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