diff --git a/Tethering/src/android/net/ip/IpServer.java b/Tethering/src/android/net/ip/IpServer.java
index de53787..659d344 100644
--- a/Tethering/src/android/net/ip/IpServer.java
+++ b/Tethering/src/android/net/ip/IpServer.java
@@ -738,7 +738,7 @@
     //
     // TODO: Evaluate using a data structure than is more directly suited to
     // communicating only the relevant information.
-    private void updateUpstreamIPv6LinkProperties(LinkProperties v6only) {
+    private void updateUpstreamIPv6LinkProperties(LinkProperties v6only, int ttlAdjustment) {
         if (mRaDaemon == null) return;
 
         // Avoid unnecessary work on spurious updates.
@@ -761,7 +761,7 @@
             params.mtu = mUsingBpfOffload ? v6only.getMtu() - 16 : v6only.getMtu();
             params.hasDefaultRoute = v6only.hasIpv6DefaultRoute();
 
-            if (params.hasDefaultRoute) params.hopLimit = getHopLimit(upstreamIface);
+            if (params.hasDefaultRoute) params.hopLimit = getHopLimit(upstreamIface, ttlAdjustment);
 
             for (LinkAddress linkAddr : v6only.getLinkAddresses()) {
                 if (linkAddr.getPrefixLength() != RFC7421_PREFIX_LENGTH) continue;
@@ -1052,12 +1052,11 @@
         }
     }
 
-    private byte getHopLimit(String upstreamIface) {
+    private byte getHopLimit(String upstreamIface, int adjustTTL) {
         try {
             int upstreamHopLimit = Integer.parseUnsignedInt(
                     mNetd.getProcSysNet(INetd.IPV6, INetd.CONF, upstreamIface, "hop_limit"));
-            // Add one hop to account for this forwarding device
-            upstreamHopLimit++;
+            upstreamHopLimit = upstreamHopLimit + adjustTTL;
             // Cap the hop limit to 255.
             return (byte) Integer.min(upstreamHopLimit, 255);
         } catch (Exception e) {
@@ -1145,7 +1144,7 @@
                     transitionTo(mUnavailableState);
                     break;
                 case CMD_IPV6_TETHER_UPDATE:
-                    updateUpstreamIPv6LinkProperties((LinkProperties) message.obj);
+                    updateUpstreamIPv6LinkProperties((LinkProperties) message.obj, message.arg1);
                     break;
                 default:
                     return NOT_HANDLED;
@@ -1209,7 +1208,7 @@
                     if (DBG) Log.d(TAG, "Untethered (ifdown)" + mIfaceName);
                     break;
                 case CMD_IPV6_TETHER_UPDATE:
-                    updateUpstreamIPv6LinkProperties((LinkProperties) message.obj);
+                    updateUpstreamIPv6LinkProperties((LinkProperties) message.obj, message.arg1);
                     sendLinkProperties();
                     break;
                 case CMD_IP_FORWARDING_ENABLE_ERROR:
diff --git a/Tethering/src/com/android/networkstack/tethering/IPv6TetheringCoordinator.java b/Tethering/src/com/android/networkstack/tethering/IPv6TetheringCoordinator.java
index d450c46..f3dcaa2 100644
--- a/Tethering/src/com/android/networkstack/tethering/IPv6TetheringCoordinator.java
+++ b/Tethering/src/com/android/networkstack/tethering/IPv6TetheringCoordinator.java
@@ -161,11 +161,28 @@
     private void updateIPv6TetheringInterfaces() {
         for (IpServer ipServer : mNotifyList) {
             final LinkProperties lp = getInterfaceIPv6LinkProperties(ipServer);
-            ipServer.sendMessage(IpServer.CMD_IPV6_TETHER_UPDATE, 0, 0, lp);
+            ipServer.sendMessage(IpServer.CMD_IPV6_TETHER_UPDATE, getTtlAdjustment(), 0, lp);
             break;
         }
     }
 
+    private int getTtlAdjustment() {
+        if (mUpstreamNetworkState == null || mUpstreamNetworkState.networkCapabilities == null) {
+            return 0;
+        }
+
+        // If upstream is cellular, set the TTL in Router Advertisements to "network-set TTL" - 1
+        // for carrier requirement.
+        if (mUpstreamNetworkState.networkCapabilities.hasTransport(
+                NetworkCapabilities.TRANSPORT_CELLULAR)) {
+            return -1;
+        }
+
+        // For other non-cellular upstream, set TTL as "network-set TTL" + 1 to preventing arbitrary
+        // distinction between tethered and untethered traffic.
+        return 1;
+    }
+
     private LinkProperties getInterfaceIPv6LinkProperties(IpServer ipServer) {
         final Downstream ds = findDownstream(ipServer);
         if (ds == null) return null;
diff --git a/Tethering/tests/unit/src/android/net/ip/IpServerTest.java b/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
index cd1ff60..307ebf1 100644
--- a/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
+++ b/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
@@ -17,6 +17,7 @@
 package android.net.ip;
 
 import static android.net.INetd.IF_STATE_UP;
+import static android.net.RouteInfo.RTN_UNICAST;
 import static android.net.TetheringManager.TETHERING_BLUETOOTH;
 import static android.net.TetheringManager.TETHERING_NCM;
 import static android.net.TetheringManager.TETHERING_USB;
@@ -74,6 +75,7 @@
 import android.net.dhcp.IDhcpServerCallbacks;
 import android.net.ip.IpNeighborMonitor.NeighborEvent;
 import android.net.ip.IpNeighborMonitor.NeighborEventConsumer;
+import android.net.ip.RouterAdvertisementDaemon.RaParams;
 import android.net.util.InterfaceParams;
 import android.net.util.InterfaceSet;
 import android.net.util.SharedLog;
@@ -196,7 +198,7 @@
         if (upstreamIface != null) {
             LinkProperties lp = new LinkProperties();
             lp.setInterfaceName(upstreamIface);
-            dispatchTetherConnectionChanged(upstreamIface, lp);
+            dispatchTetherConnectionChanged(upstreamIface, lp, 0);
         }
         reset(mNetd, mCallback);
     }
@@ -694,7 +696,7 @@
         InOrder inOrder = inOrder(mNetd);
         LinkProperties lp = new LinkProperties();
         lp.setInterfaceName(UPSTREAM_IFACE2);
-        dispatchTetherConnectionChanged(UPSTREAM_IFACE2, lp);
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE2, lp, -1);
         inOrder.verify(mNetd).tetherOffloadRuleAdd(matches(UPSTREAM_IFINDEX2, neighA, macA));
         inOrder.verify(mNetd).tetherOffloadRuleRemove(matches(UPSTREAM_IFINDEX, neighA, macA));
         inOrder.verify(mNetd).tetherOffloadRuleAdd(matches(UPSTREAM_IFINDEX2, neighB, macB));
@@ -702,7 +704,7 @@
         reset(mNetd);
 
         // When the upstream is lost, rules are removed.
-        dispatchTetherConnectionChanged(null, null);
+        dispatchTetherConnectionChanged(null, null, 0);
         verify(mNetd).tetherOffloadRuleRemove(matches(UPSTREAM_IFINDEX2, neighA, macA));
         verify(mNetd).tetherOffloadRuleRemove(matches(UPSTREAM_IFINDEX2, neighB, macB));
         reset(mNetd);
@@ -715,19 +717,19 @@
 
         // Rules can be added again once upstream IPv6 connectivity is available.
         lp.setInterfaceName(UPSTREAM_IFACE);
-        dispatchTetherConnectionChanged(UPSTREAM_IFACE, lp);
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE, lp, -1);
         recvNewNeigh(myIfindex, neighB, NUD_REACHABLE, macB);
         verify(mNetd).tetherOffloadRuleAdd(matches(UPSTREAM_IFINDEX, neighB, macB));
         verify(mNetd, never()).tetherOffloadRuleAdd(matches(UPSTREAM_IFINDEX, neighA, macA));
 
         // If upstream IPv6 connectivity is lost, rules are removed.
         reset(mNetd);
-        dispatchTetherConnectionChanged(UPSTREAM_IFACE, null);
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE, null, 0);
         verify(mNetd).tetherOffloadRuleRemove(matches(UPSTREAM_IFINDEX, neighB, macB));
 
         // When the interface goes down, rules are removed.
         lp.setInterfaceName(UPSTREAM_IFACE);
-        dispatchTetherConnectionChanged(UPSTREAM_IFACE, lp);
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE, lp, -1);
         recvNewNeigh(myIfindex, neighA, NUD_REACHABLE, macA);
         recvNewNeigh(myIfindex, neighB, NUD_REACHABLE, macB);
         verify(mNetd).tetherOffloadRuleAdd(matches(UPSTREAM_IFINDEX, neighA, macA));
@@ -788,6 +790,49 @@
         verify(mIpNeighborMonitor, never()).start();
     }
 
+    private LinkProperties buildIpv6OnlyLinkProperties(final String iface) {
+        final LinkProperties linkProp = new LinkProperties();
+        linkProp.setInterfaceName(iface);
+        linkProp.addLinkAddress(new LinkAddress("2001:db8::1/64"));
+        linkProp.addRoute(new RouteInfo(new IpPrefix("::/0"), null, iface, RTN_UNICAST));
+        final InetAddress dns = InetAddresses.parseNumericAddress("2001:4860:4860::8888");
+        linkProp.addDnsServer(dns);
+
+        return linkProp;
+    }
+
+    @Test
+    public void testAdjustTtlValue() throws Exception {
+        final ArgumentCaptor<RaParams> raParamsCaptor =
+                ArgumentCaptor.forClass(RaParams.class);
+        initTetheredStateMachine(TETHERING_WIFI, UPSTREAM_IFACE);
+        verify(mRaDaemon).buildNewRa(any(), raParamsCaptor.capture());
+        final RaParams noV6Params = raParamsCaptor.getValue();
+        assertEquals(65, noV6Params.hopLimit);
+        reset(mRaDaemon);
+
+        when(mNetd.getProcSysNet(
+                INetd.IPV6, INetd.CONF, UPSTREAM_IFACE, "hop_limit")).thenReturn("64");
+        final LinkProperties lp = buildIpv6OnlyLinkProperties(UPSTREAM_IFACE);
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE, lp, 1);
+        verify(mRaDaemon).buildNewRa(any(), raParamsCaptor.capture());
+        final RaParams nonCellularParams = raParamsCaptor.getValue();
+        assertEquals(65, nonCellularParams.hopLimit);
+        reset(mRaDaemon);
+
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE, null, 0);
+        verify(mRaDaemon).buildNewRa(any(), raParamsCaptor.capture());
+        final RaParams noUpstream = raParamsCaptor.getValue();
+        assertEquals(65, nonCellularParams.hopLimit);
+        reset(mRaDaemon);
+
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE, lp, -1);
+        verify(mRaDaemon).buildNewRa(any(), raParamsCaptor.capture());
+        final RaParams cellularParams = raParamsCaptor.getValue();
+        assertEquals(63, cellularParams.hopLimit);
+        reset(mRaDaemon);
+    }
+
     private void assertDhcpServingParams(final DhcpServingParamsParcel params,
             final IpPrefix prefix) {
         // Last address byte is random
@@ -838,9 +883,10 @@
      * @param upstreamIface String name of upstream interface (or null)
      * @param v6lp IPv6 LinkProperties of the upstream interface, or null for an IPv4-only upstream.
      */
-    private void dispatchTetherConnectionChanged(String upstreamIface, LinkProperties v6lp) {
+    private void dispatchTetherConnectionChanged(String upstreamIface, LinkProperties v6lp,
+            int ttlAdjustment) {
         dispatchTetherConnectionChanged(upstreamIface);
-        mIpServer.sendMessage(IpServer.CMD_IPV6_TETHER_UPDATE, v6lp);
+        mIpServer.sendMessage(IpServer.CMD_IPV6_TETHER_UPDATE, ttlAdjustment, 0, v6lp);
         mLooper.dispatchAll();
     }
 
diff --git a/Tethering/tests/unit/src/com/android/networkstack/tethering/IPv6TetheringCoordinatorTest.java b/Tethering/tests/unit/src/com/android/networkstack/tethering/IPv6TetheringCoordinatorTest.java
index 820f255..f2b5314 100644
--- a/Tethering/tests/unit/src/com/android/networkstack/tethering/IPv6TetheringCoordinatorTest.java
+++ b/Tethering/tests/unit/src/com/android/networkstack/tethering/IPv6TetheringCoordinatorTest.java
@@ -128,7 +128,7 @@
         final UpstreamNetworkState mobileUpstream = createDualStackUpstream(TRANSPORT_CELLULAR);
         final ArgumentCaptor<LinkProperties> lp = ArgumentCaptor.forClass(LinkProperties.class);
         mIPv6TetheringCoordinator.updateUpstreamNetworkState(mobileUpstream);
-        verify(firstServer).sendMessage(eq(IpServer.CMD_IPV6_TETHER_UPDATE), eq(0), eq(0),
+        verify(firstServer).sendMessage(eq(IpServer.CMD_IPV6_TETHER_UPDATE), eq(-1), eq(0),
                 lp.capture());
         final LinkProperties v6OnlyLink = lp.getValue();
         assertOnlyOneV6AddressAndNoV4(v6OnlyLink);
@@ -140,7 +140,7 @@
         mNotifyList.remove(firstServer);
         mIPv6TetheringCoordinator.removeActiveDownstream(firstServer);
         verify(firstServer).sendMessage(IpServer.CMD_IPV6_TETHER_UPDATE, 0, 0, null);
-        verify(secondServer).sendMessage(eq(IpServer.CMD_IPV6_TETHER_UPDATE), eq(0), eq(0),
+        verify(secondServer).sendMessage(eq(IpServer.CMD_IPV6_TETHER_UPDATE), eq(-1), eq(0),
                 lp.capture());
         final LinkProperties localOnlyLink = lp.getValue();
         assertNotNull(localOnlyLink);