Quality of Service (QoS): Managing Bandwidth More Effectively

Using QoS Classifiers To Configure QoS for Outbound Traffic

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Assigning a DSCP Policy Based on the Source-Port

This option assigns a previously configured DSCP policy (codepoint and 802.1p priority) to outbound IP packets (received from the specified source- ports). That is, the switch:

1.Selects an incoming IP packet on the basis of its source-port on the switch.

2.Overwrites the packet’s DSCP with the DSCP configured in the switch for such packets.

3.Assigns the 802.1p priority configured in the switch for the new DSCP. (Refer to “Differentiated Services Codepoint (DSCP) Mapping” on page 6-58.)

4.Forwards the packet through the appropriate outbound port queue.

On switches covered in this guide, “mixing” ToS DSCP policies and 802.1p priorities is not recommended. Refer to the Note on page 6-10.

For more on DSCP, refer to “Terminology” on page 6-6.

Steps for Creating a Policy Based on Source-Port Classifiers

You can select one DSCP per source-port. Also, configuring a new DSCP for

asource-port automatically overwrites (replaces) any previous DSCP or 802.1p priority configuration for that port.)

1.Identify the source-port classifier to which you want to assign a DSCP policy.

2.Determine the DSCP policy for packets having the selected source-port:

a.Determine the DSCP you want to assign to the selected packets. (This codepoint will be used to overwrite the DSCP carried in packets received through the source-port from upstream devices.)

b.Determine the 802.1p priority you want to assign to the DSCP.

3.Configure the DSCP policy by using qos dscp-mapto configure the priority for each codepoint. (For details, refer to the example later in this section and to “Differentiated Services Codepoint (DSCP) Mapping” on page 6-58.)

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