Operation of IGRP

From a high-altitude view, IGRP shares many operational characteristics with RIP. It is a classful distance vector protocol that periodically broadcasts its entire routing table—with the exception of routes suppressed by split horizon—to all its neighbors. Like RIP, IGRP broadcasts a request packet out all IGRP-enabled interfaces upon startup and performs a sanity check on received updates to verify that the source address of the packet belongs to the same subnet on which the update was received.[1] New update entries with reachable metrics are placed in the routing table, and an entry replaces an older entry to the same destination only if the metric is smaller. Split horizon with poisoned reverse, triggered updates, and ...

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