QoS ,CoS, DSCP question

[Bekzod Fakhriddinov]

Hi guys. I have a network which was programmed with different people  where  some routers and switches programmed with auto trust CoS  some of them auto trust dscp . I assume some of them inspecting level 2 another one inspecting dscp information level 3  to provide QoS . 

Can routers operate/process 2 different methods (CoS and DSCP) and make a correct decision ?

Is it required to bring all of them to the 1 same  mode of QoS ?

Thank you

[Francisco Granados · Accepted solution]

Bezkod,

In qos, there are cos-dscp maps that basically allow the device to translate cos to dscp. If you do 
"show mls qos" on your switch, this command will be one of the first ones you will see.

Correction: The proper command is "show run | include qos"

In my experience, you have nothing to worry about. Modern devices can make the proper decisions, and modern auto qos is very close to best practices.

Thanks,

FG

[Terry Cheema · Accepted solution]

Can routers operate/process 2 different methods (CoS and DSCP) and make a correct decision ?

No routers cant process layer 2 CoS values. CoS value is part of the 802.1Q Header or the VLAN tag which will get dropped at the L3 gateway. Hence the reason, we have cos to dscp maps on the switches.

If you are trusting the L2 values at access level, they get mapped to a dscp values configured in the cos to dscp maps and passed on as dscp marking to the L3 devices. 

So you don't have to do anything much as these maps etc. get generated automatically with auoto qos. All you need to do is configure trust on your access ports (cos or dscp) and on your trunks (dscp on trunks to L3 devices).

+5 to Francisco

-Terry

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