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:

eigrp ccna topology

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

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.

no auto-summary is enabled by default since IOS 15.

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

%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor (FastEthernet0/0) is up: new adjacency
%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor (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            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            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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Forum Replies

  1. Hi Rene…


    What an awesome article… simple and nice explanation,…

  2. Hi Rene,

    This is all I have to say, THANK YOU! :clap::clap::clap:

    Complicated concepts, made very objective.

  3. Hello Laz,

    Thanks for clarification. Now i am getting your point.

    Please make me correct if i am wrong. Now i am taking AD and FD value from R2’s perspective.

    1. Advertised distance from R3 is 9 (Path R3->R4) directly
    2. Advertise distance from R1 is 25 (Path R1->R2->R3->R4->Destnation). Second path would not be selected as per split horizon rule which is (R1->R3->R4->Destination).

    Feasible distance

    1. FD from R3 is = 9+4+5=18

    2. FD from R1 is = 25+7= 32

    Abhishek Saini

  4. Hi Ziad,

    In reality, when R3 receives an update from R1 or R2 about the destination behind R4, it won’t install them since these don’t pass the feasibility condition (AD of the feasible successor has to be lower than FD of successor).

    R3 will only advertise its successor route to other neighbors. In this topology, R4 is the successor route so normally R3 would advertise this route to R4. However, because of split horizon (don’t advertise a route to a neighbor if you learned that route from the neighbor)…this route is not advertised.

    It might be helpful to see a

    ... Continue reading in our forum

  5. The topology is being viewed from the standpoint of R3. We have the benefit here of seeing the full network topology, and you can trace if R3 used R1 or R2 as a feasible successor, to reach the destination, you’ll be going in a loop back to R3 (where you started).

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