Robert, Tony,
Please find below some clarification regarding gshut
(draft-ietf-grow-bgp-gshut):
- the g-shut community in itself has no effect on BGP path selection
- when the eBGP session is being g-shut,
- on the iBGP side, routes (from the eBGP session beeing gshut) are
readvertised with a low LOCAL_PREF (e.g. 0).
- on the eBGP side, routes (from the eBGP session beeing gshut) are
readvertised with the ghsut community. Then (if the neighbor AS is willing to
use g-shut), on the AS boundary (eBGP), routes having the g-shut community are
set to a lower LOCAL_PREF.
So in both involved ASes, route are de-preferenced because of the lower
LOCAL_PREF. (not by iBGP routers interpreting the g-shut community).
Regards,
Bruno
>From: Robert Raszuk >Sent: Wednesday, May 09, 2012 11:00 PM
>
>Jeff,
>
>I do not understand why we are not going to re-advertise "good" routes
>with lowest local preference which would not result in holes of some
>boxes understanding g-shut community and some not.
>
>In fact I spoke to Bruno in the past on that and I was hoping we all
>converged that g-shut community would be used only on the EBGP side to
>indicate to the peer that it should in turn lower local pref on his
>side. Apparently g-shut draft still calls for this new community to be
>used both on iBGP and eBGP side.
>
>Regards,
>R.
>
>> On Wed, May 09, 2012 at 03:32:52PM -0500, Tony Li wrote:
>>> Understood. I have no issues with withdrawn routes. The issue is with g-
>shut routes that continue to sink traffic.
>>
>> Perhaps I'm unclear on your reservations.
>>
>> If we don't go through something like graceful shutdown and leave the
>> peering session up, we're potentially going to pull significantly more
>> traffic toward the "bad" peering session than if we didn't do such a thing.
>>
>> -- Jeff
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>
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