mls qos trust "cos or dscp" ?

[MARVIN SPITERI]

I have an uplink from an access switch configured as a trunk 802.1q that needs to trust Qos towards the distribution switch, does this have to trust cos or dscp ? the issue is that the access switch has a local voice vlan and the trunk uses another vlan to connect to the distribution.

[Nicholas Matthews]

You don't trust "to" a device, only from.

The advice I've gotten from switching guys is "If you're not sure - just trust DSCP".

If you try to trust cos on an access port where there is no VLAN header, there is no cos, and you can have problems.

If you have a trunk to another switch, you can trust cos and you shouldn't have any problems.

hth,

nick