[c-nsp] ospf auto-cost reference-bandwidth on modern gigabit networks

[Mark Tinka]

On 29/Apr/20 17:16, Saku Ytti wrote:

>
> To me this never made any sense. It's a very atypical case where you
> want your topology to be link-bw based. The most common use-case is,
> you want distance metric, i.e. everything is equal, and you want least
> amount of hops. The 2nd most common case is role-based, that you have
> P-P lower metric than P-PE so you don't transit via PE and so forth
> (but each P-P are largely equal, due to topology having few options to
> target PE) and the 3rd most common is to have idealised latency based
> metric, so that you can model best path on nTh failure (to have bw)
> with RSVP.
>
> Reference bandwidth sounds like a very niche scenario where it would
> be sensible.

So we design metrics based on:

  * Device function (P, PE, P/PE or LAN).
  * Bandwidth.
  * Latency.

We calculate a coefficient that takes all those 3 above into account to
ensure that the right device is always carrying the right traffic over
the fastest and shortest path.

Mark.