[j-nsp] sudden jump in ping response time

[CHEN Xu]

Thanks, guys!

-Simon

On Fri, Jul 11, 2008 at 1:12 AM,  <Keegan.Holley at sungard.com> wrote:
>
> Yes, that's standard across all the vendors.  One of the things I do to
> verify that there is no latency is to ping a destination on the other side
> of the router at the same time and compare the latency.  If it's something
> external to the router the ping times will jump at the same time.  If it is
> just processor scheduling then only the ping to the router will jump.
>
> Happy Hunting,
>
> Keegan
>
> Mark Kamichoff <prox at prolixium.com>
> Sent by: juniper-nsp-bounces at puck.nether.net
>
> 07/11/2008 01:07 AM
>
> To
> CHEN Xu <simonchennj at gmail.com>
> cc
> juniper-nsp at puck.nether.net
> Subject
> Re: [j-nsp] sudden jump in ping response time
>
>
>
>
> Hi Simon -
>
> On Thu, Jul 10, 2008 at 02:36:49PM -0400, CHEN Xu wrote:
>> I am using multiple logical routers on a juniper router, they are
>> connected through logical tunnels, or VLANs, or L2VPN, etc.
>>
>> When I ping from one logical router to another, I always see some
>> glitch in ping response time, like this:
>>
>> 64 bytes from 1.1.2.1: icmp_seq=153 ttl=64 time=1.015 ms
>> 64 bytes from 1.1.2.1: icmp_seq=154 ttl=64 time=1.018 ms
>> 64 bytes from 1.1.2.1: icmp_seq=155 ttl=64 time=1.048 ms
>> 64 bytes from 1.1.2.1: icmp_seq=156 ttl=64 time=0.988 ms
>> 64 bytes from 1.1.2.1: icmp_seq=157 ttl=64 time=36.950 ms  <----
>> 64 bytes from 1.1.2.1: icmp_seq=158 ttl=64 time=1.004 ms
>> 64 bytes from 1.1.2.1: icmp_seq=159 ttl=64 time=1.005 ms
>> 64 bytes from 1.1.2.1: icmp_seq=160 ttl=64 time=1.003 ms
>>
>> This almost always happens in all setups that I played with. Does
>> anyone know what's going on and how to fix it?
>
> I believe this is par for the course in the JUNOS architecture with any
> type of setup.  ICMP echo replies (and other ICMP messages) are given
> the absolute lowest priority, so anything in the control plane will take
> priority.  I can see this too on an almost completely idle J2320, via
> MTR:
>
> Host                     Loss%  Snt  Last   Avg  Best  Wrst StDev
> 1. 2001:4830:122d:7::1    0.0%    6   0.7   0.6   0.5   0.7   0.1
> 2. 2001:4830:122d:19::2   0.0%    6   3.6 103.6   3.2 603.6 244.9
> 3. 2001:4830:122d:c::2    0.0%    6   4.4   6.3   4.3  12.4   3.4
>
> The 2nd hop is the J2320.
>
> The JUNOS Enterprise Routing book discusses this briefly (pages 519-520)
> in the CoS chapter, and even shows a PING example demonstrating the
> large variance in response times, too.  It then goes on to discuss how
> RPM can perform the ICMP timestamp reply in hardware (or via the RT
> thread on the J-series), for gathering more accurate performance
> metrics.  Depending on your needs, RPM may be something to consider
> testing.
>
> Hope this helps.
>
> - Mark
>
> --
> Mark Kamichoff
> prox at prolixium.com
> http://prolixium.com/
> Rensselaer Polytechnic Institute, Class of 2004
> [attachment "signature.asc" deleted by Keegan Holley/SAS/SunGard]
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