C3650 / IOS XE QoS Changes

[Shaun Michelson]

We're replacing our C3560 with a C3650 which is using the new "IOS XE" operating system. It looks like the "auto qos" settings have changed with this new OS and it now uses a Policy and Class mapping approach to apply auto qos settings.

We are using Avaya IP phones that do not tag COS values (they use DSCP (specifically 46) instead). So in the past, when setting up QoS on our switches, I've used the following syntax:

int range g1/0/1-48

auto qos voip trust

mls qos trust dscp

The last line "mls qos trust dscp" has been necessary for us because the default when using the "auto qos voip trust" command is to trust COS rather than DSCP.

That said, it appears that the "mls qos" command has been deprecated in IOS XE because I'm unable to run it and cant find any reference to it in the command reference guide.

So now when I run "auto qos voip trust" on the new switch, it creates a Policy map called "AutoQos-4.0-Trust-Cos-Input-Policy" and applies that to my interface (service-policy input AutoQos-4.0-Trust-Cos-Input-Policy). Just looking at the name of the policy, it seems that the default is still to trust COS. With the loss of the "mls qos trust dscp" command I'm not sure how to get it to trust DSCP rather than COS.

I'm thinking I can use the "auto qos trust dscp" command instead of "auto qos voip trust". The documentation states that the policy map "AutoQos-4.0-Trust-Dscp-Input-Policy" will be created and applied to our interfaces, which sounds more like what I want, but I want to make sure that the Avaya VoIP traffic (DSCP 46) is still getting priority using this configuration.

Anyhow, long story short, it seems like the way to proceed now with the new IOS XE is to use "auto qos trust dscp" but wanted to get some feedback from the community to make sure.

[Mohammed al Baqari]

What I suggest is to apply both commands in your test lab and compare the generated policies in both cases. This is the best way to confirm that you are getting what you are looking for.

Also, do you really need auto-qos? It is more than VoIP DSCP/CoS. Auto qos will cover all applications include voice, video, bulk, etc. Also, it includes policing, shaping, etc.

[Shaun Michelson]

Thanks for the input. What is the alternative to using auto qos? Create my own Policy/Class maps? Seems like the auto config is the easiest route.

[Wilson Samuel]

Hi Shaun,

Yes, one could configure manual Policy / Class maps and assign them to the interfaces. However make sure that you understand the underlying Queuing architecture for a given hardware platform.

The 3560/3750s I have worked on, have had 1 Ingress Queue and 4Q Outgress Queue and it works in a slightly different way than most of the Routers do the Queuing / QoS.

Here is one article which may come to your help, if you are interested.

http://blog.ine.com/2010/11/29/catalyst-qos-autoqos/

Once you understand the Queuing Architechture for a given hardware (check the config guide for the specific Hardware i.e. 3750 with IOS XE, then you would make most of it.

If you have any further help needed in the aspect, please post the sh version from the switch and we shall be glad to guide you further.

HTH

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