Quality of Service (QoS): Managing Bandwidth More Effectively
Using QoS Classifiers To Configure Quality of Service for Outbound Traffic
Figure 8-36. Example of Show Config Listing with Non-Default Priority Settings in
the DSCP Table
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 them):
802.1Q Status Outbound 802.1p
Priority
Received and Forwarded on a tagged port member of a VLAN. Unchanged
Received on an Untagged port member of a VLAN; Forwarded on a 0 (zero)—”normal”
tagged port member of a VLAN.
Forwarded on an Untagged port member of a VLAN. None
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
Note that protocol-priority is not included because a DSCP policy is not
meaningful for this classifier and therefore not configurable in this case.
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.
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