3.12 EIGRP Metric

CCNP RS 300-101, Implementing EIGRP, Uncategorized

To formulate a best path, EIGRP uses a composite metric based upon the following values. These are called K values.

  • Bandwidth (K1) – Obtained from the lowest bandwidth value on any link in the calculated path. (For example, if you have 3 hops – 100Mbps-100Mbps-50Mbps – your bandwidth is 50.)
  • Delay (K3) – The cumulative delay for all hops within the path. This value is represented in microseconds, where 1 millisecond = 1000 microseconds.
  • Reliability (K4) – Based upon keepalives, is derived from the worst reliability between source and destination.
  • Load (K2) – The worst load on any given link between the source and destination. There are two factors which determine load: configured bandwidth of the interface, and the packet rate of the interface.
  • MTU (K5) – Not actually used in the normal path selection process. MTU is merely used to identify the preferred links when the number of possible equal-cost load-balanced paths exceed the configured threshold.

Two commands useful for tracking EIGRP Metrics and K values:

  • show interface (will list all metrics, including MTU, BW, DLY, reliability, and txload/rxload)
show interface <interface>
  • show ip eigrp topology <prefix> (Shows detailed information about all K values used in the computation of the composite metric.)
show ip eigrp topology <prefix>

Note: Only the K1 (bandwidth) and K3 (delay) values are normally used for EIGRP composite metric calculation. MTU is only used to determine load-balanced paths in special circumstances, and the K2 (load) and K4 (reliability) values are set to zero by default.

Default K Values are K1 = 1, K2 = 0, K3 = 1, K4 = 0, and K5 = 0.

You can issue the show ip protocols command to verify the K value settings.

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