One source I have read states that by default a Cisco IP phone will remark all PC frames to cos 0 and leave DSCP values; and another source claims the phone will rewrite cos and dscp values.
Does anybody have a definitive answer to this? Help!
As for CoS, it will be re-marked to 0 if and only if the frames coming from the PC are tagged (i.e. a trunk)
If the frames are not tagged (i.e: not sent on a trunk), then they are forwarded toward the access switch un-tagged, and will be switched onto the native VLAN of the access switch's port.