Outbound Route Optimization

Wed Jan 21 21:05:46 UTC 2004

>             My questions are these:
> 
> "Is sub-optimal routing caused by BGP so pervasive it needs to be
> addressed?" 

that depends on your isp, and whether their routing policies (openness
or closedness of peering, shortest vs. longest exit, respect for MEDs)
are a good match for their technology/tools, skills/experience, and
resources/headroom.

> "Are these devices able to effectively address the need?"

some of the devices i've seen will address some of the weaknesses in
some of the isp's i've seen.  however, and more to what i think is the
point here, none of the devices i've seen will make an isp better since
(a) tools alone can't help, and (b) this isn't the tool that's missing.

and now for the question you didn't ask... "why not?"

controlling which paths you install based on any kind of observational or
predictive metrics is theoretically only going to be as good as those
metrics, which is usually not very good.  but there's another limit, which
is bgp path symmetry.  most tcp implementations are still stone-aged
compared to what the ietf recommends in terms of congestion avoidance and
output timing, and are therefore pretty dependent on overall isochrony and
on symmetric congestion/latency.  let's say that you had ideal metrics for
deciding which path to install -- your overall performance would then be
limited by what other people chose to install as their path toward you.
(experience says they're not going to trust your MEDs even if they're close
enough to hear them.)
-- 
Paul Vixie