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Quality of Service (QoS): Managing Bandwidth More Effectively
Differentiated Services Codepoint (DSCP) Mapping
Notes on Changing a Priority Setting
If a QoS classifier is using a policy (codepoint and associated priority) in the
DSCP Policy table, you must delete or change this usage before you can
change the priority setting on the codepoint. Otherwise the switch blocks the
change and displays this message:
Cannot modify DSCP Policy < codepoint > - in use by
other qos rules.
In this case, use show qos < classifier > to identify the specific classifiers using
the policy you want to change; that is:
show qos port-priority
show qos type-of-service
For example, suppose that the 000001 codepoint has a priority of 6, and several
classifiers use the 000001 codepoint to assign a priority to their respective
types of traffic. If you wanted to change the priority of codepoint 000001 you
would do the following:
1. Identify which QoS classifiers use the codepoint.
2. Change the classifier configurations by assigning them to a different DSCP
policy, or to an 802.1p priority, or to No-override.
3. Reconfigure the desired priority for the 000001 codepoint.
4. Either reassign the classifiers to the 00001 codepoint policy or leave them
as they were after step 2, above.
Error Messages caused by DSCP Policy Changes
Refer to the following table on ways to fix errors that may be generated when
configuring DSCP policy changes.
Message Meaning
DSCP Policy < decimal-codepoint > not
configured
You have attempted to map a QoS classifier to
a codepoint for which there is no configured
priority (No-override). Use the qos dscp-map
command to configure a priority for the
codepoint, then map the classifier to the
codepoint.