Add option to replace linkAddrCache with neighborCache

This change adds an option to replace the current implementation of ARP through
linkAddrCache, with an implementation of NUD through neighborCache. Switching
to using NUD for both ARP and NDP is beneficial for the reasons described by
RFC 4861 Section 3.1:

  "[Using NUD] significantly improves the robustness of packet delivery in the
  presence of failing routers, partially failing or partitioned links, or nodes
  that change their link-layer addresses. For instance, mobile nodes can move
  off-link without losing any connectivity due to stale ARP caches."

  "Unlike ARP, Neighbor Unreachability Detection detects half-link failures and
  avoids sending traffic to neighbors with which two-way connectivity is
  absent."

Along with these changes exposes the API for querying and operating the
neighbor cache. Operations include:
  - Create a static entry
  - List all entries
  - Delete all entries
  - Remove an entry by address

This also exposes the API to change the NUD protocol constants on a per-NIC
basis to allow Neighbor Discovery to operate over links with widely varying
performance characteristics. See [RFC 4861 Section 10][1] for the list of
constants.

Finally, an API for subscribing to NUD state changes is exposed through
NUDDispatcher. See [RFC 4861 Appendix C][3] for the list of edges.

Tests:
 pkg/tcpip/network/arp:arp_test
 + TestDirectRequest

 pkg/tcpip/network/ipv6:ipv6_test
 + TestLinkResolution
 + TestNDPValidation
 + TestNeighorAdvertisementWithTargetLinkLayerOption
 + TestNeighorSolicitationResponse
 + TestNeighorSolicitationWithSourceLinkLayerOption
 + TestRouterAdvertValidation

 pkg/tcpip/stack:stack_test
 + TestCacheWaker
 + TestForwardingWithFakeResolver
 + TestForwardingWithFakeResolverManyPackets
 + TestForwardingWithFakeResolverManyResolutions
 + TestForwardingWithFakeResolverPartialTimeout
 + TestForwardingWithFakeResolverTwoPackets
 + TestIPv6SourceAddressSelectionScopeAndSameAddress

[1]: https://tools.ietf.org/html/rfc4861#section-10
[2]: https://tools.ietf.org/html/rfc4861#appendix-C

Fixes #1889
Fixes #1894
Fixes #1895
Fixes #1947
Fixes #1948
Fixes #1949
Fixes #1950

PiperOrigin-RevId: 328365034

1 files changed, 426 insertions, 366 deletions

diff --git a/pkg/tcpip/stack/ndp_test.go b/pkg/tcpip/stack/ndp_test.go
index 21bf53010..67dc5364f 100644
--- a/pkg/tcpip/stack/ndp_test.go
+++ b/pkg/tcpip/stack/ndp_test.go
@@ -2787,7 +2787,7 @@ func TestMixedSLAACAddrConflictRegen(t *testing.T) {
 // stack.Stack will have a default route through the router (llAddr3) installed
 // and a static link-address (linkAddr3) added to the link address cache for the
 // router.
-func stackAndNdpDispatcherWithDefaultRoute(t *testing.T, nicID tcpip.NICID) (*ndpDispatcher, *channel.Endpoint, *stack.Stack) {
+func stackAndNdpDispatcherWithDefaultRoute(t *testing.T, nicID tcpip.NICID, useNeighborCache bool) (*ndpDispatcher, *channel.Endpoint, *stack.Stack) {
 	t.Helper()
 	ndpDisp := &ndpDispatcher{
 		autoGenAddrC: make(chan ndpAutoGenAddrEvent, 1),
@@ -2800,7 +2800,8 @@ func stackAndNdpDispatcherWithDefaultRoute(t *testing.T, nicID tcpip.NICID) (*nd
 			HandleRAs:              true,
 			AutoGenGlobalAddresses: true,
 		},
-		NDPDisp: ndpDisp,
+		NDPDisp:          ndpDisp,
+		UseNeighborCache: useNeighborCache,
 	})
 	if err := s.CreateNIC(nicID, e); err != nil {
 		t.Fatalf("CreateNIC(%d, _) = %s", nicID, err)
@@ -2810,7 +2811,11 @@ func stackAndNdpDispatcherWithDefaultRoute(t *testing.T, nicID tcpip.NICID) (*nd
 		Gateway:     llAddr3,
 		NIC:         nicID,
 	}})
-	s.AddLinkAddress(nicID, llAddr3, linkAddr3)
+	if useNeighborCache {
+		s.AddStaticNeighbor(nicID, llAddr3, linkAddr3)
+	} else {
+		s.AddLinkAddress(nicID, llAddr3, linkAddr3)
+	}
 	return ndpDisp, e, s
 }
 
@@ -2884,110 +2889,128 @@ func addrForNewConnectionWithAddr(t *testing.T, s *stack.Stack, addr tcpip.FullA
 // TestAutoGenAddrDeprecateFromPI tests deprecating a SLAAC address when
 // receiving a PI with 0 preferred lifetime.
 func TestAutoGenAddrDeprecateFromPI(t *testing.T) {
-	const nicID = 1
+	stacks := []struct {
+		name             string
+		useNeighborCache bool
+	}{
+		{
+			name:             "linkAddrCache",
+			useNeighborCache: false,
+		},
+		{
+			name:             "neighborCache",
+			useNeighborCache: true,
+		},
+	}
 
-	prefix1, _, addr1 := prefixSubnetAddr(0, linkAddr1)
-	prefix2, _, addr2 := prefixSubnetAddr(1, linkAddr1)
+	for _, stackTyp := range stacks {
+		t.Run(stackTyp.name, func(t *testing.T) {
+			const nicID = 1
 
-	ndpDisp, e, s := stackAndNdpDispatcherWithDefaultRoute(t, nicID)
+			prefix1, _, addr1 := prefixSubnetAddr(0, linkAddr1)
+			prefix2, _, addr2 := prefixSubnetAddr(1, linkAddr1)
 
-	expectAutoGenAddrEvent := func(addr tcpip.AddressWithPrefix, eventType ndpAutoGenAddrEventType) {
-		t.Helper()
+			ndpDisp, e, s := stackAndNdpDispatcherWithDefaultRoute(t, nicID, stackTyp.useNeighborCache)
 
-		select {
-		case e := <-ndpDisp.autoGenAddrC:
-			if diff := checkAutoGenAddrEvent(e, addr, eventType); diff != "" {
-				t.Errorf("auto-gen addr event mismatch (-want +got):\n%s", diff)
+			expectAutoGenAddrEvent := func(addr tcpip.AddressWithPrefix, eventType ndpAutoGenAddrEventType) {
+				t.Helper()
+
+				select {
+				case e := <-ndpDisp.autoGenAddrC:
+					if diff := checkAutoGenAddrEvent(e, addr, eventType); diff != "" {
+						t.Errorf("auto-gen addr event mismatch (-want +got):\n%s", diff)
+					}
+				default:
+					t.Fatal("expected addr auto gen event")
+				}
 			}
-		default:
-			t.Fatal("expected addr auto gen event")
-		}
-	}
 
-	expectPrimaryAddr := func(addr tcpip.AddressWithPrefix) {
-		t.Helper()
+			expectPrimaryAddr := func(addr tcpip.AddressWithPrefix) {
+				t.Helper()
 
-		if got, err := s.GetMainNICAddress(nicID, header.IPv6ProtocolNumber); err != nil {
-			t.Fatalf("s.GetMainNICAddress(%d, %d): %s", nicID, header.IPv6ProtocolNumber, err)
-		} else if got != addr {
-			t.Errorf("got s.GetMainNICAddress(%d, %d) = %s, want = %s", nicID, header.IPv6ProtocolNumber, got, addr)
-		}
+				if got, err := s.GetMainNICAddress(nicID, header.IPv6ProtocolNumber); err != nil {
+					t.Fatalf("s.GetMainNICAddress(%d, %d): %s", nicID, header.IPv6ProtocolNumber, err)
+				} else if got != addr {
+					t.Errorf("got s.GetMainNICAddress(%d, %d) = %s, want = %s", nicID, header.IPv6ProtocolNumber, got, addr)
+				}
 
-		if got := addrForNewConnection(t, s); got != addr.Address {
-			t.Errorf("got addrForNewConnection = %s, want = %s", got, addr.Address)
-		}
-	}
+				if got := addrForNewConnection(t, s); got != addr.Address {
+					t.Errorf("got addrForNewConnection = %s, want = %s", got, addr.Address)
+				}
+			}
 
-	// Receive PI for prefix1.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix1, true, true, 100, 100))
-	expectAutoGenAddrEvent(addr1, newAddr)
-	if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr1) {
-		t.Fatalf("should have %s in the list of addresses", addr1)
-	}
-	expectPrimaryAddr(addr1)
+			// Receive PI for prefix1.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix1, true, true, 100, 100))
+			expectAutoGenAddrEvent(addr1, newAddr)
+			if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr1) {
+				t.Fatalf("should have %s in the list of addresses", addr1)
+			}
+			expectPrimaryAddr(addr1)
 
-	// Deprecate addr for prefix1 immedaitely.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix1, true, true, 100, 0))
-	expectAutoGenAddrEvent(addr1, deprecatedAddr)
-	if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr1) {
-		t.Fatalf("should have %s in the list of addresses", addr1)
-	}
-	// addr should still be the primary endpoint as there are no other addresses.
-	expectPrimaryAddr(addr1)
+			// Deprecate addr for prefix1 immedaitely.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix1, true, true, 100, 0))
+			expectAutoGenAddrEvent(addr1, deprecatedAddr)
+			if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr1) {
+				t.Fatalf("should have %s in the list of addresses", addr1)
+			}
+			// addr should still be the primary endpoint as there are no other addresses.
+			expectPrimaryAddr(addr1)
 
-	// Refresh lifetimes of addr generated from prefix1.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix1, true, true, 100, 100))
-	select {
-	case <-ndpDisp.autoGenAddrC:
-		t.Fatal("unexpectedly got an auto-generated event")
-	default:
-	}
-	expectPrimaryAddr(addr1)
+			// Refresh lifetimes of addr generated from prefix1.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix1, true, true, 100, 100))
+			select {
+			case <-ndpDisp.autoGenAddrC:
+				t.Fatal("unexpectedly got an auto-generated event")
+			default:
+			}
+			expectPrimaryAddr(addr1)
 
-	// Receive PI for prefix2.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix2, true, true, 100, 100))
-	expectAutoGenAddrEvent(addr2, newAddr)
-	if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
-		t.Fatalf("should have %s in the list of addresses", addr2)
-	}
-	expectPrimaryAddr(addr2)
+			// Receive PI for prefix2.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix2, true, true, 100, 100))
+			expectAutoGenAddrEvent(addr2, newAddr)
+			if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
+				t.Fatalf("should have %s in the list of addresses", addr2)
+			}
+			expectPrimaryAddr(addr2)
 
-	// Deprecate addr for prefix2 immedaitely.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix2, true, true, 100, 0))
-	expectAutoGenAddrEvent(addr2, deprecatedAddr)
-	if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
-		t.Fatalf("should have %s in the list of addresses", addr2)
-	}
-	// addr1 should be the primary endpoint now since addr2 is deprecated but
-	// addr1 is not.
-	expectPrimaryAddr(addr1)
-	// addr2 is deprecated but if explicitly requested, it should be used.
-	fullAddr2 := tcpip.FullAddress{Addr: addr2.Address, NIC: nicID}
-	if got := addrForNewConnectionWithAddr(t, s, fullAddr2); got != addr2.Address {
-		t.Errorf("got addrForNewConnectionWithAddr(_, _, %+v) = %s, want = %s", fullAddr2, got, addr2.Address)
-	}
+			// Deprecate addr for prefix2 immedaitely.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix2, true, true, 100, 0))
+			expectAutoGenAddrEvent(addr2, deprecatedAddr)
+			if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
+				t.Fatalf("should have %s in the list of addresses", addr2)
+			}
+			// addr1 should be the primary endpoint now since addr2 is deprecated but
+			// addr1 is not.
+			expectPrimaryAddr(addr1)
+			// addr2 is deprecated but if explicitly requested, it should be used.
+			fullAddr2 := tcpip.FullAddress{Addr: addr2.Address, NIC: nicID}
+			if got := addrForNewConnectionWithAddr(t, s, fullAddr2); got != addr2.Address {
+				t.Errorf("got addrForNewConnectionWithAddr(_, _, %+v) = %s, want = %s", fullAddr2, got, addr2.Address)
+			}
 
-	// Another PI w/ 0 preferred lifetime should not result in a deprecation
-	// event.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix2, true, true, 100, 0))
-	select {
-	case <-ndpDisp.autoGenAddrC:
-		t.Fatal("unexpectedly got an auto-generated event")
-	default:
-	}
-	expectPrimaryAddr(addr1)
-	if got := addrForNewConnectionWithAddr(t, s, fullAddr2); got != addr2.Address {
-		t.Errorf("got addrForNewConnectionWithAddr(_, _, %+v) = %s, want = %s", fullAddr2, got, addr2.Address)
-	}
+			// Another PI w/ 0 preferred lifetime should not result in a deprecation
+			// event.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix2, true, true, 100, 0))
+			select {
+			case <-ndpDisp.autoGenAddrC:
+				t.Fatal("unexpectedly got an auto-generated event")
+			default:
+			}
+			expectPrimaryAddr(addr1)
+			if got := addrForNewConnectionWithAddr(t, s, fullAddr2); got != addr2.Address {
+				t.Errorf("got addrForNewConnectionWithAddr(_, _, %+v) = %s, want = %s", fullAddr2, got, addr2.Address)
+			}
 
-	// Refresh lifetimes of addr generated from prefix2.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix2, true, true, 100, 100))
-	select {
-	case <-ndpDisp.autoGenAddrC:
-		t.Fatal("unexpectedly got an auto-generated event")
-	default:
+			// Refresh lifetimes of addr generated from prefix2.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix2, true, true, 100, 100))
+			select {
+			case <-ndpDisp.autoGenAddrC:
+				t.Fatal("unexpectedly got an auto-generated event")
+			default:
+			}
+			expectPrimaryAddr(addr2)
+		})
 	}
-	expectPrimaryAddr(addr2)
 }
 
 // TestAutoGenAddrJobDeprecation tests that an address is properly deprecated
@@ -2996,217 +3019,236 @@ func TestAutoGenAddrJobDeprecation(t *testing.T) {
 	const nicID = 1
 	const newMinVL = 2
 	newMinVLDuration := newMinVL * time.Second
-	saved := stack.MinPrefixInformationValidLifetimeForUpdate
-	defer func() {
-		stack.MinPrefixInformationValidLifetimeForUpdate = saved
-	}()
-	stack.MinPrefixInformationValidLifetimeForUpdate = newMinVLDuration
 
-	prefix1, _, addr1 := prefixSubnetAddr(0, linkAddr1)
-	prefix2, _, addr2 := prefixSubnetAddr(1, linkAddr1)
+	stacks := []struct {
+		name             string
+		useNeighborCache bool
+	}{
+		{
+			name:             "linkAddrCache",
+			useNeighborCache: false,
+		},
+		{
+			name:             "neighborCache",
+			useNeighborCache: true,
+		},
+	}
 
-	ndpDisp, e, s := stackAndNdpDispatcherWithDefaultRoute(t, nicID)
+	for _, stackTyp := range stacks {
+		t.Run(stackTyp.name, func(t *testing.T) {
+			saved := stack.MinPrefixInformationValidLifetimeForUpdate
+			defer func() {
+				stack.MinPrefixInformationValidLifetimeForUpdate = saved
+			}()
+			stack.MinPrefixInformationValidLifetimeForUpdate = newMinVLDuration
 
-	expectAutoGenAddrEvent := func(addr tcpip.AddressWithPrefix, eventType ndpAutoGenAddrEventType) {
-		t.Helper()
+			prefix1, _, addr1 := prefixSubnetAddr(0, linkAddr1)
+			prefix2, _, addr2 := prefixSubnetAddr(1, linkAddr1)
 
-		select {
-		case e := <-ndpDisp.autoGenAddrC:
-			if diff := checkAutoGenAddrEvent(e, addr, eventType); diff != "" {
-				t.Errorf("auto-gen addr event mismatch (-want +got):\n%s", diff)
+			ndpDisp, e, s := stackAndNdpDispatcherWithDefaultRoute(t, nicID, stackTyp.useNeighborCache)
+
+			expectAutoGenAddrEvent := func(addr tcpip.AddressWithPrefix, eventType ndpAutoGenAddrEventType) {
+				t.Helper()
+
+				select {
+				case e := <-ndpDisp.autoGenAddrC:
+					if diff := checkAutoGenAddrEvent(e, addr, eventType); diff != "" {
+						t.Errorf("auto-gen addr event mismatch (-want +got):\n%s", diff)
+					}
+				default:
+					t.Fatal("expected addr auto gen event")
+				}
 			}
-		default:
-			t.Fatal("expected addr auto gen event")
-		}
-	}
 
-	expectAutoGenAddrEventAfter := func(addr tcpip.AddressWithPrefix, eventType ndpAutoGenAddrEventType, timeout time.Duration) {
-		t.Helper()
+			expectAutoGenAddrEventAfter := func(addr tcpip.AddressWithPrefix, eventType ndpAutoGenAddrEventType, timeout time.Duration) {
+				t.Helper()
 
-		select {
-		case e := <-ndpDisp.autoGenAddrC:
-			if diff := checkAutoGenAddrEvent(e, addr, eventType); diff != "" {
-				t.Errorf("auto-gen addr event mismatch (-want +got):\n%s", diff)
+				select {
+				case e := <-ndpDisp.autoGenAddrC:
+					if diff := checkAutoGenAddrEvent(e, addr, eventType); diff != "" {
+						t.Errorf("auto-gen addr event mismatch (-want +got):\n%s", diff)
+					}
+				case <-time.After(timeout):
+					t.Fatal("timed out waiting for addr auto gen event")
+				}
 			}
-		case <-time.After(timeout):
-			t.Fatal("timed out waiting for addr auto gen event")
-		}
-	}
 
-	expectPrimaryAddr := func(addr tcpip.AddressWithPrefix) {
-		t.Helper()
+			expectPrimaryAddr := func(addr tcpip.AddressWithPrefix) {
+				t.Helper()
 
-		if got, err := s.GetMainNICAddress(nicID, header.IPv6ProtocolNumber); err != nil {
-			t.Fatalf("s.GetMainNICAddress(%d, %d): %s", nicID, header.IPv6ProtocolNumber, err)
-		} else if got != addr {
-			t.Errorf("got s.GetMainNICAddress(%d, %d) = %s, want = %s", nicID, header.IPv6ProtocolNumber, got, addr)
-		}
+				if got, err := s.GetMainNICAddress(nicID, header.IPv6ProtocolNumber); err != nil {
+					t.Fatalf("s.GetMainNICAddress(%d, %d): %s", nicID, header.IPv6ProtocolNumber, err)
+				} else if got != addr {
+					t.Errorf("got s.GetMainNICAddress(%d, %d) = %s, want = %s", nicID, header.IPv6ProtocolNumber, got, addr)
+				}
 
-		if got := addrForNewConnection(t, s); got != addr.Address {
-			t.Errorf("got addrForNewConnection = %s, want = %s", got, addr.Address)
-		}
-	}
+				if got := addrForNewConnection(t, s); got != addr.Address {
+					t.Errorf("got addrForNewConnection = %s, want = %s", got, addr.Address)
+				}
+			}
 
-	// Receive PI for prefix2.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix2, true, true, 100, 100))
-	expectAutoGenAddrEvent(addr2, newAddr)
-	if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
-		t.Fatalf("should have %s in the list of addresses", addr2)
-	}
-	expectPrimaryAddr(addr2)
+			// Receive PI for prefix2.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix2, true, true, 100, 100))
+			expectAutoGenAddrEvent(addr2, newAddr)
+			if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
+				t.Fatalf("should have %s in the list of addresses", addr2)
+			}
+			expectPrimaryAddr(addr2)
 
-	// Receive a PI for prefix1.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix1, true, true, 100, 90))
-	expectAutoGenAddrEvent(addr1, newAddr)
-	if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr1) {
-		t.Fatalf("should have %s in the list of addresses", addr1)
-	}
-	if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
-		t.Fatalf("should have %s in the list of addresses", addr2)
-	}
-	expectPrimaryAddr(addr1)
+			// Receive a PI for prefix1.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix1, true, true, 100, 90))
+			expectAutoGenAddrEvent(addr1, newAddr)
+			if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr1) {
+				t.Fatalf("should have %s in the list of addresses", addr1)
+			}
+			if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
+				t.Fatalf("should have %s in the list of addresses", addr2)
+			}
+			expectPrimaryAddr(addr1)
 
-	// Refresh lifetime for addr of prefix1.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix1, true, true, newMinVL, newMinVL-1))
-	select {
-	case <-ndpDisp.autoGenAddrC:
-		t.Fatal("unexpectedly got an auto-generated event")
-	default:
-	}
-	expectPrimaryAddr(addr1)
+			// Refresh lifetime for addr of prefix1.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix1, true, true, newMinVL, newMinVL-1))
+			select {
+			case <-ndpDisp.autoGenAddrC:
+				t.Fatal("unexpectedly got an auto-generated event")
+			default:
+			}
+			expectPrimaryAddr(addr1)
 
-	// Wait for addr of prefix1 to be deprecated.
-	expectAutoGenAddrEventAfter(addr1, deprecatedAddr, newMinVLDuration-time.Second+defaultAsyncPositiveEventTimeout)
-	if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr1) {
-		t.Fatalf("should not have %s in the list of addresses", addr1)
-	}
-	if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
-		t.Fatalf("should have %s in the list of addresses", addr2)
-	}
-	// addr2 should be the primary endpoint now since addr1 is deprecated but
-	// addr2 is not.
-	expectPrimaryAddr(addr2)
-	// addr1 is deprecated but if explicitly requested, it should be used.
-	fullAddr1 := tcpip.FullAddress{Addr: addr1.Address, NIC: nicID}
-	if got := addrForNewConnectionWithAddr(t, s, fullAddr1); got != addr1.Address {
-		t.Errorf("got addrForNewConnectionWithAddr(_, _, %+v) = %s, want = %s", fullAddr1, got, addr1.Address)
-	}
+			// Wait for addr of prefix1 to be deprecated.
+			expectAutoGenAddrEventAfter(addr1, deprecatedAddr, newMinVLDuration-time.Second+defaultAsyncPositiveEventTimeout)
+			if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr1) {
+				t.Fatalf("should not have %s in the list of addresses", addr1)
+			}
+			if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
+				t.Fatalf("should have %s in the list of addresses", addr2)
+			}
+			// addr2 should be the primary endpoint now since addr1 is deprecated but
+			// addr2 is not.
+			expectPrimaryAddr(addr2)
+			// addr1 is deprecated but if explicitly requested, it should be used.
+			fullAddr1 := tcpip.FullAddress{Addr: addr1.Address, NIC: nicID}
+			if got := addrForNewConnectionWithAddr(t, s, fullAddr1); got != addr1.Address {
+				t.Errorf("got addrForNewConnectionWithAddr(_, _, %+v) = %s, want = %s", fullAddr1, got, addr1.Address)
+			}
 
-	// Refresh valid lifetime for addr of prefix1, w/ 0 preferred lifetime to make
-	// sure we do not get a deprecation event again.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix1, true, true, newMinVL, 0))
-	select {
-	case <-ndpDisp.autoGenAddrC:
-		t.Fatal("unexpectedly got an auto-generated event")
-	default:
-	}
-	expectPrimaryAddr(addr2)
-	if got := addrForNewConnectionWithAddr(t, s, fullAddr1); got != addr1.Address {
-		t.Errorf("got addrForNewConnectionWithAddr(_, _, %+v) = %s, want = %s", fullAddr1, got, addr1.Address)
-	}
+			// Refresh valid lifetime for addr of prefix1, w/ 0 preferred lifetime to make
+			// sure we do not get a deprecation event again.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix1, true, true, newMinVL, 0))
+			select {
+			case <-ndpDisp.autoGenAddrC:
+				t.Fatal("unexpectedly got an auto-generated event")
+			default:
+			}
+			expectPrimaryAddr(addr2)
+			if got := addrForNewConnectionWithAddr(t, s, fullAddr1); got != addr1.Address {
+				t.Errorf("got addrForNewConnectionWithAddr(_, _, %+v) = %s, want = %s", fullAddr1, got, addr1.Address)
+			}
 
-	// Refresh lifetimes for addr of prefix1.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix1, true, true, newMinVL, newMinVL-1))
-	select {
-	case <-ndpDisp.autoGenAddrC:
-		t.Fatal("unexpectedly got an auto-generated event")
-	default:
-	}
-	// addr1 is the primary endpoint again since it is non-deprecated now.
-	expectPrimaryAddr(addr1)
+			// Refresh lifetimes for addr of prefix1.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix1, true, true, newMinVL, newMinVL-1))
+			select {
+			case <-ndpDisp.autoGenAddrC:
+				t.Fatal("unexpectedly got an auto-generated event")
+			default:
+			}
+			// addr1 is the primary endpoint again since it is non-deprecated now.
+			expectPrimaryAddr(addr1)
 
-	// Wait for addr of prefix1 to be deprecated.
-	expectAutoGenAddrEventAfter(addr1, deprecatedAddr, newMinVLDuration-time.Second+defaultAsyncPositiveEventTimeout)
-	if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr1) {
-		t.Fatalf("should not have %s in the list of addresses", addr1)
-	}
-	if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
-		t.Fatalf("should have %s in the list of addresses", addr2)
-	}
-	// addr2 should be the primary endpoint now since it is not deprecated.
-	expectPrimaryAddr(addr2)
-	if got := addrForNewConnectionWithAddr(t, s, fullAddr1); got != addr1.Address {
-		t.Errorf("got addrForNewConnectionWithAddr(_, _, %+v) = %s, want = %s", fullAddr1, got, addr1.Address)
-	}
+			// Wait for addr of prefix1 to be deprecated.
+			expectAutoGenAddrEventAfter(addr1, deprecatedAddr, newMinVLDuration-time.Second+defaultAsyncPositiveEventTimeout)
+			if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr1) {
+				t.Fatalf("should not have %s in the list of addresses", addr1)
+			}
+			if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
+				t.Fatalf("should have %s in the list of addresses", addr2)
+			}
+			// addr2 should be the primary endpoint now since it is not deprecated.
+			expectPrimaryAddr(addr2)
+			if got := addrForNewConnectionWithAddr(t, s, fullAddr1); got != addr1.Address {
+				t.Errorf("got addrForNewConnectionWithAddr(_, _, %+v) = %s, want = %s", fullAddr1, got, addr1.Address)
+			}
 
-	// Wait for addr of prefix1 to be invalidated.
-	expectAutoGenAddrEventAfter(addr1, invalidatedAddr, time.Second+defaultAsyncPositiveEventTimeout)
-	if containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr1) {
-		t.Fatalf("should not have %s in the list of addresses", addr1)
-	}
-	if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
-		t.Fatalf("should have %s in the list of addresses", addr2)
-	}
-	expectPrimaryAddr(addr2)
+			// Wait for addr of prefix1 to be invalidated.
+			expectAutoGenAddrEventAfter(addr1, invalidatedAddr, time.Second+defaultAsyncPositiveEventTimeout)
+			if containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr1) {
+				t.Fatalf("should not have %s in the list of addresses", addr1)
+			}
+			if !containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
+				t.Fatalf("should have %s in the list of addresses", addr2)
+			}
+			expectPrimaryAddr(addr2)
 
-	// Refresh both lifetimes for addr of prefix2 to the same value.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix2, true, true, newMinVL, newMinVL))
-	select {
-	case <-ndpDisp.autoGenAddrC:
-		t.Fatal("unexpectedly got an auto-generated event")
-	default:
-	}
+			// Refresh both lifetimes for addr of prefix2 to the same value.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr2, 0, prefix2, true, true, newMinVL, newMinVL))
+			select {
+			case <-ndpDisp.autoGenAddrC:
+				t.Fatal("unexpectedly got an auto-generated event")
+			default:
+			}
 
-	// Wait for a deprecation then invalidation events, or just an invalidation
-	// event. We need to cover both cases but cannot deterministically hit both
-	// cases because the deprecation and invalidation handlers could be handled in
-	// either deprecation then invalidation, or invalidation then deprecation
-	// (which should be cancelled by the invalidation handler).
-	select {
-	case e := <-ndpDisp.autoGenAddrC:
-		if diff := checkAutoGenAddrEvent(e, addr2, deprecatedAddr); diff == "" {
-			// If we get a deprecation event first, we should get an invalidation
-			// event almost immediately after.
+			// Wait for a deprecation then invalidation events, or just an invalidation
+			// event. We need to cover both cases but cannot deterministically hit both
+			// cases because the deprecation and invalidation handlers could be handled in
+			// either deprecation then invalidation, or invalidation then deprecation
+			// (which should be cancelled by the invalidation handler).
 			select {
 			case e := <-ndpDisp.autoGenAddrC:
-				if diff := checkAutoGenAddrEvent(e, addr2, invalidatedAddr); diff != "" {
-					t.Errorf("auto-gen addr event mismatch (-want +got):\n%s", diff)
+				if diff := checkAutoGenAddrEvent(e, addr2, deprecatedAddr); diff == "" {
+					// If we get a deprecation event first, we should get an invalidation
+					// event almost immediately after.
+					select {
+					case e := <-ndpDisp.autoGenAddrC:
+						if diff := checkAutoGenAddrEvent(e, addr2, invalidatedAddr); diff != "" {
+							t.Errorf("auto-gen addr event mismatch (-want +got):\n%s", diff)
+						}
+					case <-time.After(defaultAsyncPositiveEventTimeout):
+						t.Fatal("timed out waiting for addr auto gen event")
+					}
+				} else if diff := checkAutoGenAddrEvent(e, addr2, invalidatedAddr); diff == "" {
+					// If we get an invalidation  event first, we should not get a deprecation
+					// event after.
+					select {
+					case <-ndpDisp.autoGenAddrC:
+						t.Fatal("unexpectedly got an auto-generated event")
+					case <-time.After(defaultAsyncNegativeEventTimeout):
+					}
+				} else {
+					t.Fatalf("got unexpected auto-generated event")
 				}
-			case <-time.After(defaultAsyncPositiveEventTimeout):
+			case <-time.After(newMinVLDuration + defaultAsyncPositiveEventTimeout):
 				t.Fatal("timed out waiting for addr auto gen event")
 			}
-		} else if diff := checkAutoGenAddrEvent(e, addr2, invalidatedAddr); diff == "" {
-			// If we get an invalidation  event first, we should not get a deprecation
-			// event after.
-			select {
-			case <-ndpDisp.autoGenAddrC:
-				t.Fatal("unexpectedly got an auto-generated event")
-			case <-time.After(defaultAsyncNegativeEventTimeout):
+			if containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr1) {
+				t.Fatalf("should not have %s in the list of addresses", addr1)
+			}
+			if containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
+				t.Fatalf("should not have %s in the list of addresses", addr2)
+			}
+			// Should not have any primary endpoints.
+			if got, err := s.GetMainNICAddress(nicID, header.IPv6ProtocolNumber); err != nil {
+				t.Fatalf("s.GetMainNICAddress(%d, %d): %s", nicID, header.IPv6ProtocolNumber, err)
+			} else if want := (tcpip.AddressWithPrefix{}); got != want {
+				t.Errorf("got s.GetMainNICAddress(%d, %d) = %s, want = %s", nicID, header.IPv6ProtocolNumber, got, want)
+			}
+			wq := waiter.Queue{}
+			we, ch := waiter.NewChannelEntry(nil)
+			wq.EventRegister(&we, waiter.EventIn)
+			defer wq.EventUnregister(&we)
+			defer close(ch)
+			ep, err := s.NewEndpoint(header.UDPProtocolNumber, header.IPv6ProtocolNumber, &wq)
+			if err != nil {
+				t.Fatalf("s.NewEndpoint(%d, %d, _): %s", header.UDPProtocolNumber, header.IPv6ProtocolNumber, err)
+			}
+			defer ep.Close()
+			if err := ep.SetSockOptBool(tcpip.V6OnlyOption, true); err != nil {
+				t.Fatalf("SetSockOpt(tcpip.V6OnlyOption, true): %s", err)
 			}
-		} else {
-			t.Fatalf("got unexpected auto-generated event")
-		}
-	case <-time.After(newMinVLDuration + defaultAsyncPositiveEventTimeout):
-		t.Fatal("timed out waiting for addr auto gen event")
-	}
-	if containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr1) {
-		t.Fatalf("should not have %s in the list of addresses", addr1)
-	}
-	if containsV6Addr(s.NICInfo()[nicID].ProtocolAddresses, addr2) {
-		t.Fatalf("should not have %s in the list of addresses", addr2)
-	}
-	// Should not have any primary endpoints.
-	if got, err := s.GetMainNICAddress(nicID, header.IPv6ProtocolNumber); err != nil {
-		t.Fatalf("s.GetMainNICAddress(%d, %d): %s", nicID, header.IPv6ProtocolNumber, err)
-	} else if want := (tcpip.AddressWithPrefix{}); got != want {
-		t.Errorf("got s.GetMainNICAddress(%d, %d) = %s, want = %s", nicID, header.IPv6ProtocolNumber, got, want)
-	}
-	wq := waiter.Queue{}
-	we, ch := waiter.NewChannelEntry(nil)
-	wq.EventRegister(&we, waiter.EventIn)
-	defer wq.EventUnregister(&we)
-	defer close(ch)
-	ep, err := s.NewEndpoint(header.UDPProtocolNumber, header.IPv6ProtocolNumber, &wq)
-	if err != nil {
-		t.Fatalf("s.NewEndpoint(%d, %d, _): %s", header.UDPProtocolNumber, header.IPv6ProtocolNumber, err)
-	}
-	defer ep.Close()
-	if err := ep.SetSockOptBool(tcpip.V6OnlyOption, true); err != nil {
-		t.Fatalf("SetSockOpt(tcpip.V6OnlyOption, true): %s", err)
-	}
 
-	if err := ep.Connect(dstAddr); err != tcpip.ErrNoRoute {
-		t.Errorf("got ep.Connect(%+v) = %v, want = %s", dstAddr, err, tcpip.ErrNoRoute)
+			if err := ep.Connect(dstAddr); err != tcpip.ErrNoRoute {
+				t.Errorf("got ep.Connect(%+v) = %s, want = %s", dstAddr, err, tcpip.ErrNoRoute)
+			}
+		})
 	}
 }
 
@@ -3524,110 +3566,128 @@ func TestAutoGenAddrRemoval(t *testing.T) {
 func TestAutoGenAddrAfterRemoval(t *testing.T) {
 	const nicID = 1
 
-	prefix1, _, addr1 := prefixSubnetAddr(0, linkAddr1)
-	prefix2, _, addr2 := prefixSubnetAddr(1, linkAddr1)
-	ndpDisp, e, s := stackAndNdpDispatcherWithDefaultRoute(t, nicID)
-
-	expectAutoGenAddrEvent := func(addr tcpip.AddressWithPrefix, eventType ndpAutoGenAddrEventType) {
-		t.Helper()
-
-		select {
-		case e := <-ndpDisp.autoGenAddrC:
-			if diff := checkAutoGenAddrEvent(e, addr, eventType); diff != "" {
-				t.Errorf("auto-gen addr event mismatch (-want +got):\n%s", diff)
-			}
-		default:
-			t.Fatal("expected addr auto gen event")
-		}
+	stacks := []struct {
+		name             string
+		useNeighborCache bool
+	}{
+		{
+			name:             "linkAddrCache",
+			useNeighborCache: false,
+		},
+		{
+			name:             "neighborCache",
+			useNeighborCache: true,
+		},
 	}
 
-	expectPrimaryAddr := func(addr tcpip.AddressWithPrefix) {
-		t.Helper()
+	for _, stackTyp := range stacks {
+		t.Run(stackTyp.name, func(t *testing.T) {
+			prefix1, _, addr1 := prefixSubnetAddr(0, linkAddr1)
+			prefix2, _, addr2 := prefixSubnetAddr(1, linkAddr1)
+			ndpDisp, e, s := stackAndNdpDispatcherWithDefaultRoute(t, nicID, stackTyp.useNeighborCache)
 
-		if got, err := s.GetMainNICAddress(nicID, header.IPv6ProtocolNumber); err != nil {
-			t.Fatalf("s.GetMainNICAddress(%d, %d): %s", nicID, header.IPv6ProtocolNumber, err)
-		} else if got != addr {
-			t.Errorf("got s.GetMainNICAddress(%d, %d) = %s, want = %s", nicID, header.IPv6ProtocolNumber, got, addr)
-		}
-
-		if got := addrForNewConnection(t, s); got != addr.Address {
-			t.Errorf("got addrForNewConnection = %s, want = %s", got, addr.Address)
-		}
-	}
+			expectAutoGenAddrEvent := func(addr tcpip.AddressWithPrefix, eventType ndpAutoGenAddrEventType) {
+				t.Helper()
 
-	// Receive a PI to auto-generate addr1 with a large valid and preferred
-	// lifetime.
-	const largeLifetimeSeconds = 999
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr3, 0, prefix1, true, true, largeLifetimeSeconds, largeLifetimeSeconds))
-	expectAutoGenAddrEvent(addr1, newAddr)
-	expectPrimaryAddr(addr1)
+				select {
+				case e := <-ndpDisp.autoGenAddrC:
+					if diff := checkAutoGenAddrEvent(e, addr, eventType); diff != "" {
+						t.Errorf("auto-gen addr event mismatch (-want +got):\n%s", diff)
+					}
+				default:
+					t.Fatal("expected addr auto gen event")
+				}
+			}
 
-	// Add addr2 as a static address.
-	protoAddr2 := tcpip.ProtocolAddress{
-		Protocol:          header.IPv6ProtocolNumber,
-		AddressWithPrefix: addr2,
-	}
-	if err := s.AddProtocolAddressWithOptions(nicID, protoAddr2, stack.FirstPrimaryEndpoint); err != nil {
-		t.Fatalf("AddProtocolAddressWithOptions(%d, %+v, %d) = %s", nicID, protoAddr2, stack.FirstPrimaryEndpoint, err)
-	}
-	// addr2 should be more preferred now since it is at the front of the primary
-	// list.
-	expectPrimaryAddr(addr2)
+			expectPrimaryAddr := func(addr tcpip.AddressWithPrefix) {
+				t.Helper()
 
-	// Get a route using addr2 to increment its reference count then remove it
-	// to leave it in the permanentExpired state.
-	r, err := s.FindRoute(nicID, addr2.Address, addr3, header.IPv6ProtocolNumber, false)
-	if err != nil {
-		t.Fatalf("FindRoute(%d, %s, %s, %d, false): %s", nicID, addr2.Address, addr3, header.IPv6ProtocolNumber, err)
-	}
-	defer r.Release()
-	if err := s.RemoveAddress(nicID, addr2.Address); err != nil {
-		t.Fatalf("s.RemoveAddress(%d, %s): %s", nicID, addr2.Address, err)
-	}
-	// addr1 should be preferred again since addr2 is in the expired state.
-	expectPrimaryAddr(addr1)
+				if got, err := s.GetMainNICAddress(nicID, header.IPv6ProtocolNumber); err != nil {
+					t.Fatalf("s.GetMainNICAddress(%d, %d): %s", nicID, header.IPv6ProtocolNumber, err)
+				} else if got != addr {
+					t.Errorf("got s.GetMainNICAddress(%d, %d) = %s, want = %s", nicID, header.IPv6ProtocolNumber, got, addr)
+				}
 
-	// Receive a PI to auto-generate addr2 as valid and preferred.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr3, 0, prefix2, true, true, largeLifetimeSeconds, largeLifetimeSeconds))
-	expectAutoGenAddrEvent(addr2, newAddr)
-	// addr2 should be more preferred now that it is closer to the front of the
-	// primary list and not deprecated.
-	expectPrimaryAddr(addr2)
+				if got := addrForNewConnection(t, s); got != addr.Address {
+					t.Errorf("got addrForNewConnection = %s, want = %s", got, addr.Address)
+				}
+			}
 
-	// Removing the address should result in an invalidation event immediately.
-	// It should still be in the permanentExpired state because r is still held.
-	//
-	// We remove addr2 here to make sure addr2 was marked as a SLAAC address
-	// (it was previously marked as a static address).
-	if err := s.RemoveAddress(1, addr2.Address); err != nil {
-		t.Fatalf("RemoveAddress(_, %s) = %s", addr2.Address, err)
-	}
-	expectAutoGenAddrEvent(addr2, invalidatedAddr)
-	// addr1 should be more preferred since addr2 is in the expired state.
-	expectPrimaryAddr(addr1)
+			// Receive a PI to auto-generate addr1 with a large valid and preferred
+			// lifetime.
+			const largeLifetimeSeconds = 999
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr3, 0, prefix1, true, true, largeLifetimeSeconds, largeLifetimeSeconds))
+			expectAutoGenAddrEvent(addr1, newAddr)
+			expectPrimaryAddr(addr1)
 
-	// Receive a PI to auto-generate addr2 as valid and deprecated.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr3, 0, prefix2, true, true, largeLifetimeSeconds, 0))
-	expectAutoGenAddrEvent(addr2, newAddr)
-	// addr1 should still be more preferred since addr2 is deprecated, even though
-	// it is closer to the front of the primary list.
-	expectPrimaryAddr(addr1)
+			// Add addr2 as a static address.
+			protoAddr2 := tcpip.ProtocolAddress{
+				Protocol:          header.IPv6ProtocolNumber,
+				AddressWithPrefix: addr2,
+			}
+			if err := s.AddProtocolAddressWithOptions(nicID, protoAddr2, stack.FirstPrimaryEndpoint); err != nil {
+				t.Fatalf("AddProtocolAddressWithOptions(%d, %+v, %d) = %s", nicID, protoAddr2, stack.FirstPrimaryEndpoint, err)
+			}
+			// addr2 should be more preferred now since it is at the front of the primary
+			// list.
+			expectPrimaryAddr(addr2)
 
-	// Receive a PI to refresh addr2's preferred lifetime.
-	e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr3, 0, prefix2, true, true, largeLifetimeSeconds, largeLifetimeSeconds))
-	select {
-	case <-ndpDisp.autoGenAddrC:
-		t.Fatal("unexpectedly got an auto gen addr event")
-	default:
-	}
-	// addr2 should be more preferred now that it is not deprecated.
-	expectPrimaryAddr(addr2)
+			// Get a route using addr2 to increment its reference count then remove it
+			// to leave it in the permanentExpired state.
+			r, err := s.FindRoute(nicID, addr2.Address, addr3, header.IPv6ProtocolNumber, false)
+			if err != nil {
+				t.Fatalf("FindRoute(%d, %s, %s, %d, false): %s", nicID, addr2.Address, addr3, header.IPv6ProtocolNumber, err)
+			}
+			defer r.Release()
+			if err := s.RemoveAddress(nicID, addr2.Address); err != nil {
+				t.Fatalf("s.RemoveAddress(%d, %s): %s", nicID, addr2.Address, err)
+			}
+			// addr1 should be preferred again since addr2 is in the expired state.
+			expectPrimaryAddr(addr1)
+
+			// Receive a PI to auto-generate addr2 as valid and preferred.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr3, 0, prefix2, true, true, largeLifetimeSeconds, largeLifetimeSeconds))
+			expectAutoGenAddrEvent(addr2, newAddr)
+			// addr2 should be more preferred now that it is closer to the front of the
+			// primary list and not deprecated.
+			expectPrimaryAddr(addr2)
+
+			// Removing the address should result in an invalidation event immediately.
+			// It should still be in the permanentExpired state because r is still held.
+			//
+			// We remove addr2 here to make sure addr2 was marked as a SLAAC address
+			// (it was previously marked as a static address).
+			if err := s.RemoveAddress(1, addr2.Address); err != nil {
+				t.Fatalf("RemoveAddress(_, %s) = %s", addr2.Address, err)
+			}
+			expectAutoGenAddrEvent(addr2, invalidatedAddr)
+			// addr1 should be more preferred since addr2 is in the expired state.
+			expectPrimaryAddr(addr1)
+
+			// Receive a PI to auto-generate addr2 as valid and deprecated.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr3, 0, prefix2, true, true, largeLifetimeSeconds, 0))
+			expectAutoGenAddrEvent(addr2, newAddr)
+			// addr1 should still be more preferred since addr2 is deprecated, even though
+			// it is closer to the front of the primary list.
+			expectPrimaryAddr(addr1)
+
+			// Receive a PI to refresh addr2's preferred lifetime.
+			e.InjectInbound(header.IPv6ProtocolNumber, raBufWithPI(llAddr3, 0, prefix2, true, true, largeLifetimeSeconds, largeLifetimeSeconds))
+			select {
+			case <-ndpDisp.autoGenAddrC:
+				t.Fatal("unexpectedly got an auto gen addr event")
+			default:
+			}
+			// addr2 should be more preferred now that it is not deprecated.
+			expectPrimaryAddr(addr2)
 
-	if err := s.RemoveAddress(1, addr2.Address); err != nil {
-		t.Fatalf("RemoveAddress(_, %s) = %s", addr2.Address, err)
+			if err := s.RemoveAddress(1, addr2.Address); err != nil {
+				t.Fatalf("RemoveAddress(_, %s) = %s", addr2.Address, err)
+			}
+			expectAutoGenAddrEvent(addr2, invalidatedAddr)
+			expectPrimaryAddr(addr1)
+		})
 	}
-	expectAutoGenAddrEvent(addr2, invalidatedAddr)
-	expectPrimaryAddr(addr1)
 }
 
 // TestAutoGenAddrStaticConflict tests that if SLAAC generates an address that