[c-nsp] ASR9k: RIB/FIB convergence

[Thomas Schmid]

Hi Adam,

Am 02.08.2018 um 12:23 schrieb adamv0025 at netconsultings.com:
> First thing first,
> To mitigate the damage due to RIB-FIB inconsistencies you could use the: 
> "BGP-RIB Feedback Mechanism for Update Generation"
> "To configure BGP to wait for feedback from RIB indicating that the routes that BGP installed in RIB are installed in FIB, before BGP sends out updates to neighbors, use the "update wait-install" command in router address-family IPv4 or router address-family VPNv4 configuration mode."
>

good point. Haven't heard of this from Cisco yet. Will discuss this with the TAC.

> 
> Are you seeing any log messages indicating bottleneck between RIB and FIB please?

no. 

> Do you drop BGP updates on ingress with "as-path length ge 51" please? -not only it's a good practice, but apparently long as-paths caused RIB-FIB clogging in the past.
> 
> On your note regarding the apparent relation to number of peers.
> So how long does it take for the process to complete for the 200 peers nodes is it linearly proportional to the 20-30 minutes seen on 300 peers nodes please?> Or the relation between number of peers and time follows more of an exponential function (e.g. 290 all good and then 301 bang 30min) , in which case that could also indicate something special with those "delta" peers (e.g. some peers sending somewhat funky updates) (any slow peers btw?) 
>

to be more clear: the full 700k BGP updates are only sent to a small fraction of the e/iBGP peers (10-20).

The BGP updates are sent out without delay to the neighbors. Wrt. the number of sessions when things get bad, it's hard to tell since the number of routers is 8 with 4 ASR9000 and 4 ASR9900 (many BGP peers). Within the 4 ASR9900 it looks more or less linear.

Thanks,

   Thomas