Tuning the EIGRP Metric Calculation

Tuning the EIGRP Metric Calculation

EIGRP uses a composite metric to calculate the best path to a destination network. The metric is composed of five values: bandwidth, delay, reliability, load, and MTU. These values are combined using a weighted formula to calculate the overall metric.

The default formula used by EIGRP to calculate the composite metric is:

metric = (K1 * bandwidth + (K2 * bandwidth) / (256 – load) + K3 * delay) * (K5 / (reliability + K4))

The K values are configurable and can be set to any value between 0 and 255. By default, the K values are set to:

K1 = 1

K2 = 0

K3 = 1

K4 = 0

K5 = 0

The bandwidth value is the bandwidth of the lowest bandwidth link along the path to the destination network. The delay value is the cumulative delay along the path to the destination network. The reliability value is a measure of the reliability of the path. The load value is the average load on the path. The MTU value is the minimum MTU along the path.

To tune the EIGRP metric calculation, you can adjust the K values. For example, if you want EIGRP to prioritize delay over bandwidth, you can increase the value of K3 and decrease the value of K1:

router eigrp 1

 metric weights 0 0 1 0 0 0

This would result in the following formula being used to calculate the metric:

metric = K3 * delay

You can also adjust the metric maximum-hops command to change the maximum number of hops that EIGRP will consider when calculating the metric. By default, the maximum number of hops is 100, but you can increase or decrease this value as needed.

Additionally, you can use the bandwidth and delay commands to manually adjust the bandwidth and delay values for a specific interface. This can be useful if you want to prioritize certain links over others when calculating the EIGRP metric.

Finally, you can enable EIGRP authentication to provide an additional layer of security for your EIGRP network. EIGRP authentication uses a simple password-based authentication mechanism to ensure that only authorized routers are allowed to participate in the EIGRP routing process.

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