Query propagation occurs when an Enhanced IGRP router loses a route to a destination, and therefore goes into an active state. During this process, the router queries all its neighbors for the lost destination. Query propagation stops one hop from the point of summarization and auto-summary.
This is a definite advantage—if all the routes were sent across to all the routers in the network, a remote node in one part of the network would send a query for a lost route to the other end of the network. Then, it would have to wait for a response from all the neighbors. Preventing queries from reaching end-to-end allows the network to converge more rapidly.
As an example, consider router D1 in Figure 8-13.
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