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Cat3850 - qos queue-softmax-multiplier - settings

oguarisco
Level 3
Level 3

Hi to all,

Reading through the CCO document "Catalyst 3850: Troubleshooting Output drops" I came across the command qos queue-softmax-multiplier, by default in latest IOS XE3.6/3.7 is set to a value of 100 which corresponds to 1200 soft buffers per each gigabit port with no QoS enabled.

Those 1200 soft buffers are distributed in 2 queues

  • queue 0 = 480 (40% of the total buffers reserved)
  • queue 1 = 720 (the rest => 60%)


The value of the command qos queue-softmax-multiplier could be increased to a max of 1200...
If I configure it as 200 means a total of 2400 soft buffers per Gigabit port

  • queue 0 = 960(40% of the total buffers reserved)
  • queue 1 = 1440(the rest => 60%)

since it's configured globally each Gigabit port "receive" new values and I was wondering where those soft buffers come from?

A global shared pool? What happens when you increase it on all port? is there a chance that this will create buffer availability problem since by default is very low?

Thanks for any suggestion
BR
Omar

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