Configuring Ingress Queue Characteristics; Mapping Cos Values To An Ingress Queue - Cisco Catalyst 2928 Software Configuration Manual

Configuring Standard QoS
If DSCP transparency is enabled by using the no mls qos rewrite ip dscp command, the switch does not
modify the DSCP field in the incoming packet, and the DSCP field in the outgoing packet is the same as
that in the incoming packet.
Regardless of the DSCP transparency configuration, the switch modifies the internal DSCP value of the
packet, which the switch uses to generate a CoS value that represents the priority of the traffic. The
switch also uses the internal DSCP value to select an egress queue and a threshold.
Beginning in privileged EXEC mode, follow these steps to enable DSCP transparency on a switch:
Command
Step 1 configure terminal
Step 2 mls qos
Step 3 no mls qos rewrite ip dscp
Step 4
end
Step 5
show mls qos interface [interface-id] Verify your entries.
Step 6 copy running-config startup-config
To configure the switch to modify the DSCP value based on the trust setting by disabling DSCP
transparency, use the mls qos rewrite ip dscp global configuration command.
If you disable QoS by using the no mls qos global configuration command, the CoS and DSCP values
are not changed (the default QoS setting).
If you enter the no mls qos rewrite ip dscp global configuration command to enable DSCP transparency
and then enter the mls qos trust cos interface configuration command, DSCP transparency is still
enabled.

Configuring Ingress Queue Characteristics

Depending on the complexity of your network and your QoS solution, you might need to perform all of
the tasks in the next sections. You will need to make decisions about these characteristics:
•
•
These sections contain this configuration information:
•
•

Mapping CoS Values to an Ingress Queue

You can prioritize traffic by placing packets with particular CoSs into certain queues and adjusting the
queue thresholds so that packets with lower priorities are dropped.
Catalyst 2928 Switch Software Configuration Guide
31-12
Purpose
Enter global configuration mode.
Enable QoS globally.
Enable DSCP transparency. The switch is configured to not modify the
DSCP field of the IP packet.
Return to privileged EXEC mode.
(Optional) Save your entries in the configuration file.
Which packets are assigned by CoS value to each queue?
Is there traffic (such as voice) that should be given high priority?
Mapping CoS Values to an Ingress Queue, page 31-12
Configuring the Ingress Priority Queue, page 31-13
Chapter 31
(optional)
(optional)
Configuring QoS
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