[147148] in North American Network Operators' Group
RE: bgp update destroying transit on redback routers ?
daemon@ATHENA.MIT.EDU (Jeff Tantsura)
Fri Dec 2 17:15:49 2011
From: Jeff Tantsura <jeff.tantsura@ericsson.com>
To: Alexandre Snarskii <snar@snar.spb.ru>
Date: Fri, 2 Dec 2011 17:14:35 -0500
In-Reply-To: <20111202143554.GA66539@snar.spb.ru>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
Hi Alexandre,
You are right, the behavior is exactly as per RFC4271 section 6:
"When any of the conditions described here are detected, a
NOTIFICATION message, with the indicated Error Code, Error Subcode, and Dat=
a fields, is sent, and the BGP connection is closed.
So because ASN 0 in AGGREGATOR is seen as a malformed UPDATE we send 3/9 an=
d close the connection.
Ideally it should be treated as "treat-as-withdraw" as per draft-chen-ebgp-=
error-handling, however please note - this is still a draft,=20
not a normative document and with all my support it takes time to implement=
.
Once again, we understand the implications for our customers and hence goin=
g to disable ASN 0 check.
P.S. We have strong evidence that the update in question was caused by a bu=
g on a freshly updated router (I'm not going to disclose the vendor)=20
Regards,
Jeff
-----Original Message-----
From: Alexandre Snarskii [mailto:snar@snar.spb.ru]=20
Sent: Friday, December 02, 2011 6:36 AM
To: Jeff Tantsura
Cc: nanog@nanog.org
Subject: Re: bgp update destroying transit on redback routers ?
On Thu, Dec 01, 2011 at 04:56:43PM -0500, Jeff Tantsura wrote:
> Hi,
>=20
> Let me take it over from now on, I'm the IP Routing/MPLS Product=20
> Manager at Ericsson responsible for all routing protocols.
> There's nothing wrong in checking ASN in AGGREGATOR, we don't really=20
> want see ASN 0 anywhere, that's how draft-wkumari-idr-as0=20
> (draft-ietf-idr-as0-00) came into the worlds.
This draft says that
If a BGP speaker receives a route which has an AS number of zero in the AS_=
PATH (or AS4_PATH) attribute, it SHOULD be logged and treated as a WITHDRAW=
. This same behavior applies to routes containing zero as the Aggregator or=
AS4 Aggregator.
but observed behaviour was more like following:=20
If a BGP speaker receives [bad route] it MUST close session immediately wit=
h NOTIFICATION Error Code 'Update Message Error' and subcode 'Error with op=
tional attribute'.
--
In theory, there is no difference between theory and practice.=20
But, in practice, there is.=20
