Support listener-side MLDv1

...as defined by RFC 2710. Querier (router)-side MLDv1 is not yet
supported.

The core state machine is shared with IGMPv2.

This is guarded behind a flag (ipv6.Options.MLDEnabled).

Tests: ip_test.TestMGP*

Bug #4861

PiperOrigin-RevId: 344344095

2 files changed, 16 insertions, 4 deletions

diff --git a/pkg/tcpip/header/icmpv6.go b/pkg/tcpip/header/icmpv6.go
index 4303fc5d5..2eef64b4d 100644
--- a/pkg/tcpip/header/icmpv6.go
+++ b/pkg/tcpip/header/icmpv6.go
@@ -115,6 +115,12 @@ const (
 	ICMPv6NeighborSolicit ICMPv6Type = 135
 	ICMPv6NeighborAdvert  ICMPv6Type = 136
 	ICMPv6RedirectMsg     ICMPv6Type = 137
+
+	// Multicast Listener Discovery (MLD) messages, see RFC 2710.
+
+	ICMPv6MulticastListenerQuery  ICMPv6Type = 130
+	ICMPv6MulticastListenerReport ICMPv6Type = 131
+	ICMPv6MulticastListenerDone   ICMPv6Type = 132
 )
 
 // IsErrorType returns true if the receiver is an ICMP error type.
@@ -245,10 +251,9 @@ func (b ICMPv6) SetSequence(sequence uint16) {
 	binary.BigEndian.PutUint16(b[icmpv6SequenceOffset:], sequence)
 }
 
-// NDPPayload returns the NDP payload buffer. That is, it returns the ICMPv6
-// packet's message body as defined by RFC 4443 section 2.1; the portion of the
-// ICMPv6 buffer after the first ICMPv6HeaderSize bytes.
-func (b ICMPv6) NDPPayload() []byte {
+// MessageBody returns the message body as defined by RFC 4443 section 2.1; the
+// portion of the ICMPv6 buffer after the first ICMPv6HeaderSize bytes.
+func (b ICMPv6) MessageBody() []byte {
 	return b[ICMPv6HeaderSize:]
 }
 
diff --git a/pkg/tcpip/header/mld.go b/pkg/tcpip/header/mld.go
index f70623092..ffe03c76a 100644
--- a/pkg/tcpip/header/mld.go
+++ b/pkg/tcpip/header/mld.go
@@ -23,6 +23,13 @@ import (
 )
 
 const (
+	// MLDMinimumSize is the minimum size for an MLD message.
+	MLDMinimumSize = 20
+
+	// MLDHopLimit is the Hop Limit for all IPv6 packets with an MLD message, as
+	// per RFC 2710 section 3.
+	MLDHopLimit = 1
+
 	// mldMaximumResponseDelayOffset is the offset to the Maximum Response Delay
 	// field within MLD.
 	mldMaximumResponseDelayOffset = 0