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, 4 insertions, 0 deletions

diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index 290c4e138..44f87e007 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -1192,6 +1192,10 @@ type ICMPv6ReceivedPacketStats struct {
 	// Invalid is the total number of ICMPv6 packets received that the
 	// transport layer could not parse.
 	Invalid *StatCounter
+
+	// RouterOnlyPacketsDroppedByHost is the total number of ICMPv6 packets
+	// dropped due to being router-specific packets.
+	RouterOnlyPacketsDroppedByHost *StatCounter
 }
 
 // ICMPStats collects ICMP-specific stats (both v4 and v6).