6.2 EIGRP Technology
6.2.4 The diffused update algorithm
The centerpiece of the new EIGRP technologies is DUAL, the EIGRP route-calculation engine. The full name of the EIGRP engine is DUAL finite-state machine. This engine contains all the logic used to calculate and compare routes in an EIGRP network. DUAL tracks all the routes advertised by neighbors and uses the composite metric of each route to compare them. Selected paths must be loop-free and have the lowest cost. Such routes are inserted by the DUAL protocol into a routing table for use in forwarding datagrams. -

Routes selected for insertion in a routing table are also evaluated on the basis of feasible succession. A feasible successor is a neighbor router that is the next hop in a least-cost path to any given destination. A feasible successor is a path that is loop free according to the DUAL FSM.