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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 20 Configuring 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
Step 1
configure terminal Enter global configuration mode.
Step 2
mls qos Enable QoS globally.
Step 3
interface interface-id Enter interface configuration mode, and specify the interface to be trusted.
Valid interfaces include physical interfaces.
Step 4
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 value 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 from other ports.
Even if a port was previously set to trust DSCP, CoS, or IP precedence,
this command overrides the previously configured trust state, and all
the incoming CoS values are assigned the default 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.
Step 5
end Return to privileged EXEC mode.
Step 6
show mls qos interface Verify your entries.
Step 7
copy running-config startup-config (Optional) Save your entries in the configuration file.