A diffusing update algorithm (DUAL or DUAL finite state machine) is a convergence algorithm dictating a routing protocol used by Cisco’s proprietary Enhanced Interior Gateway Routing Protocol (EIGRP) to prevent routing loops via a continuous route computation. A DUAL finite state machine (FSM) consists of many different states and scenarios. The DUAL protocol scans all routes to track the optimal path in terms of efficiency and cost. Then it adds that path in the routing table. DUAL FSM also manages backup routes in case the primary and most efficient route is lost.This term is also known as the DUAL finite state machine (DUAL FSM).
Routing protocols use several techniques to prevent any loop, which is an unreachable destination causing data packets to bounce back. Loops must be prevented because they hamper the performance of the entire network - Looped packets may have to be re-transmitted to ensure that transmission was not due to overflow or other delivery failure.UDP loops can be persistent as there is no feedback on receipt so a sending application may keep sending packets into a network black hole. These receive data at ull speed of the line is so network performance can be degraded. Distance vector routing protocols, such as EIGRP, use several techniques to avoid looping, including the diffusing update algorithm. DUAL not only avoids looping but also uses an algorithmic calculation to ascertain the best paths and alternate paths. DUAL maintains several metrics about the paths, including the successor, feasible distance, feasible successor, reported distance and feasible condition.
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