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

[Saku Ytti]

On Sat, 2 May 2020 at 04:26, Benny Lyne Amorsen via cisco-nsp
<cisco-nsp at puck.nether.net> wrote:

> You can make things more reasonable by simply taking the square root of
> the bandwidth before calculating the metric. Or logarithmic, if you
> prefer.
>
> It is not perfect, of course, but nothing is.

I think anything you do with a BW basis is going to be undesirable
SPT. This is why I think the default is so harmful, it precludes
people from thinking what should their SPT be, because it tends to
work good enough. When it does work, the x9 is actually proxy for goal
of 'never', the topologies where the behaviour is desirable they never
want to go from high-speed => low-speed => high-speed, and as long as
9x is a reasonable proxy for 'never' the SPT works reasonably for many
use-cases. But rarely it is the behaviour they actual desire. The
right behaviour in this example would be to replace the 9x proxy at
speed borders with link-penalty which guarantees high=>low=>high won't
happen, not just hope.

If SPT would do some unequal balancing based on metrics, then
discussion might be very different, and I think somehow
intuitively/subconsciously people think something like this happens 'I
will have 10x less traffic on my 1GE links'.


-- 
  ++ytti