Quality of Service (QoS): Managing Bandwidth More Effectively

Using QoS Classifiers To Configure Quality of Service for Outbound Traffic

1. Identify the IP address you want to use as a classifier for assigning a DSCP policy.

2. Determine the DSCP policy for packets carrying the selected IP address:

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. Configure the DSCP policy by using dscp-mapto configure the priority to

 

the codepoint you selected in step 2a. (For details, refer to “Differentiated

 

Services Codepoint (DSCP) Mapping” on page 15-51.)

 

 

N o t e

A codepoint must have an 802.1p priority assignment (0 - 7) before you can

 

configure a policy for prioritizing packets by IP address. If a codepoint you

 

want to use shows No-overridein the Priority column of the DSCP map (show

 

qos dscp-map), then you must assign a 0 - 7 priority before proceeding.

 

4. Configure the switch to assign the DSCP policy to packets with the

 

 

specified IP address.

 

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 policy 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 in a tagged VLAN, it carries the 802.1p

 

priority with it to the next downstream device. If the

 

packet is IPv4, the packet’s DSCP will be replaced by the

 

codepoint specified in this command. (Default: For

 

most codepoints, No-override. See figure 15-8on page

 

15-52.)

 

Syntax: qos device-priority < ip-address> dscp < codepoint >

 

Assigns a DSCP policy to packets carrying the specified IP

 

address, and overwrites the DSCP in these packets with the

 

assigned < codepoint > value. This policy includes an 802.1p

 

priority and determines the packet’s queue in the outbound

 

port to which it is sent. If the packet leaves the switch in a

 

tagged VLAN, it carries the 802.1p priority with it to the next

 

downstream device. (Default: No-override)

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