IPv6 listener discovery uses ICMPv6
MLD uses ICMPv6 messages to communicate listener state. The router sends queries and listeners report their interest on the attached link. MLDv1 reports group membership and can signal that a listener is done with a group.
IPv6 multicast routers use this local state to decide where there is receiver demand. A multicast routing protocol can use that demand to extend a tree across routers. An MLD-snooping switch can also use the control messages to constrain Layer 2 forwarding.
MLDv2 can name individual sources
MLDv2 adds source filtering. An INCLUDE list requests traffic only from the named sources. An EXCLUDE list requests traffic from sources outside the list. IPv6 source-specific multicast uses a listener request for a particular source and group.
Try it in a lab
- On an MLDv2-capable IPv6 lab link, join a scoped IPv6 SSM group from one receiver and select one source. Keep other receivers out of the group for this test.
- In a packet capture, identify the ICMPv6 listener report and its group and source record. Check that the last-hop router records that listener interest on the expected interface.
- Stop the receiver and watch the report and router state change. Verify that traffic for the channel ceases on the receiver link after the membership is cleared.