Before you can configure EIGRP (Enhanced Interior Gateway Routing Protocol), you should know the basics of EIGRP routing protocol. EIGRP is an enhanced version of IGRP. The core features of the EIGRP routing protocol remain same as provided by the IGRP protocol. However, it provides better performance and scalability than IGRP. EIGRP is one of the most preferred, best, and loved routing protocol. Unfortunately, it is a vendor-specific “Cisco-proprietary” protocol and can only be used on Cisco routers. In this post, we will discuss the basic features of EIGRP protocol, EIGRP tables, and the EIGRP configuration commands with examples.
Features of EIGRP Protocol
Some of the major characteristics and features provided by the EIGRP routing protocol are:
- It is an Interior Gateway Routing (IGP) protocol, means it can only be used to perform routing within the same autonomous system.
- It supports up to 255 hops count.
- It is used for a mid-sized network.
- It uses composite metric (bandwidth, load, reliability, delay, and MTU) to calculate the best path.
- It uses Diffusing Update Algorithm (DUAL).
- Since it has the characteristics of both, the distance vector and link-state protocols, hence, sometimes is referred as a hybrid protocol. However, I have seen many times that Cisco called it as an advanced distance-vector routing protocol.
- It supports multiple routed protocols, such as IP, Apple Talk, and IPX.
- The Administrative Distance value of the EIGRP protocol is 90.
- Unlike IGRP, it is a classless routing protocol, hence, it supports CIDR and VLSM.
- It also supports route summarization and discontinuous network.
- It supports up to six equal or unequal paths to provide load balancing for a single destination.
- The route update time of EIGRP protocol is 90 seconds.
- It supports trigger update which helps to reduce the size routing table.
- It uses 18.104.22.168 multicast address to exchange routing information between (neighbors) routers.
In a trigger update, only the partial routing changes are exchanged instead of the full routing tables. It helps to reduce CPU overhead and preserve network bandwidth.
Since the EIGRP protocol has the characteristics of link-state routing protocol, it uses three different types of tables for fast convergence.
- Neighbor table: Used to store information about the directly connected routers (called neighbors).
- Topology table: Used to store information about all the possible routes from a source to destination. In addition, it also stores the entire logical network structure.
- Routing table: Used to store routing information. The best path for a destination called successor is stored in the routing table and all other alternative paths, called feasible successors, for the same destination are stored in the topology table.
Step by Step EIGRP Configuration
Now, you have learned the basics of the EIGRP routing protocol, let us have a look EIGRP configuration. To configure EIGRP, we will use the following topology.
Configure the IP addresses, as mentioned in the preceding topology on each device. Once you have configured the appropriate IP addresses, you can start to configure EIGRP routing. Before doing so, first, look at the EIGRP configuration command’s syntax.
Router(config)#router eigrp <autonomous number> Router(config)#network <destination network>
To configure EIGRP routing, you need to perform the following steps:
- On Router1, execute the following commands.
Router1(config)#router eigrp 500 Router1(config-router)#network 10.0.0.0 Router1(config-router)#network 192.168.1.0 Router1(config-router)#exit
- On Router2, execute the following commands.
Router2(config)#router eigrp 500 Router2(config-router)#network 22.214.171.124 Router2(config-router)#network 192.168.1.0 Router2(config-router)#network 126.96.36.199 Router2(config-router)#exit
- On Router3, execute the following commands.
Router3(config)#router eigrp 500 Router3(config-router)#network 188.8.131.52 Router3(config-router)#exit
You can use various EIGRP commands to test, verify, and troubleshoot the EIGRP configuration. The following are some of the commonly used EIGRP commands.
- To view the routing table, execute the following command.
Router#show ip route
- To view the neighbor table, execute the following command.
Router#show ip eigrp neighbors
The following figure displays the EIGRP routing and neighbors tables.
As you can see in the preceding figure, the 184.108.40.206/8 ad 220.127.116.11/16 networks are added through the EIGRP routing protocol.
- To view information about the EIGRP routing protocol operations, execute the following command.
Router#show ip protocols
- To view the EIGRP metric information for an interface, execute the following command.
Router#show interface <interface name/number>
The following figure displays the EIGRP metrics for the FastEthernet 0/0 interface.
Once you have configured the EIGRP configuration, test your configuration by checking the connectivity between PC0 and Router3. To do so, open the Command Prompt window on PC0, and execute the following command.
You should be able to ping successfully as shown in the following figure.
In this post, we have discussed the basic features of EIGRP protocol, EIGRP configuration steps, and some of the important EIGRP configuration commands. Let us know if you have any query. We would love to hear you.