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Alteon OS Application Guide
Chapter 10: IGMP
16542C4911, January 2007
IGMP Relay
The GbESM can act as an IGMP Relay (or IGMP Proxy) device that relays IGMP multicast
messages and traffic between an Mrouter and end stations. IGMP Relay allows the GbESM to
participate in network multicasts with no configuration of the various multicast routing proto-
cols, so you can deploy it in the network with minimal effort.
To an IGMP host connected to the GbESM, IGMP Relay appears to be an IGMP multicast
router (Mrouter). IGMP Relay sends Membership Queries to hosts, which respond by sending
an IGMP response message. A host can also send an unsolicited Join message to the IGMP
Relay.
To a multicast router, IGMP Relay appears as a host. The Mrouter sends IGMP host queries to
IGMP Relay, and IGMP Relay responds by forwarding IGMP host reports and unsolicited join
messages from its attached hosts.
IGMP Relay also forwards multicast traffic between the Mrouter and end stations, similar
to IGMP Snooping.
You can configure up to two Mrouters to use with IGMP Relay. One Mrouter acts as the pri-
mary Mrouter, and one is the backup Mrouter. The GbESM uses health checks to select the pri-
mary Mrouter.
Configuration Guidelines
Consider the following guidelines when you configure IGMP Relay:
IGMP Relay and IGMP Snooping are mutually exclusive—if you enable IGMP Relay,
you must turn off IGMP Snooping.
Upstream Mrouters must be connected to external ports (EXT 1 - EXT 6).