Configuring EIGRP on an IOS router

In this article, we learn about EIGRP routing protocol that is used for routing packets, it’s configuration on a Cisco IOS router, and basic configuration verification steps.

EIGRP (Enhanced Interior Gateway Routing Protocol) is a Cisco proprietary routing protocol that is used to share routing information within an autonomous system (AS) in a computer network. It is an advanced distance-vector routing protocol that uses a combination of features from both distance-vector and link-state protocols.

EIGRP calculates the best path to a destination network based on a composite metric that takes into account several factors, including bandwidth, delay, reliability, load, and maximum transmission unit (MTU). EIGRP uses a hierarchical network design, which means that networks are grouped into areas to improve network scalability.

One of the key features of EIGRP is its ability to provide fast convergence in the event of a topology change. EIGRP uses a protocol known as Diffusing Update Algorithm (DUAL) to calculate the shortest path to a destination and to avoid loops in the network.

EIGRP is often used in large enterprise networks, particularly those that are predominantly Cisco-based.

Configuring EIGRP on a Cisco IOS router:

1. Enable EIGRP routing protocol on the router using the “router eigrp” command, followed by the autonomous system (AS) number. For example, to enable EIGRP with AS number 100, use the following command:
   Router(config)# router eigrp 100
2. Specify the networks that will be advertised by EIGRP using the “network” command. For example, to advertise the network 192.168.1.0/24, use the following command:
   Router(config-router)# network 192.168.1.0
3. djust the EIGRP metric weights using the “metric weights” command. This allows you to adjust the importance of various factors in calculating the best path to a destination network. For example, to make delay the most important factor, use the following command:
   Router(config-router)# metric weights 0 0 0 1 0 0
4. Configure EIGRP authentication to secure your network using the “authentication” command. EIGRP supports several authentication methods, including MD5 authentication. For example, to use MD5 authentication with a key of “cisco”, use the following commands:
   Router(config)# key chain EIGRP_AUTH
   Router(config-keychain)# key 1
   Router(config-keychain-key)# key-string cisco
   Router(config-keychain)# exit
   Router(config)# interface interface_name
   Router(config-if)# ip authentication mode eigrp 100 md5
   Router(config-if)# ip authentication key-chain eigrp 100 EIGRP_AUTH

Verifying EIGRP configuration on an IOS router:

To verify EIGRP in a Cisco router, the following commands are useful in EIGRP config verification:

1. Show EIGRP neighbors: This command displays information about the EIGRP neighbors that have been discovered on the router’s directly connected networks.
   Router# show ip eigrp neighbors
   The output of this command shows the IP addresses of the EIGRP neighbors, their interface, their hold time, and their state (whether they are in an established or non-established state).
2. Show EIGRP topology: This command displays the current EIGRP topology table, which shows the best path to each destination network in the EIGRP domain.
   Router# show ip eigrp topology
   The output of this command shows the destination network, the next hop router, the metric to the destination, and the outgoing interface.
3. Show EIGRP routes: This command displays the current EIGRP routing table, which shows the list of all known EIGRP routes in the routing domain.
   Router# show ip route eigrp
   The output of this command shows the destination network, the next hop router, the metric to the destination, and the outgoing interface.
4. Show EIGRP interfaces: This command displays information about the interfaces on the router that are running EIGRP.
   Router# show ip eigrp interfaces
   The output of this command shows the interface, the IP address of the interface, the state of the interface (whether it is up or down), and the metric weights that are being used for that interface.
5. Show EIGRP statistics: This command displays statistics about the operation of EIGRP on the router.
   Router# show ip eigrp statistics
   The output of this command shows information about the number of EIGRP packets sent and received, the number of EIGRP updates sent and received, and other statistics related to the operation of EIGRP on the router.

Depending on your network requirements, there may be additional commands such as debug. The CCNA Netsim offers dozens of labs on RIPv2, EIGRP, OSPF, BGP, and MPLS in a virtual environment, which may be useful for learning purpose.