3Com 2500 manual Routing with IP Multicast, About IP, Multicast Routing

5

ROUTING WITH IP MULTICAST

	This chapter describes the IP multicast routing implementation on the
	LANplex® system.
About IP	IP multicast routing is an extension of the Internet Protocol. Multicast
Multicast Routing	routing allows a router or switch to send packets to a specific group of
	hosts without using broadcasts or multiple unicast transmissions. This group
	can include members that reside on the local LAN, members that reside on
	different sites within a private network, or members that are scattered
	throughout the Internet. Mulitcast routing achieves this functionality
	without loops or excess transmissions.
	IP Multicast support within the LANplex system has two main components:

■Internet Group Management Protocol (IGMP)

■Distance Vector Multicast Routing Protocol (DVMRP)

This chapter describes these two protocols as well as the algorithms that the LANplex system uses for multicast routing.

IGMP	The LANplex system is capable of dynamic multicast filtering based on the
	Internet Group Management Protocol (IGMP). This protocol ensures that
	multicast packets are flooded only to the appropriate ports within a routing
	interface.
	IGMP tracks end-station group membership within a multicast group.
	Membership in a group is dynamic, and hosts are allowed to be a member
	of more than one group at a time. Broadcast domains are maintained by
	avoiding propagation of multicast broadcasts to the entire subnet by
	confining them within the group (IGMP “snooping”).