Users 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 field). 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 traffic, 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 traffic 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-Specific Query addressed to the relevant multicast
group. Hosts still interested in receiving traffic 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 traffic for that group.
MLD version 2
MLD version 2 (MLDv2) adds source-filtering capability. A node can report interest in multicast traffic only from specific source
addresses or from all sources except for specific 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-Specific Query — a query to which listeners for the specified group should respond to affirm their
membership.
○ Multicast-Address-and-Source-Specific 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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
* *
| |
* Source Address [1] *
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Multicast Listener Discovery Protocol