Latency on gateway

[mulbreizh]

Hello and sorry for my english,

I have all switch connect to Cisco 3850. I have also physicals servers and Wmware.

When i ping from servers, physical or not the gateway who is on C3850, the latency is very high, it can be 1ms and next 50ms, next 100ms, next 1ms. So it is very high.

But when i ping from one server connect to Cisco 3850 to an other server behind the 3850, the ping is very good, always 1ms.

What could be the explaination ? why the ping to the 3850 is very high ?

thanks

[mulbreizh]

the model of the switch is : 

WS-C3850-48XS

and version 

6.12.09

[MHM Cisco World]

you meaning 16.12.09 ?

MHM

[mulbreizh]

yes 16.12.09

[Joseph W. Doherty]

Sounds perfectly normal.

What's important is your ping times through the switch.

When you ping any host, generally responding to a ping, such is considered low priority.

Switches generally have dedicated hardware to support their data plane.  Pings, though, would normally be supported on the control plane, which, again, treats pings with low priority, so low in-fact, switch might not respond to all pings.

Also understand, pings were only really designed to try to determine if a host is "alive", not as a high precision performance measurement protocol.  However, Cisco has a special variant of pings, for SLA purposes, which tries to much better provide network latency by excluding host response latency.

Oh, if you're wondering how the switch can be so slow to respond to a ping when your CPU stats are not excessively high, because CPU loading isn't shown at millisecond intervals, it is a longer time period average measurement.

[mulbreizh]

but 150ms sometimes, that is very high

[Joseph W. Doherty]

Yes150 ms is high, but so what?  What's being impaired?  If I understood your OP correctly, nothing else, correct?  I.e. is any production or operational traffic or services impaired?

BTW, in one of your follow-on posts, you mentioned CPU occasionally hits 60%.  When I described pings are generally control plane, what I didn't mention, control plane is generally supported by CPU.  So, if CPU, occasionally is busy, and ping processing is low priority, that can cause delayed ping replies.

If what I suspect is the issue, you might work on determining why your CPU hits 60%, with the goal to mitigate, or determine if your 3850 supports the SLA ping responder, and try it for its latency response (the latter will also require a device that can generate SLA pings).