ICND2 – Chapter 12 – EIGRP

Delving in to Chapter 12 was made a little easier after reading chapter 11 because a lot of the OSPF concepts apply to EIGRP. They are similar in many ways although there are very different beasts as well. Here are my notes:

EIGRP sends Hello messages and perform parameter checks similar to OSPF.

Neighbors exchange full topology information.

Each router analyzes its own EIGRP topology table and chooses the lowest metric route to install in the routing table.

EIGRP maintains 3 tables:

1. Neighbor table
2. Topology table
3. Routing table

EIGRP multicasts on

EIGRP routers must all use the same AS number to become neighbors.

EIGRP has a Hold Timer which serves the same purpose as the OSPF dead interval.

Update messages are sent using Reliable Transport Protocol. (RTP)

EIGRP uses a composite metric of bandwidth and delay.

Formula used is ((10^7/least-bandwidth)+cumaltive-delay)*256

EIGRP uses Feasible Distance (FD) and Reported Distance (RD)

Feasible Distance (FD) is the metric of the best route for a subnet

Reported Distance (RD) is the neighbors calculated route metric that is learned

Serial links default to a bandwidth of 1544 and a delay of 20,000 microseconds and do not automatically adjust by link speed.

EIGRP keeps a record of each next-hop router but not topology on the whole network like OSPF.

The best metric route for each subnet is the SUCCESSOR. The next best route(s) are FEASIBLE SUCCESSORS and can be installed in the routing table immediately upon failure of the successor route.

When a route fails and no Feasible Successor exists, EIGRP runs Diffusing Update Algorithm (DUAL) to look for a new route.

EIGRP Configuration

Router(config)#router eigrp 10

Optional commands

Router(config-if)#ip hello-interval eigrp 10 (changes hello interval on an interface)
Router(config-if)#ip hold-time eigrp 45 (changes hold time on an interface)
Router(config-if)#bandwidth 1000 (changes bandwidth setting on an interface – NOT LINK SPEED)
Router(config-if)#delay 10000 (changes delay setting on an interface)

Router(router)#maximum-paths 10

Main EIGRP SHOW Commands

Router#show ip eigrp neighbors
Router#show ip eigrp interfaces
Router#show ip eigrp topology (lists only successor and feasible successor routes)
Router#show ip eigrp topology all-links (shows all routes)
Router#show ip eigrp traffic

EIGRP Authentication

Router(config)#key chain MyKeychain
Router(config-keychain)#key 1
Router(config-keychain-key)key-string mypassword

Router(config)#interface Fa0/1
Router(config-if)#ip authentication mode eigrp 10 md5
Router(config-if)#ip authentication key-chain eigrp 10 MyKeychain

Variance allows routes whose metrics are relatively close to be considered equal.


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