mls qos trust cos vs mls qos cos in cat6k

[lukaszkhalil]

Hello

I am trying to configure basic qos topology with two 6k connected to each other by the trunk port.

According to the documentation, if I set the mls qos cos value at the interface level I should modify the default cos on it, and all packets leaving incoming to this port, should be marked with the new cos value.

http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6000-series-switches/24055-173.html

Unfortunately, when I set such config, all incoming packets transmitted through this interface was tagged with cos = 0 until I set the "mls qos trust cos" on the same interface.

Does anybody can explain to me this strange behavior?

I would like to mention that both 6k was connected to each other with ws-x6548-GE-TX modules.

Thank you in advance.

Ragards

Lukas

[lukaszkhalil]

Hello

I have recieved an answer from the TAC regarding my case which might help others having the same issue.

"To use the CoS value applied with the mls qos cos command as the basis of internal DSCP:

-On a port that receives only untagged ingress traffic, configure the ingress port as trusted or configure a trust CoS policy map that matches the ingress traffic."

It seems that the "mls qos trust cos" command is required for the static cos to works.

It is not a bug but a feature :)

Best regards

Lukasz