bgp update destroying transit on redback routers ?

Jeff Tantsura jeff.tantsura at ericsson.com
Fri Dec 2 16:14:35 CST 2011


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 Data 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 and 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, 
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 going to disable ASN 0 check.

P.S. We have strong evidence that the update in question was caused by a bug on a freshly updated router (I'm not going to disclose the vendor) 

Regards,
Jeff


-----Original Message-----
From: Alexandre Snarskii [mailto:snar at snar.spb.ru] 
Sent: Friday, December 02, 2011 6:36 AM
To: Jeff Tantsura
Cc: nanog at 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,
> 
> Let me take it over from now on, I'm the IP Routing/MPLS Product 
> Manager at Ericsson responsible for all routing protocols.
> There's nothing wrong in checking ASN in AGGREGATOR, we don't really 
> want see ASN 0 anywhere, that's how draft-wkumari-idr-as0 
> (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: 

If a BGP speaker receives [bad route] it MUST close session immediately with NOTIFICATION Error Code 'Update Message Error' and subcode 'Error with optional attribute'.

--
In theory, there is no difference between theory and practice. 
But, in practice, there is. 




More information about the NANOG mailing list