diff --git a/Tethering/src/android/net/ip/IpServer.java b/Tethering/src/android/net/ip/IpServer.java
index 3acc766..38f8609 100644
--- a/Tethering/src/android/net/ip/IpServer.java
+++ b/Tethering/src/android/net/ip/IpServer.java
@@ -810,7 +810,7 @@
                     rule.dstMac.toByteArray());
             mIpv6ForwardingRules.put(rule.address, rule);
         } catch (RemoteException | ServiceSpecificException e) {
-            Log.e(TAG, "Could not add IPv6 downstream rule: " + e);
+            mLog.e("Could not add IPv6 downstream rule: ", e);
         }
     }
 
@@ -821,10 +821,17 @@
                 mIpv6ForwardingRules.remove(rule.address);
             }
         } catch (RemoteException | ServiceSpecificException e) {
-            Log.e(TAG, "Could not remove IPv6 downstream rule: " + e);
+            mLog.e("Could not remove IPv6 downstream rule: ", e);
         }
     }
 
+    private void clearIpv6ForwardingRules() {
+        for (Ipv6ForwardingRule rule : mIpv6ForwardingRules.values()) {
+            removeIpv6ForwardingRule(rule, false /*removeFromMap*/);
+        }
+        mIpv6ForwardingRules.clear();
+    }
+
     // Convenience method to replace a rule with the same rule on a new upstream interface.
     // Allows replacing the rules in one iteration pass without ConcurrentModificationExceptions.
     // Relies on the fact that rules are in a map indexed by IP address.
@@ -837,6 +844,12 @@
     // changes or if a neighbor event is received.
     private void updateIpv6ForwardingRules(int prevUpstreamIfindex, int upstreamIfindex,
             NeighborEvent e) {
+        // If we no longer have an upstream, clear forwarding rules and do nothing else.
+        if (upstreamIfindex == 0) {
+            clearIpv6ForwardingRules();
+            return;
+        }
+
         // If the upstream interface has changed, remove all rules and re-add them with the new
         // upstream interface.
         if (prevUpstreamIfindex != upstreamIfindex) {
@@ -846,13 +859,14 @@
         }
 
         // If we're here to process a NeighborEvent, do so now.
+        // mInterfaceParams must be non-null or the event would not have arrived.
         if (e == null) return;
         if (!(e.ip instanceof Inet6Address) || e.ip.isMulticastAddress()
                 || e.ip.isLoopbackAddress() || e.ip.isLinkLocalAddress()) {
             return;
         }
 
-        Ipv6ForwardingRule rule = new Ipv6ForwardingRule(mLastIPv6UpstreamIfindex,
+        Ipv6ForwardingRule rule = new Ipv6ForwardingRule(upstreamIfindex,
                 mInterfaceParams.index, (Inet6Address) e.ip, mInterfaceParams.macAddr,
                 e.macAddr);
         if (e.isValid()) {
@@ -1095,6 +1109,7 @@
 
             for (String ifname : mUpstreamIfaceSet.ifnames) cleanupUpstreamInterface(ifname);
             mUpstreamIfaceSet = null;
+            clearIpv6ForwardingRules();
         }
 
         private void cleanupUpstreamInterface(String upstreamIface) {
diff --git a/Tethering/tests/unit/src/android/net/ip/IpServerTest.java b/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
index 39742f5..948266d 100644
--- a/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
+++ b/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
@@ -43,6 +43,7 @@
 import static org.junit.Assert.fail;
 import static org.mockito.ArgumentMatchers.argThat;
 import static org.mockito.Matchers.any;
+import static org.mockito.Matchers.anyInt;
 import static org.mockito.Matchers.anyString;
 import static org.mockito.Matchers.eq;
 import static org.mockito.Mockito.doAnswer;
@@ -546,9 +547,9 @@
         reset(mNetd);
 
         // Link-local and multicast neighbors are ignored.
-        recvNewNeigh(notMyIfindex, neighLL, NUD_REACHABLE, macA);
+        recvNewNeigh(myIfindex, neighLL, NUD_REACHABLE, macA);
         verifyNoMoreInteractions(mNetd);
-        recvNewNeigh(notMyIfindex, neighMC, NUD_REACHABLE, macA);
+        recvNewNeigh(myIfindex, neighMC, NUD_REACHABLE, macA);
         verifyNoMoreInteractions(mNetd);
 
         // A neighbor that is no longer valid causes the rule to be removed.
@@ -578,6 +579,52 @@
                 eq(neighB.getAddress()), eq(myMac.toByteArray()), eq(macB.toByteArray()));
         inOrder.verify(mNetd).tetherRuleRemoveDownstreamIpv6(eq(UPSTREAM_IFINDEX),
                 eq(neighB.getAddress()));
+        reset(mNetd);
+
+        // When the upstream is lost, rules are removed.
+        dispatchTetherConnectionChanged(null, null);
+        verify(mNetd).tetherRuleRemoveDownstreamIpv6(eq(UPSTREAM_IFINDEX2),
+                eq(neighA.getAddress()));
+        verify(mNetd).tetherRuleRemoveDownstreamIpv6(eq(UPSTREAM_IFINDEX2),
+                eq(neighB.getAddress()));
+        reset(mNetd);
+
+        // If the upstream is IPv4-only, no rules are added.
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE);
+        reset(mNetd);
+        recvNewNeigh(myIfindex, neighA, NUD_REACHABLE, macA);
+        verifyNoMoreInteractions(mNetd);
+
+        // Rules can be added again once upstream IPv6 connectivity is available.
+        lp.setInterfaceName(UPSTREAM_IFACE);
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE, lp);
+        recvNewNeigh(myIfindex, neighB, NUD_REACHABLE, macB);
+        verify(mNetd).tetherRuleAddDownstreamIpv6(eq(myIfindex), eq(UPSTREAM_IFINDEX),
+                eq(neighB.getAddress()), eq(myMac.toByteArray()), eq(macB.toByteArray()));
+        verify(mNetd, never()).tetherRuleAddDownstreamIpv6(anyInt(), anyInt(),
+                eq(neighA.getAddress()), any(), any());
+
+        // If upstream IPv6 connectivity is lost, rules are removed.
+        reset(mNetd);
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE, null);
+        verify(mNetd).tetherRuleRemoveDownstreamIpv6(eq(UPSTREAM_IFINDEX), eq(neighB.getAddress()));
+
+        // When the interface goes down, rules are removed.
+        lp.setInterfaceName(UPSTREAM_IFACE);
+        dispatchTetherConnectionChanged(UPSTREAM_IFACE, lp);
+        recvNewNeigh(myIfindex, neighA, NUD_REACHABLE, macA);
+        recvNewNeigh(myIfindex, neighB, NUD_REACHABLE, macB);
+        verify(mNetd).tetherRuleAddDownstreamIpv6(eq(myIfindex), eq(UPSTREAM_IFINDEX),
+                eq(neighA.getAddress()), eq(myMac.toByteArray()), eq(macA.toByteArray()));
+        verify(mNetd).tetherRuleAddDownstreamIpv6(eq(myIfindex), eq(UPSTREAM_IFINDEX),
+                eq(neighB.getAddress()), eq(myMac.toByteArray()), eq(macB.toByteArray()));
+        reset(mNetd);
+
+        mIpServer.stop();
+        mLooper.dispatchAll();
+        verify(mNetd).tetherRuleRemoveDownstreamIpv6(eq(UPSTREAM_IFINDEX), eq(neighA.getAddress()));
+        verify(mNetd).tetherRuleRemoveDownstreamIpv6(eq(UPSTREAM_IFINDEX), eq(neighB.getAddress()));
+        reset(mNetd);
     }
 
     private void assertDhcpStarted(IpPrefix expectedPrefix) throws Exception {