By default EIGRP uses bandwidth and delay of the line to determine the best path to a remote network. However, if desired, EIGRP can use a composite of four metrics: bandwidth, delay, reliability, and load. Maximum transmission unit (MTU) is not used in EIGRP calculations but is a required parameter in some EIGRP-related commands. Also, by default, EIGRP will provide equal-cost load balancing across up to four links. You can disable load balancing by setting the ‘maximum-paths’ to ’1′. In this lab I use four Cisco 3725 routers [IOS 12.4(15)T10] to demonstrate EIGRP path selection behavior on Cisco routers. Below is a diagram of my setup.
My initial topology and routing table is displayed below.
As you can see from the above, since EIGRP provides equal-cost load balancing across for up to four links, both equal routes to the 184.108.40.206/30 network are in the topology and routing table. Below, I lower the bandwidth of the 10.0.13.0/30 link to 50 MB and since bandwidth is a metric used by EIGRP to determine the best path, you can see that the 10.0.13.0/30 link remains in the topology table but is removed from the routing table. Only the 220.127.116.11/30 link to the 18.104.22.168/30 network remains in the routing table.
Tags: bandwidth, Cisco, Cisco 3725, Cisco 3725 router, Cisco 3725 routers, delay, delay of the line, EIGRP, EIGRP calculation, eigrp load balancing, Enhanced Interior Gateway Routing Protocol, equal cost load balancing, load balancing, router, routing table, topology table