Verio Decides what parts of the internet to drop

Dr. Li wrote:

Date: Fri, 03 Dec 1999 23:35:18 -0800
From: Tony Li <>
Subject: Re: Verio Decides what parts of the internet to drop

I'll also note that this would also decrease the pressure on the address
space. No need to go get a /19 if I can get my /23 globally advertised.
The correlation with route flap should be re-examined. I suspect that this
is no longer a driving force and is more than adequately compensated for by
having flap damping parameters that scale geometrically with the prefix

To state an obvious extension of these ideas:

Without relief, space registrants are thus incented to (continue to) subvert the
spirit of the allocation scheme in order to overcome its deficiencies. In doing
so, a trend toward lower (shorter) "characteristic prefix length" is created by
networks that would otherwise be suited by smaller allocations closer to their
actual occupancy.

Metastability in interdomain routing is currently maintained by an algorithm [1]
that suppresses oscillations to an acceptable level, deferring treatment of
another "interesting problem" [2,3]. If distinctions between highly aggregated
networks and large, underoccupied ones are progressively obscured, strategies
that inversely correlate prefix length with oscillatory period may be

Past experience [*] suggests that further detraction from the elusive "global
routing stability" is more poignant and at greater issue to operators than the
combined problems of address occupancy and table population.

Indeed, it seems that a review of operational policy is in order.

Andrew Bender
Total Network Solutions, Inc.

[1] C. Villamizar, R. Chandra, R. Govindan. RFC 2439.
[2] K. Varadhan, R. Govindan, and D. Estrin. Persistent route oscillations in
inter-domain routing. USC/Information Sciences Institute, 1996.
[3] T. Griffin, G. Wilfong. An Analysis of BGP Convergence Properties. Computer
Communication Review, October 1999.

Based on past experiences, I would say that the big backbone providers
shouldn't do any filtering at all. Then, the lower tiers can do all the
filtering they want, and still rely on default routing to send the packets
to the backbone. It may not be the prettiest way to route traffic, but
this would allow smaller ISPs to filter if they cannot afford buying
bigger equipment to hold all the routes. Since the tier-1 guys are the
glue of the Internet, they should be required to take everyone routes.