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 [EMAIL PROTECTED] http://prolixium.com/ Rensselaer Polytechnic Institute, Class of 2004
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