This chapter describes how to configure enhanced interior gateway routing protocol (EIGRP). It is the improved version founded by Cisco. The feature which is different from IGRP and RIP is, they do not send updates of the periodic route. The updated information is sent only when the changes occur in the network topology.

The key factors that distinguish EIGRP from other routing protocols are:-

  • Multiple network layers are supported.
  • Subnet task having variable length get supported.
  • Updating which occurs partially are get supported.

The currently processing EIGRP contains all the neighbor routing tables’ to find the fastest route for transferring information. If such a route does not exist, the neighbor route will build a path. This process continues until another path got founded. And also another factor it includes is for reducing the number of network boundaries the variable-length subnet mask provides the route that automatically processes. And also EIGRP helps to minimize the boundary at any interface.

Another important feature is that it doesn’t provide periodic updates, instead, the information’s are partially updated only if the metric value of the route gets changed. And the information is passed to only those routes for whom the updates are required. Due to these reasons[WU1] EIGRP requires only less bandwidth.

The neighbor routes are discovered only when the networks are directly attached. To declare the presence of EIGRP on the network, they sent multicast hello packets. When the neighbor sends its hello packet, ASA receives it and sends its topology table to the neighbor by setting the initialization bit.

Hello, packets sent multicast messages and no response is required for them. The statically defined neighbors contain this exception. Neighbour command is used to configure a neighbor and the hello messages sent to them as considered as unicast messages. The updates and acknowledgment of routing are delivered as unicast messages.

When the two routers discover a relationship between them the updates that occurred are exchanged only when network topology gets changed. The relationships are maintained through hello packets .every neighbor hello packets have holding time. Between these periods ASA can accept and receive neighbor hello packets. If hello packet does not receive any packet between the times periods those packets are rejected.

Four key algorithms and four key technologies are used by EIGRP protocol. They are:

  1. Neighbor discovery/recovery.
  2. Reliable transport protocol (RTP).
  3. DUAL for route calculation.

Configuring EIGRP

This section contains a brief description of how to enable and how to restart the EIGRP process in our system.

To enable EIGRP process to follow the following steps:


router eigrp as-num

  1. Example: hostname(config)# router eigrp 2


  • Of routing process happens through this command and the user got entered into the router configuration by through this is an argument which automatically numbers the system.
  • Commandip-addr [mask]
  • hostname(config)# router eigrp 2 hostname(config-router)# network


  • Command arranges the interfaces and the network used in the particular routing task.
  • EIGRP Stub Routing

     Following steps are used to enable the ASA as a stub router, they are:

  • two steps are the same as above and the final step is


  • stub {receive-only | [connected] 


  • It configures the stub routing process.

Restarting the EIGRP process

  • The items required to restart the process can be clear distribution or can be countered. Process. for example:
  • clear eigrp PID {<1-65535> | neighbors | topology | events)}
  • The above-given command is required for it.
  • the EIGRP process
  • The following methods are required to customize the EIGRP process. they are:
  • Arrange the interfaces for EIGRP
  • Need to arrange a summary of the aggregated address of interfaces
  • Use another value when time get delayed on an interface
  • When EIGRP neighbor get defined
  • Dividing routes to EIGRP
  • Removing unwanted materials from network

Also, read…

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