North American Network Operators Group

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Re: Operational impact of depeering

  • From: Tom Vest
  • Date: Mon Oct 10 09:49:56 2005

On Oct 10, 2005, at 9:28 AM, [email protected] wrote:

It would be great if we could shift focus and think about the
operations impact of depeering vs. just the political and/or
contractual ramifications.

Have there been any proposals put forth to the NANOG PC to review
this highly visible depeering at the NANOG meeting this month?
Aside from anything else, there is this interesting topic
on the agenda:
Abstract: NetFlow-based Traffic Analysis Techniques for Peering Networks
Richard Steenbergen, nLayer Communications, and Nathan Patrick,

Seems to me that a discussion of traffic analysis could
handle a slide or two on actual impacts of this depeering.

--Michael Dillon
Here's one way of looking at it:
(copied below b/c the list is not publicly archived)


From: Tom Vest <[email protected]>
Date: October 8, 2005 6:00:32 PM EDT
To: Telecom Regulation & the Internet <CYBERTELECOM- [email protected]>
Subject: Re: [CYBERTEL] [ misc fyi ] internet "peering" breaking down (fwd)

Okay now that the flap is over and I have a few minutes to spare, I'll bite.

On Oct 6, 2005, at 10:34 AM, Peter R. wrote:

Your passionate response deserves a response:

It's not very small indeed.
Compared to what?

On 10/1/05, Cogent's network (AS174 -- a very old network) originated the equivalent of 1x /8 + 1x /9 -- that's 1.67% of the "ends" that constitute the global end-to-end network that we call the Internet. Same day/time, Level3's network (AS3356) originated the equivalent 2x /8 + 1x /9 -- or total Internet production 3.05% at that point in time.

Note: numbers are derived from the Route Views archive: snapshot-2005-10-01-0000.dat.bz2.

In an RFC 1930/2270 compliant world, 99% of networks downstream of either disputant have other, unaffected upstreams, so presumably they don't lose reachability to anyone.

Maybe there are 1b Internet users worldwide, and maybe they are distributed roughly in proportion to the distribution of Internet production. So maybe 5% of the world population was affected by the dispute -- roughly 5m users.

But affected how/how much? If every network end controlled by Cogent and L3 is no more and no less attractive than every other network end, then those 5m users are going to have real problems with roughly 5% of their Internet requirements. In the universe of end-to-end connections, roughly (0.0167 * 0.0205) potential links have been severed -- equivalent to 0.00034235 of the total. If you prefer, make the denominator US Internet production, which is about 60% of the global total on any given recent day. Assume that every US citizen is a user, and cares only about US Internet resources, and you come up with roughly 8% of the national user base having trouble with 8% of their connectivity needs -- that's still one- tenth of one percent of the theoretical (US-US) connectivity total.

And now we know that the problem solved itself in about 48 hours.

Assume that this is excessively simplistic, because of course Cogent and L3 host much more important/active users and content, because there are lots of non-compliant single-homed networks that are also affected (assume also the non-compliant networks are not responsible for their failure to conform to expected use for an ASN). Assume it is unrealistic because some other RFC-compliant networks are multi-homed to tier-2 ISPs that themselves depend significantly on the two parties. Add your own caveats on top of the above; apply your own fudge factor to the numbers until you feel comfortable with them. How skeptical do you have to be, how different do you have to assume the Internet is, or L3 and Cogent are, in order to get to a point where this episode rises to a level of importance sufficient to demand a national or global regulatory solution?

Many ISPs are single-homed to either one or the other.
What such ISPs contribute to Internet production is either counted among the IP originated directly by AS 174 or AS3356 -- i.e., in the numbers I calculated above -- or they are multi-homed (per RFC 1930), and were not stranded by the depeering -- or else they are out of compliance with the terms under which ASNs are now allocated, under which the broad architecture of the Internet is now interpreted and administered.

For instance, some Dial-up users of Alleron, purchased by Cogent, are stranded.
I don't understand what "stranded" could mean in this context. Cogent has many other direct connections to many networks other than Level3. Are you saying that the Cogent-controlled Alleron subscribers had some unique absolute dependency on connectivity with L3, or merely that they, like other Cogent customers, couldn't reach the (3.05%) share of global Internet resources that are directly controlled by L3?

A depeering between *peer* ISPs is not like a phone outage -- even under the most extreme circumstances, you lose only reachability to the Internet resources directly controlled by the counterpart ISP.

Sites hosted by PSI were stranded, like DrudgeReport. (Poor baby). It hurts the smaller ISPs more than, say, L3.
Same question, same skepticism. Henceforth, DrudgeReport will consider moving, mirroring, or multi-homing -- and in the mean time, Cogent customers who are regular DrudgeReport readers get a chance to enjoy the remaining 96.95% of the Internet that was completely unaffected, even for them.