IBM RackSwitch G8000, Application Manual

Page: 242 / 362

240
RackSwitch G8000: Application Guide
MLD Terms
Following are the commonly used MLD terms:
•
Multicast traffic: Flow of data from one source to multiple destinations.
• Group: A multicast stream to which a host can join.
• Multicast Router (Mrouter): A router configured to make routing decisions for
multicast traffic. The router identifies the type of packet received (unicast or
multicast) and forwards the packet to the intended destination.
• Querier: An Mrouter that sends periodic query messages. Only one Mrouter on
the subnet can be elected as the Querier.
• Multicast Listener Query: Messages sent by the Querier. There are three types of
queries:
– General Query: Sent periodically to learn multicast address listeners from an
attached link. G8000 uses these queries to build and refresh the Multicast
Address Listener state. General Queries are sent to the link-scope all-nodes
multicast address (FF02::1), with a multicast address field of 0, and a
maximum response delay of
query response interval .
– Multicast Address Specific Query: Sent to learn if a specific multicast
address has any listeners on an attached link. The multicast address field is
set to the IPv6 multicast address.
– Multicast Address and Source Specific Query: Sent to learn if, for a specified
multicast address, there are nodes still listening to a specific set of sources.
Supported only in MLDv2.
Note: Multicast Address Specific Queries and Multicast Address and Source
Specific Queries are sent only in response to State Change Reports, and
never in response to Current State Reports.
• Multicast Listener Report: Sent by a host when it joins a multicast group, or in
response to a Multicast Listener Query sent by the Querier. Hosts use these
reports to indicate their current multicast listening state, or changes in the
multicast listening state of their interfaces. These reports are of two types:
– Current State Report: Contains the current Multicast Address Listening State
of the host.
– State Change Report: If the listening state of a host changes, the host
immediately reports these changes through a State Change Report
message. These reports contain either Filter Mode Change records and/or
Source List Change records. State Change Reports are retransmitted
several times to ensure all Mrouters receive it.
• Multicast Listener Done: Sent by a host when it wants to leave a multicast group.
This message is sent to the link-scope all-routers IPv6 destination address of
FF02::2. When an Mrouter receives a Multicast Listener Done message from the
last member of the multicast address on a link, it stops forwarding traffic to this
multicast address.