Support performing DAD for any address

...as long as the network protocol supports duplicate address detection.

This CL provides the facilities for a netstack integrator to perform
DAD.

DHCP recommends that clients effectively perform DAD before accepting an
offer. As per RFC 2131 section 4.4.1 pg 38,

  The client SHOULD perform a check on the suggested address to ensure
  that the address is not already in use.  For example, if the client
  is on a network that supports ARP, the client may issue an ARP request
  for the suggested request.

The implementation of ARP-based IPv4 DAD effectively operates the same
as IPv6's NDP DAD - using ARP requests and responses in place of
NDP neighbour solicitations and advertisements, respectively.

DAD performed by calls to (*Stack).CheckDuplicateAddress don't interfere
with DAD performed when a new IPv6 address is added. This is so that
integrator requests to check for duplicate addresses aren't unexpectedly
aborted when addresses are removed.

A network package internal package provides protocol agnostic DAD state
management that specific protocols that provide DAD can use.

Fixes #4550.

Tests:
  - internal/ip_test.*
  - integration_test.TestDAD
  - arp_test.TestDADARPRequestPacket
  - ipv6.TestCheckDuplicateAddress
PiperOrigin-RevId: 356405593

1 files changed, 11 insertions, 0 deletions

diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index 46c1817ea..674c9a1ff 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -1466,6 +1466,17 @@ func (s *Stack) CheckNetworkProtocol(protocol tcpip.NetworkProtocolNumber) bool
 	return ok
 }
 
+// CheckDuplicateAddress performs duplicate address detection for the address on
+// the specified interface.
+func (s *Stack) CheckDuplicateAddress(nicID tcpip.NICID, protocol tcpip.NetworkProtocolNumber, addr tcpip.Address, h DADCompletionHandler) (DADCheckAddressDisposition, tcpip.Error) {
+	nic, ok := s.nics[nicID]
+	if !ok {
+		return 0, &tcpip.ErrUnknownNICID{}
+	}
+
+	return nic.checkDuplicateAddress(protocol, addr, h)
+}
+
 // CheckLocalAddress determines if the given local address exists, and if it
 // does, returns the id of the NIC it's bound to. Returns 0 if the address
 // does not exist.