EIGRP uses composite metric and K-values to calculate preferred path to a destination.
The formula for computation of EIGRP metric is –
EIGRP metric = [K1 * bandwidth + (K2 * bandwidth) / (256 – load) + K3 * delay] * [K5 / (reliability + K4)]
It’s important to understand where to find the K-values in the Cisco network devices. The command “show interfaces (interface name)” will provide the detail of all the K-values i.e. Bandwidth, Load, delay, Reliability and MTU.
Another important show command to show the K values presently used the cisco device (default values) –
Now, let’s understand from an example scenario which will illustrate how EIGRP composite metric is calculated for Network 220.127.116.11/24 (Loopback 0 of Router R1). Routers R1, R2 and R3 are all connected in series with Loopback 0 of R1 (IP =18.104.22.168/24) advertised in EIGRP domain. We are considering default K-values calculation mechanism i.e. K1 = K3 = 1 and K2=K4=K5 = 0.
Computation formula –
As above, the minimum bandwidth will be decided from one of the 2 i.e. (1) Loopback 0 of R1 (2) Interface fa0/0 of R2. For computation, bandwidth of 10000 Kbps of R2 interface Fa0/0 will be used since it’s the minimum of the 2.
As above, the minimum bandwidth calculation will be taken from one the 3 interface bandwidths (1) Loopback 0 of R1 (2)Interface Fa0/0 of R2 (3) Interface Fa0/1 of R3
For Delay calculation, again sum of following interfaces will be considered – (1) Loopback 0 of R1 and (2) Interface Fa0/0 of R2 (3) Interface Fa0/1 of R3. Hence total Delay (in microsec) comes out to be 5000 + 1000 + 1000= 7000 Microseconds.
Now we have clear understanding of EIGRP composite metric is calculated by K values. In the above case the default values of K1 and K3 were used while calculating the composite metric for destination.