diff --git a/framework-t/src/android/net/nsd/NsdServiceInfo.java b/framework-t/src/android/net/nsd/NsdServiceInfo.java
index 2621594..200c808 100644
--- a/framework-t/src/android/net/nsd/NsdServiceInfo.java
+++ b/framework-t/src/android/net/nsd/NsdServiceInfo.java
@@ -53,6 +53,8 @@
     @Nullable
     private Network mNetwork;
 
+    private int mInterfaceIndex;
+
     public NsdServiceInfo() {
     }
 
@@ -312,8 +314,11 @@
     /**
      * Get the network where the service can be found.
      *
-     * This is never null if this {@link NsdServiceInfo} was obtained from
-     * {@link NsdManager#discoverServices} or {@link NsdManager#resolveService}.
+     * This is set if this {@link NsdServiceInfo} was obtained from
+     * {@link NsdManager#discoverServices} or {@link NsdManager#resolveService}, unless the service
+     * was found on a network interface that does not have a {@link Network} (such as a tethering
+     * downstream, where services are advertised from devices connected to this device via
+     * tethering).
      */
     @Nullable
     public Network getNetwork() {
@@ -329,6 +334,26 @@
         mNetwork = network;
     }
 
+    /**
+     * Get the index of the network interface where the service was found.
+     *
+     * This is only set when the service was found on an interface that does not have a usable
+     * Network, in which case {@link #getNetwork()} returns null.
+     * @return The interface index as per {@link java.net.NetworkInterface#getIndex}, or 0 if unset.
+     * @hide
+     */
+    public int getInterfaceIndex() {
+        return mInterfaceIndex;
+    }
+
+    /**
+     * Set the index of the network interface where the service was found.
+     * @hide
+     */
+    public void setInterfaceIndex(int interfaceIndex) {
+        mInterfaceIndex = interfaceIndex;
+    }
+
     @Override
     public String toString() {
         StringBuilder sb = new StringBuilder();
@@ -375,6 +400,7 @@
         }
 
         dest.writeParcelable(mNetwork, 0);
+        dest.writeInt(mInterfaceIndex);
     }
 
     /** Implement the Parcelable interface */
@@ -405,6 +431,7 @@
                     info.mTxtRecord.put(in.readString(), valueArray);
                 }
                 info.mNetwork = in.readParcelable(null, Network.class);
+                info.mInterfaceIndex = in.readInt();
                 return info;
             }
 
diff --git a/service-t/src/com/android/server/NsdService.java b/service-t/src/com/android/server/NsdService.java
index 6def44f..95e6114 100644
--- a/service-t/src/com/android/server/NsdService.java
+++ b/service-t/src/com/android/server/NsdService.java
@@ -23,6 +23,7 @@
 import android.content.Intent;
 import android.content.pm.PackageManager;
 import android.net.ConnectivityManager;
+import android.net.INetd;
 import android.net.LinkProperties;
 import android.net.Network;
 import android.net.mdns.aidl.DiscoveryInfo;
@@ -466,7 +467,7 @@
                             // interfaces that do not have an associated Network.
                             break;
                         }
-                        servInfo.setNetwork(new Network(foundNetId));
+                        setServiceNetworkForCallback(servInfo, info.netId, info.interfaceIdx);
                         clientInfo.onServiceFound(clientId, servInfo);
                         break;
                     }
@@ -476,10 +477,11 @@
                         final String type = info.registrationType;
                         final int lostNetId = info.netId;
                         servInfo = new NsdServiceInfo(name, type);
-                        // The network could be null if it was torn down when the service is lost
-                        // TODO: avoid returning null in that case, possibly by remembering found
-                        // services on the same interface index and their network at the time
-                        servInfo.setNetwork(lostNetId == 0 ? null : new Network(lostNetId));
+                        // The network could be set to null (netId 0) if it was torn down when the
+                        // service is lost
+                        // TODO: avoid returning null in that case, possibly by remembering
+                        // found services on the same interface index and their network at the time
+                        setServiceNetworkForCallback(servInfo, lostNetId, info.interfaceIdx);
                         clientInfo.onServiceLost(clientId, servInfo);
                         break;
                     }
@@ -557,7 +559,6 @@
                         final GetAddressInfo info = (GetAddressInfo) obj;
                         final String address = info.address;
                         final int netId = info.netId;
-                        final Network network = netId == NETID_UNSET ? null : new Network(netId);
                         InetAddress serviceHost = null;
                         try {
                             serviceHost = InetAddress.getByName(address);
@@ -568,9 +569,10 @@
                         // If the resolved service is on an interface without a network, consider it
                         // as a failure: it would not be usable by apps as they would need
                         // privileged permissions.
-                        if (network != null && serviceHost != null) {
+                        if (netId != NETID_UNSET && serviceHost != null) {
                             clientInfo.mResolvedService.setHost(serviceHost);
-                            clientInfo.mResolvedService.setNetwork(network);
+                            setServiceNetworkForCallback(clientInfo.mResolvedService,
+                                    netId, info.interfaceIdx);
                             clientInfo.onResolveServiceSucceeded(
                                     clientId, clientInfo.mResolvedService);
                         } else {
@@ -590,6 +592,26 @@
        }
     }
 
+    private static void setServiceNetworkForCallback(NsdServiceInfo info, int netId, int ifaceIdx) {
+        switch (netId) {
+            case NETID_UNSET:
+                info.setNetwork(null);
+                break;
+            case INetd.LOCAL_NET_ID:
+                // Special case for LOCAL_NET_ID: Networks on netId 99 are not generally
+                // visible / usable for apps, so do not return it. Store the interface
+                // index instead, so at least if the client tries to resolve the service
+                // with that NsdServiceInfo, it will be done on the same interface.
+                // If they recreate the NsdServiceInfo themselves, resolution would be
+                // done on all interfaces as before T, which should also work.
+                info.setNetwork(null);
+                info.setInterfaceIndex(ifaceIdx);
+                break;
+            default:
+                info.setNetwork(new Network(netId));
+        }
+    }
+
     // The full service name is escaped from standard DNS rules on mdnsresponder, making it suitable
     // for passing to standard system DNS APIs such as res_query() . Thus, make the service name
     // unescape for getting right service address. See "Notes on DNS Name Escaping" on
@@ -767,9 +789,8 @@
         String type = service.getServiceType();
         int port = service.getPort();
         byte[] textRecord = service.getTxtRecord();
-        final Network network = service.getNetwork();
-        final int registerInterface = getNetworkInterfaceIndex(network);
-        if (network != null && registerInterface == IFACE_IDX_ANY) {
+        final int registerInterface = getNetworkInterfaceIndex(service);
+        if (service.getNetwork() != null && registerInterface == IFACE_IDX_ANY) {
             Log.e(TAG, "Interface to register service on not found");
             return false;
         }
@@ -781,10 +802,9 @@
     }
 
     private boolean discoverServices(int discoveryId, NsdServiceInfo serviceInfo) {
-        final Network network = serviceInfo.getNetwork();
         final String type = serviceInfo.getServiceType();
-        final int discoverInterface = getNetworkInterfaceIndex(network);
-        if (network != null && discoverInterface == IFACE_IDX_ANY) {
+        final int discoverInterface = getNetworkInterfaceIndex(serviceInfo);
+        if (serviceInfo.getNetwork() != null && discoverInterface == IFACE_IDX_ANY) {
             Log.e(TAG, "Interface to discover service on not found");
             return false;
         }
@@ -798,9 +818,8 @@
     private boolean resolveService(int resolveId, NsdServiceInfo service) {
         final String name = service.getServiceName();
         final String type = service.getServiceType();
-        final Network network = service.getNetwork();
-        final int resolveInterface = getNetworkInterfaceIndex(network);
-        if (network != null && resolveInterface == IFACE_IDX_ANY) {
+        final int resolveInterface = getNetworkInterfaceIndex(service);
+        if (service.getNetwork() != null && resolveInterface == IFACE_IDX_ANY) {
             Log.e(TAG, "Interface to resolve service on not found");
             return false;
         }
@@ -816,8 +835,17 @@
      * this is to support the legacy mdnsresponder implementation, which historically resolved
      * services on an unspecified network.
      */
-    private int getNetworkInterfaceIndex(Network network) {
-        if (network == null) return IFACE_IDX_ANY;
+    private int getNetworkInterfaceIndex(NsdServiceInfo serviceInfo) {
+        final Network network = serviceInfo.getNetwork();
+        if (network == null) {
+            // Fallback to getInterfaceIndex if present (typically if the NsdServiceInfo was
+            // provided by NsdService from discovery results, and the service was found on an
+            // interface that has no app-usable Network).
+            if (serviceInfo.getInterfaceIndex() != 0) {
+                return serviceInfo.getInterfaceIndex();
+            }
+            return IFACE_IDX_ANY;
+        }
 
         final ConnectivityManager cm = mContext.getSystemService(ConnectivityManager.class);
         if (cm == null) {
diff --git a/tests/common/Android.bp b/tests/common/Android.bp
index 509e881..58731e0 100644
--- a/tests/common/Android.bp
+++ b/tests/common/Android.bp
@@ -140,6 +140,30 @@
     ],
 }
 
+// defaults for tests that need to build against framework-connectivity's @hide APIs, but also
+// using fully @hide classes that are jarjared (because they have no API member). Similar to
+// framework-connectivity-test-defaults above but uses pre-jarjar class names.
+// Only usable from targets that have visibility on framework-connectivity-pre-jarjar, and apply
+// connectivity jarjar rules so that references to jarjared classes still match: this is limited to
+// connectivity internal tests only.
+java_defaults {
+    name: "framework-connectivity-internal-test-defaults",
+    sdk_version: "core_platform", // tests can use @CorePlatformApi's
+    libs: [
+        // order matters: classes in framework-connectivity are resolved before framework,
+        // meaning @hide APIs in framework-connectivity are resolved before @SystemApi
+        // stubs in framework
+        "framework-connectivity-pre-jarjar",
+        "framework-connectivity-t-pre-jarjar",
+        "framework-tethering.impl",
+        "framework",
+
+        // if sdk_version="" this gets automatically included, but here we need to add manually.
+        "framework-res",
+    ],
+    defaults_visibility: ["//packages/modules/Connectivity/tests:__subpackages__"],
+}
+
 // Defaults for tests that want to run in mainline-presubmit.
 // Not widely used because many of our tests have AndroidTest.xml files and
 // use the mainline-param config-descriptor metadata in AndroidTest.xml.
diff --git a/tests/unit/Android.bp b/tests/unit/Android.bp
index 5b926de..5a7208c 100644
--- a/tests/unit/Android.bp
+++ b/tests/unit/Android.bp
@@ -108,7 +108,7 @@
     name: "FrameworksNetTestsDefaults",
     min_sdk_version: "30",
     defaults: [
-        "framework-connectivity-test-defaults",
+        "framework-connectivity-internal-test-defaults",
     ],
     srcs: [
         "java/**/*.java",
diff --git a/tests/unit/java/android/net/nsd/NsdServiceInfoTest.java b/tests/unit/java/android/net/nsd/NsdServiceInfoTest.java
index e5e7ebc..892e140 100644
--- a/tests/unit/java/android/net/nsd/NsdServiceInfoTest.java
+++ b/tests/unit/java/android/net/nsd/NsdServiceInfoTest.java
@@ -125,6 +125,7 @@
         fullInfo.setPort(4242);
         fullInfo.setHost(LOCALHOST);
         fullInfo.setNetwork(new Network(123));
+        fullInfo.setInterfaceIndex(456);
         checkParcelable(fullInfo);
 
         NsdServiceInfo noHostInfo = new NsdServiceInfo();
@@ -175,6 +176,7 @@
         assertEquals(original.getHost(), result.getHost());
         assertTrue(original.getPort() == result.getPort());
         assertEquals(original.getNetwork(), result.getNetwork());
+        assertEquals(original.getInterfaceIndex(), result.getInterfaceIndex());
 
         // Assert equality of attribute map.
         Map<String, byte[]> originalMap = original.getAttributes();
diff --git a/tests/unit/java/com/android/server/NsdServiceTest.java b/tests/unit/java/com/android/server/NsdServiceTest.java
index 3c228d0..ed9e930 100644
--- a/tests/unit/java/com/android/server/NsdServiceTest.java
+++ b/tests/unit/java/com/android/server/NsdServiceTest.java
@@ -19,7 +19,9 @@
 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.assertNull;
 import static org.mockito.ArgumentMatchers.anyInt;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.Mockito.any;
@@ -36,6 +38,12 @@
 import android.compat.testing.PlatformCompatChangeRule;
 import android.content.ContentResolver;
 import android.content.Context;
+import android.net.INetd;
+import android.net.InetAddresses;
+import android.net.mdns.aidl.DiscoveryInfo;
+import android.net.mdns.aidl.GetAddressInfo;
+import android.net.mdns.aidl.IMDnsEventListener;
+import android.net.mdns.aidl.ResolutionInfo;
 import android.net.nsd.INsdManagerCallback;
 import android.net.nsd.INsdServiceConnector;
 import android.net.nsd.MDnsManager;
@@ -63,6 +71,7 @@
 import org.junit.rules.TestRule;
 import org.junit.runner.RunWith;
 import org.mockito.AdditionalAnswers;
+import org.mockito.ArgumentCaptor;
 import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 
@@ -275,6 +284,105 @@
         verify(mMockMDnsM, never()).stopDaemon();
     }
 
+    @Test
+    public void testDiscoverOnTetheringDownstream() throws Exception {
+        NsdService service = makeService();
+        NsdManager client = connectClient(service);
+
+        final String serviceType = "a_type";
+        final String serviceName = "a_name";
+        final String domainName = "mytestdevice.local";
+        final int interfaceIdx = 123;
+        final NsdManager.DiscoveryListener discListener = mock(NsdManager.DiscoveryListener.class);
+        client.discoverServices(serviceType, NsdManager.PROTOCOL_DNS_SD, discListener);
+        waitForIdle();
+
+        final ArgumentCaptor<IMDnsEventListener> listenerCaptor =
+                ArgumentCaptor.forClass(IMDnsEventListener.class);
+        verify(mMockMDnsM).registerEventListener(listenerCaptor.capture());
+        final ArgumentCaptor<Integer> discIdCaptor = ArgumentCaptor.forClass(Integer.class);
+        verify(mMockMDnsM).discover(discIdCaptor.capture(), eq(serviceType),
+                eq(0) /* interfaceIdx */);
+        // NsdManager uses a separate HandlerThread to dispatch callbacks (on ServiceHandler), so
+        // this needs to use a timeout
+        verify(discListener, timeout(TIMEOUT_MS)).onDiscoveryStarted(serviceType);
+
+        final DiscoveryInfo discoveryInfo = new DiscoveryInfo(
+                discIdCaptor.getValue(),
+                IMDnsEventListener.SERVICE_FOUND,
+                serviceName,
+                serviceType,
+                domainName,
+                interfaceIdx,
+                INetd.LOCAL_NET_ID); // LOCAL_NET_ID (99) used on tethering downstreams
+        final IMDnsEventListener eventListener = listenerCaptor.getValue();
+        eventListener.onServiceDiscoveryStatus(discoveryInfo);
+        waitForIdle();
+
+        final ArgumentCaptor<NsdServiceInfo> discoveredInfoCaptor =
+                ArgumentCaptor.forClass(NsdServiceInfo.class);
+        verify(discListener, timeout(TIMEOUT_MS)).onServiceFound(discoveredInfoCaptor.capture());
+        final NsdServiceInfo foundInfo = discoveredInfoCaptor.getValue();
+        assertEquals(serviceName, foundInfo.getServiceName());
+        assertEquals(serviceType, foundInfo.getServiceType());
+        assertNull(foundInfo.getHost());
+        assertNull(foundInfo.getNetwork());
+        assertEquals(interfaceIdx, foundInfo.getInterfaceIndex());
+
+        // After discovering the service, verify resolving it
+        final NsdManager.ResolveListener resolveListener = mock(NsdManager.ResolveListener.class);
+        client.resolveService(foundInfo, resolveListener);
+        waitForIdle();
+
+        final ArgumentCaptor<Integer> resolvIdCaptor = ArgumentCaptor.forClass(Integer.class);
+        verify(mMockMDnsM).resolve(resolvIdCaptor.capture(), eq(serviceName), eq(serviceType),
+                eq("local.") /* domain */, eq(interfaceIdx));
+
+        final int servicePort = 10123;
+        final String serviceFullName = serviceName + "." + serviceType;
+        final ResolutionInfo resolutionInfo = new ResolutionInfo(
+                resolvIdCaptor.getValue(),
+                IMDnsEventListener.SERVICE_RESOLVED,
+                null /* serviceName */,
+                null /* serviceType */,
+                null /* domain */,
+                serviceFullName,
+                domainName,
+                servicePort,
+                new byte[0] /* txtRecord */,
+                interfaceIdx);
+
+        doReturn(true).when(mMockMDnsM).getServiceAddress(anyInt(), any(), anyInt());
+        eventListener.onServiceResolutionStatus(resolutionInfo);
+        waitForIdle();
+
+        final ArgumentCaptor<Integer> getAddrIdCaptor = ArgumentCaptor.forClass(Integer.class);
+        verify(mMockMDnsM).getServiceAddress(getAddrIdCaptor.capture(), eq(domainName),
+                eq(interfaceIdx));
+
+        final String serviceAddress = "192.0.2.123";
+        final GetAddressInfo addressInfo = new GetAddressInfo(
+                getAddrIdCaptor.getValue(),
+                IMDnsEventListener.SERVICE_GET_ADDR_SUCCESS,
+                serviceFullName,
+                serviceAddress,
+                interfaceIdx,
+                INetd.LOCAL_NET_ID);
+        eventListener.onGettingServiceAddressStatus(addressInfo);
+        waitForIdle();
+
+        final ArgumentCaptor<NsdServiceInfo> resInfoCaptor =
+                ArgumentCaptor.forClass(NsdServiceInfo.class);
+        verify(resolveListener, timeout(TIMEOUT_MS)).onServiceResolved(resInfoCaptor.capture());
+        final NsdServiceInfo resolvedService = resInfoCaptor.getValue();
+        assertEquals(serviceName, resolvedService.getServiceName());
+        assertEquals("." + serviceType, resolvedService.getServiceType());
+        assertEquals(InetAddresses.parseNumericAddress(serviceAddress), resolvedService.getHost());
+        assertEquals(servicePort, resolvedService.getPort());
+        assertNull(resolvedService.getNetwork());
+        assertEquals(interfaceIdx, resolvedService.getInterfaceIndex());
+    }
+
     private void waitForIdle() {
         HandlerUtils.waitForIdle(mHandler, TIMEOUT_MS);
     }