Update dns for ipv6 addresses

internal/radvd/radvd.go

@@ -16,6 +16,7 @@
 package radvd
 
 import (
+	"fmt"
 	"log"
 	"net"
 	"net/netip"
@@ -41,6 +42,31 @@ func NewServer() (*Server, error) {
 	return &Server{}, nil
 }
 
+func (s *Server) UpdateDNS(b []byte) error {
+	m,err := ndp.ParseMessage(b)
+	if err != nil {
+		return err
+	}
+	if m.Type() != ipv6.ICMPTypeNeighborAdvertisement {
+		return fmt.Errorf("incorrect icmp message recieved expected %s, got %s", ipv6.ICMPTypeNeighborAdvertisement, m.Type())
+	}
+	n :=m.(*ndp.NeighborAdvertisement)
+	var hw net.HardwareAddr
+	for _,o := range n.Options {
+		if o.Code() == uint8(ndp.Target) {
+			ll := o.(*ndp.LinkLayerAddress)
+			hw = ll.Addr
+			break
+		}
+	}
+	if hw == nil || !n.TargetAddress.IsGlobalUnicast() || !n.Solicited {
+		// Ignore advertisements that donot provide the MAC, are not solicited and are not global unicast addresses
+		return nil
+	}
+	log.Printf("found IPv6 address %s for MAC address %s", n.TargetAddress, hw)
+	return nil
+}
+
 func (s *Server) SetPrefixes(prefixes []net.IPNet) {
 	s.mu.Lock()
 	if s.ifname != "" {
@@ -75,6 +101,7 @@ func (s *Server) Serve(ifname string, conn net.PacketConn) error {
 	var filter ipv6.ICMPFilter
 	filter.SetAll(true)
 	filter.Accept(ipv6.ICMPTypeRouterSolicitation)
+	filter.Accept(ipv6.ICMPTypeNeighborAdvertisement)
 	if err := s.pc.SetICMPFilter(&filter); err != nil {
 		return err
 	}
@@ -101,6 +128,9 @@ func (s *Server) Serve(ifname string, conn net.PacketConn) error {
 		// TODO: isn’t this guaranteed by the filter above?
 		if n == 0 ||
 			ipv6.ICMPType(buf[0]) != ipv6.ICMPTypeRouterSolicitation {
+				if ipv6.ICMPType(buf[0]) == ipv6.ICMPTypeNeighborAdvertisement{
+								s.UpdateDNS(buf)
+							}
 			continue
 		}
 		if err := s.sendAdvertisement(addr); err != nil {