How Dvmrp Supports Ip Multicast; Spanning Tree Delivery - 3Com 4007 Implementation Manual

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IP Multicast

Spanning Tree

DVMRP is a distance-vector routing protocol that allows routers to

establish shortest-path, source-rooted, IP multicast delivery trees. While it

is similar to the Routing Information Protocol (RIP), one important

difference is that DVMRP focuses on the previous hop back to a multicast

source, not the next hop to a destination. Multicast routers are concerned

with moving packets away from the source on a loopless path so that

multicast storms do not occur.

DVMRP version 3.x uses the Reverse Path Multicast (RPM) algorithm to

construct a delivery tree that begins at the source and spans out to reach

group members on a loopless path through the network. Hence, DVMRP

seeks to form a source-rooted spanning tree for each source-group pair.

The shape of each tree changes dynamically, depending on the location

of hosts that join and leave the group. As shown in Figure 52, any routing

interface that contains group members is called a leaf interface.

Figure 52 Sample IP Multicast Spanning Tree

= Active multicast group member

= Multicast router

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