5-58
Quality of Service: Managing Bandwidth More Effectively
Globally-Configured QoS
Creating a Policy Based on VLAN-ID Classifier.
1. Determine the VLAN-ID classifier to which you want to assign a DSCP
policy.
2. Determine the DSCP policy for packets carrying the selected VLAN-ID:
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 from upstream devices.)
b. Determine the 802.1p priority you want to assign to the DSCP.
3. If necessary, use the qos dscp-map < codepoint > priority < 0 - 7 > command
to configure the DSCP policy (codepoint and associated 802.1p priority)
that you want to use to mark matching packets.
Prerequisite A DSCP codepoint must have a preconfigured 802.1p priority (0 - 7) before
you can use the codepoint to mark matching packets. If a codepoint you want
to use shows No-override in the Priority column of the DSCP Policy table (show
qos dscp-map command), you must first configure a priority for the codepoint
before proceeding (qos dscp-map priority command). See “Differentiated Ser-
vices Codepoint (DSCP) Mapping” on page 5-90 for more information.
4. Configure the switch to assign the DSCP policy to packets with the
specified VLAN-ID.
Syntax: qos dscp-map < codepoint > priority < 0 - 7 >
This command is optional if a priority has already been
assigned to the < codepoint >. The command creates a DSCP
policy by assigning an 802.1p priority to a specific DSCP.
When the switch applies this priority to a packet, the priority
determines the packet’s queue in the outbound port to which
it is sent. If the packet leaves the switch on a tagged port, it
carries the 802.1p priority with it to the next downstream
device. For IP packets, the DSCP codepoint in the packet
header is replaced by the codepoint specified in this com-
mand. (Default: For most codepoints, No-override. See Figure
5-11 on page 5-91.)
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