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

[Marcin Kurek]

Hi Adam,

Thanks for the reply. I'm still in doubt though.

If we look here for example:

https://xrdocs.io/ncs5500/tutorials/ncs5500-fib-programming-speed/

we see that BGP programming speed is always faster than FIB programming 
speed.

If best path is advertised regardless of the FIB state by default, this 
would always mean a potential for longer/shorter blackhole...

Thanks,
Marcin

W dniu 26.02.2020 o 14:13, adamv0025 at netconsultings.com pisze:
> 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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