Enhanced Interior Gateway Routing Protocol, popularly known as EIGRP, is a Cisco proprietary advanced distance vector routing protocol. Eigrp uses the diffusing update algorithm to calculate the shortest path to a network, and speeds up convergence time by keeping the best routes in the routing table and the second best routes in what is known as the eigrp topology table. If your routers are all Cisco routers, then you have no excuse not to use eigrp. In this post, we will look at how to implementation eigrp on a network topology with three Cisco routers.
Before we go into the configuration lab for implementing eigrp on a network topology with three Cisco routers, let’s look at a few key points about eigrp worth committing to memory.
- Eigrp is Cisco proprietary, though there are talks to make it an industry-standard routing protocol but I am yet to come across it on other vendors routers. I stand to be corrected though.
- Eigrp has a default administrative distance of 90.
- Eigrp supports manual route summarization.
- It supports variable length subnetmask, known as VLSM
- It’s an advanced distance vector routing protocol. Some authors say it is a hybrid protocol since it also has some features of a link state routing protocol.
- It has support for neighbor authentication.
Network topology
Eigrp on a network topology with three Cisco routers
Router0
Router0>en
Router0#conf t
Router0(config)#int s0/3/0
Router0(config-if)#ip add 192.168.4.1 255.255.255.252
Router0(config-if)#desc connection to Router1
Router0(config-if)#no shut
Router0(config-if)#int f0/0
Router0(config-if)#ip add 192.168.0.1 255.255.255.0
Router0(config-if)#desc connection to LAN
Router0(config-if)#no shut
Router0(config-if)#exit
Router0(config)#router eigrp 25
Router0(config-router)#netw 192.168.4.0 0.0.0.3
Router0(config-router)#netw 192.168.0.0 0.0.0.255
Router0(config-router)#no auto
Router0(config-router)#exit
Router0(config)#exit
Router0#copy run start
Router1
Router1>en
Router1#conf t
Router1(config)#int s0/3/0
Router1(config-if)#clock rate 64000
Router1(config-if)#ip add 192.168.4.2 255.255.255.252
Router1(config-if)#desc connection to Router0
Router1(config-if)#no shut
Router1(config-if)#int s0/2/0
Router1(config-if)#clock rate 64000
Router1(config-if)#ip add 192.168.4.5 255.255.255.252
Router1(config-if)#desc connection to Router2
Router1(config-if)#no shut
Router1(config-if)#int f0/0
Router1(config-if)#ip add 192.168.1.1 255.255.255.0
Router1(config-if)#desc connection to LAN
Router1(config-if)#no shut
Router1(config-if)#exit
Router1(config)#router eigrp 25
Router1(config-router)#netw 192.168.1.0 0.0.0.255
Router1(config-router)#netw 192.168.4.0 0.0.0.3
Router1(config-router)#netw 192.168.4.4 0.0.0.3
Router1(config-router)#exit
Router1(config)#exit
Router#copy run start
Router2
Router2>en
Router2#conf t
Router2(config)#int s0/3/0
Router2(config-if)#ip add 192.168.4.6 255.255.255.252
Router2(config-if)#desc connection to Router2
Router2(config-if)#no shut
Router2(config-if)#int f0/0
Router2(config-if)#ip add 192.168.2.1 255.255.255.0
Router2(config-if)#desc connection to LAN
Router2(config-if)#no shut
Router2(config-if)#exit
Router2(config)#router eigrp 25
Router2(config-router)#netw 192.168.4.4 0.0.0.3
Router2(config-router)#netw 192.168.2.0 0.0.0.255
Router2(config-router)#no auto
Router2(config-router)#exit
Router2(config)#exit
Router2#copy run start
Verification
To verify our configuration, I will use the “show ip eigrp neighbor” and “show ip route” commands on router1 to see the routers it has formed eigrp neighbor relationships with as well as the routes learned. See output from both commands below:
The first image shows that Router1 has formed neighbor relationships with Router0 and Router2 (192.168.4.1 and 192.168.4.6) and that the LAN networks attached to both routers have been learned via eigrp. In the second image, ping tests to the IP addresses assigned to the f0/0 interfaces of Router0 and Router2 returned successfully, showing that we have full connectivity.
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