BGP Session Teardown due to AS_CONFED_SEQUENCE in AS4_PATH

Rob Shakir rjs at
Tue Jan 20 14:33:14 UTC 2009

On Tue, Jan 20, 2009 at 01:01:03PM +0100, Mikael Abrahamsson wrote:
>> have been able to demonstrate that a device running Cisco IOS release  
>> 12.0(32)S12 behaves as per this description.
> Has anyone looked into IOS XR behaviour, if it's the same as 12.0(32)S12?


Pierfrancesco Caci was kind enough to provide me with some output from an XR
box. It appears that IOS XR behaves in the same manner as Force10, and JunOS,
whereby the session is not torn down, and the path is installed, albeit with a
munged AS_PATH. The output below is for the prefix from 196629 which we
originally analysed:

Path #1: Received by speaker 0
   3356 35320 3.21 23456

Given that XR box is an AS4-speaker, one would not expect to see 23456 in the
AS_PATH, the prescence of this AS seems to be a symptom of the bug (and again
occurs on Juniper/Force10).

Kind regards,

Rob Shakir                      <rjs at>
Network Development Engineer    GX Networks/Vialtus Solutions
ddi: +44208 587 6077            mob: +44797 155 4098
pgp: 0xc07e6deb                 nic-hdl: RJS-RIPE

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