EIGRP Metrics

EIGRP uses the minimum bandwidth on the path to a destination network and the total delay to compute routing metrics.The bandwidth and delay are determined from the values configured on the router interface in the path to the desination network.

Metric Formula

The complete metric formula is:
metric = [K1 * bandwidth + (K2 * bandwidth) / (256 - load) + K3 * delay] * [K5 / (reliability + K4)]

The default values for K are:

• K1 = 1
• K2 = 0
• K3 = 1
• K4 = 0
• K5 = 0

The short version of this formula:
metric = bandwidth + delay

bandwidth = (10000000/bandwidth(i)) * 256
where bandwidth(i) is the least bandwidth of all outgoing interfaces on the route to the destination network represented in kilobits.

delay = delay(i) * 256
where delay(i) is the sum of the delays configured on the interfaces, on the route to the destination network.

EIGRP concepts

• Feasible distance - the best metric all the way to a destination network. in our simulation we mark it with green color
• Reported distance - the total metric along a path to a destination network as advertised by an upstream neighbor.
• Feasible successor - a path whose reported distance is less than the feasible distance

Simulation

Router 1 have two routes to Network C: one through Router 2 and one throught Router 4.
By default router 1 choose the path through router 2 to reach Network C because it have a better metric. In the table bellow you can see the topology table in router 1 with the different parameters. Router 1 does not choose the route through router 4 as a feasible successor since the reported distance is not less than the feasible distance.

You can configure the different interfaces with different bandwidth to observe how the metric and reported distance changes. you can mouseover the metric and reported distance to see the actual calculation of these parameters.

Hint: Try to configure the network in such a way the Router 1 will choose the path through Router 4 as the feasible distance and the router 2 as a feasible successor.