3.5.c Classic metric

Composite Metric


EIGRP uses a composite metric of bandwidth and delay by default similar to IGRP but modifed by a factor of 256. This combination is known as the feasible distance. http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094cb7.shtml#eigrpmetrics


Although bandwidth and delay are the recommended values commonly used for manipulation, there are a total of 5:


Bandwidth: in kilobytes, a value that can be adjusted per interface using the bandwidth command. Use with caution as this can affect other protocols as well.


Delay: in microseconds, adjusted using the delay command. Delay is the preferred value adjustment.


Reliability: as an integer value between 1 and 255. 1 is unreliable; 255 most reliable.


Load: as an integer value between 1 and 255. 1 is least loaded.


MTU: as a byte value; the least value recorded in the path. MTU is maximum transmission unit and is not used in the calculation.


Default integer values:


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


Metric calculation (actual):


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


Equation after default K5 (0) value:


[K1 * bandwidth + (K2 * bandwidth)/(256 – load) + K3 * delay]


And further given K2 = 0 (per the default):


metric = bandwidth + delay


Important; the reasons an EIGRP adjacency will not form other than a physical link problem:


Mismatched AS, not in the same subnet and mismatched K values.