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

[James Bensley]

On Thu, 30 Apr 2020 at 10:13, Saku Ytti <saku at ytti.fi> wrote:
>
> On Thu, 30 Apr 2020 at 11:33, James Bensley
> <jwbensley+cisco-nsp at gmail.com> wrote:
>
> > APE has a wavelength from provider A to P-1 and a 2nd wavelength from
> > provider B to P-2. I’ve asked each provider for a 2nd wavelength from
> > me PE to P-1 and P-2, to increase the core facing capacity of the PE.
>
> I just don't think the topologies are realistic for BW based. It's
> just the lower BW links are then useless and never used, and wasted
> money. Idea that I'll rather travel exactly 9 10GE links than 1 1GE
> link is ridiculously atypical.
>
> If you have BW problems, then you want some sort of idealised latency
> metric and RSVP to put traffic on the best possible path with BW
> remaining.

None of these methods are perfect. For sure, bw based is flawed as you
said above, hoping 9 hops vs. 1 in a cross-country scenario would be
bad for most typical service providers, hopping 9 hops instead of 1
across an inner city metro however is virtually unnoticeable to the
average user.

Equally and adversely; what do you do in your scenario above when you
have if you have 1.000001Gbps of traffic between that ingress PE and a
remote egress PE? If you actually only have less than 1Gbps of
traffic, why do you have 10G links if you only have sub-1Gbps of
bandwidth, that is wasted money on 10Gbps links? The problem in that
scenario is surely that you have at least 1Gbps of traffic, which is
what justified the spend on 9x 10Gbps, and that the 1Gbps link still
hasn't been upgraded yet to match the other 9x 10Gbps links you have,
so actually bw-based metrics in that scenario, would have prevented
congested.

My point is that it's all about context. We'll have to agree to
disagree perhaps, because I think there is a place for role based
metrics, latency based metrics, a combination of both, and bw based
metrics, and I don't think bw based is that uncommon or unusual.

Cheers,
James.