switchport priority extend cos 0

[mahesh18]

Hi all,

if we have cisco IP phone and it is connected to switch and

pc is connected  to the  IP phone and we have this config

interface fa0/1

mls qos trust cos
mls qos trust device cisco-phone
switchport priority extend cos 0

if someone can explain me what this command will do  switchport priority extend cos 0

1>to packets coming from pc to IP phone access port?

regards

mahesh

[jonathanaxford · Accepted solution]

Hi Mahesh,

The command you refer to will instruct the switch to remark any traffic received from the PC (Via the IP Phone)  with a CoS value of 0. I think this is the default value in most cases.

This is from the 2950 software config guide:

Overriding the CoS Priority of Incoming Data Frames

You can connect a PC or other data device to a Cisco 7960 IP Phone port.  The PC can generate packets with an assigned CoS value. You can  configure the switch to override the priority of frames arriving on the  IP phone port from connected devices.

Beginning in privileged EXEC mode, follow these steps to override the  CoS priority received from the nonvoice port on the Cisco 7960 IP Phone:

	Command	Purpose
Step 1	configure terminal	Enter global configuration mode.
Step 2	interface interface-id	Enter interface configuration mode, and specify the interface connected to the IP phone.
Step 3	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.
Step 4	end	Return to privileged EXEC mode.
Step 5	show interfaces interface-id switchport	Verify your entries.
Step 6	copy running-config startup-config	(Optional) Save your entries in the configuration file.

Hope this helps

Jonathan

[mahesh18]

Hi,

thanks for reply

i check the port config and it does not show the command

switchport priority extend cos 0

so as this is default config thats the reason it is not showing  up in running config?

second when IP phone port receive the packet from pc the default cos 0 means that traffic is not given any priority right?

regards

mahesh

[cadet alain · Accepted solution]

Hi,

to verify this command you have to do sh  interface XX switchport because this is default config and so won't appear in the running.

second when IP phone port receive the packet from pc the default cos 0 means that traffic is not given any priority right?

It means the original  L2 QoS marking of the traffic  is not trusted and reset to 0.

Regards.

Alain.

[mahesh18]

Hi Alain and jonathan,

Many thanks for taking your time and explaining this to me.

regards

mahesh