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" <gra...@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 >