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Jan 27

EIGRP Delay Settings

Cisco EIGRP has the default behaviour of equal cost load balancing. It does that after calculation the metric which considers the minimum Bandwidth and total Delay along the path for a destination. Now, if there are equal paths available to a destination network and we don't want EIGRP to do equal cost load balancing we will be targeting to get metric calculations for both paths.

So, we can either change the bandwidth or delay on an interface to get the desired result. Usually changing the bandwidth is not the best possible option as we might have QoS policies configured on the interface and can be effected by changing interface bandwidth. The other option available is to change delay on router interface.

The question I had in my mind if router has incoming and outgoing interface, on what interface  I will be changing this delay.

Now, the question is on what interface we will be changing delay? The diagram below explains this in details. From Router R5 perspective, the cumulative delay it will be considering will be sums of delay on all Fa0/0 Interfaces on all routers.

We can change on any router's Fa0/0 interface and will effect the path selection for R5 or any other downstream routers. Now depends where want this metric to change. We can either do it on R1, R2, R3, R4 & R5's incoming Interface.

Now, the same goes for R1, from R1 perspective even if we change the bandwidth for Fa0/0 on one the routers in path, it would still consider network attached to R5 to be accessible from two equal paths. To change that we will have to consider changing delay on Fa0/1 interface on any of the in path routers.

Click on the Diagram below to get the large diagram.

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