MLS QOS Map

[Cisco Freak]

Hi Guys,

I am trying to understand the MLS QoS map concept.

Switch#show mls qos maps cos-dscp
   Cos-dscp map:
        cos:   0  1  2  3  4  5  6  7 
     --------------------------------
       dscp:   0  8 16 24 32 46 48 56 

Switch#

Switch#sh mls qos interface fa0/1
FastEthernet0/1
trust state: trust cos
trust mode: trust cos
trust enabled flag: ena
COS override: dis
default COS: 0
DSCP Mutation Map: Default DSCP Mutation Map
Trust device: none
qos mode: port-based

So this configuration means, the switch is trusting the Cos marking in the interface. And the DSCP marking for the port will be based on the CoS-DSCP value.

So my question is what if a client send a frame with CoS value 5 and DSCP value 40. Will this switch overwrite the DSCP value to 46 before it sends out?

CF

[Terry Cheema]

Yes your understanding is accurate. CoS 5 will be converted into dscp 46 and transmitted. (Obviously if your trunk links are set to trust)

-Terry

Please rate all helpful posts and mark the thread as answered if you have no more questions.

[Cisco Freak]

Thanks Terry!!

I have one more question.

SW2#show mls qos input-queue 
Queue     :       1       2
----------------------------------------------
buffers   :      90      10
bandwidth :       4       4
priority  :      40       0
threshold1:     100     100
threshold2:     100     100

Does this output shows that the input queue 1 will get 40% priority BW and then each queue will get 4% BW in the round robin fashion. And this configuration is not fully utilizing the 100% BW of the interface. Am I right in my understanding?

CF  

[Cisco Freak]

I checked again and this configuration doesn't make sense to me.

SW2#show mls qos input-queue 
Queue     :       1       2
----------------------------------------------
buffers   :      90      10
bandwidth :     100     100
priority  :      40       0
threshold1:     100     100
threshold2:     100     100

How can queue 1 and 2 have 100% bandwidth along with 40% priority BW for queue 1. Totally confused now!! :( :(

CF 

[Cisco Freak]

I am answering this myself.

SW7(config)#mls qos srr input bandwidth ?
  <1-100>  enter bandwidth weight for queue id 1

SW7(config)#mls qos srr input bandwidth 1 ?
  <1-100>  enter bandwidth weight for queue id 2

SW7(config)#mls qos srr input bandwidth 1 1 ?
  <cr>

Its the weight that we mention here. Not the percentage directly.

SW2#show mls qos input-queue 
Queue     :       1       2
----------------------------------------------
buffers   :      90      10
bandwidth :     100     100
priority  :      40       0
threshold1:     100     100
threshold2:     100     100

This will give 40% priority BW to queue and remaining 60% will equally share between bot the queues as their weights are same.

CF

[Terry Cheema]

Yes exactly right. Its documented here: http://www.cisco.com/c/en/us/support/docs/switches/catalyst-3750-series-switches/91862-cat3750-qos-config.html#concept241

Default Scheduler Configuration:

Queue 2 is the priority queue. SRR services the priority queue for its configured weight which is 10%. Then, SRR shares the remaining bandwidth (90%) with both ingress queues and services them as specified by the configured weights. In this case, queue 1 and queue 2 are serviced at the rate of 45% each.

Distribution1#show mls qos input-queue
Queue     :       1       2
----------------------------------------------
buffers   :      90      10
bandwidth :       4       4
priority  :       0      10
threshold1:     100     100
threshold2:     100     100

-Terry

Please rate all helpful posts and mark the thread as answered if you have no more queries.