Features of EIGRP
Diffusing Update Algorithm - DUAL guarantees loop-free and backup paths throughout the routing
domain. Using DUAL, EIGRP stores all available backup routes for destinations so that it can quickly
adapt to alternate routes when necessary.
Establishing Neighbor Adjacencies - EIGRP establishes relationships with directly connected routers that
are also enabled for EIGRP. Neighbor adjacencies are used to track the status of these neighbors.
Reliable Transport Protocol - The Reliable Transport Protocol (RTP) is unique to EIGRP and provides
delivery of EIGRP packets to neighbors. RTP and the tracking of neighbor adjacencies set the stage for
DUAL.
Partial and Bounded Updates - The term partial means that the update only includes information about
the route changes, such as a new link or a link becoming unavailable. The term bounded refers to the
propagation of partial updates that are sent only to those routers that the changes affect.
Equal and Unequal Cost Load Balancing - EIGRP supports equal cost load balancing and unequal cost
load balancing, which allows administrators to better distribute traffic flow in their networks.
Protocol Dependent Modules
PDMs are responsible for network layer protocol-specific tasks, including:
Maintaining the neighbor and topology tables of EIGRP routers that belong to that protocol
suite
Building and translating protocol-specific packets for DUAL
Interfacing DUAL to the protocol-specific routing table
Computing the metric and passing this information to DUAL
Implementing filtering and access lists
Performing redistribution functions to and from other routing protocols
Redistributing routes that are learned by other routing protocols
Reliable Transport Protocol
IGRP uses Reliable Transport Protocol (RTP) for the delivery and reception of EIGRP packets. EIGRP
cannot use the services of UDP or TCP. It support reliable and unreliable delivery of packages, Reliable
RTP requires an acknowledgment to be returned by the receiver to the sender. An unreliable RTP packet
does not require an acknowledgment. RTP can send EIGRP packets as unicast or multicast.
