EIGRP Metric Components: K-Values

Normally, EIGRP metric calculation is done using contraining bandwidth and cumulative delay. Other values can be used and configured to tailor the metric and customize routes to match your environment. The default formula for EIGRP metric calculation is 256*(bw + delay), however, the full formula is:

EIGRP Metric = 256*([K₁*Bw + K₂*Bw/(256-Load) + K₃*Delay]*[K₅/(Reliability + K₄)]).

And the default values are:

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

As can be seen from the above formula, K1 and K2 affect bandwidth & load, K3 affects delay, while K4 and 5 affect reliability. If K5 is equal to zero, then the entire section of the formula is ignored, hence we arrive at the default formula. While not recommended by Cisco, K-values can be used to influence route calculation by modifying the weight of each respective metric component. For instance, in a lab situation bandwidth can be disabled to simplify metric calculation and make it easier to learn the concepts of EIGRP.

It is important to note that mismatched K-values can prevent a neighborship from taking place, and IOS will log mismatched K-values when the router receives an EIGRP packet.

To set K-values, you use the following commands:

router eigrp 1
metric weights 1 0 1 0 0

This command would set the values to the default configuration. To verify that K-values are configured properly, we use "show ip protocols" which would list the K-values.

While K-values are rarely modified, it is beneficial to understand exactly how EIGRP comes up with its configuration. Understanding how and why things work is the greatest troubleshooting tool a network engineer can have.