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I have assigned all voip-related ports to one vlan. I want to set up the QoS priority for that vlan. Which commands can help and in which mode?

I have assigned all required ports to one vlan. I tries "vlan # qos priority (0-7)" in interface as well as global config mode.

I have not created any policy. only enabled global QoS and done vlan config and assigned port to it.

vlan # qos priority (0-7)

vlan interface mode and the global config terminal mode are not accepting it as command. Which mode it has to be configure ? is that command right? Is it must to create policy ?

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    You need to use policies to prioritize your traffic. Please remember, that QoS has no effect on your network unless it is congested. I would suggest you read: networkengineering.stackexchange.com/questions/42660/… – user56700 Jul 10 '19 at 5:41
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer. – Ron Maupin Dec 15 '19 at 4:26
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user56700 is absolutely wrong.

Congestion avoidance is a mechanism in QoS that allows you to do just that, avoid the congestion before it happens. Microbursts of just a few seconds will cause drops on a 'blocking' switch, where all the ports cannot be forwarded at line rate. Additionally, applying a shaper outbound on internet circuits will allow you to specify max bandwidths for certain classes (voip and the LLQ) to avoid overrunning other classes of traffic. QoS on your switch and router will be different and you will often want both, in conjunction with each other to provide the desired result.

Keep in mind, there is no right answer for how your QoS should look, this is very environment specific.

To avoid explaining QoS here (very very extensive topic) I will just say that auto QoS may be your best option.

There are tons of options for making your goal happen, most phones will automatically mark the traffic appropriately (EF for the rtsp stream and CS3 for control) as long as you trust the markings and disable ip dscp rewrite on the switch, and all routers along the path that you intend to provide a differentiated quality of service you will see the appropriate markings.

Alternatively, you can mark cos on a per port basis. Take a look at this document and remember that after you mark you need to take action on that marking or it becomes useless.

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960/software/release/15-0_2_se/configuration/guide/scg2960/swqos.pdf

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