EIGRP K-VALUES

 

eigrp-k-values

EIGRP uses composite metric and K-values to calculate preferred path to a destination.

Below table details on the 5 K-value types and corresponding default Cisco value on devices while calculating EIGRP metric 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.eigrp-k-values

Another important show command to show the K values presently used the cisco device (default values) –

“Show ip protocols”eigrp-k-values

Now, let’s understand from an example scenario which will illustrate how EIGRP composite metric is calculated for Network 1.1.1.0/24 (Loopback 0 of Router R1). Routers R1, R2 and R3 are all connected in series with Loopback 0 of R1 (IP =1.1.1.1/24) advertised in EIGRP domain. We are considering default K-values calculation mechanism i.e. K1 = K3 = 1 and K2=K4=K5 = 0.

 

Computation formula –

Metric for network 1.1.1.0/24 = 256 * (10^7/BW in Kbps) + 256 * (Sum of delay in Microsec/10)eigrp-k-values

On Router R1, since Loopback 0 (1.1.1.0/24) is directly connected, hence the metric comes out to be 0. Now let’s see how R2 interprets metric for reaching Loopback 0 of R1 –eigrp-k-values

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.eigrp-k-values

For Delay calculation, sum of both the (1) Loopback 0 of R1 and (2) Interface Fa0/0 of R2 will be taken. Hence total Delay (in microsec ) comes out to be 5000 + 1000 = 6000 Microseconds.eigrp-k-values

The final computation of metric for R2 to reach Loopback 0 of R1 comes to be 49600.Now let’s understand how R3 computes the Metric to reach Loopback 0 of R1.eigrp-k-values

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

Since the minimal bandwidth is 10000 Kbps on Fa0/0 of R2 and Fa0/1 of R3, the same will be used in computation as shown in above diagram.eigrp-k-values

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.eigrp-k-values

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.

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One Response

  1. Marcus Vinícius da Silva
    June 1, 2018

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