Metrics

EIGRP and IGRP use the same equation to calculate their metrics; however, the EIGRP metric is obtained by multiplying the IGRP metric by 256. In other words:

where the IGRP metric is shown in Equation 6-1.

By default, the K values of K1 and K3 are 0; therefore, the EIGRP metric simplifies to this:

Equation 6-1 IGRP Metric

K1, K2, K3, K4, K5 =Constants

Default values: K1 = K3 = 1,K2 = K4 = K5=0

BW = 10 ⁷ / (min bandwidth along paths in kilobits per second)

Delay = (Sum of delays along paths in milliseconds )/10

Load = Load of interface

Reli = Reliability of the interface

EIGRP is different than IGRP metric by a factor of 256 because of the Metric field: IGRP uses only 24 bits in its update packet for the Metric field, whereas EIGRP uses 32 bits in its update packet for the Metric field. The difference of 8 bits requires the IGRP metric to be multiplied by 256 to obtain the EIGRP metric. For example, if the IGRP metric to a destination network is 8586, the EIGRP metric would be 8586 x 256 = 2,198,016.