- Understanding the Theory of Voice VLANs
- Configuring Voice VLANs
- Power over Ethernet
- Essential Network Services: DHCP and NTP
- Understanding the Phone Bootup Process
- Installing Cisco IP Phone Firmware and XML Configuration Files
- Exam Prep Questions
- Answers to Exam Prep Questions
- Suggested Reading and Resources
Configuring Voice VLANs
This and the following sections define how VoIP and data traffic can use the same physical link while operating on separate Layer 2 VLANs. Figure 7.2 shows the PC communicating using untagged frames on VLAN 12 and the IP phone communicating on VLAN 112 with 802.1Q frames. The VLANs are configured on the infrastructure switch, as shown in Figure 7.1.
Figure 7.2 Voice and data VLANs coexist on a single physical connection.
Listing 7.1 shows a sample switch port configuration.
Listing 7.1. Switch Port Configuration
Switch(config)# interface FastEthernet0/1 Switch(config-if)# switchport access vlan 12 Switch(config-if)# switchport mode access Switch(config-if)# switchport voice vlan 112 Switch(config-if)# spanning-tree portfast
The switchport access vlan command statically configures the access VLAN for the PC traffic.
The switchport mode access command statically configures the port in access mode.
The switchport voice vlan vlan-id command identifies the VLAN provided by the switch to the Cisco IP phone using CDP so that the Cisco IP phone can insert the voice VLAN ID and the 802.1P class of service (CoS) values for the VoIP control and media frames. By default, the IP phone sets the CoS setting in the 802.1Q header to a priority of 5 for voice streaming traffic and a priority of 3 for the call control traffic.
The spanning-tree portfast command eliminates the normal 30- to 50-second spanning tree delay before traffic is forwarded on a switch port.
You can verify your voice VLAN configuration on the Cisco Catalyst switch using the show interface mod/port switchport command, as shown in Listing 7.2.
Listing 7.2. Using the show interface mod/port switchport Command
Switch# show interface fa0/17 switchport Name: Fa0/17Switchport: Enabled Administrative mode: static access Operational Mode: static access Administrative Trunking Encapsulation: negotiate Operational Trunking Encapsulation: native Negotiation of Trunking: Off Access Mode VLAN: 12 (VLAN0012) Trunking Native Mode VLAN: 1 (default) Voice VLAN: 112 (VLAN0112) Trunking VLANs Enabled: ALL Pruning VLANs Enabled: 2-1001 Appliance trust: none
For IP communications to access the voice and data VLANs, you need to provide a Layer 3 IP interface. There are three methods used to provide this access: an external router connected to a switch, a Layer 3 switch, and a router with built-in switch ports.
VLANs and an External Router
The commands used to connect an external router to access the voice and data VLANs created in the preceding section follow in Listing 7.3.
Listing 7.3. External Router—Layer 3 VLAN Configuration
CMErouter(config)# interface fa0/0.12 CMErouter(config-if)# encapsulation dot1q 12 CMErouter(config-if)# ip address 10.1.12.1 255.255.255.0 CMErouter(config)# interface fa0/0.112 CMErouter(config-if)# encapsulation dot1q 112 CMErouter(config-if)# ip address 10.1.112.1 255.255.255.0
Router with Built-in Switch Ports
Listing 7.4 shows the commands used to connect a Layer 3 switch or a router with internal switch ports to access the voice and data VLANs created previously.
Listing 7.4. Router with Built-in Switch—Layer 3 VLAN Configuration
CMErouter(config)# interface vlan 12 CMErouter(config-if)# ip address 10.1.12.1 255.255.255.0 CMErouter(config)# interface vlan 112 CMErouter(config-if)# ip address 10.1.112.1 255.255.255.0