Re: OSPF Costs Formula that include delay.

[Jeff Tantsura <jeff.tantsura () ericsson com>]

A path to a destination must be loop free, irrespectively.
So it is not a combination of multiple but rather a list of loop free paths to a destination where any other metrics 
are used as tie-breakers.
Another story - how do you get all that state distributed, inter-area cases, how do you make it actually useful ( LSDB 
vs TED ) and not to forget - FEC definition. 


Regards,
Jeff

> On Jan 24, 2014, at 10:13 PM, "Graham Beneke" <graham () apolix co za> wrote:
>
> 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