[c-nsp] bgp update wait-install - RIB/FIB inconsistency

[adamv0025 at netconsultings.com]

Hi Marcin,
There was a thread on the topic of slow FIB  download/upload on this forum
some time back.

Yes BGP will advertise the best path regardless of the FIB state by default.
I'd recommend enabling it. (though subject to testing on your code version
as always)

adam
> -----Original Message-----
> From: cisco-nsp <cisco-nsp-bounces at puck.nether.net> On Behalf Of Marcin
> Kurek
> Sent: Friday, February 21, 2020 10:40 AM
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] bgp update wait-install - RIB/FIB inconsistency
> 
> Hi all,
> 
> During a recent MW I ran into a fishy situation.
> 
> Long story short - ASR9001 running XR 6.4.2 SP4 was rebooted, after it
went
> back online I noticed slow route installation in FIB. It took around 20
minutes
> to install > 700k prefixes.
> 
> Apparently, some customers experienced problems at that time, so I'm
> suspecting some RIB/FIB inconsistency here.
> 
> I've been researching this topic for a while and now I'm even more
confused.
> 
> Can someone help me answer below questions, please?
> 
> Assuming our router has established its e/iBGP sessions and finished
> receiving updates from its neighbors, will it advertise its best paths
even
> though FIB programming is still in progress?
> 
> Common sense answer would be "no", because if it starts advertising
> prefixes that are not installed in FIB, it also starts attracting and
possibly
> blackholing traffic.
> 
> But I discovered the command "update wait-install" as part of BGP RIB
> feedback mechanism introduced in XR 4.3. When it's enabled, routes that
> have not been installed in FIB are not advertised. Looks like that it's
turned
> off by default though.
> 
> If so, the answer to my 1st question should be "yes", although to me, it
> doesn't make much sense.
> 
> I've been trying to find best practices / recommendations for that
command,
> but without luck.
> 
> Can anyone shed some light on that, please?
> 
> Thanks,
> 
> marcin
> 
> 
> 
> 
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