EIGRP-Enhanced Interior Gateway Routing Protocol

EIGRP-Enhanced Interior Gateway Routing Protocol

· EIGRP is a hybrid routing protocol developed by Cisco to replace IGRP.
· It uses the Diffusing Update Algorithm (DUAL).
· Maximum hop count 224.
· EIGRP sends updates only when there is a change in the network.

EIGRP Features:

· Fast convergence
· Support for VLSM
· Partial updates conserve network bandwidth
· Support for IP, AppleTalk, and IPX
· Support for all layer 2 (data link layer) protocols and topologies
· Sophisticated metric that supports unequal-metric proportional load-balancing
· Use of multicasts (and unicasts where appropriate) instead of broadcasts
· Support for authentication

There are five EIGRP messages:
Hello : Identifies neighbors and serves as a keepalive mechanism
Update : Reliably sends route information
Query : Reliably requests specific route information
Reply : Reliably responds to a query
ACK : Acknowledgment

EIGRP PATH Calculation
EIGRP uses Diffusing Update Algoritm to calculate and maintain loop-free path and provide fast convergence.
The following is a list of the terminilogy DUAL uses to select a route;
Successor : The primary route used to reach a destination.The successor route is kept in the routing table.
Feasible successor : The backup route must have an AD less than the FD of the current successor route.
Adversited distance (AD): The lowest-cost route between the next -hop router and the destination.
Feasible distance (FD) : The sum of the AD plus the cost between the local route and the next-hop router.

EIGRP maintains three tables:
1-Neighbor table
2-Topology table
3-Routing table

EIGRP Metric
The criteria that EIGRP uses by default to calculate its metric:
· Bandwidth
· Delay
The optional criteria that EIGRP can be configured to use when calculating its metric:
· Reliability
· Load
Note: Although MTU is exchanged in EIGRP packets between neighbor routers, MTU is not factored into the EIGRP metric calculation.

Configuring EIGRP
Router (config)# router eigrp autonomous-system
Router(config-router)# network network-number
Similar to RIP version 2 and OSPF, EIGRP can be a classless routing protocol. By default, it is classful. To enable classless routing, type the following command under the routing process:

Router(config-router)#no auto-summary

RTA(config)#router eigrp 65
RTA(config-router)#network 172.16.10.0
RTA(config-router)#network 172.16.20.0
RTA(config-router)# no auto-summary

RTB(config)#router eigrp 65
RTB(config-router)#network 172.16.10.0
RTB(config-router)#network 172.16.20.0
RTB(config-router)# no auto-summary

EIGRP Load Balancing

Router (config-router)# variance multiplier

Multiplier : A value from 1 to 128, used for load balancing. The default is 1, which indicates that only equal-cost load balancing is being performed. The multiplier defines the range of metric values that are accepted for load
balancing by the EIGRP process.

· Allows the router to load-balance across routes with a metric smaller than the multiplier value times the minimum metric route to that destination.
· The default variance is 1, which means equal-cost load balancing.

EIGRP Authentication
Eigrp support MD5 authentication.The following steps enable authentication on a cisco router.
Step1: Enter the interface you want to configure authentication on.
Step2 : Enable MD5 authentication using the
ip authentication mode eigrp process-id md5 command.
Step3 : Create an authentication key using the
ip authentication key-chain eigrp process-id key-chain command.
The key-chain paremater is the name of the key you want to create.
Step4 : Exit interface configure mode.
Step5 : Identify the key chain you configured in Step3 using the key chain name-of-key-chain command.
Step6 : Create a key number: key number.
Step7 : Identify the key string using the key-string text command.

The following example configures MD5 authentication with thewayofcisco as the key:
RouterA(config)#interface s0/0
RouterA(config-if)#ip authentication mode eigrp 65 md5
RouterA(config-if)#ip authentication key-chain eigrp 65 thewayofccie
RouterA(config-if)#exit
RouterA(config)#key chain thewayofccie
RouterA(config-keychain-key)#key 1
RouterA(config-keychain-key)#key-string mykey

Verifying EIGRP
RouterA#show ip eigrp neighbors
Displays information drawn from the neighbor table.
RouterA#show ip eigrp topology
Displays information drawn from the topology table.
RouterA#show ip eigrp traffic
Shows statistics about the EIGRP traffic reaching the router.
RouterA#debug eigrp packet
Shows EIGRP packets sent and received.
RouterA#debug ip eigrp neighbors
Shows the hello packets sent and received by the router and the neighbors discovered by this process.
RouterA#debug ip eigrp summary
Shows when a summary is changed on the router.