Pass NetworkInterface to LinkAddressRequest

Previously a link endpoint was passed to
stack.LinkAddressResolver.LinkAddressRequest. With this change,
implementations that want a route for the link address request may
find one through the stack. Other implementations that want to send
a packet without a route may continue to do so using the network
interface directly.

Test: - arp_test.TestLinkAddressRequest
      - ipv6.TestLinkAddressRequest
PiperOrigin-RevId: 338577474

16 files changed, 158 insertions, 86 deletions

diff --git a/pkg/tcpip/network/arp/arp.go b/pkg/tcpip/network/arp/arp.go
index 7df77c66e..d8174e8f7 100644
--- a/pkg/tcpip/network/arp/arp.go
+++ b/pkg/tcpip/network/arp/arp.go
@@ -18,6 +18,7 @@
 package arp
 
 import (
+	"fmt"
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -153,25 +154,33 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
 			e.nud.HandleProbe(remoteAddr, localAddr, ProtocolNumber, remoteLinkAddr, e.protocol)
 		}
 
-		// As per RFC 826, under Packet Reception:
-		//   Swap hardware and protocol fields, putting the local hardware and
-		//   protocol addresses in the sender fields.
-		//
-		//   Send the packet to the (new) target hardware address on the same
-		//   hardware on which the request was received.
-		origSender := h.HardwareAddressSender()
-		r.RemoteLinkAddress = tcpip.LinkAddress(origSender)
 		respPkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
 			ReserveHeaderBytes: int(e.nic.MaxHeaderLength()) + header.ARPSize,
 		})
 		packet := header.ARP(respPkt.NetworkHeader().Push(header.ARPSize))
 		packet.SetIPv4OverEthernet()
 		packet.SetOp(header.ARPReply)
-		copy(packet.HardwareAddressSender(), r.LocalLinkAddress[:])
-		copy(packet.ProtocolAddressSender(), h.ProtocolAddressTarget())
-		copy(packet.HardwareAddressTarget(), origSender)
-		copy(packet.ProtocolAddressTarget(), h.ProtocolAddressSender())
-		_ = e.nic.WritePacket(r, nil /* gso */, ProtocolNumber, respPkt)
+		// TODO(gvisor.dev/issue/4582): check copied length once TAP devices have a
+		// link address.
+		_ = copy(packet.HardwareAddressSender(), e.nic.LinkAddress())
+		if n := copy(packet.ProtocolAddressSender(), h.ProtocolAddressTarget()); n != header.IPv4AddressSize {
+			panic(fmt.Sprintf("copied %d bytes, expected %d bytes", n, header.IPv4AddressSize))
+		}
+		origSender := h.HardwareAddressSender()
+		if n := copy(packet.HardwareAddressTarget(), origSender); n != header.EthernetAddressSize {
+			panic(fmt.Sprintf("copied %d bytes, expected %d bytes", n, header.EthernetAddressSize))
+		}
+		if n := copy(packet.ProtocolAddressTarget(), h.ProtocolAddressSender()); n != header.IPv4AddressSize {
+			panic(fmt.Sprintf("copied %d bytes, expected %d bytes", n, header.IPv4AddressSize))
+		}
+
+		// As per RFC 826, under Packet Reception:
+		//   Swap hardware and protocol fields, putting the local hardware and
+		//   protocol addresses in the sender fields.
+		//
+		//   Send the packet to the (new) target hardware address on the same
+		//   hardware on which the request was received.
+		_ = e.nic.WritePacketToRemote(tcpip.LinkAddress(origSender), nil /* gso */, ProtocolNumber, respPkt)
 
 	case header.ARPReply:
 		addr := tcpip.Address(h.ProtocolAddressSender())
@@ -227,26 +236,28 @@ func (*protocol) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
 }
 
 // LinkAddressRequest implements stack.LinkAddressResolver.LinkAddressRequest.
-func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress, linkEP stack.LinkEndpoint) *tcpip.Error {
-	r := &stack.Route{
-		NetProto:          ProtocolNumber,
-		RemoteLinkAddress: remoteLinkAddr,
-	}
-	if len(r.RemoteLinkAddress) == 0 {
-		r.RemoteLinkAddress = header.EthernetBroadcastAddress
+func (*protocol) LinkAddressRequest(targetAddr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress, nic stack.NetworkInterface) *tcpip.Error {
+	if len(remoteLinkAddr) == 0 {
+		remoteLinkAddr = header.EthernetBroadcastAddress
 	}
 
 	pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
-		ReserveHeaderBytes: int(linkEP.MaxHeaderLength()) + header.ARPSize,
+		ReserveHeaderBytes: int(nic.MaxHeaderLength()) + header.ARPSize,
 	})
 	h := header.ARP(pkt.NetworkHeader().Push(header.ARPSize))
+	pkt.NetworkProtocolNumber = ProtocolNumber
 	h.SetIPv4OverEthernet()
 	h.SetOp(header.ARPRequest)
-	copy(h.HardwareAddressSender(), linkEP.LinkAddress())
-	copy(h.ProtocolAddressSender(), localAddr)
-	copy(h.ProtocolAddressTarget(), addr)
-
-	return linkEP.WritePacket(r, nil /* gso */, ProtocolNumber, pkt)
+	// TODO(gvisor.dev/issue/4582): check copied length once TAP devices have a
+	// link address.
+	_ = copy(h.HardwareAddressSender(), 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))
+	}
+	return nic.WritePacketToRemote(remoteLinkAddr, nil /* gso */, ProtocolNumber, pkt)
 }
 
 // ResolveStaticAddress implements stack.LinkAddressResolver.ResolveStaticAddress.
diff --git a/pkg/tcpip/network/arp/arp_test.go b/pkg/tcpip/network/arp/arp_test.go
index 626af975a..870c50238 100644
--- a/pkg/tcpip/network/arp/arp_test.go
+++ b/pkg/tcpip/network/arp/arp_test.go
@@ -423,6 +423,36 @@ func TestDirectRequestWithNeighborCache(t *testing.T) {
 	}
 }
 
+var _ stack.NetworkInterface = (*testInterface)(nil)
+
+type testInterface struct {
+	stack.LinkEndpoint
+}
+
+func (*testInterface) ID() tcpip.NICID {
+	return 1
+}
+
+func (*testInterface) IsLoopback() bool {
+	return false
+}
+
+func (*testInterface) Name() string {
+	return ""
+}
+
+func (*testInterface) Enabled() bool {
+	return true
+}
+
+func (t *testInterface) WritePacketToRemote(remoteLinkAddr tcpip.LinkAddress, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) *tcpip.Error {
+	r := stack.Route{
+		NetProto:          protocol,
+		RemoteLinkAddress: remoteLinkAddr,
+	}
+	return t.LinkEndpoint.WritePacket(&r, gso, protocol, pkt)
+}
+
 func TestLinkAddressRequest(t *testing.T) {
 	tests := []struct {
 		name           string
@@ -449,7 +479,7 @@ func TestLinkAddressRequest(t *testing.T) {
 		}
 
 		linkEP := channel.New(defaultChannelSize, defaultMTU, stackLinkAddr)
-		if err := linkRes.LinkAddressRequest(stackAddr, remoteAddr, test.remoteLinkAddr, linkEP); err != nil {
+		if err := linkRes.LinkAddressRequest(stackAddr, remoteAddr, test.remoteLinkAddr, &testInterface{LinkEndpoint: linkEP}); err != nil {
 			t.Errorf("got p.LinkAddressRequest(%s, %s, %s, _) = %s", stackAddr, remoteAddr, test.remoteLinkAddr, err)
 		}
 
diff --git a/pkg/tcpip/network/ip_test.go b/pkg/tcpip/network/ip_test.go
index f20b94d97..5cc60b98b 100644
--- a/pkg/tcpip/network/ip_test.go
+++ b/pkg/tcpip/network/ip_test.go
@@ -304,6 +304,10 @@ func (t *testInterface) setEnabled(v bool) {
 	t.mu.disabled = !v
 }
 
+func (*testInterface) WritePacketToRemote(tcpip.LinkAddress, *stack.GSO, tcpip.NetworkProtocolNumber, *stack.PacketBuffer) *tcpip.Error {
+	return tcpip.ErrNotSupported
+}
+
 func TestSourceAddressValidation(t *testing.T) {
 	rxIPv4ICMP := func(e *channel.Endpoint, src tcpip.Address) {
 		totalLen := header.IPv4MinimumSize + header.ICMPv4MinimumSize
diff --git a/pkg/tcpip/network/ipv6/icmp.go b/pkg/tcpip/network/ipv6/icmp.go
index 40908ddaa..fa6c3787b 100644
--- a/pkg/tcpip/network/ipv6/icmp.go
+++ b/pkg/tcpip/network/ipv6/icmp.go
@@ -651,52 +651,46 @@ func (*protocol) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
 }
 
 // LinkAddressRequest implements stack.LinkAddressResolver.
-func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress, linkEP stack.LinkEndpoint) *tcpip.Error {
-	// TODO(b/148672031): Use stack.FindRoute instead of manually creating the
-	// route here. Note, we would need the nicID to do this properly so the right
-	// NIC (associated to linkEP) is used to send the NDP NS message.
-	r := stack.Route{
-		LocalAddress:      localAddr,
-		RemoteAddress:     addr,
-		LocalLinkAddress:  linkEP.LinkAddress(),
-		RemoteLinkAddress: remoteLinkAddr,
+func (p *protocol) LinkAddressRequest(targetAddr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress, nic stack.NetworkInterface) *tcpip.Error {
+	remoteAddr := targetAddr
+	if len(remoteLinkAddr) == 0 {
+		remoteAddr = header.SolicitedNodeAddr(targetAddr)
+		remoteLinkAddr = header.EthernetAddressFromMulticastIPv6Address(remoteAddr)
 	}
 
-	// If a remote address is not already known, then send a multicast
-	// solicitation since multicast addresses have a static mapping to link
-	// addresses.
-	if len(r.RemoteLinkAddress) == 0 {
-		r.RemoteAddress = header.SolicitedNodeAddr(addr)
-		r.RemoteLinkAddress = header.EthernetAddressFromMulticastIPv6Address(r.RemoteAddress)
+	r, err := p.stack.FindRoute(nic.ID(), localAddr, remoteAddr, ProtocolNumber, false /* multicastLoop */)
+	if err != nil {
+		return err
 	}
+	defer r.Release()
+	r.ResolveWith(remoteLinkAddr)
 
 	optsSerializer := header.NDPOptionsSerializer{
-		header.NDPSourceLinkLayerAddressOption(linkEP.LinkAddress()),
+		header.NDPSourceLinkLayerAddressOption(nic.LinkAddress()),
 	}
 	neighborSolicitSize := header.ICMPv6NeighborSolicitMinimumSize + optsSerializer.Length()
 	pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
-		ReserveHeaderBytes: int(linkEP.MaxHeaderLength()) + header.IPv6MinimumSize + neighborSolicitSize,
+		ReserveHeaderBytes: int(r.MaxHeaderLength()) + neighborSolicitSize,
 	})
 	pkt.TransportProtocolNumber = header.ICMPv6ProtocolNumber
 	packet := header.ICMPv6(pkt.TransportHeader().Push(neighborSolicitSize))
 	packet.SetType(header.ICMPv6NeighborSolicit)
 	ns := header.NDPNeighborSolicit(packet.NDPPayload())
-	ns.SetTargetAddress(addr)
+	ns.SetTargetAddress(targetAddr)
 	ns.Options().Serialize(optsSerializer)
 	packet.SetChecksum(header.ICMPv6Checksum(packet, r.LocalAddress, r.RemoteAddress, buffer.VectorisedView{}))
 
-	length := uint16(pkt.Size())
-	ip := header.IPv6(pkt.NetworkHeader().Push(header.IPv6MinimumSize))
-	ip.Encode(&header.IPv6Fields{
-		PayloadLength: length,
-		NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-		HopLimit:      header.NDPHopLimit,
-		SrcAddr:       r.LocalAddress,
-		DstAddr:       r.RemoteAddress,
-	})
+	stat := p.stack.Stats().ICMP.V6PacketsSent
+	if err := r.WritePacket(nil /* gso */, stack.NetworkHeaderParams{
+		Protocol: header.ICMPv6ProtocolNumber,
+		TTL:      header.NDPHopLimit,
+	}, pkt); err != nil {
+		stat.Dropped.Increment()
+		return err
+	}
 
-	// TODO(stijlist): count this in ICMP stats.
-	return linkEP.WritePacket(&r, nil /* gso */, ProtocolNumber, pkt)
+	stat.NeighborSolicit.Increment()
+	return nil
 }
 
 // ResolveStaticAddress implements stack.LinkAddressResolver.
diff --git a/pkg/tcpip/network/ipv6/icmp_test.go b/pkg/tcpip/network/ipv6/icmp_test.go
index 8dc33c560..3b4583b64 100644
--- a/pkg/tcpip/network/ipv6/icmp_test.go
+++ b/pkg/tcpip/network/ipv6/icmp_test.go
@@ -122,17 +122,13 @@ func (*stubNUDHandler) HandleUpperLevelConfirmation(addr tcpip.Address) {
 var _ stack.NetworkInterface = (*testInterface)(nil)
 
 type testInterface struct {
-	stack.NetworkLinkEndpoint
-
-	linkAddr tcpip.LinkAddress
-}
+	stack.LinkEndpoint
 
-func (i *testInterface) LinkAddress() tcpip.LinkAddress {
-	return i.linkAddr
+	nicID tcpip.NICID
 }
 
 func (*testInterface) ID() tcpip.NICID {
-	return 0
+	return nicID
 }
 
 func (*testInterface) IsLoopback() bool {
@@ -147,6 +143,14 @@ func (*testInterface) Enabled() bool {
 	return true
 }
 
+func (t *testInterface) WritePacketToRemote(remoteLinkAddr tcpip.LinkAddress, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) *tcpip.Error {
+	r := stack.Route{
+		NetProto:          protocol,
+		RemoteLinkAddress: remoteLinkAddr,
+	}
+	return t.LinkEndpoint.WritePacket(&r, gso, protocol, pkt)
+}
+
 func TestICMPCounts(t *testing.T) {
 	tests := []struct {
 		name             string
@@ -1235,6 +1239,8 @@ func TestICMPChecksumValidationWithPayloadMultipleViews(t *testing.T) {
 }
 
 func TestLinkAddressRequest(t *testing.T) {
+	const nicID = 1
+
 	snaddr := header.SolicitedNodeAddr(lladdr0)
 	mcaddr := header.EthernetAddressFromMulticastIPv6Address(snaddr)
 
@@ -1269,7 +1275,18 @@ func TestLinkAddressRequest(t *testing.T) {
 		}
 
 		linkEP := channel.New(defaultChannelSize, defaultMTU, linkAddr0)
-		if err := linkRes.LinkAddressRequest(lladdr0, lladdr1, test.remoteLinkAddr, linkEP); err != nil {
+		if err := s.CreateNIC(nicID, linkEP); err != nil {
+			t.Fatalf("s.CreateNIC(%d, _): %s", nicID, err)
+		}
+		if err := s.AddAddress(nicID, ProtocolNumber, lladdr1); err != nil {
+			t.Fatalf("s.AddAddress(%d, %d, %s): %s", nicID, ProtocolNumber, lladdr1, 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.
+		if err := linkRes.LinkAddressRequest(lladdr0, lladdr1, test.remoteLinkAddr, &testInterface{LinkEndpoint: linkEP, nicID: nicID}); err != nil {
 			t.Errorf("got p.LinkAddressRequest(%s, %s, %s, _) = %s", lladdr0, lladdr1, test.remoteLinkAddr, err)
 		}
 
@@ -1698,7 +1715,7 @@ func TestCallsToNeighborCache(t *testing.T) {
 				t.Fatalf("cannot find protocol instance for network protocol %d", ProtocolNumber)
 			}
 			nudHandler := &stubNUDHandler{}
-			ep := netProto.NewEndpoint(&testInterface{linkAddr: linkAddr0}, &stubLinkAddressCache{}, nudHandler, &stubDispatcher{})
+			ep := netProto.NewEndpoint(&testInterface{LinkEndpoint: channel.New(0, header.IPv6MinimumMTU, linkAddr0)}, &stubLinkAddressCache{}, nudHandler, &stubDispatcher{})
 			defer ep.Close()
 
 			if err := ep.Enable(); err != nil {
diff --git a/pkg/tcpip/stack/forwarding_test.go b/pkg/tcpip/stack/forwarding_test.go
index cf042309e..380688038 100644
--- a/pkg/tcpip/stack/forwarding_test.go
+++ b/pkg/tcpip/stack/forwarding_test.go
@@ -178,7 +178,7 @@ func (*fwdTestNetworkProtocol) Close() {}
 
 func (*fwdTestNetworkProtocol) Wait() {}
 
-func (f *fwdTestNetworkProtocol) LinkAddressRequest(addr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress, linkEP LinkEndpoint) *tcpip.Error {
+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)
diff --git a/pkg/tcpip/stack/linkaddrcache.go b/pkg/tcpip/stack/linkaddrcache.go
index 6f73a0ce4..c9b13cd0e 100644
--- a/pkg/tcpip/stack/linkaddrcache.go
+++ b/pkg/tcpip/stack/linkaddrcache.go
@@ -180,7 +180,7 @@ func (c *linkAddrCache) getOrCreateEntryLocked(k tcpip.FullAddress) *linkAddrEnt
 }
 
 // get reports any known link address for k.
-func (c *linkAddrCache) get(k tcpip.FullAddress, linkRes LinkAddressResolver, localAddr tcpip.Address, linkEP LinkEndpoint, waker *sleep.Waker) (tcpip.LinkAddress, <-chan struct{}, *tcpip.Error) {
+func (c *linkAddrCache) get(k tcpip.FullAddress, linkRes LinkAddressResolver, localAddr tcpip.Address, nic NetworkInterface, waker *sleep.Waker) (tcpip.LinkAddress, <-chan struct{}, *tcpip.Error) {
 	if linkRes != nil {
 		if addr, ok := linkRes.ResolveStaticAddress(k.Addr); ok {
 			return addr, nil, nil
@@ -221,7 +221,7 @@ func (c *linkAddrCache) get(k tcpip.FullAddress, linkRes LinkAddressResolver, lo
 			}
 
 			entry.done = make(chan struct{})
-			go c.startAddressResolution(k, linkRes, localAddr, linkEP, entry.done) // S/R-SAFE: link non-savable; wakers dropped synchronously.
+			go c.startAddressResolution(k, linkRes, localAddr, nic, entry.done) // S/R-SAFE: link non-savable; wakers dropped synchronously.
 		}
 
 		return entry.linkAddr, entry.done, tcpip.ErrWouldBlock
@@ -240,11 +240,11 @@ func (c *linkAddrCache) removeWaker(k tcpip.FullAddress, waker *sleep.Waker) {
 	}
 }
 
-func (c *linkAddrCache) startAddressResolution(k tcpip.FullAddress, linkRes LinkAddressResolver, localAddr tcpip.Address, linkEP LinkEndpoint, done <-chan struct{}) {
+func (c *linkAddrCache) startAddressResolution(k tcpip.FullAddress, linkRes LinkAddressResolver, localAddr tcpip.Address, nic NetworkInterface, 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.Addr, localAddr, "" /* linkAddr */, linkEP)
+		linkRes.LinkAddressRequest(k.Addr, localAddr, "" /* linkAddr */, nic)
 
 		select {
 		case now := <-time.After(c.resolutionTimeout):
diff --git a/pkg/tcpip/stack/linkaddrcache_test.go b/pkg/tcpip/stack/linkaddrcache_test.go
index 33806340e..d2e37f38d 100644
--- a/pkg/tcpip/stack/linkaddrcache_test.go
+++ b/pkg/tcpip/stack/linkaddrcache_test.go
@@ -49,8 +49,8 @@ type testLinkAddressResolver struct {
 	onLinkAddressRequest func()
 }
 
-func (r *testLinkAddressResolver) LinkAddressRequest(addr, _ tcpip.Address, _ tcpip.LinkAddress, _ LinkEndpoint) *tcpip.Error {
-	time.AfterFunc(r.delay, func() { r.fakeRequest(addr) })
+func (r *testLinkAddressResolver) LinkAddressRequest(targetAddr, _ tcpip.Address, _ tcpip.LinkAddress, _ NetworkInterface) *tcpip.Error {
+	time.AfterFunc(r.delay, func() { r.fakeRequest(targetAddr) })
 	if f := r.onLinkAddressRequest; f != nil {
 		f()
 	}
diff --git a/pkg/tcpip/stack/neighbor_cache_test.go b/pkg/tcpip/stack/neighbor_cache_test.go
index fcd54ed83..a73f63896 100644
--- a/pkg/tcpip/stack/neighbor_cache_test.go
+++ b/pkg/tcpip/stack/neighbor_cache_test.go
@@ -195,10 +195,10 @@ type testNeighborResolver struct {
 
 var _ LinkAddressResolver = (*testNeighborResolver)(nil)
 
-func (r *testNeighborResolver) LinkAddressRequest(addr, localAddr tcpip.Address, linkAddr tcpip.LinkAddress, linkEP LinkEndpoint) *tcpip.Error {
+func (r *testNeighborResolver) LinkAddressRequest(targetAddr, _ tcpip.Address, _ tcpip.LinkAddress, _ NetworkInterface) *tcpip.Error {
 	// Delay handling the request to emulate network latency.
 	r.clock.AfterFunc(r.delay, func() {
-		r.fakeRequest(addr)
+		r.fakeRequest(targetAddr)
 	})
 
 	// Execute post address resolution action, if available.
diff --git a/pkg/tcpip/stack/neighbor_entry.go b/pkg/tcpip/stack/neighbor_entry.go
index be61a21af..ab3cf6e9d 100644
--- a/pkg/tcpip/stack/neighbor_entry.go
+++ b/pkg/tcpip/stack/neighbor_entry.go
@@ -236,7 +236,7 @@ func (e *neighborEntry) setStateLocked(next NeighborState) {
 				return
 			}
 
-			if err := e.linkRes.LinkAddressRequest(e.neigh.Addr, e.neigh.LocalAddr, "", e.nic.LinkEndpoint); err != nil {
+			if err := e.linkRes.LinkAddressRequest(e.neigh.Addr, e.neigh.LocalAddr, "", e.nic); 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.
@@ -277,7 +277,7 @@ func (e *neighborEntry) setStateLocked(next NeighborState) {
 				return
 			}
 
-			if err := e.linkRes.LinkAddressRequest(e.neigh.Addr, e.neigh.LocalAddr, e.neigh.LinkAddr, e.nic.LinkEndpoint); err != nil {
+			if err := e.linkRes.LinkAddressRequest(e.neigh.Addr, e.neigh.LocalAddr, e.neigh.LinkAddr, e.nic); err != nil {
 				e.dispatchRemoveEventLocked()
 				e.setStateLocked(Failed)
 				return
diff --git a/pkg/tcpip/stack/neighbor_entry_test.go b/pkg/tcpip/stack/neighbor_entry_test.go
index 3ee2a3b31..ba4041487 100644
--- a/pkg/tcpip/stack/neighbor_entry_test.go
+++ b/pkg/tcpip/stack/neighbor_entry_test.go
@@ -202,9 +202,9 @@ 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(addr, localAddr tcpip.Address, linkAddr tcpip.LinkAddress, linkEP LinkEndpoint) *tcpip.Error {
+func (r *entryTestLinkResolver) LinkAddressRequest(targetAddr, localAddr tcpip.Address, linkAddr tcpip.LinkAddress, _ NetworkInterface) *tcpip.Error {
 	p := entryTestProbeInfo{
-		RemoteAddress:     addr,
+		RemoteAddress:     targetAddr,
 		RemoteLinkAddress: linkAddr,
 		LocalAddress:      localAddr,
 	}
diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index dcd4319bf..b97f4380a 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -273,6 +273,15 @@ func (n *NIC) WritePacket(r *Route, gso *GSO, protocol tcpip.NetworkProtocolNumb
 	return n.writePacket(r, gso, protocol, pkt)
 }
 
+// WritePacketToRemote implements NetworkInterface.
+func (n *NIC) WritePacketToRemote(remoteLinkAddr tcpip.LinkAddress, gso *GSO, protocol tcpip.NetworkProtocolNumber, pkt *PacketBuffer) *tcpip.Error {
+	r := Route{
+		NetProto:          protocol,
+		RemoteLinkAddress: remoteLinkAddr,
+	}
+	return n.writePacket(&r, gso, protocol, pkt)
+}
+
 func (n *NIC) writePacket(r *Route, gso *GSO, protocol tcpip.NetworkProtocolNumber, pkt *PacketBuffer) *tcpip.Error {
 	// WritePacket takes ownership of pkt, calculate numBytes first.
 	numBytes := pkt.Size()
diff --git a/pkg/tcpip/stack/nic_test.go b/pkg/tcpip/stack/nic_test.go
index 97a96af62..4af04846f 100644
--- a/pkg/tcpip/stack/nic_test.go
+++ b/pkg/tcpip/stack/nic_test.go
@@ -169,7 +169,7 @@ func (*testIPv6Protocol) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
 }
 
 // LinkAddressRequest implements LinkAddressResolver.
-func (*testIPv6Protocol) LinkAddressRequest(_, _ tcpip.Address, _ tcpip.LinkAddress, _ LinkEndpoint) *tcpip.Error {
+func (*testIPv6Protocol) LinkAddressRequest(_, _ tcpip.Address, _ tcpip.LinkAddress, _ NetworkInterface) *tcpip.Error {
 	return nil
 }
 
diff --git a/pkg/tcpip/stack/registration.go b/pkg/tcpip/stack/registration.go
index defb9129b..203f3b51f 100644
--- a/pkg/tcpip/stack/registration.go
+++ b/pkg/tcpip/stack/registration.go
@@ -490,6 +490,9 @@ type NetworkInterface interface {
 
 	// Enabled returns true if the interface is enabled.
 	Enabled() bool
+
+	// WritePacketToRemote writes the packet to the given remote link address.
+	WritePacketToRemote(tcpip.LinkAddress, *GSO, tcpip.NetworkProtocolNumber, *PacketBuffer) *tcpip.Error
 }
 
 // NetworkEndpoint is the interface that needs to be implemented by endpoints
@@ -764,13 +767,13 @@ type InjectableLinkEndpoint interface {
 // A LinkAddressResolver is an extension to a NetworkProtocol that
 // can resolve link addresses.
 type LinkAddressResolver interface {
-	// LinkAddressRequest sends a request for the LinkAddress of addr. Broadcasts
-	// the request on the local network if remoteLinkAddr is the zero value. The
-	// request is sent on linkEP with localAddr as the source.
+	// 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.
 	//
-	// A valid response will cause the discovery protocol's network
-	// endpoint to call AddLinkAddress.
-	LinkAddressRequest(addr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress, linkEP LinkEndpoint) *tcpip.Error
+	// 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
 
 	// ResolveStaticAddress attempts to resolve address without sending
 	// requests. It either resolves the name immediately or returns the
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index 3a07577c8..d3f75cb36 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -1323,7 +1323,7 @@ func (s *Stack) GetLinkAddress(nicID tcpip.NICID, addr, localAddr tcpip.Address,
 
 	fullAddr := tcpip.FullAddress{NIC: nicID, Addr: addr}
 	linkRes := s.linkAddrResolvers[protocol]
-	return s.linkAddrCache.get(fullAddr, linkRes, localAddr, nic.LinkEndpoint, waker)
+	return s.linkAddrCache.get(fullAddr, linkRes, localAddr, nic, waker)
 }
 
 // Neighbors returns all IP to MAC address associations.
diff --git a/pkg/tcpip/transport/udp/udp_test.go b/pkg/tcpip/transport/udp/udp_test.go
index b4604ba35..f9fbfa954 100644
--- a/pkg/tcpip/transport/udp/udp_test.go
+++ b/pkg/tcpip/transport/udp/udp_test.go
@@ -1452,6 +1452,10 @@ func (*testInterface) Enabled() bool {
 	return true
 }
 
+func (*testInterface) WritePacketToRemote(tcpip.LinkAddress, *stack.GSO, tcpip.NetworkProtocolNumber, *stack.PacketBuffer) *tcpip.Error {
+	return tcpip.ErrNotSupported
+}
+
 func TestTTL(t *testing.T) {
 	for _, flow := range []testFlow{unicastV4, unicastV4in6, unicastV6, unicastV6Only, multicastV4, multicastV4in6, multicastV6, broadcast, broadcastIn6} {
 		t.Run(fmt.Sprintf("flow:%s", flow), func(t *testing.T) {