I'm very new to QOS and have some questions.
1. If I enable "mls qos" on the access layer switches will the MLS QOS markings set at the access layer be automatically read at the core/distribution layer, or does the "mls qos" option need enabling on every switch on the network.
2. Is it possible to configure QOS on a trunk interface carrying voice and data that connects into a suppliers MPLS router. This interface is connected at the core switch level.
Thanks in advance
QOS must be enable on all switches as a best practice, depending on the switch model that you have at the core/distribution layer you will need to enable it and trust the interfaces between the switches to maintain the QOS markings.
Yes, it is possible to configure QOS on trunks ports.
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The defaults for switches (except for the pretty recent) is, if QoS isn't enabled, switch ignores any markings, it will forward them without change, and there's no different traffic treatment. With QoS enabled, switch will reset CoS/ToS (unless configured otherwise) and will provide some, default, different traffic treatment.
For your first question, whether you need to configure every switch, or even any, depends on your QoS goals.
For your second question, it's an "it depends" answer. Generally, for trunks, you trust whatever QoS marking are received, on ingress, and for egress, you prioritize and/or drop according to your QoS policy.