QOS on 3750

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Dec 23rd, 2009
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Here you have all the question regarding the operations of the Queues:

1.  About the default behavior and values before enable the "mls qos":

a.  what are the default values of the Queue (buffers, threshold, etc)?

b.  what are the default values of the dscp-cos to queue-threshold? Because we've seen that traffic going to Queue 3 (IOS number 4).

What are the queues numbered 0 to 7 for if only number 4 is in use?

2.  After enable the "mls qos":

a.  We assumed that the values of the buffers, thresholsds, etc, applied are the ones from the "show mls qos queue-set 1". Regarding its parameters:

                        i.   Buffers:

1.  how can I see the total number of system assigned buffers for an interface?

2.  Is this a fixed value by platform?

3.  Is this connected with the "show buffers" in same way?

ii.   Threshold1 and 2 and maximum: I supposed that these two values have the same meaning as the "maximum" value. The threshold1 and 2 must be lower or equal to the maximum, and
they define the granularity of two possible levels of dropping, is that correct?

b.  About dscp-cos to queue-threshold mapping, if the packet has a DSCP "00", we've notice that the queue-threshold has to be 2-1.

c.  Regarding the output of the sh platform port-asic stats drop gigabitEthernet

i.   The Queues 0 to 3 are the queues 1 to 4 of the queue-set 1. What are the 4 to 7

                      ii.   What are the Weight 0, 1 and 2?

3.  When I want to know in which queue and which threshold will apply to a packet, what mapping should I look: Dscp-outputq-threshold map or Cos-outputq-threshold map? When does
the switch use the Dscp-cos map and Cos-dscp map?

4.  The only documentation I've found about all this issue is

Do you have any other relevant document?

Thanks in advance .

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