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EIGRP design features

EIGRP design features
3.1.4

This page will describe some key design features of EIGRP.
EIGRP operates quite differently from IGRP. EIGRP is an advance distance vector routing protocol, but also acts as a link-state protocol in the way that it updates neighbors and maintains routing information. The following are advantages of EIGRP over simple distance vector protocols:
  • Rapid convergence
  • Efficient use of bandwidth
  • Support for VLSM and CIDR.
  • Multiple network layer support
  • Independence from routed protocols.
Independence from routed protocols means that protocol-dependent modules (PDMs) protect EIGRP from lengthy revision. As routed protocols evolve, they may need new protocol modules, but changes to EIGRP will not be necessary.
EIGRP routers converge quickly because they rely on DUAL. DUAL guarantees loop-free operation throughout a route computation which allows all routers involved in a topology change to synchronize at the same time.
EIGRP sends partial, bounded updates and makes efficient use of bandwidth. EIGRP uses minimal bandwidth when the network is stable. EIGRP routers do not send the complete tables, but instead, send partial, incremental updates. This is similar to OSPF operation, except that EIGRP routers send these partial updates only to the routers that need the information, not to all routers in an area. For this reason, they are called bounded updates. Instead of timed routing updates, EIGRP routers use small hello packets to keep in touch with each other. Though exchanged regularly, hello packets do not use up a significant amount of bandwidth.
EIGRP supports IP, IPX, and AppleTalk through PDMs. EIGRP can redistribute IPX-RIP and IPX SAP information to improve overall performance. In effect, EIGRP can take over for these two protocols. EIGRP routers receive routing and service updates, and update other routers only when changes in the SAP or routing tables occur. In EIGRP networks, routing updates occur in partial updates.
EIGRP can also take over for the AppleTalk RTMP. As a distance vector routing protocol, RTMP relies on periodic and complete exchanges of routing information. To reduce overhead, EIGRP uses event-driven updates to redistributes AppleTalk routing information. EIGRP also uses a configurable composite metric to determine the best route to an AppleTalk network. RTMP uses hop count, which can result in suboptimal routing. AppleTalk clients expect RTMP information from local routers, so EIGRP for AppleTalk should be run only on a clientless network, such as a WAN link.
The next page will discuss some EIGRP technologies.

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