EIGRP Diffusing Computations

Another important enhancement in EIGRP that works in tandem with the Feasibility Condition is the use of diffusing computations.

When a router detects a network change that could influence the feasible distance of the route to change in a way that it would no longer be considered an eligible path.  EIGRP can actively query its neighbors to update their own best path regarding the topology change that occurred.  These neighbors would then reply with their updated distances to the affected network.

To handle multiple topology changes EIGRP implements a finite state machine called Diffusing Update Algorithm (DUAL) that controls the run of a diffusing computation, processing the replies and inserting the gathered information into the routing table or performing additional diffusing computations.

DUAL.PNG

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