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Axel Luttgens
Beginner

Simulating the "no QoS" behavior when "mls qos" is issued on 2960-S and 3750G

Hello,

Document at https://supportforums.cisco.com/docs/DOC-8093 is quite interesting, yet leaves several questions unanswered.

One of these goes about the behavior of a switch (2960-S and 3750G) when QoS is not enabled vs the one when QoS is simply enabled with "mls qos".

What additional commands, beside "mls qos", would be needed so as to simulate as accurately as possible the switch's behavior when QoS is not enabled?

I would really be pleased to have some kind of reference configuration so as to (hopefully) be able to interpret some QoS problems encountered here.

Many thanks in advance,

Axel

(31/01/2012: Changed 3750 into 3750G; minor editing)

3 REPLIES 3
Shashank Singh
Cisco Employee

Hi Luttgens,

With just mls qos in place and no trust configured on ingress interface, normally the switch would rewrite the QoS markings to 0, as dscp rewrite is enabled by default.

What additional commands, beside "mls qos", would be needed so as to simulate as accurately as possible the switch's behavior when QoS is not enabled?

I am not sure if I got your requirement, could you please elaborate/rephrase your question.

Regards,

Shashank

Hello  Shashank,

Well, I'm going to try... ;-)

Unless I'm wrong, paquets go thru the same circuitry (asics) wheter QoS is activated or not.

Activating the QoS on the switch by just entering "mls qos" reprograms that circuitry and selects default values for various user-configurable parameters (in fact, I am referring to section 2.1.1 of above document).

This would also mean that, when QoS is not activated, another set of (fixed) default values must be in use; let's call that set of values the noqos-set.

Now, let's say I activate QoS on the switch by entering "mls qos" into its config but want to reproduce as nearly as possible the switch's behavior when QoS is not activated. I would thus need to enter various additional QoS-related commands into the config, so as to try to reproduce the noqos-set.

Thanks for your follow-up,

Axel

Axel Luttgens
Beginner

Dear list fellows,

Could someone point me to some resource (written or human) liable to provide accurate information about that "noqos-set"?

TIA,

Axel