EIGRP rib-scale

EIGRP wide metrics are supported for EIGRP named mode and are actually enabled automatically. They can't be disabled when using named mode. EIGRP routers will detect if their neighbors support wide metrics. If so, wide metrics are automatically used, otherwise classic metrics are used.

Wide metrics use a 64 bit value while the metric used in the Routing Table is a 32 bit value. In order to install the metric successfully into the routing table, the metric is scaled down using what is known as the rib-scale. Specifically, the wide metric is divided by the rib-scale value, which by default is 128.

Using a rib-scale of 128 may still not be enough to scale down the metric so that it fits into the 32-bit value of the routing table. Whenever the value exceeds what can be accommodated, the metric installed is a metric of infinity.

The rib-scale default value of 128 works for most EIGRP networks. For some extensively large networks, you may find that metrics of infinity will be seen more often. If this happens, you are able to modify the rib scale value. This can be done using the metric rib-scale.