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

[James Bensley]

On Thu, 30 Apr 2020 at 09:58, Mark Tinka <mark.tinka at seacom.mu> wrote:
>
>
>
> On 30/Apr/20 10:33, James Bensley wrote:
>
> > Role based and metric based IGP costs are a good idea in theory. They
> > are a lot more difficult in practice. Another problem with role based
> > IGP costs is “who has more capacity between a pair of PEs than those
> > PEs have to their upstream P nodes”? If you find yourself in that
> > scenario, it isn’t role based IGP costs you need, it’s a long hard
> > look in the mirror.
>
> I disagree here.
>
> I've built - across 3 networks on 2 continents - role-based, bandwidth
> and latency-linked metrics in IS-IS since 2007.
>
> Each of these networks was differently sized, with the latest being the
> largest one, spanning several countries and 3 continents. So it does
> work in practice, but it's a concept that took me about a year to
> design, for each network.

Hi Mark,

You say you disagree, I didn't say it couldn't or shouldn't be done, I
said that "They are a lot more difficult in practice", and you said it
took you a year to design, so actually I think you agree with me ;)

> And yes, I have found myself in situations where "longer" links were
> required for service alongside "shorter" links due to some reason or
> another, e.g., backbone failure on the path, urgent need for more
> tactical capacity, e.t.c. That is okay. Networks are living things - you
> have to be able to react to situations even though you have fundamentals
> in place.

^ This! This last statement 100% "Networks are living things" <- that
is my point. Saku's advise reads to me that bw-based metrics can AND
should never ever be used unless there is no other choice. I am
disagreeing with *that*. There is a time and a place for each method,
and it depends on your context, not that one method is should be
preferred over another "unless you have to", each method should be
equally evaluated against the requirements.

Cheers,
James.