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New Member

QoS question, 3560 catalyst

Platform - Catalyst 3560.

IOS - 12.2(25)SEC2

TEST(config)#no mls qos

TEST(config)#mls qos rewrite ip dscp

TEST(config)#end

TEST#sh mls qos

QoS is disabled

QoS ip packet dscp rewrite is enabled

Will this disable all QoS functions except for changing all DSCP values to 0? It seems strange that the switch would allow the command "mls qos rewrite ip dscp" after "no mls qos" if there were no effect. It would also seem logical that without "mls qos", "mls rewrite ip dscp" would be rendered useless.

3 REPLIES
Silver

Re: QoS question, 3560 catalyst

With mls qos disabled , all the ports are in "trusted" state which means the switch will not change the dscp whatsoever. So even having the "mls qos rewrite ip dscp" should not have any effect when the qos is disabled. It does not really matter that you have this command or not , whats important is the port trust state and thats always "trusted" when qos is disabled and this is true for all switching platforms.

Thanks

Salman Z.

New Member

Re: QoS question, 3560 catalyst

Thanks for the quick reply.

My biggest concern is that by simply issuing the command "mls qos" performance on large file transfers almost doubles. I'm not a great QoS mind by any means.

Do I need to adjust ingress or egress queues? My queue sets are posted below. I want to be certain that all DSCP is set to 0 while maintaining performance as much as possible.

TEST(config)#mls qos

TEST(config)#mls qos rewrite ip dscp

TEST(config)#exit

TEST#sh mls qos queue-set

Queueset: 1

Queue : 1 2 3 4

----------------------------------------------

buffers : 25 25 25 25

threshold1: 100 200 100 100

threshold2: 100 200 100 100

reserved : 50 50 50 50

maximum : 400 400 400 400

Queueset: 2

Queue : 1 2 3 4

----------------------------------------------

buffers : 25 25 25 25

threshold1: 100 200 100 100

threshold2: 100 200 100 100

reserved : 50 50 50 50

maximum : 400 400 400 400

TEST#

Thanks again!

Silver

Re: QoS question, 3560 catalyst

Its best to leave the qos settings at default. If you are running anything lower then 12.2(25)SEB , then be aware of CSCeg29704. By enabling qos , since the port goes to untrusted state , all dscps will be rewritten to 0. So just by enabling qos , you will get what you want . Although it surprises me that just by enabling qos , you are getting double the performance w/o enabling any kind of classification.

Thanks

Salman Z.

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