01-11-2015 03:43 AM - edited 03-07-2019 10:10 PM
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
01-11-2015 04:41 AM
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
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01-11-2015 10:28 AM
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
01-11-2015 10:34 AM
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
01-11-2015 11:20 AM
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
01-11-2015 01:22 PM
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
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