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Routing & Switching · Intermediate

Feasibility Condition (FC)

EIGRP's loop-free test: a neighbor qualifies as a feasible successor only if its reported distance is less than the current feasible distance.

Definition

If RD < FD, the neighbor cannot be routing through the local router, so its path is loop-free. The condition is conservative, so some loop-free paths may fail it. It is evaluated whenever topology changes.

Example

FD 3072, neighbor RD 3100: fails the FC and cannot be a feasible successor.

Exam tip

RD equal to FD fails the condition; it must be strictly less.

Related terms