
Configuring IP Multicasting and Multimedia Services
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Routing Table
Table 4-1 shows the principal items in a 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 if the datagram has 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.
Table 4-1. Parts of a 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
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