To avoid classification at all switches within a QoS domain, a switch port may be configured in a trusted state.
Which two statements are true regarding the trust state configuration of a switch port? (Choose two.)
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A. B. C. D. E.DE.
QoS (Quality of Service) is a network feature that allows network administrators to prioritize different types of traffic in order to guarantee a certain level of service to certain types of traffic. In Cisco switches, QoS can be configured to use either CoS (Class of Service) or DSCP (Differentiated Services Code Point) for QoS classification.
To avoid classification at all switches within a QoS domain, a switch port may be configured in a trusted state. When a switch port is in a trusted state, it trusts the QoS markings of the incoming traffic and forwards the traffic without any modification. This is useful when the QoS markings have already been set by a trusted device upstream, such as a router.
Here are the correct statements regarding the trust state configuration of a switch port:
A. When mls qos trust is not configured on the port, the default port trust state is DSCP. This statement is false. The default port trust state when mls qos trust is not configured on the port is actually "untrusted". The port will not trust any QoS markings and will use the default CoS value of 0 for all incoming packets.
B. When mls qos trust is not configured on the port, the default port trust state is CoS. This statement is true. When mls qos trust is not configured on the port, the default port trust state is CoS. The port will trust the CoS value of the incoming packet and forward the packet based on that CoS value.
C. The port trust state can be CoS or DSCP only. This statement is true. The port trust state can be configured to trust either CoS or DSCP, but not both at the same time.
D. When mls qos trust cos is configured on the port, the port default CoS value is used for an untagged packet. This statement is true. When mls qos trust cos is configured on the port, the switch will use the default CoS value of the port for any untagged packet that comes into the port.
E. When mls qos trust cos is configured on the port, the switch classifies an ingress packet by using the packet CoS value. This statement is false. When mls qos trust cos is configured on the port, the switch will trust the CoS value of the incoming packet and use that value for forwarding decisions. The switch will not classify the packet based on the CoS value.