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Question about Qos and trust on 3850's

Hi all

I have a setup in which with have non-cisco phones (NEC's) connecting to Cisco 3850's and 3750's. My questions regarding the 3850's is this:

Given the config onthe interface is this:

interface GigabitEthernet1/0/1
description PCs and Phones
switchport access vlan 204
switchport mode access
switchport voice vlan 304
auto qos trust
spanning-tree portfast
service-policy input AutoQos-4.0-Trust-Cos-Input-Policy
service-policy output AutoQos-4.0-Output-Policy

  1. If I have a port where the auto qos trust command is entered (no dscp or cos on the end) which takes higher precedence, is it the DSCP or the COS marking? 
  2. Does auto qos trust trust DSCP markings from the PC(access) port if a PC is hanging off the phone given the above config?
  3. If I just wanted to trust the phone and discard the DSCP marking from the PC, would the auto qos trust voip achieve this? And again, which marking does it trust, COS or DSCP?

Thanks in advance

Paul

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