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Configuring IP Multicasting and Multimedia Services

4-6

117355-D Rev 00

Routing Table

Table 4-1 shows the principal items in a DVMRP routing table entry.

Note that the source subnet and the previous-hop router in the DVMRP routing

table are the opposite of the destination subnet and next-hop router in a RIP

routing table.

Using this information, the router can:

1. Receive a multicast datagram and determine whether the datagram arrived on

the interface that is on the shortest path to the source network.

2. Drop the datagram if it has not arrived on the shortest-path interface.

3. Flood the multicast datagram to all active downstream DVMRP neighbors.

Shortest-Path Trees

Route information used by DVMRP is independent of any other routing

information used by the router -- for example, routes provided by RIP. The

purpose of DVMRP routing information is to create a shortest-path tree entry in

the routing table for the propagation of multicast datagrams.

The shortest-path tree entry indicates the interface that provides the shortest path

to the network that is the source of the multicast datagram.

In Figure 4-1

on page 4-3, for example, the routing table on router D includes an

entry describing the shortest-path route to the network connected to router A. The

entry indicates that interface d1 provides the shortest path to that source network.

A shortest-path tree also indicates those interfaces that are on the shortest path to

that source network from a neighboring router.

Table 4-1. DVMRP Routing Table Entry

Item Description

Source subnet address and

mask

Address and mask of a subnetwork containing a host

sourcing multicast datagrams

From-gateway Previous-hop router leading back to the source subnet

TTL Number of seconds before this entry is removed from the

routing table

1 2 ... 91 92 93 94 95 96 97 98 99 100 101 ... 379 380

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Avaya Configuring IP Multicasting and Multimedia Services Manual de usuario Pagina 96