Hi Marcin, Well yes you’re right, hence the path in form of a “update wait-install” feature,
Though the best remedy to this slow FIB programming problem is to maintain the FIB entries no matter what, Opt1 Having two sessions on a single box in case one fails the other will keep the FIB entries in place -just NH changes would follow -which in todays hierarchical FIBs is a single pointer change operation. Opt2 “advertise best external” feature so in case you have a box with just a single eBGP session it learns prefixes via iBGP from some other border node with the “advertise best external” feature enabled. adam From: Marcin Kurek <[email protected]> Sent: Friday, February 28, 2020 1:19 PM To: [email protected]; [email protected] Subject: Re: [c-nsp] bgp update wait-install - RIB/FIB inconsistency 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/> 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, [email protected] <mailto:[email protected]> 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 <mailto:[email protected]> <[email protected]> On Behalf Of Marcin Kurek Sent: Friday, February 21, 2020 10:40 AM To: [email protected] <mailto:[email protected]> 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 _______________________________________________ cisco-nsp mailing list [email protected] <mailto:[email protected]> https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/ _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
