CCNA Study Guide

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Wednesday, March 15, 2006


•Cisco introduced an enhanced version of IGRP on IOS Software Release 9.21. EIGRP is an enhanced version of IGRP.
•Is a Cisco proprietary classless routing protocol
•Considered as a hybrid routing protocol as it combines the advantages of link state protocols with the advantages of distance vector protocols.
•Based on distance vector but has improved convergence properties and the operating efficiency.
•EIGRP is network layer protocol independent and support AppleTalk, IP and Novell IPX.


•Advance distance vector routing protocol
•Also know as hybrid routing protocol
•A combination of best of distance vector and link state routing protocol
–Combines very fast convergence with lower memory requirement and less processor utilization and get its speed and efficiency by acting as link-state protocol
–Operation is primarily distance vector protocol
•When an update is received by a router, it will flood the update to all routers in the entire network
•When a routing change is necessary, updates are send directly to connected neighbours, who in turn update their neighbours.


•EIGRP is based on Distance Vector routing protocol but has the characteristics of Link State routing protocol
–Sends updates only to directly connected neighbours like DV protocol but in a reliable fashion
–Sends route information rather than link-state information in its updates but information need not be sent to all routers in an AS.
–Use DUAL to shares detailed information regarding the best loop-free path to a given destination.
–DUAL reduces the routing protocol overhead traffic.
–Use split-horizon to prevents routing loops.
–EIGRP use a proprietary mechanism to guarantee ordered delivery of some of its messages. EIGRP update and query/reply packets use Cisco Reliable Transport Protocol (RTP).


•Relatively simple to configure
•DUAL is use to provide virtually free of routing loops and has a fast convergence time.
•Consumes less bandwidth and router internal resources
•Support VLSM (variable length subnet mask) and automatic route aggregation
•Allows for routing of discontiguous subnets without confusing or overlapping route aggregation
•Employs a reliable transport protocol (RTP) to ensure that routing updates are successfully exchanged between neighbours.
•Support multiple network protocols, maintaining separate neighbour, topology, and routing tables for each protocol, and allow for automatic route redistribution between IGRP, IPX SAP and RTMP.


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