[j-nsp] JUNOS precision-timers for BGP

[Adam Chappell]

Does anyone have positive or negative experience with this feature in 14.1
please?

Currently in a situation troubleshooting consequences of high CPU usage
with a number of aggravating factors. Most sensitive to the scarcity of CPU
resources however is a number of BGP sessions with aggressive timers.

Quite often a commit operation seems to make rpd block sufficiently enough
(or indeed it's already starved out by other processes) to neglect
keepalives for these unforgiving BGP sessions and we end up losing them.

Juniper have recommended to us consideration of "precision-timers", a
global BGP knob which, if I understand it well, offloads all of the crucial
BGP session management functionality to a different rpd thread in order to
leave the main thread able to handle config requests etc. - not too
dissimilar to the session management separation in openbgpd etc.

The Juniper documentation says this feature is recommended for low hold
timers, and from what we can ascertain rpd is able to transition to
off-thread session management without a down/up which is pretty neat.

I'm aware of PR1044141 which apparently causes pain when used in
conjunction with traceoptions, but I'm keen to understand if others have
operational experience.

We're also making inroads to lower CPU demands through the use of
distributed PPM etc., but the regular pattern I tend to see there is that
this doesn't fly once the PPM'd protocol has a security knob added, eg.
adding authentication to BFD, VRRP etc.

-- Adam.