Map IPv{4,6} addresses to ethernet addresses

...in accordance with RFCs 1112 and 2464.

Fixes IPv4 multicast when IP_MULTICAST_IF is specified.

Don't return ErrNoRoute when no route is needed.
Don't set Route.NextHop when no route is needed.

PiperOrigin-RevId: 236199813
Change-Id: I48ed33e1b7f760deaa37e18ad7f1b8b62819ab43

2 files changed, 38 insertions, 1 deletions

diff --git a/pkg/tcpip/network/arp/arp.go b/pkg/tcpip/network/arp/arp.go
index 2e0024925..ed39640c1 100644
--- a/pkg/tcpip/network/arp/arp.go
+++ b/pkg/tcpip/network/arp/arp.go
@@ -160,9 +160,27 @@ func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, linkEP stack.
 
 // ResolveStaticAddress implements stack.LinkAddressResolver.
 func (*protocol) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bool) {
-	if addr == "\xff\xff\xff\xff" {
+	if addr == header.IPv4Broadcast {
 		return broadcastMAC, true
 	}
+	if header.IsV4MulticastAddress(addr) {
+		// RFC 1112 Host Extensions for IP Multicasting
+		//
+		// 6.4. Extensions to an Ethernet Local Network Module:
+		//
+		// An IP host group address is mapped to an Ethernet multicast
+		// address by placing the low-order 23-bits of the IP address
+		// into the low-order 23 bits of the Ethernet multicast address
+		// 01-00-5E-00-00-00 (hex).
+		return tcpip.LinkAddress([]byte{
+			0x01,
+			0x00,
+			0x5e,
+			addr[header.IPv4AddressSize-3] & 0x7f,
+			addr[header.IPv4AddressSize-2],
+			addr[header.IPv4AddressSize-1],
+		}), true
+	}
 	return "", false
 }
 
diff --git a/pkg/tcpip/network/ipv6/icmp.go b/pkg/tcpip/network/ipv6/icmp.go
index 5a3c17768..e43253d3e 100644
--- a/pkg/tcpip/network/ipv6/icmp.go
+++ b/pkg/tcpip/network/ipv6/icmp.go
@@ -206,6 +206,25 @@ func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, linkEP stack.
 
 // ResolveStaticAddress implements stack.LinkAddressResolver.
 func (*protocol) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bool) {
+	if header.IsV6MulticastAddress(addr) {
+		// RFC 2464 Transmission of IPv6 Packets over Ethernet Networks
+		//
+		// 7. Address Mapping -- Multicast
+		//
+		// An IPv6 packet with a multicast destination address DST,
+		// consisting of the sixteen octets DST[1] through DST[16], is
+		// transmitted to the Ethernet multicast address whose first
+		// two octets are the value 3333 hexadecimal and whose last
+		// four octets are the last four octets of DST.
+		return tcpip.LinkAddress([]byte{
+			0x33,
+			0x33,
+			addr[header.IPv6AddressSize-4],
+			addr[header.IPv6AddressSize-3],
+			addr[header.IPv6AddressSize-2],
+			addr[header.IPv6AddressSize-1],
+		}), true
+	}
 	return "", false
 }