Implement neighbor unreachability detection for ARP and NDP.

This change implements the Neighbor Unreachability Detection (NUD) state
machine, as per RFC 4861 [1]. The state machine operates on a single neighbor
in the local network. This requires the state machine to be implemented on each
entry of the neighbor table.

This change also adds, but does not expose, several APIs. The first API is for
performing basic operations on the neighbor table:
 - Create a static entry
 - List all entries
 - Delete all entries
 - Remove an entry by address

The second API is used for changing 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][2] for the list of
constants.

Finally, the last API is for allowing users to subscribe to NUD state changes.
See [RFC 4861 Appendix C][3] for the list of edges.

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

Tests:
 pkg/tcpip/stack:stack_test
 - TestNeighborCacheAddStaticEntryThenOverflow
 - TestNeighborCacheClear
 - TestNeighborCacheClearThenOverflow
 - TestNeighborCacheConcurrent
 - TestNeighborCacheDuplicateStaticEntryWithDifferentLinkAddress
 - TestNeighborCacheDuplicateStaticEntryWithSameLinkAddress
 - TestNeighborCacheEntry
 - TestNeighborCacheEntryNoLinkAddress
 - TestNeighborCacheGetConfig
 - TestNeighborCacheKeepFrequentlyUsed
 - TestNeighborCacheNotifiesWaker
 - TestNeighborCacheOverflow
 - TestNeighborCacheOverwriteWithStaticEntryThenOverflow
 - TestNeighborCacheRemoveEntry
 - TestNeighborCacheRemoveEntryThenOverflow
 - TestNeighborCacheRemoveStaticEntry
 - TestNeighborCacheRemoveStaticEntryThenOverflow
 - TestNeighborCacheRemoveWaker
 - TestNeighborCacheReplace
 - TestNeighborCacheResolutionFailed
 - TestNeighborCacheResolutionTimeout
 - TestNeighborCacheSetConfig
 - TestNeighborCacheStaticResolution
 - TestEntryAddsAndClearsWakers
 - TestEntryDelayToProbe
 - TestEntryDelayToReachableWhenSolicitedOverrideConfirmation
 - TestEntryDelayToReachableWhenUpperLevelConfirmation
 - TestEntryDelayToStaleWhenConfirmationWithDifferentAddress
 - TestEntryDelayToStaleWhenProbeWithDifferentAddress
 - TestEntryFailedGetsDeleted
 - TestEntryIncompleteToFailed
 - TestEntryIncompleteToIncompleteDoesNotChangeUpdatedAt
 - TestEntryIncompleteToReachable
 - TestEntryIncompleteToReachableWithRouterFlag
 - TestEntryIncompleteToStale
 - TestEntryInitiallyUnknown
 - TestEntryProbeToFailed
 - TestEntryProbeToReachableWhenSolicitedConfirmationWithSameAddress
 - TestEntryProbeToReachableWhenSolicitedOverrideConfirmation
 - TestEntryProbeToStaleWhenConfirmationWithDifferentAddress
 - TestEntryProbeToStaleWhenProbeWithDifferentAddress
 - TestEntryReachableToStaleWhenConfirmationWithDifferentAddress
 - TestEntryReachableToStaleWhenConfirmationWithDifferentAddressAndOverride
 - TestEntryReachableToStaleWhenProbeWithDifferentAddress
 - TestEntryReachableToStaleWhenTimeout
 - TestEntryStaleToDelay
 - TestEntryStaleToReachableWhenSolicitedOverrideConfirmation
 - TestEntryStaleToStaleWhenOverrideConfirmation
 - TestEntryStaleToStaleWhenProbeUpdateAddress
 - TestEntryStaysDelayWhenOverrideConfirmationWithSameAddress
 - TestEntryStaysProbeWhenOverrideConfirmationWithSameAddress
 - TestEntryStaysReachableWhenConfirmationWithRouterFlag
 - TestEntryStaysReachableWhenProbeWithSameAddress
 - TestEntryStaysStaleWhenProbeWithSameAddress
 - TestEntryUnknownToIncomplete
 - TestEntryUnknownToStale
 - TestEntryUnknownToUnknownWhenConfirmationWithUnknownAddress

 pkg/tcpip/stack:stack_x_test
 - TestDefaultNUDConfigurations
 - TestNUDConfigurationFailsForNotSupported
 - TestNUDConfigurationsBaseReachableTime
 - TestNUDConfigurationsDelayFirstProbeTime
 - TestNUDConfigurationsMaxMulticastProbes
 - TestNUDConfigurationsMaxRandomFactor
 - TestNUDConfigurationsMaxUnicastProbes
 - TestNUDConfigurationsMinRandomFactor
 - TestNUDConfigurationsRetransmitTimer
 - TestNUDConfigurationsUnreachableTime
 - TestNUDStateReachableTime
 - TestNUDStateRecomputeReachableTime
 - TestSetNUDConfigurationFailsForBadNICID
 - TestSetNUDConfigurationFailsForNotSupported

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

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

PiperOrigin-RevId: 324070795

1 files changed, 0 insertions, 16 deletions

diff --git a/pkg/tcpip/stack/ndp.go b/pkg/tcpip/stack/ndp.go
index 9dce11a97..5174e639c 100644
--- a/pkg/tcpip/stack/ndp.go
+++ b/pkg/tcpip/stack/ndp.go
@@ -33,12 +33,6 @@ const (
 	// Default = 1 (from RFC 4862 section 5.1)
 	defaultDupAddrDetectTransmits = 1
 
-	// defaultRetransmitTimer is the default amount of time to wait between
-	// sending NDP Neighbor solicitation messages.
-	//
-	// Default = 1s (from RFC 4861 section 10).
-	defaultRetransmitTimer = time.Second
-
 	// defaultMaxRtrSolicitations is the default number of Router
 	// Solicitation messages to send when a NIC becomes enabled.
 	//
@@ -79,16 +73,6 @@ const (
 	// Default = true.
 	defaultAutoGenGlobalAddresses = true
 
-	// minimumRetransmitTimer is the minimum amount of time to wait between
-	// sending NDP Neighbor solicitation messages. Note, RFC 4861 does
-	// not impose a minimum Retransmit Timer, but we do here to make sure
-	// the messages are not sent all at once. We also come to this value
-	// because in the RetransmitTimer field of a Router Advertisement, a
-	// value of 0 means unspecified, so the smallest valid value is 1.
-	// Note, the unit of the RetransmitTimer field in the Router
-	// Advertisement is milliseconds.
-	minimumRetransmitTimer = time.Millisecond
-
 	// minimumRtrSolicitationInterval is the minimum amount of time to wait
 	// between sending Router Solicitation messages. This limit is imposed
 	// to make sure that Router Solicitation messages are not sent all at