qos config on catalyst

[tg.hansen]

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?

[thisisshanky]

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.

[brocknathan]

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

http://www.cisco.com/en/US/customer/products/hw/switches/ps607/products_tech_note09186a0080116ffe.shtml

[tg.hansen]

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.