Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

qos config on catalyst

I have configured a voice vlan and I'm planning to use Cisco Ip phones. As I understand the catalyst switches have 2/4 transmit queues per egress port. The IP-phones mark the packet with COS 5 when the switchport are configured with:

switchport trunk encapsulation dot1q

switchport trunk native vlan 2

switchport mode trunk

switchport voice vlan 20

switchport priority extend cos 0

If I choose to use default scheduling then I don't have to do any qos settings on my catalyst 2950/3500XL/4506 switches. Correct?


Re: qos config on catalyst

You ll need to add another command, to make the switch trust the ingress packets COS values.

Switch(config)#mls qos trust cos

anyway the IP phone would reset the Cos value to 0 so you dont need the command " switchport priority extend cos 0 " on the port.

New Member

Re: qos config on catalyst

The port is trusted by default if it is a 3500 or 2900. It looks good to go. If you have any questions take a look at this link

New Member

Re: qos config on catalyst

I can't see why I need to Issue the mls qos trust cos. The IP phone will mark the packet with COS=5.

Cisco recommendation for QOS on 3500XL

Configure the ports connected to Cisco IP phones with a PC attached to the secondary port by issuing the extended trust configuration switchport priority extend cos <0-3> command so that these frames are queued in the low priority queue.

CreatePlease to create content