A technician is configuring a switch to allow access both to IP phones and to PCs on interface Fa0/12. The technician enters the interface command mls qos trust cos. What is the reason for including that command?

Question:
A technician is configuring a switch to allow access both to IP phones and to PCs on interface Fa0/12. The technician enters the interface command mls qos trust cos. What is the reason for including that command?

• It is used in conjuction with STP PortFast to ensure that interface Fa0/12, in case of a shutdown, regains an “up” state immediately.
• It is used to verify service levels and to ensure that congestion over serial interfaces is minimized for voice traffic.
• It is used to set the trusted state of an interface to allow classification of traffic for QoS based on the CoS value of the IP phone.
• It is used to provide higher categories of security for voice and video traffic.

Explanation: The class of service (CoS) value is a number placed inside a field in the 802.1Q or ISL trunking header and used for prioritizing traffic and providing quality of service (QoS). The mls qos trust cos command is used when a VoIP phone attaches to a Cisco switch and QoS is implemented.

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