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The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  TCP/IP Routing Protocols (Gateway Protocols)                 9  TCP/IP Interior Routing Protocols (RIP, OSPF, GGP, HELLO, IGRP, EIGRP)                      9  Other Interior Routing Protocols

Interior Gateway Routing Protocol (IGRP) 1 2 TCP/IP Exterior Gateway/Routing Protocols (BGP and EGP)

Other Features of EIGRP

In order to build the tables of information it needs to calculate routes, EIGRP requires that each router make and maintain contact with other routers on their local networks. To facilitate this, EIGRP incorporates a neighbor discovery/recovery process. This system involves the exchange of small Hello messages that let routers discover which other routers on the local network, and to periodically check their reachability. This is very similar to the use of the identically-named Hello messages in OSPF, and has a low impact on bandwidth use because the messages are small and infrequently sent.

Some of the features in IGRP carry through to its successor, such as the use of split horizon with poisoned reverse for improved stability. In addition to the basic improvements of efficiency and route convergence that accrue from the algorithm itself, EIGRP includes some other features. These include support for variable length subnet masks (VLSM) and support for multiple network-layer protocols. This means that EIGRP could be configured to function on a network running IP as well as another layer three protocol.

Interior Gateway Routing Protocol (IGRP) 1 2 TCP/IP Exterior Gateway/Routing Protocols (BGP and EGP)