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Configuring IP Multicasting

7-3

Internet Group Management Protocol

Any host system on any IP network can send a message to a multicast group using

the group’s IP multicast address. To receive a message addressed to a multicast

group, however, the host must be a member of the group and must reside on a

network where that group is registered with a local multicast router.

The Internet Group Management Protocol (IGMP) allows a host to register its

local network with the local router to receive any datagrams sent to this router and

targeted to a speciﬁc IP multicast address. Bay Networks routers support IGMP

Version 2.

How IGMP Works

A multicast router periodically sends IGMP host membership queries to its

attached local networks. Routers that conform to RFC 1112 generate Version 1

queries. Beginning with Version 9.0, Bay Networks routers conﬁgured with IGMP

generate Version 2 queries.

If multiple multicast routers exist on the network, one router is chosen to generate

host queries. Routers use the following rules to determine the designated router.

• Choose a router that generates Version 1 queries over a router that generates

Version 2 queries.

• Choose the router with the lowest IP address.

Hosts on the networks respond with host membership reports, one report for each

supported multicast group. If at least one host on the local network speciﬁes that

group in a report, the router will forward to that network all datagrams bearing the

group’s multicast address.

When a Version 2 host leaves a group, it sends a Host Leave message. The

multicast router on the network issues a host query to determine whether there are

other group members on the network. If no host responds to the query, the router

assumes that no members belonging to that group exist on that interface.

For instructions on using Site Manager to conﬁgure IGMP on the router and on IP

interfaces, see “Editing IGMP Global Conﬁguration Parameters” on page 7-28 and

“Editing IGMP Entry Interface Parameters” on page 7-30.

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Avaya Configuring IP Services Bedienungsanleitung Seite 285