Quality of Service (QoS): Managing Bandwidth More Effectively
Effect of "No-override"
In the QoS Type-of-Service differentiated services mode, a No-override
assignment for the codepoint of an outbound packet means that QoS is
effectively disabled for such packets. That is, QoS does not affect the packet
queuing priority or VLAN tagging. In this case, the packets are handled as
follows (as long as no other QoS feature creates priority assignments for
Received and Forwarded on a tagged port member of a VLAN.
Received on an Untagged port member of a VLAN; Forwarded on a
tagged port member of a VLAN.
Forwarded on an Untagged port member of a VLAN.
Note 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 device-priority
show qos port-priority
show qos tcp-udp-port-priority
show qos vlan-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.
Using QoS Classifiers To Configure QoS for Outbound Traffic