Flapping prefixes and dialup networks. Discuss.

Sean Doran smd at icp.net
Mon Sep 11 05:05:25 UTC 1995


I sent a network provider (who shall remain protected 
by a pseudonym like "AS 174") a brief note stating that
they had a prefix that was flapping rather heavily
throughout the day.

I cut and pasted a show ip bgp on the route, pointing out
that the prefix flaps on the order of once a minute and was
happily being dampened.  (cf. my comments Monday afternoon on

BGP routing table entry for, version 656911
Paths: (2 available, no best path)
  1239 174 (history entry) (metric 15) from (
      Origin IGP, metric 1, localpref 90, external
      Dampinfo: penalty 2915, flapped 199 times in 3:27:31
  1239 174 (history entry) (metric 15) from (
      Origin IGP, metric 1, localpref 90, external
      Dampinfo: penalty 2917, flapped 198 times in 3:27:07

I also asked this nameless service provider to kindly check
into this somewhat excessive amount of flap with a view to
seeing how it could be made to flap less.

Here was the reply.

Hopefully saner and more patient folks than me might point
out to service provider X that announcing to the entire
world when a dialup user comes and goes is not healthy for
the Internet, and it shouldn't happen, particularly not at
this rate.

Why I am not quite in the, "it doesn't matter, they'll
be dampened" frame of mind will get explained during
the NANOG session.

- --

>From nisc at psi.com Sun Sep 10 18:12:58 1995
From:	PSI NISC <nisc at psi.com>
To:	Sean Doran <smd at icp.net>
Subject: nisc-03292 (ticket update) badly flapping prefix (204.4.27/24)

Ticket #nisc-03292 	09/10/95-18:12:08 silvera 	SUBJECT: badly flapping prefix (204.4.27/24)
Posted by: Aaron Silver

	The customer that this network belongs to is a dial-up customer, and
as such, when his connection is up, we broadcast his network IP, and stop
broadcasting when he disables his connection. We are unable to prevent his 
route from propagating in the face of what could be frequent log-in/log-outs.

Aaron Silver
PSI Customer Support 

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