[14962] in North American Network Operators' Group
Re: with a flap flap here and a flap flap there...
daemon@ATHENA.MIT.EDU (Sean M. Doran)
Wed Feb 4 13:18:24 1998
To: Marc Slemko <marcs@znep.com>
Cc: nanog@merit.edu
From: "Sean M. Doran" <smd@clock.org>
Date: 04 Feb 1998 10:10:16 -0800
In-Reply-To: Marc Slemko's message of "Sun, 1 Feb 1998 21:28:48 -0700 (MST)"
Marc Slemko <marcs@znep.com> writes:
> 3333 6905 5623 1136 3300 7018 6478 1 701 814 7189 1691 852 6171 (history entry)
> Am I the only one that has a problem with this? You withdraw a
> route once, and it has flapped enough to be dampened in numerous
> places. I could have been half convinced that we had gone back to
> distance vector routing seeing this going on...
BGP *is* a distance-vector routing protocol.
What you were witnessing was a counting-to-infinity
problem that is bounded by timers and toplogical constraints.
Welcome to the wonderful world of BGP == RIP.
This is precisely why a mechanism which constrains
the amount of prefix transitions is so important:
magnification of flapping is predictable.
However, welcome to the wonderful world of lack of
filtering, too. There is no apparent reason why a number
of those ASes should have reannounced your routes to each
other. Each BGP peering (customer and peer alike) should
either explicitly allow announcements only from a list of
appropriate ASes, or explicitly disallow announcements
which have been through peers and (at least large) other
BGP-talking customers. This is an Incredibly Smart Thing To Do.
On a Cisco, the _ operator is your best regexp friend...
Sean.
