Quality of Service (QoS): Managing Bandwidth More Effectively

Using QoS Classifiers to Configure Quality of Service for Outbound Traffic

Operating Notes Different applications may use the same DSCP in their IP packets. Also, the same application may use multiple DSCPs if the application originates on different clients, servers, or other devices. Using an edge switch enables you to select the packets you want and mark them with predictable DSCPs that can be used by downstream switches to honor policies set in the edge switch.

When enabled, the switch applies direct 802.1p prioritization to all packets having codepoints that meet these criteria:

The codepoint is configured with an 802.1p priority in the DSCP table. (Codepoints configured with No-overrideare not used.)

The codepoint is not configured for a new DSCP policy assignment.

Thus, the switch does not allow the same incoming codepoint (DSCP) to be used simultaneously for directly assigning an 802.1p priority and also assigning a DSCP policy. For a given incoming codepoint, if you configure one option and then the other, the second overwrites the first.

To use this option:

1.Identify a DSCP used to set a policy in packets received from an upstream or edge switch.

2.Determine the 802.1p priority (0 - 7) you want to apply to packets carrying the identified DSCP. (You can either maintain the priority assigned in the upstream or edge switch, or assign a new priority.)

3.Use qos dscp-map < codepoint > priority < 0 - 7 > to assign the 802.1p priority you want to the specified DSCP. (For more on this topic, refer to “Differ- entiated Services Codepoint (DSCP) Mapping” on page 5-33.)

4.Enable diff-services.

Syntax: qos type-of-service diff-services < codepoint >

Causes the switch to read the < codepoint > (DSCP) of an incoming IPv4 packet and, when a match occurs, assign a corresponding 802.1p priority, as configured in the switch’s DSCP table (page 5-34).

no qos type-of-service

Disables all ToS classifier operation.

no qos dscp-map < codepoint >

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