3750(config-if)# switchport priority extend ? Override 802.1p priority of devices on appliance trust Trust 802.1p priorities of devices on appliance Voice VLAN I prefer to trust the PC's CoS values, as different software on the PC may have different values. For example, the user may wish to run a soft-phone application on the PC. Overriding the CoS values set by this software might lead to voice quality issues for the soft phone. Here, I've configured an interface to use VLAN 10 for voice while trusting the CoS values set by the user's PC and phone: interface GigabitEthernet1/0/20 switchport access vlan 100 switchport voice vlan 10 switchport priority extend trust mls qos trust cos To see which VLAN is configured as the Voice VLAN, use the show interface interface-name switchport command: 3750# sho int g1/0/20 switchport Name: Gi1/0/20 Switchport: Enabled Administrative Mode: static access Operational Mode: down Administrative Trunking Encapsulation: negotiate Negotiation of Trunking: off Access Mode VLAN: 1 (default) Trunking Native Mode VLAN: 1 (default) Administrative Native VLAN tagging: enabled Voice VLAN: 10 (Inactive) Administrative private-vlan host-association: none Administrative private-vlan mapping: none Administrative private-vlan trunk native VLAN: none Administrative private-vlan trunk Native VLAN tagging: enabled Administrative private-vlan trunk encapsulation: dot1q Administrative private-vlan trunk normal VLANs: none Administrative private-vlan trunk private VLANs: none Operational private-vlan: none Trunking VLANs Enabled: ALL Pruning VLANs Enabled: 2-1001 Capture Mode Disabled Capture VLANs Allowed: ALL Protected: false Unknown unicast blocked: disabled Unknown multicast blocked: disabled Appliance trust: none Chapter 18: Catalyst 3750 Features Quality of Service is covered in detail in Chapter 29, and it's a topic that could easily fill an entire book. In this section, I will focus on some 3750-specific QoS features. One of the useful features of the 3750 is the ability to enable AutoQoS, whi