How are you configuring BFD timers?

James Bensley jwbensley at
Thu Mar 22 08:47:32 UTC 2018

On 21 March 2018 at 16:37, Luke Guillory <lguillory at> wrote:
> He's asking because if it was dark the interface would go down when the link was lost and the router would pull routes. But PA to FL would lead me to believe it'll be a wave from some type of DWDM gear which brings us to BFD.

Could it not also help with a unidirectional failure of the fibre?
E.g. Loss of signal in only one direction might not bring the link
down, but if one BFD peer stops receiving BFD packets it'll bring the
link down.

On 21 March 2018 at 17:10, Jason Lixfeld <jason+nanog at> wrote:
> A few years ago I did some testing and found that the time between the transceiver detecting LOS and the routing protocol (ISIS in this case) being informed that the link was down (triggering the recalculation) took longer than it took BFD to signal ISIS to recalculate.

Have you looked at testing and adding this command to your IOS devices:

ip routing protocol purge interface

Also have you tried to set the carrier delay to zero?

carrier-delay down 0

I haven't compared them to BFD explicitly, but I would expect the two
commands together to have the same effect as you're seeing with BFD
(the link down is signaled to the IGP ASAP).


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