Refer to the exhibit. Based upon the information that is given, how will voice traffic from the
phone and data traffic from the PC be handled by SW_1?
A.
The switch port will perform marking for the ingress voice and data traffic by using the
default CoS value at the switch port.
B.
The switch port will trust the CoS value of the ingress voice and data traffic that comes
into the switch port.
C.
The switch port will trust the CoS value of the ingress voice traffic. Data traffic will be
marked at the switch port with the default CoS value.
D.
The switch port will trust the CoS value of the ingress data traffic. Voice traffic will be
marked at the switch port with the default CoS value.
Explanation:
In a typical network, you connect a Cisco IP Phone to a switch port. Traffic sent from the
telephone to the switch is typically marked with a tag that uses the 802.1Q header. The
header contains the VLAN information and the CoS 3-bit field, which determines the priority
of the packet. For most Cisco IP Phone configurations, the traffic sent from the telephone to
the switch is trusted to ensure that voice traffic is properly prioritized over other types of
traffic in the network. By using the mls qos trust cos interface configuration command, you
can configure the switch port to which the telephone is connected to trust the CoS labels of
all traffic received on that port.
After you enter the mls qos trust cos command, the DSCP values are changed according to
the default values, which are listed below:
http://www.cisco.com/en/US/docs/switches/lan/catalyst2940/software/release/12.1_19_ea1/c
onfiguration/guide/swqos.html
