EIGRP (Enhanced Interior Gateway Routing Protocol), is a Cisco proprietary routing protocol (until recently). When a router runs EIGRP, it keeps a copy of its neighbors routing table. If I router cannot find a route it its, or its neighbor's routing table, it will query its neighbors who in turn query their neighbors.
Exactly how routing protocols work is serious business, but dont worry we are not going to go into that here. Below is the process that I used to setup EIGRP on a Cisco 2811.
Before we do anything, lets get into Configuration mode (conf t).
Your first step is going to be to enable IP Routing on your device. But before you do so, make sure that you have configured a Gateway of Last Restort. I did not and had to hook up the old console cable.
The IP of this router is 10.1.0.2, and its directly connected to 10.1.0.1, which is its last resort first hop, so lets configure that .
r-2811-1(config)#ip route 0.0.0.0 0.0.0.0 10.1.0.1
Ok so now lets enable IP Routing
Now lets start EIGRP and chose an AS number. Note that I used 10 on the other three routers in my setup so thats what we are going to use here.
r-2811-1(config)#router eigrp 10
Now we need to tell the router what networks are connected to it (or in this case, will be connected to it). This is the information that the router will share with its neighbors.
In this instance my ourside interface is on 10.1.0.0/16, and its inside interface will serve up 10.3.0.0./16.
Dont forget to save your work
r-2811-1#copy run start