From: Carlos Trujillo (carlos.trujillo.jimenez@gmail.com)
Date: Sat Mar 29 2008 - 11:06:41 ART
Gary, you are trying to manipulate the route path selection in a transit as
where you dont have control right?
Using AS path Prepending instead of setting metrics, ensures the whole bgp
domians see the prefixes marked with the # of ASs you prepended (because the
AS PATH attribute is TRANSITIVE and it propagates from AS TO AS) so there
you can manipulate the bgp transit pathway the packets choose not only in
the connection between your AS and your provider AS, but also in the TRANSIT
AS where you dont have any sort of control. Whit as prepending you can!.
Contrary to the MED attribute who is a NON-TRANSITIVE attribute where you
can ONLY control the packets pathway between your LOCAL AS and your NEIGHBOR
AS. When your provider AS recibes the route MARKED with the mettric
attribute the route gets passed to the NEXT AS with the attribute is
stripped off.
2008/3/29, Sadiq Yakasai <sadiqtanko@gmail.com>:
>
> Hi Gary,
>
> Yes, you can prepend AS_PATH information for transit prefixes on a
> router in BGP.
>
> I know you are a big fan of CCIE Routing and Switching Exam
> Certification Guide by Odom (second edition), check page 458 - 460 and
> you would find an example of what you are trying to accomplish.
>
> HTH
>
> Sadiq
>
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