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Re: bgp update destroying transit on redback routers ?
From: Olivier Benghozi <olivier.benghozi () wifirst fr>
Date: Thu, 22 Dec 2011 14:20:21 +0100

Aha, it looks that our Quebecer friends from Hostlogistic (AS46609) have again been advertising their now famous funny 
aggregate with their mad Brocade router, since yesterday 10pm UTC (that is 5pm in Quebec)...
Same route to, same AGGREGATOR attribute full of 0.

At least I can say that the patched Ericsson's bgpd stopped reseting the sessions.


Le 2 déc. 2011 à 23:14, Jeff Tantsura a écrit :

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) 


-----Original Message-----
From: Alexandre Snarskii [mailto:snar () snar spb ru] 
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:

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 

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'.

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