6-36
Quality of Service (QoS): Managing Bandwidth More Effectively
Using QoS Types To Configure QoS for Outbound Traffic
Note on DSCP Use 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-override are 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 6-58.)
4. Enable diff-services.
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