Enhanced Interior Gateway Routing Protocol (EIGRP) is an evolved version of IGRP that addresses the demands of large-scale internetworks and the changes in network technology that have been developed since the implementation of IGRP.
Routers that already use IGRP can use EIGRP because the metrics for both protocols are directly translatable, i.e., they are as easily comparable as if they were routes that originated in their own autonomous systems.
A router running EIGRP stores copies of all its neighbors’ routing tables so that it can quickly adapt to alternate routes. If no appropriate route exists, EIGRP queries its neighbors to discover an alternate route. These queries propagate until an alternate route is found. Unlike some earlier routing protocols that would send an entire table to neighboring routers when one routing table entry changed, EIGRP notifies the neighbors of only the specific change in the table.
Unlike IGRP, EIGRP uses the Diffusing-Update Algorithm (DUAL) developed at SRI International.
