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24-8
Catalyst 2940 Switch Software Configuration Guide
78-15507-02
Chapter 24 Configuring QoS
Configuring QoS
Enabling Pass-Through Mode
When the switch is in pass-through mode, it uses the CoS value of incoming packets without modifying
the DSCP value and sends the packets from one of the four egress queues. By default, pass-through mode
is disabled. The switch assigns a CoS value of 0 to all incoming packets without modifying the packets.
The switch offers best-effort service to each packet regardless of the packet contents or size and sends
it from a single egress queue.
Beginning in privileged EXEC mode, follow these steps to enable pass-through mode:
To disable pass-through mode, use the no mls qos trust pass-through dscp interface configuration
command.
If you enter the mls qos cos override and the mls qos trust [cos] interface commands when pass-through
mode is enabled, pass-through mode is disabled.
If you enter the mls qos trust cos pass-through dscp interface configuration command when the mls
qos cos override and the mls qos trust [cos] interface commands are already configured, pass-through
mode is disabled.
Configuring the Egress Queues
This section describes how to configure the egress queues:
• Configuring CoS Priority Queues, page 24-9
• Configuring WRR Priority, page 24-9
For more information about the egress queues, see the “Egress CoS Queues” section on page 24-3.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Enter interface configuration mode, and specify the interface on which
pass-through mode is enabled.
Valid interfaces include physical interfaces.
Step 3
mls qos trust cos pass-through dscp Enable pass-through mode. The interface is configured to trust the CoS
value of the incoming packets and to send them without modifying the
DSCP value.
Step 4
end Return to privileged EXEC mode.
Step 5
show mls qos interface [interface-id] Verify your entries.
Step 6
copy running-config startup-config (Optional) Save your entries in the configuration file.