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EIGRP Configuration for CCNA Students

EIGRP is one of the routing protocols you need to master if you want to pass the Cisco CCNA exam. In this lesson I’ll walk you through the configuration. If you have no idea what EIGRP is or how it works you should read my Introduction to EIGRP first. This is the topology that we will use:

In the topology above I have 4 routers. All interfaces are FastEthernet with the exception of the link between R1 and R2, that’s where we use an Ethernet link. Behind R4 there is a loopback interface.

Let’s start by configuring EIGRP between R1 and R3:

R1(config)#router eigrp 1
R1(config-router)#no auto-summary 
R1(config-router)#network 192.168.13.0

R3(config)#router eigrp 1
R3(config-router)#no auto-summary 
R3(config-router)#network 192.168.13.0

Configuring EIGRP is similar to RIP. The “1” is the AS number and it has to be the same on all routers! We require the no auto-summary command because by default EIGRP behave classful and we want it to be classless.

Auto-summary is enabled by default since IOS 15.

After typing in these commands this is what you will see:

R1#
%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 192.168.13.3 (FastEthernet0/0) is up: new adjacency

R3#
%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 192.168.13.1 (FastEthernet0/0) is up: new adjacency

Our routers have become EIGRP neighbors. We can also verify this with a command:

R1#show ip eigrp neighbors 
IP-EIGRP neighbors for process 1
H   Address                Interface       Hold Uptime   SRTT   RTO  Q  Seq
                                           (sec)         (ms)       Cnt Num
0   192.168.13.3            Fa0/0             12 00:11:58 1275  5000  0  3

R3#show ip eigrp neighbors 
IP-EIGRP neighbors for process 1
H   Address                Interface       Hold Uptime   SRTT   RTO  Q  Seq
                                           (sec)         (ms)       Cnt Num
0   192.168.13.1            Fa0/0             14 00:11:47   15   200  0  3

Use show ip eigrp neighbors to verify that we have a working EIGRP neighbor adjacency. This seems to be the case.

Let’s configure all the network commands so all routers become EIGRP neighbors and advertise their networks:

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Introduction to EIGRP

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EIGRP Packets

Forum Replies

ReneMolenaar says:

I just changed the text so that I can explain it a bit more.

158720 = feasible distance (FD) of successor.
412160 = feasible distance (FD) of feasible successor.

All feasible successors that have a FD that is lower than FD of successor X multiplier will be used in load balancing.

158720 x 3 (multiplier)= 476160

412160 (FD of feasible successor) is lower than 476160 so we will use this feasible successor.

I hope this explains it better.

Rene
ReneMolenaar says:

Hi Alex,

Glad to hear you like it!

For unequal load balancing to work, you have to mess with the variance. By default EIGRP only does load balancing over equal cost paths. I doubt you will see this much in the real world…when you use EIGRP on a LAN, you probably use the same interfaces pretty much everywhere. If you want redundancy, you probably add some extra interfaces and you will use equal cost load balancing. Even if you have some low bandwidth interfaces, I doubt anyone would want to mess with the variance to use them.

Rene
ReneMolenaar says:

Hi Rocky,

The FD of your successor is 158720 and the FD of your feasible successor is 2300416.

To make unequal load balancing work, the FD of your feasible successor has to be smaller than the FD of the successor multiplied with the variance.

2300416 / 158720 = 14,59

So if you set your variance to 15, you should be good to go
lagapides says:

Hello Regis

First of all, your topology is slightly different than that in the lab. In the lab, the connection between R1 and R2 is an Ethernet connection (10 Mbps) as opposed to your FastEthernet connection (100 Mbps). In the lab, this results in having only a single route entered into the routing table for the destination network of 4.4.4.0/24, specifically, the route via R3. This is due to the fact that bandwidth is included in the metric of EIGRP. The bandwidth available via R3 is better than that available via R2, so the route via R3 is preferred.

In y
... Continue reading in our forum
RegisTB says:

I really like the time you took to explain this to me.
Thank you!!

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