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Internet Group Management Protocol (IGMP)

IGMP was primarily designed for hosts on multi-access networks to inform locally attached routers of their group membership information. This is performed by hosts multicasting IGMP Host Membership Reports. Multicast routers listen for these messages and then can exchange group membership information with other multicast routers. This allows distribution trees to be formed to deliver multicast datagrams. The original version of IGMP was defined in [RFC 1112].

Extensions to IGMP have been developed and released in later releases of the IP Multicast distribution from Xerox PARC. These extensions, known as IGMP version 2, include explicit leave messages for faster pruning and multicast traceroute messages. GATED is aware of both IGMP Version 1 and Version 2 messages. However, the multicast traceroute features have not yet been implemented. Of course, this will be done "real soon now".

The IGMP Statement

igmp yes | no | on | off [ { queryinterval sec ; timeoutinterval sec ; interface interface_list enable | disable; traceoptions trace_options ; } ] ;

The igmp statement enables or disables the IGMP protocol. If the igmp statement is not specified the default is igmp off; If enabled, IGMP will default to enabling all interfaces that are both broadcast and multicast capable. These interfaces are identified by the IFF_BROADCAST and IFF_MULTICAST interface flags. IGMP must be enabled before one of the IP Multicast routing protocols are enabled.

The options are as follows:

Tracing options

Packet tracing options (which may be modified with detail, send or recv):

All IGMP packets.

IGMP Host Membership Query packets

IGMP Host Membership Reports and New Host Membership Reports

IGMP Host Leave messages

IGMP Multicast trace route request and response packets plus Cisco multicast trace messages.

next up previous contents index
Next: DVMRP Up: Configuration Guide Previous: IS_IS

Laurent Joncheray
Wed Jun 12 15:35:22 EDT 1996