high ping

[alpushkarev11]

                                 Hello.

I discovered a strange network  problem.  Network  Core consist from two 3750 in stack. There are 18 Vlans on Cisco 3750. 

 Each port of core connect to switch. When I ping  gate of the vlan, for example Vlan8,  I see that a time of ping change (1-16)

 proc cpu history at that time ~ 25-30 %

Reply from 192.168.8.1: bytes=32 time=2ms TTL=255
Reply from 192.168.8.1: bytes=32 time=2ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=2ms TTL=255
Reply from 192.168.8.1: bytes=32 time=2ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=3ms TTL=255
Reply from 192.168.8.1: bytes=32 time=3ms TTL=255
Reply from 192.168.8.1: bytes=32 time=3ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=2ms TTL=255
Reply from 192.168.8.1: bytes=32 time=2ms TTL=255
Reply from 192.168.8.1: bytes=32 time<1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=2ms TTL=255
Reply from 192.168.8.1: bytes=32 time=2ms TTL=255
Reply from 192.168.8.1: bytes=32 time=2ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time<1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=2ms TTL=255
Reply from 192.168.8.1: bytes=32 time=3ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=2ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=4ms TTL=255
Reply from 192.168.8.1: bytes=32 time=2ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=3ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=3ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=3ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=3ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time<1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=2ms TTL=255
Reply from 192.168.8.1: bytes=32 time=2ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255
Reply from 192.168.8.1: bytes=32 time=1ms TTL=255

Ping statistics for 192.168.8.1:
    Packets: Sent = 67, Received = 67, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 0ms, Maximum = 16ms, Average = 1ms
Control-C

==============================================

show proc cpu history

      222222222222222222222222222222222222222222222222222222222222
      444443333355555444442222211111333331111144444444445555577777
  100
   90
   80
   70
   60
   50
   40
   30           *****                                   ********
   20 **********************************************************
   10 **********************************************************
     0....5....1....1....2....2....3....3....4....4....5....5....6
               0    5    0    5    0    5    0    5    0    5    0
               CPU% per second (last 60 seconds)

      323232323232323232643232323232323232323432323232863232323232
      793535584625594657494757786635876735484146365875644425775747
  100
   90                                                 *
   80                                                 *
   70                                                 *
   60                   *                             **
   50                   **                            **
   40 *     *     *   * **  * * *   * *      *    * * **    * *
   30 #*******#*******#*#*****#*#***#*#******##*******##* **#*#*
   20 ##########################################################
   10 ##########################################################
     0....5....1....1....2....2....3....3....4....4....5....5....6
               0    5    0    5    0    5    0    5    0    5    0
               CPU% per minute (last 60 minutes)
              * = maximum CPU%   # = average CPU%

I

[Jon Marshall]

What happens if you ping from a client to another client in terms of response times ?

When you ping from a client to a client the switch simply forwards the packet in hardware.

When you ping an IP on the switch itself this is handled differently because  now you have go up through the TCP/IP stack on the switch and often switches handle this in software not hardware.

So if your clients are fine and only pings to and from your switches show higher response times there is nothing to worry about.

Jon

[alpushkarev11]

I see that the ping from one client to another is not more 1ms.

Thank.

[alpushkarev11]

The time of ping is changing  time from time. What could be causing of it ?

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Transient latency, such a transient queuing/buffering will cause variability in ping times.  Frame/packet sizes can also cause ping variable times, including for the ping requests/replies.  (Try pinging with larger packets - you'll likely see an increase in ping times.)

BTW, somewhat similar to what I've already posted for Cisco devices, ping was not designed/expected to be a highly accurate measure of RTT latency.

[Jon Marshall]

Don't get too bogged down in ping response times.

As Joseph says it is not really a reliable indicator of latency in your network.

I can ping from a device at different times and get different response times.

If you are not experiencing any network performance issues with your users then it is really nothing to worry about.

Jon

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Just to add to what Jon has already noted, Cisco devices generally treat pings, to the device, with low priority, as this is not the device's primary purpose.  This can result in very variable response times (from the device) when there's nothing wrong.