The EIGRP DUAL Finite State Machine

Below describes the input events for the DUAL finite state machine. A finite state machine (FSM) is a model of behavior composed of a finite number of states, transitions between the states, and actions. Note: FC is referred to as feasible condition, which states that a feasible successor is considered valid when the AD from a neighbor is less than the FD to the destination.

Input Event	Description
IE1	Any input event for which FC is satisfied or the destination in unreachable.
IE2	Query received from the successor; feasibility condition is not satisfied.
IE3	Input event other than a query from the successor; FC is not satisfied.
IE4	Input event other than last reply or a query from the successor.
IE5	Input event other than last reply, a query from the successor, or an increase in distance to destination.
IE6	Input event other than last reply.
IE7	Input event other than last reply or increase in distance to destination.
IE8	Increase of distance to destination.
IE9	Last reply received; FC is not satisfied with current feasible distance.
IE10	Query received from the successor.
IE11	Last reply received; FC is satisfied with current feasible distance.
IE12	Last reply received; set feasible distance to infinity.