[c-nsp] Forcing BGP to propagate only after route is in the FIB

[Saku Ytti]

Hey Octavio,

> We are noticing our ASR 1002 is propagating BGP-learned routes to its
> neighbors after the path is chosen but before the route gets installed
> in the FIB.
>
> With the increasing size of the BGP table, this is causing race
> conditions that turn into traffic loops during convergence. The router
> attracts traffic but returns it back to somebody else because the route
> is not yet in the FIB or it is outdated in the FIB.
>
> Is there a way to force the router to wait until a route is installed
> all the way in the FIB before having it propagated to the neighbors?

I don't think so. This is issue which has plagued Juniper RPD for years.

Technically I believe fix would be to add flag to FIB entries
signalling HW presence. Then when HW installs it, it should raise
interrupt or such, to get this flag inserted. But it might be that HW
does not support this (At any reasonable performance).

I've personally not seen this yet (in bothersome level) in any Cisco
gear, so this is very interesting observation, I sort of assumed what
every Cisco is doing, they're doing in manner that they are protected
from this problem. Thanks for the heads up!

-- 
  ++ytti