3Com 2500 To a multicast router, Provider, Tunnels on page 6 for more information about tunnels

5-2 CHAPTER 5: ROUTING WITH IP MULTICAST

DVMRP	The Distance Vector Multicast Routing Protocol (DVMRP) establishes
	the multicast delivery path over a series of routing devices. DVMRP is a
	simple distance vector routing protocol, similar to the IP Routing
	Information Protocol (RIP). Multicast routers exchange distance vector
	updates that contain lists of destinations as well as the distance in hops
	to each destination. They maintain this information in a routing table.
	DVMRP is the current routing protocol used on the Internet Multicast
	Backbone (MBONE). Full support of DVMRP allows the LANplex system
	to fully establish the delivery path without requiring a direct connection
	to a multicast router.
	The MBONE The MBONE is an experimental “Multicast Backbone” network that exists
	on the Internet. Users can test multicast applications and technology on
	the MBONE without waiting for Internet multicast standards to be set.
	You can gain access to the MBONE through any Internet service
	provider.
	The MBONE routers forward mulitcast packets over an interface or over
	a multicast tunnel only if the Time-To-Live (TTL) value present in the
	packet is larger than the tunnel’s threshold. (See the section “Multicast
	Tunnels” on page 6 for more information about tunnels.)
	LANplex 2500 systems at revisions earlier than 8.0 support up to 16 IP
	multicast tunnels or routing interfaces when connected to the MBONE
	network. LANplex 2500 systems at revision 8.0 or later can support up to
	32 IP multicast tunnels or routing interfaces when connected to the
	MBONE.