This How To explains the fundamentals of configuring EIGRP.  EIGRP is an advanced distance-vector routing protocol that is used on a computer network to help automate routing decisions and configuration. The protocol was designed by Cisco Systems as a proprietary protocol, available only on Cisco routers, but Cisco converted it to an open standard in 2013.

EIGRP allows a router to share information it knows about the network with neighboring routers within the same logical area known as an autonomous system. Contrary to other well known routing protocols, such as RIP, EIGRP only shares information that a neighboring router would not have, rather than sending all of its information. EIGRP is optimized to help reduce the workload of the router and the amount of data that needs to be transmitted between routers.

Before starting, if you have not set the bandwidth of the interfaces, set them now. For correct routing decisions, you need to set the bandwidth for the serial interfaces depending on the WAN technologies that you are using. This is done using the following command on each serial interface:

Router(config-if)#bandwidth XX

  • where XX is the bandwidth of the WAN connection in kilobits per second.  If you want to understand more deeply what the bandwidth command does, click here.

1. Enable EIGRP on the router with the command,

Router(config)#router eigrp AS

  • where AS is the Autonomous System number. The same AS number must be used for all the routers that you want to exchange routing information.

2. Instruct the router to advertise the networks that are directly connected to it,

Router(config-router)#network XXX.XXX.XXX.XXX

  • where XXX.XXX.XXX.XXX is the network id of a network that is directly connected to the router. Repeat this step for each network that is directly connected to the specific router that you are configuring. Remember that you need only to write the supernet of a group of subnets and the router will automatically identify the subnets.

For example, if the router is connected to the networks, 172.16.1.0, 172.16.2.0, and 172.16.3.0, you will need to do one ‘network’ command with the address 172.16.0.0.

3. Although it is not recommended, if you need to change the way the metrics of the routes are calculated, you can set them using the command:

Router(config-router)#metric weights tos k1 k2 k3 k4 k5

where,

  • tos is the type of service index
  • and the values of k1-k5 are used to calculate the metric using the following equation:
  • metric=[k1*bandwidth + (k2*bandwidth) / (256-load) + (k3*delay)]*[k5/(reliability+k4)]
  • the default values are k1=k3=1 and k2=k4=k5=0

It is highly recommended that you leave the metric in the default values unless you are a highly experienced network designer.

4. By default, EIGRP packets consume a maximum of 50 percent of the link bandwidth, as configured with the ‘bandwidth’ interface configuration command. You might want to change that value if a different level of link utilization is required or if the configured bandwidth does not match the actual link bandwidth (it may have been configured to influence route metric calculations). Use the following command to set the percentage of bandwidth to be used on each interface separately:

Router(config-if)#ip bandwidth-percent eigrp XX

  • where XX is the percentage of bandwidth to be used (ex: 70).

5. You can change the intervals of the hello packets and the holddown timer on each interface using command:

Router(config-if)#ip hello-interval eigrp AS TIME

  • where AS is the autonomous system number and TIME is the new hello-packet interval time in seconds.

Router(config-if)#ip hold-time eigrp AS TIME

  • where AS is the autonomous system number and TIME is the new holddown time in seconds.

6. Check your configuration on the routers after configuring all the routers in the internetwork using the following commands:

show ip eigrp interfaces [interface] [as-number]

Display information about interfaces configured for EIGRP.

show ip eigrp neighbors [type number]

Display the EIGRP discovered neighbors.

show ip eigrp topology [autonomous-system-number | [[ip-address] mask]]

Display the EIGRP topology table for a given process.

show ip eigrp traffic [autonomous-system-number]

Display the number of packets sent and received for all or a specified EIGRP process.

 

Configure EIGRP Route Authentication

EIGRP route authentication provides MD5 authentication of routing updates from the EIGRP routing protocol. The MD5 keyed digest in each EIGRP packet prevents the introduction of unauthorized or false routing messages from unapproved sources. Before you can enable EIGRP route authentication, you must enable EIGRP.

The steps for setting the EIGRP route authentication are:

1. Identify a key-chain to be used in the authentication,

Router(config)#key chain NAME

  • where NAME is the name of the key-chain that will be created

2. Identify the key number,

Router(config-keychain)#key NO

  • where NO is the number of the key

3. Identify the key string,

Router(config-keychain)#key-string STRNG

  • where STRNG is the key string

4. You can stop here or setup a period in which the key will be effective,

Router(config-keychain)#accept-lifetime START-TIME {INFINITE | END-TIME | DURATION}

Router(config-keychain)#send-lifetime START-TIME {INFINITE | END-TIME | DURATION}

You can set a start time and either end time, or duration in seconds, or you can leave the operation infinite.

Implementation notes:

1. If you are using discontigous networks, which is mostly the case, you should turn off auto-summarization using the following command:

Router(config)#no ip auto-summary

2. You can set manual summary addresses using the following command:

Router(config-if)#ip summary-address AS MASK

  • where AS is the autonomous system number and MASK is the address mask.

3. When you are using non-broadcast networking technologies like FrameRelay and SMDS, you will need to turn off split-horizon to let EIGRP perform efficiently.

Router(config-if)#no ip split-horizon AS

  • where AS is the autonomous system number.

4. To clear the neighbor table use the command,

Router#clear ip eigrp neighbors

We hope that this How To on EIGRP helps you understand how to use EIGRP.

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