Concept Guide

Joining a Multicast Group
The Querier periodically sends a General Query to the all-nodes multicast address FF02::1. A host that wants to join a multicast group
responds to the general query with a report that contains the group address; the report is also addressed to the group (in the IPv6
Destination Address eld). To avoid duplicate reporting, any host that hears a report from another host for the same group in which it itself
is interested cancels its report for that group.
A host does not have to wait for a General Query to join a group. If a host wants to become a member of a group for which the router is
not currently forwarding trac, it should send an unsolicited report.
When a router receives a report for a group, it either creates a new entry in the group membership table, or it updates an existing entry by
adding the interface on which the report arrived to the outgoing interface list for the group.
Leaving a Multicast Group
A receiver that is no longer interested in trac for a particular group should leave the group by sending a Done message to the link-scope
all-routers multicast address, FF02::02.
When a Querier receives a Done message, it sends a Multicast-Address-Specic Query addressed to the relevant multicast group. Hosts
still interested in receiving trac for that group (according to the suppression mechanism) so that the group table entry is maintained. If no
reports are received in response to the query, the group membership entry is cleared and the router stops forwarding trac for that group.
MLD version 2
MLD version 2 (MLDv2) adds source-ltering capability. A node can report interest in multicast trac only from specic source addresses
or from all sources except for specic source addresses. MLDv2 is backwards compatible with MLD version 1.
NOTE
: MLDV2 is the default MLD version.
There are two types of MLDv2 messages
• Multicast Listener Query — a message sent by the Querier to discover multicast listeners.
– General Query — a query to which all listeners should respond.
– Multicast-Address-Specic Query — a query to which listeners for the specied group should respond to arm their
membership.
– Multicast-Address-and-Source-Specic Query — a query to determine if there are any listeners interested in a group and source
pair.
• Version 2 Multicast Listener Report — a response to a query indicating listening state or state changes.
Multicast Listener Queries are sent by multicast routers in Querier State to query the multicast listening state of neighboring interfaces.
Queries have the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 130 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum Response Code | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
* *
| |
* Multicast Address *
| |
* *
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Resv |S| QRV | QQIC | Number of Sources (N) |
Multicast Listener Discovery Protocol
613