Diffusing update algorithm
DUAL stands for Diffusing Update ALgorithm and is the algorithm used by EIGRP to ensure that a given route is recalculated globally when it might cause a routing loop.
EIGRP uses a feasibility condition to ensure that only loop-free routes are ever selected. Unfortunately, the feasibility condition may, under some conditions, cause all routes to a given destination to be rejected.
When no feasible route to a destination is available, the DUAL algorithm[1] invokes a Diffusing Computation [2] to ensure that all traces of the problematic route are eliminated from the network. At which point the normal Bellman-Ford algorithm is used to recover a new route.
References
- ^ The DUAL Algorithm
- ^ Termination Detection for Diffusing Computations - Dijkstra, Scholten - 1980
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