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AS7170 flaps and resulting non-event

  • From: John Todd
  • Date: Thu Dec 02 02:25:26 1999



Starting on the 19th of this month, the Merit routing report shows that AT&T-DISC(AS7170) is having some serious flapping issues with the Merit route server at the MAE-East (ten million updates in a day, as an example.) Among other things, I'm interested if these flaps are being made to all peers of AS7170 at the MAE-East. If that is the case, then nobody has noticed, or nobody cares, or nobody has raised it in a public forum yet. If the silence has been caused by one of the first two situations, I'm interested in which is the true reason that there has been no hue and cry over this abnormal number of route insertions/removals.


A few questions and items to chew on:
1: Is this something that anyone other than Merit is noticing? Could it be that AS7170 just doesn't have that many peers, or that the routes are flapping only to Merit's route server?
2: Is this just being dampened to the point where nobody notices?
3: Is the silence on this issue somehow indicative of the increased speed/memory of core routers in the North American and other routing structures? [main point] If so, then this changes some arguments about who and why one will/will not peer, as well as dragging the corpse of "Sprint filtering" out of the grave.[/main point]
4: Am I just reading this data incorrectly? I don't have a direct peer with 7170 anywhere, so I can't look at my own records for double-checking.


Side notes:
A: This isn't AT&T's only AS number - they have two others (7018 and 5075) that seem to be used for quite a few announcements. In fact, 7170 may not be the "primary" AS for AT&T - again, I don't have a crystal ball to see how they structure their announcements across the multiple AS'es.
B: It's not easily possible for me to find which routes were flapping; could this be just a few routes out of the N that 7170 announces? (See http://www.merit.edu/~ipma/cooked/routing_table/view_in/mae-east/mae-e ast.7170.view.991128 for an exhaustive list of 7170's routes to Merit on the 28th) If it's only a few of the routes, then perhaps dampening by peers simply quashed the rogue networks into oblivion without anyone noticing that these few routes were missing.
C: Could this be related? http://www.infoworld.com/cgi-bin/displayStory.pl?99121.icatt.htm I don't think so, but it's an interesting note nonetheless. I don't see how DNS could be attached to the route flaps, but again I don't have a crystal ball into AT&T's network.

I've included selected sections from Merit's daily route flap mail. To see a complete list of the messages, browse to http://www.merit.net/mail.archives/html/routing-problems/ for more detail.

Largest Sources of BGP Instability
----------------------------------
(announcements + withdraws = total)

Dec 01: 1. AT&T-DISC (AS7170) at Mae-East 10432535 + 36800 = 10469335 BGP prefix updates
Nov 30: 1. AT&T-DISC (AS7170) at Mae-East 10432535 + 36800 = 10469335 BGP prefix updates
Nov 29: 1. AT&T-DISC (AS7170) at Mae-East 11122216 + 16465 = 11138681 BGP prefix updates
Nov 28: 1. AT&T-DISC (AS7170) at Mae-East 10256555 + 17732 = 10274287 BGP prefix updates
Nov 27: 1. AT&T-DISC (AS7170) at Mae-East 9882016 + 23527 = 9905543 BGP prefix updates
.
. [similar results in here]
.
Nov 19: 1. AT&T-DISC (AS7170) at Mae-East 2462647 + 93171 = 2555818 BGP prefix updates

[AT&T-DISC does not show up in the mail from the 18th or 17th, leading me to think these flaps started during the measured interval reported on the 19th.]

---
JT
[email protected]