OSPF Costs Formula that include delay.

Graham Beneke graham at apolix.co.za
Sat Jan 25 06:10:54 UTC 2014

The auto-cost capability in some vendors devices seems to have left many
people ignoring the link metrics within their IGP. From what I recall in
the standards - bandwidth is one possible link metric but certainly not
the only one. Network designers are free (and I would encourage to) pick
whatever metric is relevant to them.

On 24/01/2014 22:26, Erik Sundberg wrote:
> I am looking for a formula that other people are using .p

I've started to use a combination of 3 metrics to determine my costing:

* The traditional auto-cost calculation based on a 100Gbps reference
which gives far more useful values than the old 100Mbps reference.

* An average or nominal link latency multiplied by a factor of 200.
Sometimes adjusted if I want two geographically diverse paths between
the same endpoints to have equivalent costs.

* Path length in km multiplied by 2. This accounts for situations when
the nominal latency is too small to accurately determine and assumes 1
ms per 100 km.

I then pick the largest of the above 3 metrics as my OSPF cost.

Graham Beneke

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