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New Member

QOS & COS Design Help

Hi All,

First off I would like to state that my field of knowledge with these two subjects are very limited. That being said I am going to go ahead and explain my situation.

We have two sites connected to each through a leased 100 MEG MPLS. Each of these sites runs on a router on a stick concept, with layer 3 switch as the core routing solution.

In site 1 VLAN 6 is our voice vlan. In site 2 VLAN 5 is the voice vlan.

Site 2 has to reach Site 1 as our main PRI's are all in this site.

So I am under the assumption that I have to COS all VLAN 5 Traffic. The core L3 switch would then QOS all traffic headed to the IP address over at SITE 1 which is the main voice server w/ PRI's etc.

Conceptually thats what i understand I might have to do. I could be totally wrong.

can someone please shed some light on what the best way to go about this is?

I dont have any access to the leased line MPLS unforunately.

Everyone's tags (4)

Re: QOS & COS Design Help

Hi Steve,

u might already solve it but lets see if this information can help

yes you need to trust cos fron your site 2 if its layer 2 inter face and trust DSCP on layer 3 interface,

check this document and hopefully it will help you.

Please rate if this helps.


New Member

QOS & COS Design Help

Hi Amrinder,

I am not sure if you can or will continue helping me with this problem, but I now have the time and resource to now tackle this problem.

I have read your document, and i have also purchased Cisco Catalyst QoS to help gain some great understanding of QoS.

I want to break down my problem or I should say procedure one step at a time, starting at the access layer on a Catalyst 2960.

My current default config is as follows for my access layer ports. I have a Mitel Voip Phone Connected to the Catalyst.

interface GigabitEthernet1/0/9
description Gi1/0/9 SRAdm&Voip
switchport access vlan 10
switchport mode access
switchport voice vlan 6
mls qos trust cos


My Phone is set for a CoS Priority of 5. It is also set for a DSCP value of 46. (I chose this as it is the default value for EF)

I have added the line:

mls qos trust cos

to trust the cos of the tagged frames the phones puts out and to leave untagged frames with a default value of COS 0.

The only thing I have not done yet is enable mls qos globally.

I just want to confirm if so far my steps are correct. Also i realize I will have to do a cos-dscp mapping so that COS 5 is equal to DSCP 46.

So far is there anything I am missing?

Now since this is only an access layer switch, which connect directly to our core switch, I realize I will have to trust the uplink ports. What would the config be for those?

Would it also be:

mls qos trust cos


mls qos trust dscp

Thanks in advance.


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