[c-nsp] Cisco IOS ping utility reports lower RTT than possible

[Octavio Alvarez]

On 5/3/19 5:14 AM, Martin T wrote:
> Hi Octavio,
> 
> instead of a two-card laptop I used the available ports in server
> named "svr", but in principle I built the setup you described:
> 
> CISCO1921[Gi0/0] <-> [eno1]test-br[eno2] <-> [eno3]svr

I intended to have an independent measurement tool (including an
independent clock) but that should be good enough too, as it's highly
unlikely that you have serious clock drifting issues.

> Success rate is 100 percent (5/5), round-trip min/avg/max = 8/9/12 ms

> As seen above, minimum measurement was 8ms and average was 9ms.

I don't know how far (in ms) is the router from the server but max=12ms
also looks way off.

> Cisco IOS ping command inserts the timestamp into the payload of the
> ICMP "echo request" message and at least it seems to increment it, i.e
> that part seems to be fine.

Does it? If you are referring to the -ttt output than that is done by
tcpdump.

Good experiment. Sorry to say that I don't know why the measurements are
so inaccurate. I kow the Cisco ISR 1912 is a very low-end device but I
don't know if so enough to get into this level of inaccuracy.

Octavio.