Marc Slemko <marcs@znep.com> writes:
But the loop avoidance from having paths constrains you to the width of the Internet in terms of ASes. It isn't completely a distance vector protocol.
Yakov Rekhter also made a similar observation. I was caught up in rhetoric and was imprecise. (I could also be wrong; it happens.) BGP records paths and the loop avoidance scheme prevents a count-to-infinity problem in a way slightly better than RIP with split horizons does. In a network like this: C /| A--B< | \| D if A-B goes down in a split-horizons RIP network, there can still be a count-to-infinity problem between C and D announcing reachability to A. BGP does not have this problem. However, a withdrawal of a network from D can cause A to see a transition from ABD to ABCD to unreachable. This effect is what was complained about in the message I initally followed-up to. BGP is also not formally a distance vector protocol because the AS_PATH attribute is a trail of breadcrumbs rather than a distance. However, I argue that in common practice, it is a distance, and offer up AS-path prepending to affect path selection remotely as evidence.
I guess I'm just suprised at how wide the Internet has grown and at the lack of noticeable public acknowledgment of the resulting problems.
I'm not so surprised by the first bit, and I think I have become jaded about the second. Sean.