The Journey of a Network Engineer

May 20 2011   12:01PM GMT

How to congifure EIGRP?

Sulaiman Syed Profile: Sulaiman Syed

EIGRP is a Cisco proprietary protocol. It is one of the most widely used within enterprises that use Cisco switches/ routers. It stands for Enhanced Interior Gateway Routing Protocol. The reason for such widely deployment is the ease of use compared to OSPF, and the effectiveness of the protocol.

Before EIGRP can update and send topology information, building relationships between EIGRP enabled routers is the first process. For two routers to become neighbors, the following conditions should be met.

  • Autonomous System number should be same.
  • The K values should be same. (they are same if left on default).
  • The routers should be in the same subnet.

Here is the syntax for configuring EIGRP

Router> enable
Router# config terminal
Router(config)# router eigrp 1
Router(config-router)# network ?
  A.B.C.D  EIGRP wild card bits
Router(config-router)# network
Router(config-router)# no auto-summary
Router(config-router)# end

EIGRP by default uses Auto-Summary for routes within certain condition. The router will summarize when it is residing between two different Networks (not subnets). For example between and since they are two different class C networks.

The calculation of Metrics (cost) is complicated slightly, but when using default K values =1. The equation is straight forward. Here is the Equation

Cost = [(K1 X Bandwidth + ((K2 X bandwidth)/(256-load)) +K3 X delay) X K5/(K4+reliability)] X 256

With default values K1, K3=1, and K2, K4, K5 = 0. the equation becomes.

Cost = (Bandwidth + delay) X 256

Where bandwidth is the minimum in the link, and delay is cumulative.

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