Understanding Voice VLAN
The voice VLAN feature enables access ports to carry IP voice traffic from an IP phone. The switch can connect to a Cisco 7960 IP Phone and carry IP voice traffic. Because the sound quality of an IP phone call can deteriorate if the data is unevenly sent, the switch supports quality of service (QoS) based on IEEE 802.1P class of service (CoS). QoS uses classification and scheduling to send network traffic from the switch in a predictable manner. For more information on QoS, see Chapter 29, "Configuring QoS." The Cisco 7960 IP Phone is a configurable device, and you can configure it to forward traffic with an 802.1P priority. You can configure the switch to trust or override the traffic priority assigned by an IP Phone.
The Cisco 7960 IP Phone contains an integrated three-port 10/100 switch as shown in Figure 14-1. The ports provide dedicated connections to these devices:
•
Port 1 connects to the switch or other voice-over-IP (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.
Figure 14-1 shows one way to connect a Cisco 7960 IP Phone.
Figure 14-1 Cisco 7960 IP Phone Connected to a Switch
When the IP Phone connects to the switch, the access port (PC-to-telephone jack) of the IP phone can connect to a PC. Packets to and from the PC and to or from the IP phone share the same physical link to the switch and the same switch port. For deployment examples that use voice VLANs, refer to the "Network Configuration Examples" section on page 1-9.
Configuring Voice VLAN
This section describes how to configure voice VLAN on access ports. It contains this configuration information:
• Default Voice VLAN Configuration
• Voice VLAN Configuration Guidelines
• Configuring a Port to Connect to a Cisco 7960 IP Phone
Default Voice VLAN Configuration
The voice VLAN feature is disabled by default.
When the voice VLAN feature is enabled, all untagged traffic is sent according to the default CoS priority of the port.
The default CoS value is 0 for incoming traffic.
The CoS value is not trusted for 802.1P or 802.1Q tagged traffic.
The IP Phone overrides the priority of all incoming traffic (tagged and untagged) and sets the CoS value to 0.
Voice VLAN Configuration Guidelines
These are the voice VLAN configuration guidelines:
•You should configure voice VLAN on switch access ports.
•Before you enable voice VLAN, we recommend that you enable QoS on the switch by entering the mls qos global configuration command and configure the port trust state to trust by entering the mls qos trust cos interface configuration command.
•The Port Fast feature is automatically enabled when voice VLAN is configured. When you disable voice VLAN, the Port Fast feature is not automatically disabled.
•When you enable port security on an interface that is also configured with a voice VLAN, you must set the maximum allowed secure addresses on the port to at least two.
•If any type of port security is enabled on the access VLAN, dynamic port security is automatically enabled on the voice VLAN.
•You cannot configure static secure or sticky secure MAC addresses on a voice VLAN.
•Voice VLAN ports can also be these port types:
–
Dynamic a
ccess port. See the "Configuring Dynamic Access Ports on VMPS Clients" section on page 12-32 for more information.
–Secure port. See the "Configuring Port Security" section on page 21-8 for more information.
–802.1X authenticated port. See the "Using 802.1X with Voice VLAN Ports" section for more information.
–Protected port. See the "Configuring Protected Ports" section on page 21-5 for more information.
Configuring a Port to Connect to a Cisco 7960 IP Phone
Because a Cisco 7960 IP Phone also supports a connection to a PC or other device, a port connecting the switch to a Cisco 7960 IP Phone can carry mixed traffic.
You can configure the port to carry voice traffic in one of these ways:
• Configuring Ports to Carry Voice Traffic in 802.1Q Frames
• Configuring Ports to Carry Voice Traffic in 802.1P Priority-Tagged Frames
You can configure the IP phone to carry data traffic in one of these ways:
• Overriding the CoS Priority of Incoming Data Frames
• Configuring the IP Phone to Trust the CoS Priority of Incoming Data Frames
----------------------------总结-----------------------------
override:替代
语音流量的配置控制:
switchport voice vlan dot1p :
Instruct the switch port to use IEEE 802.1p priority tagging for voice traffic and to use the default native VLAN (VLAN 0) to carry all traffic. By default, the Cisco IP phone forwards the voice traffic with an IEEE 802.1p priority of 5.
switchport voice vlan vlan-id
Instruct the Cisco IP Phone to forward all voice traffic through the specified VLAN. By default, the Cisco IP Phone forwards the voice traffic with an 802.1Q priority of 5. Valid VLAN IDs are from 1 to 4094.
switchport voice vlan dot1p配置方法将导致交换机和IP电话之间使用802.1p标记语音帧,且使用NATIVE vlan来传输(所有,包含语音)数据.
switchport voice vlan vlan-id方式导致交换机和IP电话之间使用802.1Q标记帧传输语音.且使用NATIVE vlan传输其他数据.
不管使用那种方式,非语音流量不会被打上VLAN标记.
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引用CISCO 另一份文档内容:
Switch(config-if)#switchport voice vlan ?
<1-4094> Vlan for voice traffic
dot1p Priority tagged on PVID
none Do not tell telephone about voice vlan
untagged Untagged on PVID
Enter a voice VLAN ID in order to send CDP packets that configure the IP phone to transmit voice traffic in 802.1Q frames, tagged with the voice VLAN ID and a Layer 2 CoS value (the default is 5 for voice traffic and 3 for voice control traffic). Valid VLAN IDs are from 1 to 4094. The switch puts the 802.1Q voice traffic into the voice VLAN.
Enter the dot1p keyword in order to send CDP packets that configure the IP phone to transmit voice traffic in 802.1p frames, tagged with VLAN ID 0 and a Layer 2 CoS value (the default is 5 for voice traffic and 3 for voice control traffic). The switch puts the 802.1p voice traffic into the access VLAN.
Enter the untagged keyword in order to send CDP packets that configure the IP phone to transmit untagged voice traffic. The switch puts the untagged voice traffic into the access VLAN.
Enter the none keyword in order to allow the IP phone to use its own configuration and transmit untagged voice traffic. The switch puts the untagged voice traffic into the access VLAN.
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对于PC数据流量的配置控制
switchport priority extend cos value :
Set the IP phone access port to override the priority received from the PC or the attached device.
The CoS value is a number from 0 to 7. Seven is the highest priority. The default is 0.
switchport priority extend trust
Set the IP phone access port to trust the priority received from the PC or the attached device.
switchport priority extend cos vlaue 用这个vlaue值替换PC中的数据COS,默认用0替换
switchport prioriy extend trust 信任Pc数据里的COS
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