Refer to the exhibit.
A trunk link is connected between switch A_SW and switch D_SW.
Based on the configuration shown in the exhibit, how would the traffic coming from the
switch A_SW be managed?
A.
The trunk port Fa0/1 on switch A_SW will trust all CoS values on the frames coming from
the IP phone.
B.
The trunk port Fa0/1 on switch A_SW will trust all CoS values on the frames received on
the IP phone.
C.
The trunk port Fa0/1 on switch D_SW will trust all CoS values on the frames coming from
port Fa0/1 on A_SW.
D.
The trunk port Fa0/1 on switch D_SW will trust all CoS values on the frames received on
the A_SW switch port Fa0/4.
E.
The trunk port Fa0/1 on switch D_SW will trust all CoS values on the frames received on
the IP phone port.
Explanation:
To enable to QOS, you should enter the msl qos command in global configuration mode.
When inbound packets are accepted into a switch, the switch can be selective about which
(if any)
of each packet’s QoS information will be trusted. If the packets originate from a trusted
source, the QoS information can be safely trusted, too. Usually, it is a best practice to configure switches at
the edge of a trusted QoS domain to verify or overwrite any QoS information that comes into the
domain. This way, any other switch or router within the domain can blindly trust QoS information that is seen.
You can configure QoS trust in two ways:
Per-interface
As part of a QoS policy on specific types of traffic
The per-interface trust is described in the next section. Policy trust is described as part of the
section,
“Defining a QoS Policy.”
Trust QoS on an Interface
On each interface where consistent QoS trust is to be defined, use the following interface
configuration command:
Switch(config-if)# mls qos trust {cos | dscp | ip-precedence}
Applying QoS Trust 407
Here, one of the following values can be trusted and used internally as the switch makes
forwarding
decisions:
The inbound CoS, which is taken from trunking tags
DSCP, which is taken from the inbound IP packet headers
IP P re ce de nce , which is a ls o take n from the inbound IP packet headers