switchport priority extend命令详解及IP Phone的东东！

 （以下均资料来自权威Cisco官方手册。Writed by liucheng749，转载请注明出处与作者。参考资料：Catalyst 3550软件配置手册、Catalyst 6500软件配置手册等）
一、解释是这样的，
Use the switchport priority extend interface configuration command to set a port priority for the incoming untagged frames or the priority of frames received by the IP phone connected to the specified port.Use the no form of this command to return to the default setting.
翻译：
通过使用swichport priority extend的接口配置命令来做下面这两件事，
1是为入站未打tag的帧设置一个接口priority值；
2是设置通过连接到IP phone的指定端口接收的帧的prioriy值。
使用no命令返回到默认设置。
switchport priority extend {cos value | trust}
no switchport priority extend

二、语法，
cos value：Set the IP phone port to override the priority received from the PC or the attached device. The class of service (CoS) value is a number from 0 to 7. Seven is the highest priority. The default is 0.
翻译：设置IP phone端口不考虑从PC（或其他附着设备）收到的priorty值。COS值是一个0到7的数，最高的priorty是7，默认是0。
trust： Set the IP phone port to trust the priority received from the PC or the attached device.
翻译：设置IP phone端口信任从PC（或其他附着设备）收到的priorty值

三、默认，
The port priority is not set, and the default value for untagged frames received on the port is 0. The IP phone connected to the port is set to not trust the priority of incoming traffic and overrides the priority with the CoS value of 0.
翻译：默认情况下，端口priority没有设置，并且从端口收到的未打tag的帧的默认值是0；连接到IP Phone的端口设置不信任入站流量的priority，并且也不考虑COS为的0的priority。

四、命令模式，
Interface configuration 

五、使用guideline，
In Cisco IOS Release 12.1(13)EA1 or later, the trust keyword replaces the none keyword. To instruct the IP Phone to not trust the priority, you can use the no switchport priority extend or the switchport priority extend cos 0 interface configuration command. In software releases earlier than Cisco IOS Release 12.1(13)EA1, use the switchport priority extend none interface configuration command.
翻译：在12.1EA1或更新的版本，关键字“trust”取代了“none”。为了指示IP phone不信任priority，你可以使用 no switchport priority extend或者the switchport priority extend cos 0的接口命令。在发布版软件12.1EA1更早的版本里，使用的是switchport priority extend none的接口命令。

When configuring the way in which the Cisco IP phone transmits data traffic, note the following information:
? To send CDP packets that configure the Cisco IP phone to trust tagged traffic received from a device connected to the access port on the Cisco IP phone, do not enter the cos keyword and CoS value.
? To send CDP packets that configure the Cisco IP phone to mark tagged ingress traffic received from a device connected to the access port on the Cisco IP phone, enter the cos keyword and CoS value (valid values are 0 through 7).
? You cannot use Cisco IOS software commands to configure whether or not traffic sent from a device attached to the access port on the Cisco IP phone is tagged.
翻译：当配置IP phone以哪种方式传送数据流时，注意以下几点：
1为了发送CDP包来配置IP phone，去信任（信任就是不修改）从附着在IP phone接入接口上的设备收到的打了tag的流，不要输入“cos”关键字和具体值。
2为了发送CDP包来配置IP phone，去标记(同时不信任，不信任就代表修改)从附着在IP phone接入接口上的设备收到的打了tag的入站流，输入“cos”关键字和具体值。
3你不能使用IOS命令来配置从附着在IP phone接入接口上的设备发送的流是否打tag。

六、例子，
This example shows how to configure the IP phone connected to the specified port to trust the received IEEE 802.1p priority:
Switch(config-if)# switchport priority extend trust
You can verify your settings by entering the show interfaces interface-id switchport privileged EXEC command.
翻译：这个例子展示了怎样配置一个连接到IP phone的指定端口来信任接受到的802.1p priority。
你还可以通过输入show interfaces interface-id switchport的特权命令来检查你的设置
以下几个例子是来自Catalyst 6500，意思一样，具体命令可能会有差异。
This example shows how to configure Fast Ethernet port 5/1 to send CDP packets that tell the Cisco IP phone to configure its access port as untrusted and to mark all tagged traffic received from a device connected to the access port on the Cisco IP phone with CoS 3:
Router# configure terminal 
Router(config)# interface fastethernet 5/1 
Router(config-if)# mls qos trust extend cos 3 
翻译：这个例子展示了怎样配置f5/1发送CDP包去告诉IP phone来配置其自身的接入端口作为非信任，和标记所有从连接到IP phone接入端口的设备收到的打了tag的流量的COS值为3。

（“不信任”就是“不考虑”，此时可以修改COS值。）

This example shows how to configure Fast Ethernet port 5/1 to send CDP packets that tell the Cisco IP phone to configure its access port as trusted:
Router# configure terminal 
Router(config)# interface fastethernet 5/1 
Router(config-if)# mls qos trust extend 
翻译：这个例子展示了怎样配置f5/1发送CDP包去告诉IP phone来配置其自身的接入端口作为信任。

This example shows how to verify the configuration on Fast Ethernet port 5/1:
Router# show queueing interface fastethernet 5/1 | include Extend 
Extend trust state: trusted
翻译：这个例子展示了怎样检查f5/1的配置。






七、关于Cisco IP phone的补充，

1.Cisco IP Phone Voice Traffic
The Cisco IP phone transmits voice traffic with Layer 3 IP precedence and Layer 2 CoS values, which are both set to 5 by default. The sound quality of a Cisco IP phone call can deteriorate if the voice traffic is transmitted unevenly. To provide more predictable voice traffic flow, you can configure QoS to trust the Layer 3 IP precedence or Layer 2 CoS value in the voice traffic (refer to Chapter 42, “Configuring PFC QoS”).
You can configure a Layer 2 access port with an attached Cisco IP phone to use one VLAN for voice traffic and another VLAN for data traffic from a device attached to the Cisco IP phone. 
翻译：Cisco IP phone携带DSCP和COS发送语音流量，两种值默认都是5。如果语音流量不平滑的传送，Cisco IP phone呼叫的声音质量能将会恶化。为了提供更多的可预见的语音流，你可以配置QOS来信任DSCP或者COS值。
你可以配置Cisco IP phone使用一个VLAN，然后来自于附着在IP phone上的设备的数据使用另一个VLAN。
You can configure Layer 2 access ports on the switch to send Cisco Discovery Protocol (CDP) packets that instruct an attached Cisco IP phone to transmit voice traffic to the switch in any of the following ways:
? In the voice VLAN, tagged with a Layer 2 CoS priority value 
? In the access VLAN, tagged with a Layer 2 CoS priority value 
? In the access VLAN, untagged (no Layer 2 CoS priority value) 
翻译：你可以配置交换机上的二层接入端口发送CDP包来指示IP phone来以下面任何一种方式传送语音流量
You cannot use Cisco IOS software commands to configure the frame type used by data traffic sent from a device attached to the access port on the Cisco IP phone. 
翻译：你不能使用IOS命令来配置从附着于IP phone接入接口上的设备发送的，被数据流所使用的帧类型

2.Cisco IP Phone Data Traffic

Untagged traffic from the device attached to the Cisco IP phone passes through the Cisco IP phone unchanged, regardless of the trust state of the access port on the Cisco IP phone.
翻译：从附着在IP phone上来的未打tag的流量，不管IP phone的接入端口(图上的P3)的信任状态如何，在IP phone传递它们时不对他们修改。

To process tagged data traffic (traffic in 802.1Q or 802.1p frame types) from the device attached to the access port on the Cisco IP phone (see Figure 17-1), you can configure Layer 2 access ports on the switch to send CDP packets that instruct an attached Cisco IP phone to configure the access port on the Cisco IP phone to either of these two modes:
? Trusted mode—All traffic received through the access port on the Cisco IP phone passes through the Cisco IP phone unchanged. 
? Untrusted mode—All traffic in 802.1Q or 802.1p frames received through the access port on the Cisco IP phone is marked with a configured Layer 2 CoS value. The default Layer 2 CoS value is 0. 
Untrusted mode is the default.

翻译：为了处理(来自附着在IP phone端口的)设备(如PC)打了tag的数据流量(dot1Q或者dot1p帧类型里的流量)，你可以配置交换机上的二层接入端口来发送CDP包来指示(附着在交换机上的)IP phone来配置它自己的接入端口(图上的P3)为下面两种之一的模式：
信任模式 - 所有通过IP phone接入接口收到的流量在被传递时不被IP phone修改。
非信任模式 - 所有通过IP phone接入接口收到的dot1Q或者dot1p流量，被IP phone标记上二层的COS值。

非信任模式是默认模式。

3.Cisco IP Phone Support Configuration Guidelines and Restrictions
The following guidelines and restrictions apply when configuring Cisco IP phone support:
? You must enable the Cisco Discovery Protocol (CDP) on the Catalyst 6500 series switch port connected to the Cisco IP phone to send configuration information to the Cisco IP phone. 
? You can configure a voice VLAN only on a Layer 2 LAN port.
? You can configure the ports on WS-X6548-RJ-45 and WS-X6548-RJ-21 switching modules to trust received Layer 2 CoS values (QoS port architecture 1p1q0t/1p3q1t). The WS-X6548-RJ-45 and WS-X6548-RJ-21 switching modules cannot supply power to Cisco IP phones.
? You cannot configure 10/100 Mbps ports with QoS port architecture 1p4t/2q2t to trust received Layer 2 CoS values. Configure policies to trust the Layer 3 IP precedence value on switching modules with QoS port architecture 1p4t/2q2t.
? The following conditions indicate that the Cisco IP phone and a device attached to the Cisco IP phone are in the same VLAN and must be in the same IP subnet:
– If they both use 802.1p or untagged frames
– If the Cisco IP phone uses 802.1p frames and the device uses untagged frames
– If the Cisco IP phone uses untagged frames and the device uses 802.1p frames
– If the Cisco IP phone uses 802.1Q frames and the voice VLAN is the same as the access VLAN
? The Cisco IP phone and a device attached to the Cisco IP phone cannot communicate if they are in the same VLAN and subnet but use different frame types, because traffic between devices in the same subnet is not routed (routing would eliminate the frame type difference).
? You cannot use Cisco IOS software commands to configure the frame type used by traffic sent from a device attached to the access port on the Cisco IP phone.
? If you enable port security on a port configured with a voice VLAN and if there is a PC connected to the Cisco IP phone, set the maximum allowed secure addresses on the port to at least 3.
? You cannot configure static secure MAC addresses in the voice VLAN.
? Ports configured with a voice VLAN can be secure ports (refer to Chapter 48, “Configuring Port Security”).
? In all configurations, the voice traffic carries a Layer 3 IP precedence value (the default is 5 for voice traffic and 3 for voice control traffic).
简单翻译一下吧：必须打开CDP、语音VLAN只能在二层接口配、帧类型不同时IP电话直接和IP电话连起来不能通信、开启端口安全时的最大允许MAC数目至少为3、不能在语音VLAN里配置静态安全MAC、有语音VLAN在的端口可以被配成安全端口等等。
附记，
sw(config-if)#mls qos trust cos命令的解释是：Classify ingress traffic packets with packet CoS values. For untagged packets, use the port default CoS value
翻译：用包的COS值分类入站流量。对于未打tag的包，使用端口默认的COS值。
源：http://blog.163.com/hgd1127blog/blog/static/8345409320093231161538/