[j-nsp] improving global unicast convergence (with or without BGP-PIC)

[adamv0025 at netconsultings.com]

> Alexander Arseniev
> Sent: Wednesday, April 19, 2017 5:19 PM
> 
> Hi Michael,
> 
> JUNOS INH helps at FIB programming stage, not at BGP best path reselection
> stage. Additionally in recent JUNOS versions, there are improvements made
> regarding FIB programming speed, please ask Your Juniper account team for
> details.
> 
Yeah I've seen the preso but I'm not convinced. 
FIB programming time has always been a memory write limitation, router memories used for lookup are streamlined for read performance, sacrificing read performance to reduce the cost, so there's only so fast you can go and with the forwarding tables ever growing it's a lost battle, and a meaningless one as well, since we already have elegant solutions to work around this limitation. I mean it's good they're fixing crappy code to catch up with the actual HW limits at hand though.  

BGP+BFD would be my first choice. 
> would personally rate BFD as tool of last resort as (a) BFD being an UDP/IP
> protocol means there are many other failures  that affect BFD like access-lists
Well but misconfigured ACL is not a failure.  

> (b) even when BFD is down, the BGP session may be still up whereas You
> want the BFD to follow BGP 
Now how can that happen other than bug?  

> and (c) BFD failure does not bring the interface
> down, it just tears down the BGP session whereas LACP failure/EOAM failure
> brings the logical interface down. Presumably, someone will point out to
> uBFD over LAG but it still requires LACP so
> LACP+uBFD is overkill for a simple network UNLESS You are really into
> microseconds convergence. 

In my experience LACP+uBFD or LACP+LFM is BAU, unless you can afford to wait 3 seconds to detect link down in case L1 didn't kick in for some reason. 


adam

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