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Lessons

Config Lessons

#eigrp #eigrpconfiguration #eigrpexample

EIGRP Overview
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EIGRP Protocol is one of the most used Dynamic Routing Protocol as IGP (Interior Gateway Protocol). Especially it is used for Routing purpose inside the networks that is mostly consist of Cisco devices.

EIGRP (Enhanced Interior Gateway Routing Protocol) is a Hybrid Routing Protocol that show both Distance Vector and Link-State Routing Protocol properties. It was developed by Cisco as an enhancement to IGRP (Interior Gateway Routing Protocol) and as a Cisco proprietary protocol and it is only available on Cisco devices.

You can test your Routing Knowledge on CCNP Route Practice Tests Page!
EIGRP DUAL Algorithm


EIGRP uses DUAL (Diffusing Update Algorithm) for routing calculations. Periodic Updates are not used but if a change occurs in the network like up/down links, update messages are sent.

With DUAL Algotirhm, Topology table is built. In Topology Table both the Best Routes and the Backup Routes to a destination are stored. This provides, a Fast Convergence characteristic, a Fast Convergence Mechanims to EIGRP.

The most important characteristic of EIGRP is that, it is a Fast Converged Routing Protocol. EIGRP keeps the “Backup Routes” beside the “Best Route” to a destination in the Topology table. So, during a failure, it does not need to calculate a new route. Instead, it uses the Backup Route towards the destination.

EIGRP Messages
EIGRP uses different types of messages to build neighbourship, to keep the connection and for the updates. These main messages are :



Hello
Update
Query
Reply
Ack
Hello Packets are used to establish and maintain EIGRP Neighbourship.

Update Packets are used to send routing updates.

Query Packets are used to ask for any routing update, requests an update.

Reply Packets are used as a response to the Query Packets.

ACK Packets are used as a feedback to the Update, Query or Reply packets as a feedback mechanism.

We will learn these EIGRP Packets detailly in next lessons.

EIGRP Tables


EIGRP has three tables. These tables are used on Routing Operation. The EIGRP Tables are given below:

Neighbour Table
Topology Table
Routing Table
Neighbor Table is the table that keeps All EIGRP Neighbour Routers.

Topology Table is the table that keeps All Routes to all the destinations

Routing Table is the table that keeps the Best Routes to any destinations.