
Multicasting Overview
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Multicast Protocols
An IP router fully configured for multicasting runs a host group membership
protocol and a multicast routing protocol.
Group Membership Protocols
A group membership protocol allows a router to learn the existence of group
members on its directly attached networks. The router periodically sends a group
query to each of its local networks. Any host that is a member of a multicasting
group identifies itself by responding.
Bay Networks implements the Internet Group Management Protocol (IGMP),
which is described in Chapter 3.
Routing Protocols
A multicast routing protocol defines data paths that enable routers to forward
multicast datagrams from a single source to multiple destinations.
There are two types of IP routing protocols:
• A dense-mode routing protocol is designed to support groups whose members
are located in a single internet region.
Bay Networks currently implements one IP dense-mode routing protocol,
DVMRP (Distance Vector Multicast Routing Protocol). DVMRP is described
in Chapter 4.
• A sparse-mode routing protocol is designed to support groups whose
members are located in multiple internet regions.
Note that the terms “dense” and “sparse” refer to the distribution of members in a
group -- not to the number of members in the group.
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