[j-nsp] What exactly causes inconsistent RTT seen using ping utility in Junos?

[Saku Ytti]

Hey Martin,

> This is well know behavior and documented in several KB articles.
> However, what exactly causes this?

I think just CPU doing something else before given time to do the ICMP
packets. Like busy running some RPD task. You are facing uphill battle
if you need to rely on precise ICMP echo times, it is of course
technically possible, but will not be easy to convince vendor that it
is needed.

> Based on this information I changed the CoS configuration in two MX
> series routers. First I tried with vMX(runs in performance mode) and
> configured RE-sent ICMP "echo request" messages into forwarding-class
> named "ef" and associated this class with low-latency queue:

This won't do anything, this is only applicable for forwarding-plane
traffic. For control-plane you want 'set class-of-service
host-outbound-traffic forwarding-class ef'. However this won't do
anything to give CPU scheduling priority on sending and receiving ICMP
messages.

-- 
  ++ytti