I am trying to configure Voice VLAN. While going through the document a point raised when read the following Guidelines from Cisco.
"The Cisco IP Phone uses IEEE 802.1Q frames for Voice VLAN traffic.Voice VLAN is only supported on access ports and not on trunk ports,even though the configuration is allowed"
It seems ironical that when the device sends the CoS bit set, It should have ISL/802.1Q Frame. If the switch port is configured as Access Ports, how the device connected to the port (In this case IP Phone) is sending the CoS Bits to Switch?
Can you please help me in understanding this?
My understanding is that it depends on the way you configure the port. If it's an access port and uses a voice vlan, CDP will convey that information to the switch, as well as the CoS markings. If you have configured the port to trust CoS settings, then the switch will. If not, the switch will mark the voice packets in accordance with theQoS policy you have configured.
If the interface is configuraed as a trunk port, the CoS markings will be conveyed via the dot1q tag in the dot1q packet. As far as trusting, it is the same paradigm as the access port.