EIGRP is a Cisco proprietary protocol. It is one of the most widely used within enterprises that use Cisco switches/ routers. It stands for Enhanced Interior Gateway Routing Protocol. The reason for such widely deployment is the ease of use compared to OSPF, and the effectiveness of the protocol.
Before EIGRP can update and send topology information, building relationships between EIGRP enabled routers is the first process. For two routers to become neighbors, the following conditions should be met.
- Autonomous System number should be same.
- The K values should be same. (they are same if left on default).
- The routers should be in the same subnet.
Here is the syntax for configuring EIGRP
Router> enable Router# config terminal Router(config)# router eigrp 1 Router(config-router)# network 10.2.9.0 ? A.B.C.D EIGRP wild card bits <cr> Router(config-router)# network
0 0.0.0.255 Router(config-router)# no auto-summary Router(config-router)# end
EIGRP by default uses Auto-Summary for routes within certain condition. The router will summarize when it is residing between two different Networks (not subnets). For example between 192.168.1.0 and 192.168.2.0 since they are two different class C networks.
The calculation of Metrics (cost) is complicated slightly, but when using default K values =1. The equation is straight forward. Here is the Equation
Cost = [(K1 X Bandwidth + ((K2 X bandwidth)/(256-load)) +K3 X delay) X K5/(K4+reliability)] X 256
With default values K1, K3=1, and K2, K4, K5 = 0. the equation becomes.
Cost = (Bandwidth + delay) X 256
Where bandwidth is the minimum in the link, and delay is cumulative.