VLAN priority - how to find whether there are drops from low priority vlans

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Jul 22nd, 2010
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Hi ,

I have a performance issue on a network which has few vlans.  for some vlans we have high priority configured.  When clients on the vlan with high priority  try to connect to a server on a low priority they complain about poor response times. I like to do some analysis to find out whether the vlan priority configuration affects this performance issues. I have attached part of the switch onfig with this. clients are in the vlan 30  and server is on vlan 100. What kind of commands and tools can I use to analyse this issue? any ideas will be really great helpful


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Nagaraja Thanthry Fri, 07/23/2010 - 06:21
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When you say VLAN Priority what priority you are referring to? If you are referring to VLAN port-priority, then that should not affect the performance. It just helps spanning-tree in calcularing the topology. You might want to start with tracing the path of packet transfer i.e. look at every interface through which the data has to pass through and look for any interface errors (input/output queue drops, CRC errors, Ignores etc). Also, if the packets are getting routed across the VLANs, then I would suggest checking the core switch and see if the packets are geting forwarded by the hardware cache or by the CPU. This would help you identify the root cause of the slowness.

Hope this helps.



bonnardopjl Tue, 07/27/2010 - 02:41
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The statement:

srr-queue bandwidth shape  40  0  0  0

limit the bandwidth for Q1 to 1/40 th of the bandwidth,

that is to say 2,5%.

Is this value you intended to configure ?


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