As shown in Figure 1, the F0/18 port on S3 is configured to be in voice mode so that voice frames will be tagged with VLAN 150. Data frames coming through the Cisco IP phone from PC5 are left untagged. Data frames destined for PC5 coming from port F0/18 are tagged with VLAN 20 on the way to the phone. The phone strips the VLAN tag before the data is forwarded to PC5.
The Cisco IP Phone contains an integrated three-port 10/100 switch. The ports provide dedicated connections to these devices:
- Port 1 connects to the switch or other VoIP device.
- Port 2 is an internal 10/100 interface that carries the IP phone traffic.
- Port 3 (access port) connects to a PC or other device.
When the switch port has been configured with a voice VLAN, the link between the switch and the IP phone acts as a trunk to carry both the tagged voice traffic and untagged data traffic. Communication between the switch and IP phone is facilitated by the Cisco Discovery Protocol (CDP).
Sample Configuration
Figure 2 shows a sample output. A discussion of voice Cisco IOS commands are beyond the scope of this course but the highlighted areas in the sample output show the F0/18 interface configured with a VLAN configured for data (VLAN 20) and a VLAN configured for voice (VLAN 150).