Peering versus Transit

From: Sean Doran <>
Date: Sun, 29 Sep 1996 23:41:28 -0800

In one hypothetical case, consider a large provider that
is being dumped upon by another provider which is
outraged that the large provider consistently refuses to
peer with them. This could have the result of pushing
traffic inbound towards the larger provider over the
threshold at which the difficulties in buffer management
become highly noticeable, which leads to some 15% packet
loss at times for customers of the larger provider trying
to make use of that exchange point.

(Leaving out the over-the-water case for the moment)

I don't understand. Let's hypothesize an exchange point at which NSPs
S, M, U all meet and peer, and which also includes N, the new provider
who buys transit from U and somehow (How? Maybe by peering with M) has
a router on the switching fabric at the exchange point.

Packets from N for S's customers therefore are supposed to flow from
N's router to U's router to S's router, yes? One day, N decides to
save the double hop through the switching fabric, and puts in a static
route for (some of) S's customers so that packets flow directly from
N's router to S's router. Certainly this is unauthorized. But how
has the rate of packets into S's router changed? Moreover, the return
path is still S->U->N, so there's no reason to expect that the packet
rate through S's router will be different in and out.

All this would be quite different if N pointed default to S, I agree.
It would also be different if for some reason S did not advertise all of
its customer routes to U's router at this particular exchange point. Is
that actually done, and is this relevant to the over-the-water case?

Barney Wolff <>