The first update packet will include INIT-flag set, which indicates that the packet contains the complete routing table.
The first step toward building a routing table involves building the topology table. Unlike traditional distance-vector protocols, Enhanced IGRP does not rely on a forwarding table to hold all the routing information. Instead, it builds a separate table, known as a topology table, from which it constructs the routing table. The topology table contains information about the feasible successor, the next hop, and the metric (feasible distance) that is needed to reach the destination.
The topology table is built using information received from the neighbor network. This information indicates the distance that the neighbor needs to reach the destination.
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