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New Member

QoS - DSCP or CoS

Our Environment: 

-We have about 200 Polycom VoIP phones (SoundPoint IP335). These phones utilize DSCP - EF. However, CDP is currently disabled by our provider. These phones are 100% cloud managed. Every call, even the internal between two local phones has to go out to the cloud and back.

-We have 53 Cisco access points AIR-CAP3502I-A-K9 connected to our Cisco WLC-5508 controllers.

-We have 2960-S stackable access layer switches as well as primary and secondary L2/L3 Core switches WS-C3560E-12D-E. 


1. We would like to implement an End-To-End QoS solution in our environment utilizing the Auto QoS configuration macros for both the Wi-Fi Access Points that use QoS and WiFi Controllers.

2. We would like to implement an End-To-End QoS solution in our environment utilizing the Auto QoS configuration macros for our VoIP phones.

Proposed solution:

1. Enable QoS on ALL switches and ultimately Routers by using :

mls qos 

2. On the switchports facing the Access Points use:

mls qos trust dscp

3. On the switchport facing the Polycom VoIP phones use:

auto qos voip trust
mls qos trust dscp

4. On the trunks between the access layers switches and our Cores, we would like to use DSCP. Lots of different documentations state to use CoS should be used acrooss layer 2 uplinks and that DSCP should be used across Layer 3 uplinks. However, DSCP is able to pass these layer 2 links without any rewrite by CoS. Trunks between all L2/L3 switches would be configured as follows:

auto qos voip trust
mls qos trust dscp


-is this configuration valid? 

-Is this design future-proof enough so that it NOT only serves the VoIP traffic in the future but other traffic possible future traffic such as video, and etc.

-Should we be using CoS vs. DSCP?

-i noticed that our 2960-S switches have "auto qos srnd4" configured BUT our 
Core Switches don't. Should this be enabled on the Core switches as well? I noticed that "auto qos srnd4" enabled causes our 2960S switches change the "auto qos voip trust" being displayed in the running configuration as "auto qos trust". Not sure why is this happening. But if you turn off "auto qos srnd4" the command sticks and it is shown properly within the 2060-S running config.


Hello.I doubt if "auto qos


I doubt if "auto qos voip trust" would suit you on inter-switch links, as per documentation the command applies policy-map that gives only 320K for voice and signalling traffic (+ remarking exceeded traffic to BE).

If you want to protect your video traffic in the future, you will have to design new QoS policy and apply it per link.

Regarding "trust dscp" toward WLC/AP - if you configure this, all your laptops will be able to inject marked traffic into your network, abusing your QoS policy; that is why the best practice for VoIP phones is to be placed into dedicated voice VLAN + trust cos (not dscp).

PS: I would suggest you to try the command[s] on one switch and see what configuration will be applied per port (+global).

New Member

Thanks Vasili --> sorry for

Thanks Vasili --> sorry for the late response. The project had to be put on hold and will resume this summer.