Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco-proprietary routing protocol based on Interior Gateway Routing Protocol (IGRP).

Unlike IGRP, which is a classful routing protocol, EIGRP supports classless interdomain routing (CIDR), allowing network designers to maximize address space by using CIDR and variable-length subnet mask (VLSM). Compared to IGRP, EIGRP boasts faster convergence times, improved scalability, and superior handling of routing loops.

Furthermore, EIGRP can replace Novell Routing Information Protocol (RIP) and AppleTalk Routing Table Maintenance Protocol (RTMP), serving both IPX and AppleTalk networks with powerful efficiency.

EIGRP is often described as a hybrid routing protocol, offering the best of distance vector and link-state algorithms.

EIGRP is an advanced routing protocol that relies on features commonly associated with link-state protocols. Some of the best features of OSPF, such as partial updates and neighbor discovery, are similarly put to use by EIGRP. However, EIGRP is easier to configure than OSPF.

EIGRP is an ideal choice for large, multi-protocol networks built primarily on Cisco routers.

(Source: CISCO)