From 2d90bc54809766927e6028fac5b9f67cd2a13c3e Mon Sep 17 00:00:00 2001
From: Ghanan Gowripalan <ghanan@google.com>
Date: Sat, 30 Jan 2021 11:35:35 -0800
Subject: Implement LinkAddressResolver on NetworkEndpoints

This removes the need to provide the link address request with the NIC
the request is being performed on since the NetworkEndpoints already
have a reference to the NIC.

PiperOrigin-RevId: 354721940
---
 pkg/tcpip/network/arp/BUILD            |  1 -
 pkg/tcpip/network/arp/arp.go           | 59 ++++++-----------------
 pkg/tcpip/network/arp/arp_test.go      | 86 +++++++---------------------------
 pkg/tcpip/network/arp/stats_test.go    | 42 -----------------
 pkg/tcpip/network/ipv6/icmp.go         | 35 +++++---------
 pkg/tcpip/network/ipv6/icmp_test.go    | 27 ++++++-----
 pkg/tcpip/network/ipv6/ipv6.go         |  1 +
 pkg/tcpip/stack/forwarding_test.go     | 18 +++----
 pkg/tcpip/stack/linkaddrcache.go       |  8 ++--
 pkg/tcpip/stack/linkaddrcache_test.go  | 44 ++++++++---------
 pkg/tcpip/stack/neighbor_cache_test.go |  2 +-
 pkg/tcpip/stack/neighbor_entry.go      |  4 +-
 pkg/tcpip/stack/neighbor_entry_test.go |  2 +-
 pkg/tcpip/stack/nic.go                 | 43 +++++++++++++----
 pkg/tcpip/stack/nic_test.go            | 20 --------
 pkg/tcpip/stack/nud_test.go            | 49 +++++++------------
 pkg/tcpip/stack/registration.go        |  8 +---
 pkg/tcpip/stack/route.go               |  2 +-
 pkg/tcpip/stack/stack.go               | 18 +------
 19 files changed, 152 insertions(+), 317 deletions(-)

diff --git a/pkg/tcpip/network/arp/BUILD b/pkg/tcpip/network/arp/BUILD
index c7ab876bf..933845269 100644
--- a/pkg/tcpip/network/arp/BUILD
+++ b/pkg/tcpip/network/arp/BUILD
@@ -10,7 +10,6 @@ go_library(
     ],
     visibility = ["//visibility:public"],
     deps = [
-        "//pkg/sync",
         "//pkg/tcpip",
         "//pkg/tcpip/buffer",
         "//pkg/tcpip/header",
diff --git a/pkg/tcpip/network/arp/arp.go b/pkg/tcpip/network/arp/arp.go
index 7838cc753..5c79d6485 100644
--- a/pkg/tcpip/network/arp/arp.go
+++ b/pkg/tcpip/network/arp/arp.go
@@ -22,7 +22,6 @@ import (
 	"reflect"
 	"sync/atomic"
 
-	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
@@ -35,6 +34,8 @@ const (
 	ProtocolNumber = header.ARPProtocolNumber
 )
 
+var _ stack.LinkAddressResolver = (*endpoint)(nil)
+
 // ARP endpoints need to implement stack.NetworkEndpoint because the stack
 // considers the layer above the link-layer a network layer; the only
 // facility provided by the stack to deliver packets to a layer above
@@ -101,9 +102,7 @@ func (e *endpoint) MaxHeaderLength() uint16 {
 	return e.nic.MaxHeaderLength() + header.ARPSize
 }
 
-func (e *endpoint) Close() {
-	e.protocol.forgetEndpoint(e.nic.ID())
-}
+func (*endpoint) Close() {}
 
 func (*endpoint) WritePacket(*stack.Route, *stack.GSO, stack.NetworkHeaderParams, *stack.PacketBuffer) tcpip.Error {
 	return &tcpip.ErrNotSupported{}
@@ -154,7 +153,7 @@ func (e *endpoint) HandlePacket(pkt *stack.PacketBuffer) {
 		if e.nud == nil {
 			e.linkAddrCache.AddLinkAddress(remoteAddr, remoteLinkAddr)
 		} else {
-			e.nud.HandleProbe(remoteAddr, ProtocolNumber, remoteLinkAddr, e.protocol)
+			e.nud.HandleProbe(remoteAddr, ProtocolNumber, remoteLinkAddr, e)
 		}
 
 		respPkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
@@ -221,19 +220,10 @@ func (e *endpoint) Stats() stack.NetworkEndpointStats {
 }
 
 var _ stack.NetworkProtocol = (*protocol)(nil)
-var _ stack.LinkAddressResolver = (*protocol)(nil)
 
 // protocol implements stack.NetworkProtocol and stack.LinkAddressResolver.
 type protocol struct {
 	stack *stack.Stack
-
-	mu struct {
-		sync.RWMutex
-
-		// eps is keyed by NICID to allow protocol methods to retrieve the correct
-		// endpoint depending on the NIC.
-		eps map[tcpip.NICID]*endpoint
-	}
 }
 
 func (p *protocol) Number() tcpip.NetworkProtocolNumber { return ProtocolNumber }
@@ -257,43 +247,26 @@ func (p *protocol) NewEndpoint(nic stack.NetworkInterface, linkAddrCache stack.L
 	stackStats := p.stack.Stats()
 	e.stats.arp.init(&e.stats.localStats.ARP, &stackStats.ARP)
 
-	p.mu.Lock()
-	p.mu.eps[nic.ID()] = e
-	p.mu.Unlock()
-
 	return e
 }
 
-func (p *protocol) forgetEndpoint(nicID tcpip.NICID) {
-	p.mu.Lock()
-	defer p.mu.Unlock()
-	delete(p.mu.eps, nicID)
-}
-
 // LinkAddressProtocol implements stack.LinkAddressResolver.LinkAddressProtocol.
-func (*protocol) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
+func (*endpoint) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
 	return header.IPv4ProtocolNumber
 }
 
 // LinkAddressRequest implements stack.LinkAddressResolver.LinkAddressRequest.
-func (p *protocol) LinkAddressRequest(targetAddr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress, nic stack.NetworkInterface) tcpip.Error {
-	nicID := nic.ID()
-
-	p.mu.Lock()
-	netEP, ok := p.mu.eps[nicID]
-	p.mu.Unlock()
-	if !ok {
-		return &tcpip.ErrNotConnected{}
-	}
+func (e *endpoint) LinkAddressRequest(targetAddr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress) tcpip.Error {
+	nicID := e.nic.ID()
 
-	stats := netEP.stats.arp
+	stats := e.stats.arp
 
 	if len(remoteLinkAddr) == 0 {
 		remoteLinkAddr = header.EthernetBroadcastAddress
 	}
 
 	if len(localAddr) == 0 {
-		addr, ok := p.stack.GetMainNICAddress(nicID, header.IPv4ProtocolNumber)
+		addr, ok := e.protocol.stack.GetMainNICAddress(nicID, header.IPv4ProtocolNumber)
 		if !ok {
 			return &tcpip.ErrUnknownNICID{}
 		}
@@ -304,13 +277,13 @@ func (p *protocol) LinkAddressRequest(targetAddr, localAddr tcpip.Address, remot
 		}
 
 		localAddr = addr.Address
-	} else if p.stack.CheckLocalAddress(nicID, header.IPv4ProtocolNumber, localAddr) == 0 {
+	} else if e.protocol.stack.CheckLocalAddress(nicID, header.IPv4ProtocolNumber, localAddr) == 0 {
 		stats.outgoingRequestBadLocalAddressErrors.Increment()
 		return &tcpip.ErrBadLocalAddress{}
 	}
 
 	pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
-		ReserveHeaderBytes: int(nic.MaxHeaderLength()) + header.ARPSize,
+		ReserveHeaderBytes: int(e.nic.MaxHeaderLength()) + header.ARPSize,
 	})
 	h := header.ARP(pkt.NetworkHeader().Push(header.ARPSize))
 	pkt.NetworkProtocolNumber = ProtocolNumber
@@ -318,14 +291,14 @@ func (p *protocol) LinkAddressRequest(targetAddr, localAddr tcpip.Address, remot
 	h.SetOp(header.ARPRequest)
 	// TODO(gvisor.dev/issue/4582): check copied length once TAP devices have a
 	// link address.
-	_ = copy(h.HardwareAddressSender(), nic.LinkAddress())
+	_ = copy(h.HardwareAddressSender(), e.nic.LinkAddress())
 	if n := copy(h.ProtocolAddressSender(), localAddr); n != header.IPv4AddressSize {
 		panic(fmt.Sprintf("copied %d bytes, expected %d bytes", n, header.IPv4AddressSize))
 	}
 	if n := copy(h.ProtocolAddressTarget(), targetAddr); n != header.IPv4AddressSize {
 		panic(fmt.Sprintf("copied %d bytes, expected %d bytes", n, header.IPv4AddressSize))
 	}
-	if err := nic.WritePacketToRemote(remoteLinkAddr, nil /* gso */, ProtocolNumber, pkt); err != nil {
+	if err := e.nic.WritePacketToRemote(remoteLinkAddr, nil /* gso */, ProtocolNumber, pkt); err != nil {
 		stats.outgoingRequestsDropped.Increment()
 		return err
 	}
@@ -334,7 +307,7 @@ func (p *protocol) LinkAddressRequest(targetAddr, localAddr tcpip.Address, remot
 }
 
 // ResolveStaticAddress implements stack.LinkAddressResolver.ResolveStaticAddress.
-func (*protocol) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bool) {
+func (*endpoint) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bool) {
 	if addr == header.IPv4Broadcast {
 		return header.EthernetBroadcastAddress, true
 	}
@@ -369,9 +342,5 @@ func (*protocol) Parse(pkt *stack.PacketBuffer) (proto tcpip.TransportProtocolNu
 func NewProtocol(s *stack.Stack) stack.NetworkProtocol {
 	return &protocol{
 		stack: s,
-		mu: struct {
-			sync.RWMutex
-			eps map[tcpip.NICID]*endpoint
-		}{eps: make(map[tcpip.NICID]*endpoint)},
 	}
 }
diff --git a/pkg/tcpip/network/arp/arp_test.go b/pkg/tcpip/network/arp/arp_test.go
index b0f07aa44..d753a97af 100644
--- a/pkg/tcpip/network/arp/arp_test.go
+++ b/pkg/tcpip/network/arp/arp_test.go
@@ -530,52 +530,19 @@ func TestDirectRequestWithNeighborCache(t *testing.T) {
 	}
 }
 
-var _ stack.NetworkInterface = (*testInterface)(nil)
+var _ stack.LinkEndpoint = (*testLinkEndpoint)(nil)
 
-type testInterface struct {
+type testLinkEndpoint struct {
 	stack.LinkEndpoint
 
-	nicID tcpip.NICID
-
 	writeErr tcpip.Error
 }
 
-func (t *testInterface) ID() tcpip.NICID {
-	return t.nicID
-}
-
-func (*testInterface) IsLoopback() bool {
-	return false
-}
-
-func (*testInterface) Name() string {
-	return ""
-}
-
-func (*testInterface) Enabled() bool {
-	return true
-}
-
-func (*testInterface) Promiscuous() bool {
-	return false
-}
-
-func (t *testInterface) WritePacket(r *stack.Route, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
-	return t.LinkEndpoint.WritePacket(r.Fields(), gso, protocol, pkt)
-}
-
-func (t *testInterface) WritePackets(r *stack.Route, gso *stack.GSO, pkts stack.PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
-	return t.LinkEndpoint.WritePackets(r.Fields(), gso, pkts, protocol)
-}
-
-func (t *testInterface) WritePacketToRemote(remoteLinkAddr tcpip.LinkAddress, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
+func (t *testLinkEndpoint) WritePacket(r stack.RouteInfo, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
 	if t.writeErr != nil {
 		return t.writeErr
 	}
 
-	var r stack.RouteInfo
-	r.NetProto = protocol
-	r.RemoteLinkAddress = remoteLinkAddr
 	return t.LinkEndpoint.WritePacket(r, gso, protocol, pkt)
 }
 
@@ -709,32 +676,31 @@ func TestLinkAddressRequest(t *testing.T) {
 			s := stack.New(stack.Options{
 				NetworkProtocols: []stack.NetworkProtocolFactory{arp.NewProtocol, ipv4.NewProtocol},
 			})
-			p := s.NetworkProtocolInstance(arp.ProtocolNumber)
-			linkRes, ok := p.(stack.LinkAddressResolver)
-			if !ok {
-				t.Fatal("expected ARP protocol to implement stack.LinkAddressResolver")
-			}
-
 			linkEP := channel.New(defaultChannelSize, defaultMTU, stackLinkAddr)
-			if err := s.CreateNIC(nicID, linkEP); err != nil {
+			if err := s.CreateNIC(nicID, &testLinkEndpoint{LinkEndpoint: linkEP, writeErr: test.linkErr}); err != nil {
 				t.Fatalf("s.CreateNIC(%d, _): %s", nicID, err)
 			}
 
+			ep, err := s.GetNetworkEndpoint(nicID, arp.ProtocolNumber)
+			if err != nil {
+				t.Fatalf("s.GetNetworkEndpoint(%d, %d): %s", nicID, arp.ProtocolNumber, err)
+			}
+			linkRes, ok := ep.(stack.LinkAddressResolver)
+			if !ok {
+				t.Fatalf("expected %T to implement stack.LinkAddressResolver", ep)
+			}
+
 			if len(test.nicAddr) != 0 {
 				if err := s.AddAddress(nicID, ipv4.ProtocolNumber, test.nicAddr); err != nil {
 					t.Fatalf("s.AddAddress(%d, %d, %s): %s", nicID, ipv4.ProtocolNumber, test.nicAddr, err)
 				}
 			}
 
-			// We pass a test network interface to LinkAddressRequest with the same
-			// NIC ID and link endpoint used by the NIC we created earlier so that we
-			// can mock a link address request and observe the packets sent to the
-			// link endpoint even though the stack uses the real NIC to validate the
-			// local address.
-			iface := testInterface{LinkEndpoint: linkEP, nicID: nicID, writeErr: test.linkErr}
-			err := linkRes.LinkAddressRequest(remoteAddr, test.localAddr, test.remoteLinkAddr, &iface)
-			if diff := cmp.Diff(test.expectedErr, err); diff != "" {
-				t.Fatalf("unexpected error from p.LinkAddressRequest(%s, %s, %s, _), (-want, +got):\n%s", remoteAddr, test.localAddr, test.remoteLinkAddr, diff)
+			{
+				err := linkRes.LinkAddressRequest(remoteAddr, test.localAddr, test.remoteLinkAddr)
+				if diff := cmp.Diff(test.expectedErr, err); diff != "" {
+					t.Fatalf("unexpected error from p.LinkAddressRequest(%s, %s, %s, _), (-want, +got):\n%s", remoteAddr, test.localAddr, test.remoteLinkAddr, diff)
+				}
 			}
 
 			if got := s.Stats().ARP.OutgoingRequestsSent.Value(); got != test.expectedRequestsSent {
@@ -782,19 +748,3 @@ func TestLinkAddressRequest(t *testing.T) {
 		})
 	}
 }
-
-func TestLinkAddressRequestWithoutNIC(t *testing.T) {
-	s := stack.New(stack.Options{
-		NetworkProtocols: []stack.NetworkProtocolFactory{arp.NewProtocol, ipv4.NewProtocol},
-	})
-	p := s.NetworkProtocolInstance(arp.ProtocolNumber)
-	linkRes, ok := p.(stack.LinkAddressResolver)
-	if !ok {
-		t.Fatal("expected ARP protocol to implement stack.LinkAddressResolver")
-	}
-
-	err := linkRes.LinkAddressRequest(remoteAddr, "", remoteLinkAddr, &testInterface{nicID: nicID})
-	if _, ok := err.(*tcpip.ErrNotConnected); !ok {
-		t.Fatalf("got p.LinkAddressRequest(%s, %s, %s, _) = %s, want = %s", remoteAddr, "", remoteLinkAddr, err, &tcpip.ErrNotConnected{})
-	}
-}
diff --git a/pkg/tcpip/network/arp/stats_test.go b/pkg/tcpip/network/arp/stats_test.go
index 036fdf739..d3b56c635 100644
--- a/pkg/tcpip/network/arp/stats_test.go
+++ b/pkg/tcpip/network/arp/stats_test.go
@@ -34,48 +34,6 @@ func (t *testInterface) ID() tcpip.NICID {
 	return t.nicID
 }
 
-func knownNICIDs(proto *protocol) []tcpip.NICID {
-	var nicIDs []tcpip.NICID
-
-	for k := range proto.mu.eps {
-		nicIDs = append(nicIDs, k)
-	}
-
-	return nicIDs
-}
-
-func TestClearEndpointFromProtocolOnClose(t *testing.T) {
-	s := stack.New(stack.Options{
-		NetworkProtocols: []stack.NetworkProtocolFactory{NewProtocol},
-	})
-	proto := s.NetworkProtocolInstance(ProtocolNumber).(*protocol)
-	nic := testInterface{nicID: 1}
-	ep := proto.NewEndpoint(&nic, nil, nil, nil).(*endpoint)
-	var nicIDs []tcpip.NICID
-
-	proto.mu.Lock()
-	foundEP, hasEndpointBeforeClose := proto.mu.eps[nic.ID()]
-	nicIDs = knownNICIDs(proto)
-	proto.mu.Unlock()
-
-	if !hasEndpointBeforeClose {
-		t.Fatalf("expected to find the nic id %d in the protocol's endpoint map (%v)", nic.ID(), nicIDs)
-	}
-	if foundEP != ep {
-		t.Fatalf("found an incorrect endpoint mapped to nic id %d", nic.ID())
-	}
-
-	ep.Close()
-
-	proto.mu.Lock()
-	_, hasEndpointAfterClose := proto.mu.eps[nic.ID()]
-	nicIDs = knownNICIDs(proto)
-	proto.mu.Unlock()
-	if hasEndpointAfterClose {
-		t.Fatalf("unexpectedly found an endpoint mapped to the nic id %d in the protocol's known nic ids (%v)", nic.ID(), nicIDs)
-	}
-}
-
 func TestMultiCounterStatsInitialization(t *testing.T) {
 	s := stack.New(stack.Options{
 		NetworkProtocols: []stack.NetworkProtocolFactory{NewProtocol},
diff --git a/pkg/tcpip/network/ipv6/icmp.go b/pkg/tcpip/network/ipv6/icmp.go
index 7298bd061..8db2454d3 100644
--- a/pkg/tcpip/network/ipv6/icmp.go
+++ b/pkg/tcpip/network/ipv6/icmp.go
@@ -290,7 +290,7 @@ func (e *endpoint) handleICMP(pkt *stack.PacketBuffer, hasFragmentHeader bool) {
 			received.invalid.Increment()
 			return
 		} else if e.nud != nil {
-			e.nud.HandleProbe(srcAddr, header.IPv6ProtocolNumber, sourceLinkAddr, e.protocol)
+			e.nud.HandleProbe(srcAddr, header.IPv6ProtocolNumber, sourceLinkAddr, e)
 		} else {
 			e.linkAddrCache.AddLinkAddress(srcAddr, sourceLinkAddr)
 		}
@@ -578,7 +578,7 @@ func (e *endpoint) handleICMP(pkt *stack.PacketBuffer, hasFragmentHeader bool) {
 			if e.nud != nil {
 				// A RS with a specified source IP address modifies the NUD state
 				// machine in the same way a reachability probe would.
-				e.nud.HandleProbe(srcAddr, ProtocolNumber, sourceLinkAddr, e.protocol)
+				e.nud.HandleProbe(srcAddr, ProtocolNumber, sourceLinkAddr, e)
 			}
 		}
 
@@ -628,7 +628,7 @@ func (e *endpoint) handleICMP(pkt *stack.PacketBuffer, hasFragmentHeader bool) {
 		// If the RA has the source link layer option, update the link address
 		// cache with the link address for the advertised router.
 		if len(sourceLinkAddr) != 0 && e.nud != nil {
-			e.nud.HandleProbe(routerAddr, ProtocolNumber, sourceLinkAddr, e.protocol)
+			e.nud.HandleProbe(routerAddr, ProtocolNumber, sourceLinkAddr, e)
 		}
 
 		e.mu.Lock()
@@ -694,24 +694,13 @@ func (e *endpoint) handleICMP(pkt *stack.PacketBuffer, hasFragmentHeader bool) {
 	}
 }
 
-var _ stack.LinkAddressResolver = (*protocol)(nil)
-
 // LinkAddressProtocol implements stack.LinkAddressResolver.
-func (*protocol) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
+func (*endpoint) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
 	return header.IPv6ProtocolNumber
 }
 
 // LinkAddressRequest implements stack.LinkAddressResolver.
-func (p *protocol) LinkAddressRequest(targetAddr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress, nic stack.NetworkInterface) tcpip.Error {
-	nicID := nic.ID()
-
-	p.mu.Lock()
-	netEP, ok := p.mu.eps[nicID]
-	p.mu.Unlock()
-	if !ok {
-		return &tcpip.ErrNotConnected{}
-	}
-
+func (e *endpoint) LinkAddressRequest(targetAddr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress) tcpip.Error {
 	remoteAddr := targetAddr
 	if len(remoteLinkAddr) == 0 {
 		remoteAddr = header.SolicitedNodeAddr(targetAddr)
@@ -719,22 +708,22 @@ func (p *protocol) LinkAddressRequest(targetAddr, localAddr tcpip.Address, remot
 	}
 
 	if len(localAddr) == 0 {
-		addressEndpoint := netEP.AcquireOutgoingPrimaryAddress(remoteAddr, false /* allowExpired */)
+		addressEndpoint := e.AcquireOutgoingPrimaryAddress(remoteAddr, false /* allowExpired */)
 		if addressEndpoint == nil {
 			return &tcpip.ErrNetworkUnreachable{}
 		}
 
 		localAddr = addressEndpoint.AddressWithPrefix().Address
-	} else if p.stack.CheckLocalAddress(nicID, ProtocolNumber, localAddr) == 0 {
+	} else if e.protocol.stack.CheckLocalAddress(e.nic.ID(), ProtocolNumber, localAddr) == 0 {
 		return &tcpip.ErrBadLocalAddress{}
 	}
 
 	optsSerializer := header.NDPOptionsSerializer{
-		header.NDPSourceLinkLayerAddressOption(nic.LinkAddress()),
+		header.NDPSourceLinkLayerAddressOption(e.nic.LinkAddress()),
 	}
 	neighborSolicitSize := header.ICMPv6NeighborSolicitMinimumSize + optsSerializer.Length()
 	pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
-		ReserveHeaderBytes: int(nic.MaxHeaderLength()) + header.IPv6FixedHeaderSize + neighborSolicitSize,
+		ReserveHeaderBytes: int(e.nic.MaxHeaderLength()) + header.IPv6FixedHeaderSize + neighborSolicitSize,
 	})
 	pkt.TransportProtocolNumber = header.ICMPv6ProtocolNumber
 	packet := header.ICMPv6(pkt.TransportHeader().Push(neighborSolicitSize))
@@ -751,9 +740,9 @@ func (p *protocol) LinkAddressRequest(targetAddr, localAddr tcpip.Address, remot
 		panic(fmt.Sprintf("failed to add IP header: %s", err))
 	}
 
-	stat := netEP.stats.icmp.packetsSent
+	stat := e.stats.icmp.packetsSent
 
-	if err := nic.WritePacketToRemote(remoteLinkAddr, nil /* gso */, ProtocolNumber, pkt); err != nil {
+	if err := e.nic.WritePacketToRemote(remoteLinkAddr, nil /* gso */, ProtocolNumber, pkt); err != nil {
 		stat.dropped.Increment()
 		return err
 	}
@@ -763,7 +752,7 @@ func (p *protocol) LinkAddressRequest(targetAddr, localAddr tcpip.Address, remot
 }
 
 // ResolveStaticAddress implements stack.LinkAddressResolver.
-func (*protocol) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bool) {
+func (*endpoint) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bool) {
 	if header.IsV6MulticastAddress(addr) {
 		return header.EthernetAddressFromMulticastIPv6Address(addr), true
 	}
diff --git a/pkg/tcpip/network/ipv6/icmp_test.go b/pkg/tcpip/network/ipv6/icmp_test.go
index db1c2e663..a5c88444e 100644
--- a/pkg/tcpip/network/ipv6/icmp_test.go
+++ b/pkg/tcpip/network/ipv6/icmp_test.go
@@ -1346,29 +1346,32 @@ func TestLinkAddressRequest(t *testing.T) {
 			s := stack.New(stack.Options{
 				NetworkProtocols: []stack.NetworkProtocolFactory{NewProtocol},
 			})
-			p := s.NetworkProtocolInstance(ProtocolNumber)
-			linkRes, ok := p.(stack.LinkAddressResolver)
-			if !ok {
-				t.Fatalf("expected IPv6 protocol to implement stack.LinkAddressResolver")
-			}
 
 			linkEP := channel.New(defaultChannelSize, defaultMTU, linkAddr0)
 			if err := s.CreateNIC(nicID, linkEP); err != nil {
 				t.Fatalf("s.CreateNIC(%d, _): %s", nicID, err)
 			}
+
+			ep, err := s.GetNetworkEndpoint(nicID, ProtocolNumber)
+			if err != nil {
+				t.Fatalf("s.GetNetworkEndpoint(%d, %d): %s", nicID, ProtocolNumber, err)
+			}
+			linkRes, ok := ep.(stack.LinkAddressResolver)
+			if !ok {
+				t.Fatalf("expected %T to implement stack.LinkAddressResolver", ep)
+			}
+
 			if len(test.nicAddr) != 0 {
 				if err := s.AddAddress(nicID, ProtocolNumber, test.nicAddr); err != nil {
 					t.Fatalf("s.AddAddress(%d, %d, %s): %s", nicID, ProtocolNumber, test.nicAddr, err)
 				}
 			}
 
-			// We pass a test network interface to LinkAddressRequest with the same NIC
-			// ID and link endpoint used by the NIC we created earlier so that we can
-			// mock a link address request and observe the packets sent to the link
-			// endpoint even though the stack uses the real NIC.
-			err := linkRes.LinkAddressRequest(lladdr0, test.localAddr, test.remoteLinkAddr, &testInterface{LinkEndpoint: linkEP, nicID: nicID})
-			if diff := cmp.Diff(test.expectedErr, err); diff != "" {
-				t.Fatalf("unexpected error from p.LinkAddressRequest(%s, %s, %s, _), (-want, +got):\n%s", lladdr0, test.localAddr, test.remoteLinkAddr, diff)
+			{
+				err := linkRes.LinkAddressRequest(lladdr0, test.localAddr, test.remoteLinkAddr)
+				if diff := cmp.Diff(test.expectedErr, err); diff != "" {
+					t.Fatalf("unexpected error from p.LinkAddressRequest(%s, %s, %s, _), (-want, +got):\n%s", lladdr0, test.localAddr, test.remoteLinkAddr, diff)
+				}
 			}
 
 			if test.expectedErr != nil {
diff --git a/pkg/tcpip/network/ipv6/ipv6.go b/pkg/tcpip/network/ipv6/ipv6.go
index caa62b3a2..b55a35525 100644
--- a/pkg/tcpip/network/ipv6/ipv6.go
+++ b/pkg/tcpip/network/ipv6/ipv6.go
@@ -164,6 +164,7 @@ func getLabel(addr tcpip.Address) uint8 {
 	panic(fmt.Sprintf("should have a label for address = %s", addr))
 }
 
+var _ stack.LinkAddressResolver = (*endpoint)(nil)
 var _ stack.LinkResolvableNetworkEndpoint = (*endpoint)(nil)
 var _ stack.GroupAddressableEndpoint = (*endpoint)(nil)
 var _ stack.AddressableEndpoint = (*endpoint)(nil)
diff --git a/pkg/tcpip/stack/forwarding_test.go b/pkg/tcpip/stack/forwarding_test.go
index 63a42a2ea..1e4ddf0d5 100644
--- a/pkg/tcpip/stack/forwarding_test.go
+++ b/pkg/tcpip/stack/forwarding_test.go
@@ -41,6 +41,7 @@ const (
 	protocolNumberOffset = 2
 )
 
+var _ LinkAddressResolver = (*fwdTestNetworkEndpoint)(nil)
 var _ NetworkEndpoint = (*fwdTestNetworkEndpoint)(nil)
 
 // fwdTestNetworkEndpoint is a network-layer protocol endpoint.
@@ -153,7 +154,6 @@ type fwdTestNetworkEndpointStats struct{}
 // IsNetworkEndpointStats implements stack.NetworkEndpointStats.
 func (*fwdTestNetworkEndpointStats) IsNetworkEndpointStats() {}
 
-var _ LinkAddressResolver = (*fwdTestNetworkProtocol)(nil)
 var _ NetworkProtocol = (*fwdTestNetworkProtocol)(nil)
 
 // fwdTestNetworkProtocol is a network-layer protocol that implements Address
@@ -219,23 +219,23 @@ func (*fwdTestNetworkProtocol) Close() {}
 
 func (*fwdTestNetworkProtocol) Wait() {}
 
-func (f *fwdTestNetworkProtocol) LinkAddressRequest(addr, _ tcpip.Address, remoteLinkAddr tcpip.LinkAddress, _ NetworkInterface) tcpip.Error {
-	if f.onLinkAddressResolved != nil {
-		time.AfterFunc(f.addrResolveDelay, func() {
-			f.onLinkAddressResolved(f.addrCache, f.neigh, addr, remoteLinkAddr)
+func (f *fwdTestNetworkEndpoint) LinkAddressRequest(addr, _ tcpip.Address, remoteLinkAddr tcpip.LinkAddress) tcpip.Error {
+	if fn := f.proto.onLinkAddressResolved; fn != nil {
+		time.AfterFunc(f.proto.addrResolveDelay, func() {
+			fn(f.proto.addrCache, f.proto.neigh, addr, remoteLinkAddr)
 		})
 	}
 	return nil
 }
 
-func (f *fwdTestNetworkProtocol) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bool) {
-	if f.onResolveStaticAddress != nil {
-		return f.onResolveStaticAddress(addr)
+func (f *fwdTestNetworkEndpoint) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bool) {
+	if fn := f.proto.onResolveStaticAddress; fn != nil {
+		return fn(addr)
 	}
 	return "", false
 }
 
-func (*fwdTestNetworkProtocol) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
+func (*fwdTestNetworkEndpoint) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
 	return fwdTestNetNumber
 }
 
diff --git a/pkg/tcpip/stack/linkaddrcache.go b/pkg/tcpip/stack/linkaddrcache.go
index 930b8f795..cd2bb3417 100644
--- a/pkg/tcpip/stack/linkaddrcache.go
+++ b/pkg/tcpip/stack/linkaddrcache.go
@@ -199,7 +199,7 @@ func (c *linkAddrCache) getOrCreateEntryLocked(k tcpip.Address) *linkAddrEntry {
 }
 
 // get reports any known link address for k.
-func (c *linkAddrCache) get(k tcpip.Address, linkRes LinkAddressResolver, localAddr tcpip.Address, nic NetworkInterface, onResolve func(LinkResolutionResult)) (tcpip.LinkAddress, <-chan struct{}, tcpip.Error) {
+func (c *linkAddrCache) get(k tcpip.Address, linkRes LinkAddressResolver, localAddr tcpip.Address, onResolve func(LinkResolutionResult)) (tcpip.LinkAddress, <-chan struct{}, tcpip.Error) {
 	c.mu.Lock()
 	entry := c.getOrCreateEntryLocked(k)
 	entry.mu.Lock()
@@ -224,7 +224,7 @@ func (c *linkAddrCache) get(k tcpip.Address, linkRes LinkAddressResolver, localA
 		}
 		if entry.mu.done == nil {
 			entry.mu.done = make(chan struct{})
-			go c.startAddressResolution(k, linkRes, localAddr, nic, entry.mu.done) // S/R-SAFE: link non-savable; wakers dropped synchronously.
+			go c.startAddressResolution(k, linkRes, localAddr, entry.mu.done) // S/R-SAFE: link non-savable; wakers dropped synchronously.
 		}
 		return entry.mu.linkAddr, entry.mu.done, &tcpip.ErrWouldBlock{}
 	default:
@@ -232,11 +232,11 @@ func (c *linkAddrCache) get(k tcpip.Address, linkRes LinkAddressResolver, localA
 	}
 }
 
-func (c *linkAddrCache) startAddressResolution(k tcpip.Address, linkRes LinkAddressResolver, localAddr tcpip.Address, nic NetworkInterface, done <-chan struct{}) {
+func (c *linkAddrCache) startAddressResolution(k tcpip.Address, linkRes LinkAddressResolver, localAddr tcpip.Address, done <-chan struct{}) {
 	for i := 0; ; i++ {
 		// Send link request, then wait for the timeout limit and check
 		// whether the request succeeded.
-		linkRes.LinkAddressRequest(k, localAddr, "" /* linkAddr */, nic)
+		linkRes.LinkAddressRequest(k, localAddr, "" /* linkAddr */)
 
 		select {
 		case now := <-time.After(c.resolutionTimeout):
diff --git a/pkg/tcpip/stack/linkaddrcache_test.go b/pkg/tcpip/stack/linkaddrcache_test.go
index 466a5e8d9..40017c8b6 100644
--- a/pkg/tcpip/stack/linkaddrcache_test.go
+++ b/pkg/tcpip/stack/linkaddrcache_test.go
@@ -48,7 +48,7 @@ type testLinkAddressResolver struct {
 	onLinkAddressRequest func()
 }
 
-func (r *testLinkAddressResolver) LinkAddressRequest(targetAddr, _ tcpip.Address, _ tcpip.LinkAddress, _ NetworkInterface) tcpip.Error {
+func (r *testLinkAddressResolver) LinkAddressRequest(targetAddr, _ tcpip.Address, _ tcpip.LinkAddress) tcpip.Error {
 	// TODO(gvisor.dev/issue/5141): Use a fake clock.
 	time.AfterFunc(r.delay, func() { r.fakeRequest(targetAddr) })
 	if f := r.onLinkAddressRequest; f != nil {
@@ -80,7 +80,7 @@ func (*testLinkAddressResolver) LinkAddressProtocol() tcpip.NetworkProtocolNumbe
 func getBlocking(c *linkAddrCache, addr tcpip.Address, linkRes LinkAddressResolver) (tcpip.LinkAddress, tcpip.Error) {
 	var attemptedResolution bool
 	for {
-		got, ch, err := c.get(addr, linkRes, "", nil, nil)
+		got, ch, err := c.get(addr, linkRes, "", nil)
 		if _, ok := err.(*tcpip.ErrWouldBlock); ok {
 			if attemptedResolution {
 				return got, &tcpip.ErrTimeout{}
@@ -104,23 +104,23 @@ func TestCacheOverflow(t *testing.T) {
 	for i := len(testAddrs) - 1; i >= 0; i-- {
 		e := testAddrs[i]
 		c.AddLinkAddress(e.addr, e.linkAddr)
-		got, _, err := c.get(e.addr, nil, "", nil, nil)
+		got, _, err := c.get(e.addr, nil, "", nil)
 		if err != nil {
-			t.Errorf("insert %d, c.get(%s, nil, '', nil, nil): %s", i, e.addr, err)
+			t.Errorf("insert %d, c.get(%s, nil, '', nil): %s", i, e.addr, err)
 		}
 		if got != e.linkAddr {
-			t.Errorf("insert %d, got c.get(%s, nil, '', nil, nil) = %s, want = %s", i, e.addr, got, e.linkAddr)
+			t.Errorf("insert %d, got c.get(%s, nil, '', nil) = %s, want = %s", i, e.addr, got, e.linkAddr)
 		}
 	}
 	// Expect to find at least half of the most recent entries.
 	for i := 0; i < linkAddrCacheSize/2; i++ {
 		e := testAddrs[i]
-		got, _, err := c.get(e.addr, nil, "", nil, nil)
+		got, _, err := c.get(e.addr, nil, "", nil)
 		if err != nil {
-			t.Errorf("check %d, c.get(%s, nil, '', nil, nil): %s", i, e.addr, err)
+			t.Errorf("check %d, c.get(%s, nil, '', nil): %s", i, e.addr, err)
 		}
 		if got != e.linkAddr {
-			t.Errorf("check %d, got c.get(%s, nil, '', nil, nil) = %s, want = %s", i, e.addr, got, e.linkAddr)
+			t.Errorf("check %d, got c.get(%s, nil, '', nil) = %s, want = %s", i, e.addr, got, e.linkAddr)
 		}
 	}
 	// The earliest entries should no longer be in the cache.
@@ -154,12 +154,12 @@ func TestCacheConcurrent(t *testing.T) {
 	// can fit in the cache, so our eviction strategy requires that
 	// the last entry be present and the first be missing.
 	e := testAddrs[len(testAddrs)-1]
-	got, _, err := c.get(e.addr, linkRes, "", nil, nil)
+	got, _, err := c.get(e.addr, linkRes, "", nil)
 	if err != nil {
-		t.Errorf("c.get(%s, _, '', nil, nil): %s", e.addr, err)
+		t.Errorf("c.get(%s, _, '', nil): %s", e.addr, err)
 	}
 	if got != e.linkAddr {
-		t.Errorf("got c.get(%s, _, '', nil, nil) = %s, want = %s", e.addr, got, e.linkAddr)
+		t.Errorf("got c.get(%s, _, '', nil) = %s, want = %s", e.addr, got, e.linkAddr)
 	}
 
 	e = testAddrs[0]
@@ -177,9 +177,9 @@ func TestCacheAgeLimit(t *testing.T) {
 	e := testAddrs[0]
 	c.AddLinkAddress(e.addr, e.linkAddr)
 	time.Sleep(50 * time.Millisecond)
-	_, _, err := c.get(e.addr, linkRes, "", nil, nil)
+	_, _, err := c.get(e.addr, linkRes, "", nil)
 	if _, ok := err.(*tcpip.ErrWouldBlock); !ok {
-		t.Errorf("got c.get(%s, _, '', nil, nil) = %s, want = ErrWouldBlock", e.addr, err)
+		t.Errorf("got c.get(%s, _, '', nil) = %s, want = ErrWouldBlock", e.addr, err)
 	}
 }
 
@@ -188,21 +188,21 @@ func TestCacheReplace(t *testing.T) {
 	e := testAddrs[0]
 	l2 := e.linkAddr + "2"
 	c.AddLinkAddress(e.addr, e.linkAddr)
-	got, _, err := c.get(e.addr, nil, "", nil, nil)
+	got, _, err := c.get(e.addr, nil, "", nil)
 	if err != nil {
-		t.Errorf("c.get(%s, nil, '', nil, nil): %s", e.addr, err)
+		t.Errorf("c.get(%s, nil, '', nil): %s", e.addr, err)
 	}
 	if got != e.linkAddr {
-		t.Errorf("got c.get(%s, nil, '', nil, nil) = %s, want = %s", e.addr, got, e.linkAddr)
+		t.Errorf("got c.get(%s, nil, '', nil) = %s, want = %s", e.addr, got, e.linkAddr)
 	}
 
 	c.AddLinkAddress(e.addr, l2)
-	got, _, err = c.get(e.addr, nil, "", nil, nil)
+	got, _, err = c.get(e.addr, nil, "", nil)
 	if err != nil {
-		t.Errorf("c.get(%s, nil, '', nil, nil): %s", e.addr, err)
+		t.Errorf("c.get(%s, nil, '', nil): %s", e.addr, err)
 	}
 	if got != l2 {
-		t.Errorf("got c.get(%s, nil, '', nil, nil) = %s, want = %s", e.addr, got, l2)
+		t.Errorf("got c.get(%s, nil, '', nil) = %s, want = %s", e.addr, got, l2)
 	}
 }
 
@@ -228,12 +228,12 @@ func TestCacheResolution(t *testing.T) {
 	// Check that after resolved, address stays in the cache and never returns WouldBlock.
 	for i := 0; i < 10; i++ {
 		e := testAddrs[len(testAddrs)-1]
-		got, _, err := c.get(e.addr, linkRes, "", nil, nil)
+		got, _, err := c.get(e.addr, linkRes, "", nil)
 		if err != nil {
-			t.Errorf("c.get(%s, _, '', nil, nil): %s", e.addr, err)
+			t.Errorf("c.get(%s, _, '', nil): %s", e.addr, err)
 		}
 		if got != e.linkAddr {
-			t.Errorf("got c.get(%s, _, '', nil, nil) = %s, want = %s", e.addr, got, e.linkAddr)
+			t.Errorf("got c.get(%s, _, '', nil) = %s, want = %s", e.addr, got, e.linkAddr)
 		}
 	}
 }
diff --git a/pkg/tcpip/stack/neighbor_cache_test.go b/pkg/tcpip/stack/neighbor_cache_test.go
index 2870e4f66..0f7925774 100644
--- a/pkg/tcpip/stack/neighbor_cache_test.go
+++ b/pkg/tcpip/stack/neighbor_cache_test.go
@@ -194,7 +194,7 @@ type testNeighborResolver struct {
 
 var _ LinkAddressResolver = (*testNeighborResolver)(nil)
 
-func (r *testNeighborResolver) LinkAddressRequest(targetAddr, _ tcpip.Address, _ tcpip.LinkAddress, _ NetworkInterface) tcpip.Error {
+func (r *testNeighborResolver) LinkAddressRequest(targetAddr, _ tcpip.Address, _ tcpip.LinkAddress) tcpip.Error {
 	if !r.dropReplies {
 		// Delay handling the request to emulate network latency.
 		r.clock.AfterFunc(r.delay, func() {
diff --git a/pkg/tcpip/stack/neighbor_entry.go b/pkg/tcpip/stack/neighbor_entry.go
index 53ac9bb6e..a037ca6f9 100644
--- a/pkg/tcpip/stack/neighbor_entry.go
+++ b/pkg/tcpip/stack/neighbor_entry.go
@@ -254,7 +254,7 @@ func (e *neighborEntry) setStateLocked(next NeighborState) {
 				return
 			}
 
-			if err := e.linkRes.LinkAddressRequest(e.neigh.Addr, "" /* localAddr */, e.neigh.LinkAddr, e.nic); err != nil {
+			if err := e.linkRes.LinkAddressRequest(e.neigh.Addr, "" /* localAddr */, e.neigh.LinkAddr); err != nil {
 				e.dispatchRemoveEventLocked()
 				e.setStateLocked(Failed)
 				return
@@ -340,7 +340,7 @@ func (e *neighborEntry) handlePacketQueuedLocked(localAddr tcpip.Address) {
 			//  address SHOULD be placed in the IP Source Address of the outgoing
 			//  solicitation.
 			//
-			if err := e.linkRes.LinkAddressRequest(e.neigh.Addr, localAddr, "", e.nic); err != nil {
+			if err := e.linkRes.LinkAddressRequest(e.neigh.Addr, localAddr, ""); err != nil {
 				// There is no need to log the error here; the NUD implementation may
 				// assume a working link. A valid link should be the responsibility of
 				// the NIC/stack.LinkEndpoint.
diff --git a/pkg/tcpip/stack/neighbor_entry_test.go b/pkg/tcpip/stack/neighbor_entry_test.go
index 140b8ca00..c5c3d266b 100644
--- a/pkg/tcpip/stack/neighbor_entry_test.go
+++ b/pkg/tcpip/stack/neighbor_entry_test.go
@@ -193,7 +193,7 @@ func (p entryTestProbeInfo) String() string {
 
 // LinkAddressRequest sends a request for the LinkAddress of addr. Broadcasts
 // to the local network if linkAddr is the zero value.
-func (r *entryTestLinkResolver) LinkAddressRequest(targetAddr, localAddr tcpip.Address, linkAddr tcpip.LinkAddress, _ NetworkInterface) tcpip.Error {
+func (r *entryTestLinkResolver) LinkAddressRequest(targetAddr, localAddr tcpip.Address, linkAddr tcpip.LinkAddress) tcpip.Error {
 	p := entryTestProbeInfo{
 		RemoteAddress:     targetAddr,
 		RemoteLinkAddress: linkAddr,
diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index e56a624fe..0707c3ce2 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -42,7 +42,8 @@ type NIC struct {
 
 	// The network endpoints themselves may be modified by calling the interface's
 	// methods, but the map reference and entries must be constant.
-	networkEndpoints map[tcpip.NetworkProtocolNumber]NetworkEndpoint
+	networkEndpoints  map[tcpip.NetworkProtocolNumber]NetworkEndpoint
+	linkAddrResolvers map[tcpip.NetworkProtocolNumber]LinkAddressResolver
 
 	// enabled is set to 1 when the NIC is enabled and 0 when it is disabled.
 	//
@@ -133,12 +134,13 @@ func newNIC(stack *Stack, id tcpip.NICID, name string, ep LinkEndpoint, ctx NICC
 	nic := &NIC{
 		LinkEndpoint: ep,
 
-		stack:            stack,
-		id:               id,
-		name:             name,
-		context:          ctx,
-		stats:            makeNICStats(),
-		networkEndpoints: make(map[tcpip.NetworkProtocolNumber]NetworkEndpoint),
+		stack:             stack,
+		id:                id,
+		name:              name,
+		context:           ctx,
+		stats:             makeNICStats(),
+		networkEndpoints:  make(map[tcpip.NetworkProtocolNumber]NetworkEndpoint),
+		linkAddrResolvers: make(map[tcpip.NetworkProtocolNumber]LinkAddressResolver),
 	}
 	nic.linkResQueue.init(nic)
 	nic.linkAddrCache = newLinkAddrCache(nic, ageLimit, resolutionTimeout, resolutionAttempts)
@@ -146,7 +148,7 @@ func newNIC(stack *Stack, id tcpip.NICID, name string, ep LinkEndpoint, ctx NICC
 
 	// Check for Neighbor Unreachability Detection support.
 	var nud NUDHandler
-	if ep.Capabilities()&CapabilityResolutionRequired != 0 && len(stack.linkAddrResolvers) != 0 && stack.useNeighborCache {
+	if ep.Capabilities()&CapabilityResolutionRequired != 0 && stack.useNeighborCache {
 		rng := rand.New(rand.NewSource(stack.clock.NowNanoseconds()))
 		nic.neigh = &neighborCache{
 			nic:   nic,
@@ -170,7 +172,13 @@ func newNIC(stack *Stack, id tcpip.NICID, name string, ep LinkEndpoint, ctx NICC
 	for _, netProto := range stack.networkProtocols {
 		netNum := netProto.Number()
 		nic.mu.packetEPs[netNum] = new(packetEndpointList)
-		nic.networkEndpoints[netNum] = netProto.NewEndpoint(nic, nic.linkAddrCache, nud, nic)
+
+		netEP := netProto.NewEndpoint(nic, nic.linkAddrCache, nud, nic)
+		nic.networkEndpoints[netNum] = netEP
+
+		if r, ok := netEP.(LinkAddressResolver); ok {
+			nic.linkAddrResolvers[r.LinkAddressProtocol()] = r
+		}
 	}
 
 	nic.LinkEndpoint.Attach(nic)
@@ -593,13 +601,28 @@ func (n *NIC) confirmReachable(addr tcpip.Address) {
 	}
 }
 
+func (n *NIC) getLinkAddress(addr, localAddr tcpip.Address, protocol tcpip.NetworkProtocolNumber, onResolve func(LinkResolutionResult)) tcpip.Error {
+	linkRes, ok := n.linkAddrResolvers[protocol]
+	if !ok {
+		return &tcpip.ErrNotSupported{}
+	}
+
+	if linkAddr, ok := linkRes.ResolveStaticAddress(addr); ok {
+		onResolve(LinkResolutionResult{LinkAddress: linkAddr, Success: true})
+		return nil
+	}
+
+	_, _, err := n.getNeighborLinkAddress(addr, localAddr, linkRes, onResolve)
+	return err
+}
+
 func (n *NIC) getNeighborLinkAddress(addr, localAddr tcpip.Address, linkRes LinkAddressResolver, onResolve func(LinkResolutionResult)) (tcpip.LinkAddress, <-chan struct{}, tcpip.Error) {
 	if n.neigh != nil {
 		entry, ch, err := n.neigh.entry(addr, localAddr, linkRes, onResolve)
 		return entry.LinkAddr, ch, err
 	}
 
-	return n.linkAddrCache.get(addr, linkRes, localAddr, n, onResolve)
+	return n.linkAddrCache.get(addr, linkRes, localAddr, onResolve)
 }
 
 func (n *NIC) neighbors() ([]NeighborEntry, tcpip.Error) {
diff --git a/pkg/tcpip/stack/nic_test.go b/pkg/tcpip/stack/nic_test.go
index 2f719fbe5..3564202d8 100644
--- a/pkg/tcpip/stack/nic_test.go
+++ b/pkg/tcpip/stack/nic_test.go
@@ -111,8 +111,6 @@ type testIPv6EndpointStats struct{}
 // IsNetworkEndpointStats implements stack.NetworkEndpointStats.
 func (*testIPv6EndpointStats) IsNetworkEndpointStats() {}
 
-var _ LinkAddressResolver = (*testIPv6Protocol)(nil)
-
 // We use this instead of ipv6.protocol because the ipv6 package depends on
 // the stack package which this test lives in, causing a cyclic dependency.
 type testIPv6Protocol struct{}
@@ -169,24 +167,6 @@ func (*testIPv6Protocol) Parse(*PacketBuffer) (tcpip.TransportProtocolNumber, bo
 	return 0, false, false
 }
 
-// LinkAddressProtocol implements LinkAddressResolver.
-func (*testIPv6Protocol) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
-	return header.IPv6ProtocolNumber
-}
-
-// LinkAddressRequest implements LinkAddressResolver.
-func (*testIPv6Protocol) LinkAddressRequest(_, _ tcpip.Address, _ tcpip.LinkAddress, _ NetworkInterface) tcpip.Error {
-	return nil
-}
-
-// ResolveStaticAddress implements LinkAddressResolver.
-func (*testIPv6Protocol) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bool) {
-	if header.IsV6MulticastAddress(addr) {
-		return header.EthernetAddressFromMulticastIPv6Address(addr), true
-	}
-	return "", false
-}
-
 func TestDisabledRxStatsWhenNICDisabled(t *testing.T) {
 	// When the NIC is disabled, the only field that matters is the stats field.
 	// This test is limited to stats counter checks.
diff --git a/pkg/tcpip/stack/nud_test.go b/pkg/tcpip/stack/nud_test.go
index ebfd5eb45..504acc246 100644
--- a/pkg/tcpip/stack/nud_test.go
+++ b/pkg/tcpip/stack/nud_test.go
@@ -72,17 +72,17 @@ func TestSetNUDConfigurationFailsForBadNICID(t *testing.T) {
 }
 
 // TestNUDConfigurationFailsForNotSupported tests to make sure we get a
-// NotSupported error if we attempt to retrieve NUD configurations when the
-// stack doesn't support NUD.
+// NotSupported error if we attempt to retrieve or set NUD configurations when
+// the stack doesn't support NUD.
 //
 // The stack will report to not support NUD if a neighbor cache for a given NIC
 // is not allocated. The networking stack will only allocate neighbor caches if
-// a protocol providing link address resolution is specified (e.g. ARP, IPv6).
+// the NIC requires link resolution.
 func TestNUDConfigurationFailsForNotSupported(t *testing.T) {
 	const nicID = 1
 
 	e := channel.New(0, 1280, linkAddr1)
-	e.LinkEPCapabilities |= stack.CapabilityResolutionRequired
+	e.LinkEPCapabilities &^= stack.CapabilityResolutionRequired
 
 	s := stack.New(stack.Options{
 		NUDConfigs:       stack.DefaultNUDConfigurations(),
@@ -91,38 +91,21 @@ func TestNUDConfigurationFailsForNotSupported(t *testing.T) {
 	if err := s.CreateNIC(nicID, e); err != nil {
 		t.Fatalf("CreateNIC(%d, _) = %s", nicID, err)
 	}
-	_, err := s.NUDConfigurations(nicID)
-	if _, ok := err.(*tcpip.ErrNotSupported); !ok {
-		t.Fatalf("got s.NDPConfigurations(%d) = %v, want = %s", nicID, err, &tcpip.ErrNotSupported{})
-	}
-}
 
-// TestNUDConfigurationFailsForNotSupported tests to make sure we get a
-// NotSupported error if we attempt to set NUD configurations when the stack
-// doesn't support NUD.
-//
-// The stack will report to not support NUD if a neighbor cache for a given NIC
-// is not allocated. The networking stack will only allocate neighbor caches if
-// a protocol providing link address resolution is specified (e.g. ARP, IPv6).
-func TestSetNUDConfigurationFailsForNotSupported(t *testing.T) {
-	const nicID = 1
-
-	e := channel.New(0, 1280, linkAddr1)
-	e.LinkEPCapabilities |= stack.CapabilityResolutionRequired
-
-	s := stack.New(stack.Options{
-		NUDConfigs:       stack.DefaultNUDConfigurations(),
-		UseNeighborCache: true,
+	t.Run("Get", func(t *testing.T) {
+		_, err := s.NUDConfigurations(nicID)
+		if _, ok := err.(*tcpip.ErrNotSupported); !ok {
+			t.Fatalf("got s.NDPConfigurations(%d) = %v, want = %s", nicID, err, &tcpip.ErrNotSupported{})
+		}
 	})
-	if err := s.CreateNIC(nicID, e); err != nil {
-		t.Fatalf("CreateNIC(%d, _) = %s", nicID, err)
-	}
 
-	config := stack.NUDConfigurations{}
-	err := s.SetNUDConfigurations(nicID, config)
-	if _, ok := err.(*tcpip.ErrNotSupported); !ok {
-		t.Fatalf("got s.SetNDPConfigurations(%d, %+v) = %v, want = %s", nicID, config, err, &tcpip.ErrNotSupported{})
-	}
+	t.Run("Set", func(t *testing.T) {
+		config := stack.NUDConfigurations{}
+		err := s.SetNUDConfigurations(nicID, config)
+		if _, ok := err.(*tcpip.ErrNotSupported); !ok {
+			t.Fatalf("got s.SetNDPConfigurations(%d, %+v) = %v, want = %s", nicID, config, err, &tcpip.ErrNotSupported{})
+		}
+	})
 }
 
 // TestDefaultNUDConfigurationIsValid verifies that calling
diff --git a/pkg/tcpip/stack/registration.go b/pkg/tcpip/stack/registration.go
index 510da8689..64b5627e1 100644
--- a/pkg/tcpip/stack/registration.go
+++ b/pkg/tcpip/stack/registration.go
@@ -824,16 +824,12 @@ type InjectableLinkEndpoint interface {
 	InjectOutbound(dest tcpip.Address, packet []byte) tcpip.Error
 }
 
-// A LinkAddressResolver is an extension to a NetworkProtocol that
-// can resolve link addresses.
+// A LinkAddressResolver handles link address resolution for a network protocol.
 type LinkAddressResolver interface {
 	// LinkAddressRequest sends a request for the link address of the target
 	// address. The request is broadcasted on the local network if a remote link
 	// address is not provided.
-	//
-	// The request is sent from the passed network interface. If the interface
-	// local address is unspecified, any interface local address may be used.
-	LinkAddressRequest(targetAddr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress, nic NetworkInterface) tcpip.Error
+	LinkAddressRequest(targetAddr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress) tcpip.Error
 
 	// ResolveStaticAddress attempts to resolve address without sending
 	// requests. It either resolves the name immediately or returns the
diff --git a/pkg/tcpip/stack/route.go b/pkg/tcpip/stack/route.go
index 4ae0f2a1a..1c8ef6ed4 100644
--- a/pkg/tcpip/stack/route.go
+++ b/pkg/tcpip/stack/route.go
@@ -174,7 +174,7 @@ func makeRoute(netProto tcpip.NetworkProtocolNumber, gateway, localAddr, remoteA
 	}
 
 	if r.outgoingNIC.LinkEndpoint.Capabilities()&CapabilityResolutionRequired != 0 {
-		if linkRes, ok := r.outgoingNIC.stack.linkAddrResolvers[r.NetProto]; ok {
+		if linkRes, ok := r.outgoingNIC.linkAddrResolvers[r.NetProto]; ok {
 			r.linkRes = linkRes
 		}
 	}
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index 119c4c505..e720d676f 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -376,7 +376,6 @@ func (u *uniqueIDGenerator) UniqueID() uint64 {
 type Stack struct {
 	transportProtocols map[tcpip.TransportProtocolNumber]*transportProtocolState
 	networkProtocols   map[tcpip.NetworkProtocolNumber]NetworkProtocol
-	linkAddrResolvers  map[tcpip.NetworkProtocolNumber]LinkAddressResolver
 
 	// rawFactory creates raw endpoints. If nil, raw endpoints are
 	// disabled. It is set during Stack creation and is immutable.
@@ -635,7 +634,6 @@ func New(opts Options) *Stack {
 	s := &Stack{
 		transportProtocols: make(map[tcpip.TransportProtocolNumber]*transportProtocolState),
 		networkProtocols:   make(map[tcpip.NetworkProtocolNumber]NetworkProtocol),
-		linkAddrResolvers:  make(map[tcpip.NetworkProtocolNumber]LinkAddressResolver),
 		nics:               make(map[tcpip.NICID]*NIC),
 		cleanupEndpoints:   make(map[TransportEndpoint]struct{}),
 		PortManager:        ports.NewPortManager(),
@@ -666,9 +664,6 @@ func New(opts Options) *Stack {
 	for _, netProtoFactory := range opts.NetworkProtocols {
 		netProto := netProtoFactory(s)
 		s.networkProtocols[netProto.Number()] = netProto
-		if r, ok := netProto.(LinkAddressResolver); ok {
-			s.linkAddrResolvers[r.LinkAddressProtocol()] = r
-		}
 	}
 
 	// Add specified transport protocols.
@@ -1561,18 +1556,7 @@ func (s *Stack) GetLinkAddress(nicID tcpip.NICID, addr, localAddr tcpip.Address,
 		return &tcpip.ErrUnknownNICID{}
 	}
 
-	linkRes, ok := s.linkAddrResolvers[protocol]
-	if !ok {
-		return &tcpip.ErrNotSupported{}
-	}
-
-	if linkAddr, ok := linkRes.ResolveStaticAddress(addr); ok {
-		onResolve(LinkResolutionResult{LinkAddress: linkAddr, Success: true})
-		return nil
-	}
-
-	_, _, err := nic.getNeighborLinkAddress(addr, localAddr, linkRes, onResolve)
-	return err
+	return nic.getLinkAddress(addr, localAddr, protocol, onResolve)
 }
 
 // Neighbors returns all IP to MAC address associations.
-- 
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