Cat6500 behavior with QoS disabled

Answered Question
Oct 12th, 2007

Can someone answer this question for me? Will the 6500 strip or remark the DSCP markings in a packet with mls qos disabled?

Our phones mark their packets with a DSCP of 46. We want the switch to honor that marking and leave it untouched. By default, with QoS disabled, the ports trust the DSCP as shown below:

QoS is disabled globally

Trust state: trust DSCP

Extend trust state: not trusted [COS = 0]

So it trusts the incoming DSCP markings. Will it pass them thru the switch and leave them marked as DSCP 46?

Thanks for your help.

I have this problem too.
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Correct Answer by wochanda about 9 years 2 weeks ago

Yes, we will not re-mark packets when 'mls qos' is disabled.

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Overall Rating: 5 (1 ratings)
Correct Answer
wochanda Fri, 10/12/2007 - 10:22

Yes, we will not re-mark packets when 'mls qos' is disabled.

darrenj Fri, 10/12/2007 - 10:24

What I believe will happen here is that the DSCP will be left untouched, but no QOS will be applied to it. Therefore, the switch treats a packet marked with DSCP value 46 exactly the same as all other packets.

In most cases, people give QOS preference to packets such as DSCP 46 because they are more important (for example voice is more critical and not tolerent to jitter, as opposed to web traffic).

Getting back to your original question, with no QOS enabled, the DSCP value is ignored and passes out of the switch the same as it enters :-)



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