Global Crossing Contact / BGP and SONET interaction question

Ian Mason nanog at
Wed Jul 26 13:03:25 UTC 2006

On 26 Jul 2006, at 08:29, Forrest W Christian wrote:

> Randy Epstein wrote:
>> I don't have an answer to the root cause of your problem, and I'm  
>> not looking for a discussion on route dampening (there are enough  
>> debates onthis issue to make your head spin), but may I suggest  
>> you raise your hold timers to prevent your BGP sessions from going  
>> down on short disturbances as these?
> From what I can tell the disturbances are less than a second in  
> duration.   It doesn't appear that this is a hold-timer issue,  
> although I would like GX to set it at something higher than 90  
> seconds (mine is already at a higher value- but the lower value  
> wins during negotiation).    I really suspect that either a) GX has  
> some semi-weird configuration where the SONET ring switching from  
> the normal to the protect path and back causes BGP to reset on the  
> border router I'm attached to or b) There is a separate issue which  
> is causing BGP to flap.  Or of course, something else completely  
> different.
> Unfortunately, I haven't been able to figure out how to talk to  
> anyone at GX which actually has access to the routers and knows  
> anything about BGP.
> -forrest

The timing of protection switching on a SONET ring is of completely  
the wrong order to upset a BGP session. From memory there's a  
designed in upper bound of 200 mS from fault to fully restored with  
typical values being more like 50 mS.

One possibility that occurs to me is that the A end here might be  
using a router with a SONET card, and the router software is  
propagating a SONET event through the stack causing BGP to react to  
an event it wouldn't even see on a physically separate SONET ADM.  
That is pure speculation though.

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