EIGRP Wide Metric Calculation

Using Throughput, Reliability, Load, and extended metrics EIGRP computes the composite metric using the following formula:

WideMetricCalculation.PNG

EIGRP Wide Metrics are supported where EIGRP named mode is possible.  The calculated value of the Wide Metrics can be much larger than the allowable 32 bit metrics the IPv4 RIB will accept.  As a result the composite metric has to be downscaled to be useable.

This is done by dividing the composite value by a factor configured in the metric rib-scale EIGRP command.  The default value is 128 and can be configured as necessary.

To clarify, EIGRP does not make its best path selection based on the downscaled value, instead it decides on the best path using the composite metric, and the successor path value is then downscaled and installed into the RIB.

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