1 files changed, 41 insertions, 6 deletions

diff --git a/pkg/tcpip/network/arp/arp.go b/pkg/tcpip/network/arp/arp.go
index 920872c3f..cbbe5b77f 100644
--- a/pkg/tcpip/network/arp/arp.go
+++ b/pkg/tcpip/network/arp/arp.go
@@ -46,6 +46,7 @@ type endpoint struct {
 	nicID         tcpip.NICID
 	linkEP        stack.LinkEndpoint
 	linkAddrCache stack.LinkAddressCache
+	nud           stack.NUDHandler
 }
 
 // DefaultTTL is unused for ARP. It implements stack.NetworkEndpoint.
@@ -78,7 +79,7 @@ func (e *endpoint) WritePacket(*stack.Route, *stack.GSO, stack.NetworkHeaderPara
 
 // NetworkProtocolNumber implements stack.NetworkEndpoint.NetworkProtocolNumber.
 func (e *endpoint) NetworkProtocolNumber() tcpip.NetworkProtocolNumber {
-	return e.protocol.Number()
+	return ProtocolNumber
 }
 
 // WritePackets implements stack.NetworkEndpoint.WritePackets.
@@ -99,9 +100,25 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
 	switch h.Op() {
 	case header.ARPRequest:
 		localAddr := tcpip.Address(h.ProtocolAddressTarget())
-		if e.linkAddrCache.CheckLocalAddress(e.nicID, header.IPv4ProtocolNumber, localAddr) == 0 {
-			return // we have no useful answer, ignore the request
+
+		if e.nud == nil {
+			if e.linkAddrCache.CheckLocalAddress(e.nicID, header.IPv4ProtocolNumber, localAddr) == 0 {
+				return // we have no useful answer, ignore the request
+			}
+
+			addr := tcpip.Address(h.ProtocolAddressSender())
+			linkAddr := tcpip.LinkAddress(h.HardwareAddressSender())
+			e.linkAddrCache.AddLinkAddress(e.nicID, addr, linkAddr)
+		} else {
+			if r.Stack().CheckLocalAddress(e.nicID, header.IPv4ProtocolNumber, localAddr) == 0 {
+				return // we have no useful answer, ignore the request
+			}
+
+			remoteAddr := tcpip.Address(h.ProtocolAddressSender())
+			remoteLinkAddr := tcpip.LinkAddress(h.HardwareAddressSender())
+			e.nud.HandleProbe(remoteAddr, localAddr, ProtocolNumber, remoteLinkAddr, e.protocol)
 		}
+
 		pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
 			ReserveHeaderBytes: int(e.linkEP.MaxHeaderLength()) + header.ARPSize,
 		})
@@ -113,11 +130,28 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
 		copy(packet.HardwareAddressTarget(), h.HardwareAddressSender())
 		copy(packet.ProtocolAddressTarget(), h.ProtocolAddressSender())
 		_ = e.linkEP.WritePacket(r, nil /* gso */, ProtocolNumber, pkt)
-		fallthrough // also fill the cache from requests
+
 	case header.ARPReply:
 		addr := tcpip.Address(h.ProtocolAddressSender())
 		linkAddr := tcpip.LinkAddress(h.HardwareAddressSender())
-		e.linkAddrCache.AddLinkAddress(e.nicID, addr, linkAddr)
+
+		if e.nud == nil {
+			e.linkAddrCache.AddLinkAddress(e.nicID, addr, linkAddr)
+			return
+		}
+
+		// The solicited, override, and isRouter flags are not available for ARP;
+		// they are only available for IPv6 Neighbor Advertisements.
+		e.nud.HandleConfirmation(addr, linkAddr, stack.ReachabilityConfirmationFlags{
+			// Solicited and unsolicited (also referred to as gratuitous) ARP Replies
+			// are handled equivalently to a solicited Neighbor Advertisement.
+			Solicited: true,
+			// If a different link address is received than the one cached, the entry
+			// should always go to Stale.
+			Override: false,
+			// ARP does not distinguish between router and non-router hosts.
+			IsRouter: false,
+		})
 	}
 }
 
@@ -134,12 +168,13 @@ func (*protocol) ParseAddresses(v buffer.View) (src, dst tcpip.Address) {
 	return tcpip.Address(h.ProtocolAddressSender()), ProtocolAddress
 }
 
-func (p *protocol) NewEndpoint(nicID tcpip.NICID, linkAddrCache stack.LinkAddressCache, dispatcher stack.TransportDispatcher, sender stack.LinkEndpoint, st *stack.Stack) stack.NetworkEndpoint {
+func (p *protocol) NewEndpoint(nicID tcpip.NICID, linkAddrCache stack.LinkAddressCache, nud stack.NUDHandler, dispatcher stack.TransportDispatcher, sender stack.LinkEndpoint, st *stack.Stack) stack.NetworkEndpoint {
 	return &endpoint{
 		protocol:      p,
 		nicID:         nicID,
 		linkEP:        sender,
 		linkAddrCache: linkAddrCache,
+		nud:           nud,
 	}
 }