Distributed Update Algorithm (DUAL) is used by Enhanced IGRP to achieve fast, loop-free convergence with little impact on CPU cost and overhead. DUAL involves only the nodes affected by topology change and takes corrective action, such as sending queries about the lost route across only the affected nodes.
Nodes that are unaffected simply reply that they have an alternate path. DUAL works well when more than one change occurs simultaneously because only the affected nodes are responsible for processing information. Therefore, if multiple changes occur within the network, the entire network is not involved in recomputation.
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