EIGRP (Enhanced Interior Gateway Routing Protocol)

Satish Tiwary's picture
eigrp tutorial


EIGRP is a Cisco proprietary routing protocol. and since  it is proprietary, one can use it only in a Cisco network which is a draw back of this routing protocol.Now have a look on the technology used in this routing protocol.Technology used in EIGRP  (Diffused Update Algorithm) is similar to Distance Vector Protocol.

EIGRP is based on a distance vector algorithm to determine the best path to a destination and yeah please don't misunderstood best path as shortest path.The Router uses only the information which it receives from it's directly connected networks for making it's routing decesions.Therefore received information can be further filtered for security reasons.


Features of EIGRP:

  • It's easy to configure EIGRP.

  • It can be used over Dial-up network.

  • EIGRP supports three protocol families:IP,IPX and AppleTalk.

  • Information sent to neighbours can also be filtered before being sent.So it is secure.

  • The router announces only the route it is using to it's directly connected neighbour.

  • It is fast and reliable.

  • EIGRP can accommodate larger networks than RIP.

  • EIGRP needs a different algorithm for loop removal.

  • It uses a more sophisticated algorithm is called Diffusing Update Algorithm (DUAL).DUAL algorithm ensures that every router can individually make sure that its routing table is always free from loops.

  • It stores all routes received from all neighbours in it's topology table,not only the best route it has received so far.

  • It uses very little bandwidth which makes it more beneficials especially  in WAN configurations use.



  • This is a Cisco propriety Protocol(so it only runs on Cisco device)
  • It's Classless / VLSM
  • IGP(Interior Gateway Protocol)
  • It's Dynamic
  • It's also known as Hybrid Protocol
  • Metric (Bandwidth / Delay )
  • Trigger update
  • Hop count 255 (100 default)
  • Maintain:
  •              Neighbor Table
  •              Topology Table
  •              Routing Table



Reliable Transmission Protocol -This  is a connection oriented protocols

   Lets see RTP in a flash.In short it is known as RTP.

  • Hello =  whose on the link
  • Update
  • Query –
  • Reply – neighbor reply about the packet
  • Ack


Successor (It has Two types successor)

  • Primary Successor: It is the shortest route which is placed in RT.In short it is known as PS.


  • Feasible Successor: It is the backup route of the PS, which is placed in TT.In short it is known as FS.



Benefits of using EIGRP:


  • EIGRP operates very efficiently in a large networks so it is extremely good for large networks.
  • It is quick because Knowledge of more than one route enable EIGRP to quickly switch to an alternative route.
  • Not only this but It is also extremely efficient over LAN portions of a network
  • It doesn't leak off the local segment and neither confuse routers elsewhere in the network.
  • It's easier to configure in a medium-sized to large network than other protocols with similar capabilities
  • It uses very little bandwidth.
  • Apple Talk is the third protocol family supported by EIGRP.
  • You can filter the routes that EIGRP receives on a particular interface.
  • We can easily redistribute routes into EIGRP uses the redistribute command.
  • We can easily modify the metrics of routes that EIGRP learns through a particular interface.
  • There are two important EIGRP timers, the hello interval and the hold time. You can adjust both of these timers separately on each interface on a router.
  • It supports MD5-based EIGRP packet authentication.


 Note:This is just an authentication system.


What happen in this authentication process?

In authentication process the routers never used to encrypt the routing update packets as they send them through the network.



What is the Real Scenario behind the authentication process?

In reality they just authenticate these packets using MD5.


What is the effect of this authentication Process?

It prevents people from either accidentally or maliciously injecting routes into your network which  is turns to be helpful in environments where you don't have control over all of the routers.


How we can Optimize routing through EIGRP


  • Reduce the size of your routing tables to improve the stability and efficiency of the routing process.
  • Modify the amount of bandwidth percentage available to EIGRP.
  • Stabilize your network by sending smaller routing tables.
  • Reducie the scope of EIGRP queries.
  • tag specific routes to prevent routing loops.



In Next Post We will Learn How to configure EIGRP.

We perform the EIGRP LAB geven below.

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