Was [Re: Sprint peering policy]

Sat Jun 29 16:48:01 UTC 2002

Stephen,

>> I think this is the key point. Its common sense that peering
>> with the downstreams will improve user quality of service by
>> both reducing latency and taking unnecessary points of failure
>> out of the network. 

Is it really common sense? If so, is the common sense correct?
In fact, there is a lot of recent work that suggests that there
can be a very poor (and as it turns out poorly understood)
interaction between richness of interconnection and BGP dynamics;
this is due, at least in part, to amplification and coupling
effects that appear in some large systems. So many argue that 
that given the current set of protocols (i.e. BGP and its
implementations), increased topological richness beyond some
threshold can actually hurt robustness and reliability. And just
to be clear about this, this is not a statement about peering
policies themselves (I'm explicitly not commenting on that), but
rather about our current understanding of some of the dynamics
that exist in today's Internet.   

I've been trying to capture some of this in the following
document (with the able help of Randy, Tim, and many others): 

http://www.ietf.org/internet-drafts/draft-ymbk-arch-guidelines-03.txt

On the topic of interconnection richness and its (possibly
unanticipated) effects, Craig and Abha's early work on this is
maybe the canonical reference. For something a little more
recent, see "What is the Sound of One Route Flapping", Timothy
G. Griffin,  IPAM Workshop on Large-Scale Communication Networks:
Topology, Routing, Traffic, and Control, March, 2002. 

In any event, I guess the bottom line here is that sometimes what
looks like common sense (or even what we have a tendency to call
"conventional wisdom") may just be wrong. 

Dave