEquals(mobile, new ArrayList<>(caps.getUnderlyingNetworks()).get(0));
+        assertEquals(wifi, new ArrayList<>(caps.getUnderlyingNetworks()).get(1));
 
+        caps = new NetworkCapabilities(initialCaps);
         mService.applyUnderlyingCapabilities(null, initialCapsNotMetered, caps);
         assertEquals(withWifiUnderlying, caps);
+        assertEquals(1, new ArrayList<>(caps.getUnderlyingNetworks()).size());
+        assertEquals(wifi, new ArrayList<>(caps.getUnderlyingNetworks()).get(0));
     }
 
     @Test
@@ -7329,51 +7365,78 @@
         final NetworkRequest request = new NetworkRequest.Builder()
                 .removeCapability(NET_CAPABILITY_NOT_VPN).build();
 
-        mCm.registerNetworkCallback(request, callback);
+        runAsShell(NETWORK_SETTINGS, () -> {
+            mCm.registerNetworkCallback(request, callback);
 
-        // Bring up a VPN that specifies an underlying network that does not exist yet.
-        // Note: it's sort of meaningless for a VPN app to declare a network that doesn't exist yet,
-        // (and doing so is difficult without using reflection) but it's good to test that the code
-        // behaves approximately correctly.
-        mMockVpn.establishForMyUid(false, true, false);
-        assertUidRangesUpdatedForMyUid(true);
-        final Network wifiNetwork = new Network(mNetIdManager.peekNextNetId());
-        mMockVpn.setUnderlyingNetworks(new Network[]{wifiNetwork});
-        callback.expectAvailableCallbacksUnvalidated(mMockVpn);
-        assertTrue(mCm.getNetworkCapabilities(mMockVpn.getNetwork())
-                .hasTransport(TRANSPORT_VPN));
-        assertFalse(mCm.getNetworkCapabilities(mMockVpn.getNetwork())
-                .hasTransport(TRANSPORT_WIFI));
+            // Bring up a VPN that specifies an underlying network that does not exist yet.
+            // Note: it's sort of meaningless for a VPN app to declare a network that doesn't exist
+            // yet, (and doing so is difficult without using reflection) but it's good to test that
+            // the code behaves approximately correctly.
+            mMockVpn.establishForMyUid(false, true, false);
+            callback.expectAvailableCallbacksUnvalidated(mMockVpn);
+            assertUidRangesUpdatedForMyUid(true);
+            final Network wifiNetwork = new Network(mNetIdManager.peekNextNetId());
+            mMockVpn.setUnderlyingNetworks(new Network[]{wifiNetwork});
+            // onCapabilitiesChanged() should be called because
+            // NetworkCapabilities#mUnderlyingNetworks is updated.
+            CallbackEntry ce = callback.expectCallback(CallbackEntry.NETWORK_CAPS_UPDATED,
+                    mMockVpn);
+            final NetworkCapabilities vpnNc1 = ((CallbackEntry.CapabilitiesChanged) ce).getCaps();
+            // Since the wifi network hasn't brought up,
+            // ConnectivityService#applyUnderlyingCapabilities cannot find it. Update
+            // NetworkCapabilities#mUnderlyingNetworks to an empty array, and it will be updated to
+            // the correct underlying networks once the wifi network brings up. But this case
+            // shouldn't happen in reality since no one could get the network which hasn't brought
+            // up. For the empty array of underlying networks, it should be happened for 2 cases,
+            // the first one is that the VPN app declares an empty array for its underlying
+            // networks, the second one is that the underlying networks are torn down.
+            //
+            // It shouldn't be null since the null value means the underlying networks of this
+            // network should follow the default network.
+            final ArrayList<Network> underlyingNetwork = new ArrayList<>();
+            assertEquals(underlyingNetwork, vpnNc1.getUnderlyingNetworks());
+            // Since the wifi network isn't exist, applyUnderlyingCapabilities()
+            assertTrue(mCm.getNetworkCapabilities(mMockVpn.getNetwork())
+                    .hasTransport(TRANSPORT_VPN));
+            assertFalse(mCm.getNetworkCapabilities(mMockVpn.getNetwork())
+                    .hasTransport(TRANSPORT_WIFI));
 
-        // Make that underlying network connect, and expect to see its capabilities immediately
-        // reflected in the VPN's capabilities.
-        mWiFiNetworkAgent = new TestNetworkAgentWrapper(TRANSPORT_WIFI);
-        assertEquals(wifiNetwork, mWiFiNetworkAgent.getNetwork());
-        mWiFiNetworkAgent.connect(false);
-        // TODO: the callback for the VPN happens before any callbacks are called for the wifi
-        // network that has just connected. There appear to be two issues here:
-        // 1. The VPN code will accept an underlying network as soon as getNetworkCapabilities() for
-        //    it returns non-null (which happens very early, during handleRegisterNetworkAgent).
-        //    This is not correct because that that point the network is not connected and cannot
-        //    pass any traffic.
-        // 2. When a network connects, updateNetworkInfo propagates underlying network capabilities
-        //    before rematching networks.
-        // Given that this scenario can't really happen, this is probably fine for now.
-        callback.expectCallback(CallbackEntry.NETWORK_CAPS_UPDATED, mMockVpn);
-        callback.expectAvailableCallbacksUnvalidated(mWiFiNetworkAgent);
-        assertTrue(mCm.getNetworkCapabilities(mMockVpn.getNetwork())
-                .hasTransport(TRANSPORT_VPN));
-        assertTrue(mCm.getNetworkCapabilities(mMockVpn.getNetwork())
-                .hasTransport(TRANSPORT_WIFI));
+            // Make that underlying network connect, and expect to see its capabilities immediately
+            // reflected in the VPN's capabilities.
+            mWiFiNetworkAgent = new TestNetworkAgentWrapper(TRANSPORT_WIFI);
+            assertEquals(wifiNetwork, mWiFiNetworkAgent.getNetwork());
+            mWiFiNetworkAgent.connect(false);
+            // TODO: the callback for the VPN happens before any callbacks are called for the wifi
+            // network that has just connected. There appear to be two issues here:
+            // 1. The VPN code will accept an underlying network as soon as getNetworkCapabilities()
+            //    for it returns non-null (which happens very early, during
+            //    handleRegisterNetworkAgent).
+            //    This is not correct because that that point the network is not connected and
+            //    cannot pass any traffic.
+            // 2. When a network connects, updateNetworkInfo propagates underlying network
+            //    capabilities before rematching networks.
+            // Given that this scenario can't really happen, this is probably fine for now.
+            ce = callback.expectCallback(CallbackEntry.NETWORK_CAPS_UPDATED, mMockVpn);
+            final NetworkCapabilities vpnNc2 = ((CallbackEntry.CapabilitiesChanged) ce).getCaps();
+            // The wifi network is brought up, NetworkCapabilities#mUnderlyingNetworks is updated to
+            // it.
+            underlyingNetwork.add(wifiNetwork);
+            assertEquals(underlyingNetwork, vpnNc2.getUnderlyingNetworks());
+            callback.expectAvailableCallbacksUnvalidated(mWiFiNetworkAgent);
+            assertTrue(mCm.getNetworkCapabilities(mMockVpn.getNetwork())
+                    .hasTransport(TRANSPORT_VPN));
+            assertTrue(mCm.getNetworkCapabilities(mMockVpn.getNetwork())
+                    .hasTransport(TRANSPORT_WIFI));
 
-        // Disconnect the network, and expect to see the VPN capabilities change accordingly.
-        mWiFiNetworkAgent.disconnect();
-        callback.expectCallback(CallbackEntry.LOST, mWiFiNetworkAgent);
-        callback.expectCapabilitiesThat(mMockVpn, (nc) ->
-                nc.getTransportTypes().length == 1 && nc.hasTransport(TRANSPORT_VPN));
+            // Disconnect the network, and expect to see the VPN capabilities change accordingly.
+            mWiFiNetworkAgent.disconnect();
+            callback.expectCallback(CallbackEntry.LOST, mWiFiNetworkAgent);
+            callback.expectCapabilitiesThat(mMockVpn, (nc) ->
+                    nc.getTransportTypes().length == 1 && nc.hasTransport(TRANSPORT_VPN));
 
-        mMockVpn.disconnect();
-        mCm.unregisterNetworkCallback(callback);
+            mMockVpn.disconnect();
+            mCm.unregisterNetworkCallback(callback);
+        });
     }
 
     private void assertGetNetworkInfoOfGetActiveNetworkIsConnected(boolean expectedConnectivity) {
@@ -10697,6 +10760,14 @@
         return fakeNai(wifiNc, info);
     }
 
+    private NetworkAgentInfo fakeVpnNai(NetworkCapabilities nc) {
+        final NetworkCapabilities vpnNc = new NetworkCapabilities.Builder(nc)
+                .addTransportType(TRANSPORT_VPN).build();
+        final NetworkInfo info = new NetworkInfo(TYPE_VPN, 0 /* subtype */,
+                ConnectivityManager.getNetworkTypeName(TYPE_VPN), "" /* subtypeName */);
+        return fakeNai(vpnNc, info);
+    }
+
     private NetworkAgentInfo fakeNai(NetworkCapabilities nc, NetworkInfo networkInfo) {
         return new NetworkAgentInfo(null, new Network(NET_ID), networkInfo, new LinkProperties(),
                 nc, new NetworkScore.Builder().setLegacyInt(0).build(),
@@ -10831,6 +10902,36 @@
     }
 
     @Test
+    public void testUnderlyingNetworksWillBeSetInNetworkAgentInfoConstructor() throws Exception {
+        assumeTrue(SdkLevel.isAtLeastT());
+        final Network network1 = new Network(100);
+        final Network network2 = new Network(101);
+        final List<Network> underlyingNetworks = new ArrayList<>();
+        final NetworkCapabilities ncWithEmptyUnderlyingNetworks = new NetworkCapabilities.Builder()
+                .setUnderlyingNetworks(underlyingNetworks)
+                .build();
+        final NetworkAgentInfo vpnNaiWithEmptyUnderlyingNetworks =
+                fakeVpnNai(ncWithEmptyUnderlyingNetworks);
+        assertEquals(underlyingNetworks,
+                Arrays.asList(vpnNaiWithEmptyUnderlyingNetworks.declaredUnderlyingNetworks));
+
+        underlyingNetworks.add(network1);
+        underlyingNetworks.add(network2);
+        final NetworkCapabilities ncWithUnderlyingNetworks = new NetworkCapabilities.Builder()
+                .setUnderlyingNetworks(underlyingNetworks)
+                .build();
+        final NetworkAgentInfo vpnNaiWithUnderlyingNetwokrs = fakeVpnNai(ncWithUnderlyingNetworks);
+        assertEquals(underlyingNetworks,
+                Arrays.asList(vpnNaiWithUnderlyingNetwokrs.declaredUnderlyingNetworks));
+
+        final NetworkCapabilities ncWithoutUnderlyingNetworks = new NetworkCapabilities.Builder()
+                .build();
+        final NetworkAgentInfo vpnNaiWithoutUnderlyingNetwokrs =
+                fakeVpnNai(ncWithoutUnderlyingNetworks);
+        assertNull(vpnNaiWithoutUnderlyingNetwokrs.declaredUnderlyingNetworks);
+    }
+
+    @Test
     public void testRegisterConnectivityDiagnosticsCallbackCallsOnConnectivityReport()
             throws Exception {
         // Set up the Network, which leads to a ConnectivityReport being cached for the network.