EIGRPRouting Protocols and Concepts – Chapter 9

Developed in 1985 to overcome RIPv1’s limited hop count -Distance vector routing protocol -Metrics used b IGRP M ti d by bandwidth (used by default) Delay (used by default) Reliability (not used by default) Load (not used by default) -Discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)S
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EIGRPRouting Protocols and Concepts – Chapter 9 EIGRP Routing Protocols and Concepts – Chapter 9ITE PC v4.0 1Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Introduction IntroductionITE PC v4.0 2Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public EIGRP Roots of EIGRP: IGRP -Developed in 1985 to overcome RIPv1’s limited hop count -Distance vector routing protocol -Metrics used by IGRP IGRP bandwidth (used by default) Delay (used by default) (used by default) Reliability (not used by default) Load (not used by default) Load (not used by default) -Discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)SITE PC v4.0 3Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public EIGRP EIGRP is a distance vector, classless routing protocol that was released in 1992 with IOS released in 1992 with IOS 9.21. As its name suggests, EIGRP is an enhancement of Cisco IGRP (Interior Gateway Routing Protocol). Both are Cisco proprietary protocols and only operate on Cisco Both are Cisco proprietary protocols and only operate on Cisco routers. The main purpose in Ciscos development of EIGRP was to create a classless version of IGRP. EIGRP includes several features that are not commonly found in other distance vector features that are not commonly found in other distance vector routing protocols like RIP (RIPv1 and RIPv2) and IGRP. These features include: –Reliable Transport Protocol (RTP) –Bounded Updates –Diffusing Update Algorithm (DUAL) –Establishing Adjacencies –Neighbor and Topology Tables Alth Although EIGRP may act like a link-state routing protocol, it is EIGRP lik li it still a distance vector routing protocol. –Note: The term hybrid routing protocol is sometimes used to define EIGRP. However, this term is misleading because EIGRP is not a hybrid between distance vector and link hybrid between distance vector and link-state routing protocols - it is routing protocols it is solely a distance vector routing protocol. Therefore, Cisco is no longer using this term to refer to EIGRP.ITE PC v4.0 4Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public EIGRP The Algorithm Algorithm –EIGRP uses the Diffusing Update Algorithm (DUAL). –EIGRP does not send periodic updates and route entries do not age out out. –Only changes in the routing information, such as a new link or a li link becoming unavailable cause a routing update to occur. –EIGRP routing updates are still vectors of distances transmitted to directly connected neighbors.ITE PC v4.0 5Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public EIGRP Path Determination –EIGRPs DUAL maintains a topology table separate from the routing table, which includes both the best path to a destination network and any backup destination network and any backup paths that DUAL has determined to be loop-free. –If a route becomes unavailable, DUAL If route becomes unavailable DUAL will search its topology table for a valid backup path. •If one exists, that route is If th immediately entered into the routing table. •If one does not exist, DUAL performs If DUAL a network discovery process to see if there happens to be a backup path that did not meet the requirement of that did not meet the requirement of the feasibility condition.ITE PC v4.0 6Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public EIGRP Convergence –EIGRP does not use holddown timers. –Instead, loop-free paths are loop paths are achieved through a system of route calculations (diffusing computations) that are performed in coordinated that are performed in a coordinated fashion among the route ...