Quality of Service (QoS): Managing Bandwidth More Effectively

Using QoS Types To Configure QoS for Outbound Traffic

Effect of “No-override”.In the QoS Type-of-Service differentiated services mode, a No-overrideassignment 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 type 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 < type > to identify the specific type using the policy you want to change; that is:

show qos type-of-service

For example, if you wanted to change the priority of codepoint 000001 you would do the following:

1.Identify which QoS type uses the codepoint.

2.Change the type 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 using the qos dscp-mapcommand.

4.Either reassign the type to the 00001 codepoint policy or leave them as they were after step 2, above.

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