3.5 EIGRP [for IPv4 and IPv6]

EIGRP offers the following features:

● Fast convergence—The DUAL algorithm allows routing information to converge as quickly as any currently available routing protocol.

● Partial updates—EIGRP sends incremental updates when the state of a destination changes, instead of sending the entire contents of the routing table. This feature minimizes the bandwidth required for EIGRP packets.

● Less CPU usage than IGRP—This occurs because full update packets need not be processed each time they are received.

● Neighbor discovery mechanism—This is a simple hello mechanism used to learn about neighboring routers. It is protocol-independent. Security requirements do not allow dynamic learning of neighbors. BFD should be used to detect loss of a neighbor.

● Variable-length subnet masks (VLSMs).

● Arbitrary route summarization.

● Scaling—EIGRP scales to large networks.

EIGRP uses split horizon or advertises a route as unreachable when:

● two routers are in startup mode (exchanging topology tables for the first time)

● advertising a topology table change

● sending a query

Poison reverse is a loop avoidance mechanism that states that once you learn of a route through an interface, advertise it as unreachable back through that same interface.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 3007-3011).  . Kindle Edition.

http://www.cisco.com/c/en/us/td/docs/ios/12_2/ip/configuration/guide/fipr_c/1cfeigrp.html