EIGRP is one of the routing protocols you must 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 four 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 192.168.13.0R3(config)#router eigrp 1
R3(config-router)#no auto-summary
R3(config-router)#network 192.168.13.0Configuring 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 behaves 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:
R1#
%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 192.168.13.3 (FastEthernet0/0) is up: new adjacencyR3#
%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 192.168.13.1 (FastEthernet0/0) is up: new adjacencyOur 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 3R3#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 3Use 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:
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
By the way I used ios 15 for this lab, but I don’t think that this is a reason.
Hey,
Comment below;
“The feasible successor will be used if its feasible distance is lower than the feasible distance multiplied with a multiplier”
Thanks,
I got the multiplier concept, it is explained in later chapters.
Rene - Best explanations of EIGRP I have seen and used. I’ve worked through many courses for CCNA but have yet to mess with the variance. It seems most kind of skip over that because it may not be required for the exam. My question is - do we have to manually set the variance in order for unequal cost load balancing to take place in EIGRP? I guess I just assumed EIGRP did equal and unequal cost load balancing by default. And for the heck of it, is there a real world or general consensus as to what is a good variance number to use or ballpark figure to stay around?
Thanks a ton!