Link to home
Start Free TrialLog in
Avatar of DBCSNA
DBCSNAFlag for United States of America

asked on

"mls qos trust dscp" not working on new cisco 2960 poe switch


We are in the process of upgrading our current Cisco Catalyst 3560 Series POE switch to a Cisco Catalyst 2960 Plus Series SI POE.

The config below is what we have in our current switches
 when we try to transfer the config to the new switch, we get an error on the line below:
mls qos trust cscp

it does not like cscp, its not recognized. if I change it to COS it does not take,

my question is why it does not take cscp and what the difference is between CSCP and COS. We run voice over ip phones on these switches. the phones and phone system are Siemens.

interface FastEthernet0/46
 switchport access vlan 501
 switchport mode access
 switchport voice vlan 101
 speed 100
 duplex full
 priority-queue out
 mls qos trust dscp
 spanning-tree portfast
Avatar of kevinhsieh
Flag of United States of America image

If I am not mistaken, the 3650 is a L3 switch and the 2960 is L2. DSCP is L3 QoS which isn't understood by L2 switch, which only understands COS.

You probably only need priority queuing on interfaces where there is a difference in bandwidth and there is contention,  like on your WAN interface. I have IP phones on over a dozen different 2960 switches and have no issues without using COS. I do have QoS on the WAN interfaces of my routers, but nothing for the LAN.
Avatar of Predrag Jovic
Predrag Jovic
Flag of Poland image

Link to home
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
Start Free Trial
Avatar of DBCSNA


Thank you KevinHSieh and Predrag Jovic, for helping clarify some of the confusion that i had.

Indeed the catalyst 3650 switches are layer 3 and the new switches 2960 are layer 2.