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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter20 Co nf iguring QoS
Configuring QoS
Configuring the CoS Value for an Interface
QoS assigns the CoS value specified with the mls qos cos interface configuration command to untagged
frames received on trusted and untrusted ports.
Beginning in privileged EXEC mode, follow these steps to define the default CoS value of a port or to
assign the default CoS to all incoming packets on the port:
To return to the default setting, use the no mls qos cos {default-cos | override} interface configuration
command.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 mls qos Enable QoS globally.
Step3 interface interface-id Enter interface configuration mode, and specify the interface to be trusted.
Valid interfaces include physical interfaces.
Step4 mls qos cos {default-cos | override} Configure the default CoS value for the port.
For default-cos, specify a default CoS value to be assigned to a port. If
the port is CoS trusted and packets are untagged, the default CoS value
becomes the CoS value for the packet. The CoS range is 0 to 7. The
default is 0.
Use the override keyword to override the previously configured trust
state of the incoming packets and to apply the default port CoS val ue to
all incoming packets. By default, CoS override is disabled .
Use the override keyword when all incoming packets on certain ports
deserve higher or lower priority than packets entering fr om other ports.
Even if a port was previously set to trust DSCP, CoS, or IP precedence,
this command overrides the previously configured trust sta te, a nd all
the incoming CoS values are assigned the defaul t CoS value configured
with this command. If an incoming packet is tagged, the CoS value of
the packet is modified with the default CoS of the port at the ingress
port.
Step5 end Return to privileged EXEC mode.
Step6 show mls qos interface Verify your entries.
Step7 copy running-config startup-config (Optional) Save your entries in the configuration file.