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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 20 Configuring QoS
Configuring QoS
Configuring the DSCP-to-CoS Map
You use the DSCP-to-CoS map to generate a CoS value, which is used to select one of the four egress
queues.
Table 20-5 shows the default DSCP-to-CoS map.
If these values are not appropriate for your network, you need to modify them.
Beginning in privileged EXEC mode, follow these steps to modify the DSCP-to-CoS map:
To return to the default map, use the no mls qos dscp-cos global configuration command.
This example shows how to map DSCP values 0, 8, 16, 24, 32, 40, 48, and 50 to CoS value 0 and to
display the map:
Switch# configure terminal
Switch(config)# mls qos map dscp-cos 0 8 16 24 32 40 48 50 to 0
Switch(config)# end
Switch# show mls qos maps dscp-cos
Dscp-cos map:
d1 : d2 0 1 2 3 4 5 6 7 8 9
---------------------------------------
0 : 00 00 00 00 00 00 00 00 00 01
1 : 01 01 01 01 01 01 00 02 02 02
2 : 02 02 02 02 00 03 03 03 03 03
3 : 03 03 00 04 04 04 04 04 04 04
4 : 00 05 05 05 05 05 05 05 00 06
5 : 00 06 06 06 06 06 07 07 07 07
6 : 07 07 07 07
Note In the above DSCP-to-CoS map, the CoS values are shown in the body of the matrix. The d1 column
specifies the most-significant digit of the DSCP; the d2 row specifies the least-significant digit of the
DSCP. The intersection of the d1 and d2 values provides the CoS value. For example, in the
DSCP-to-CoS map, a DSCP value of 08 corresponds to a CoS value of 0.
Table 20-5 Default DSCP-to-CoS Map
DSCP value 0–78–15 16–23 24–31 32–39 40–47 48–55 56–63
CoS value 0 1 2 3 4 5 6 7
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
mls qos map dscp-cos dscp-list to cos Modify the DSCP-to-CoS map.
• For dscp-list, enter up to 8 DSCP values separated by spaces. Then
enter the to keyword.
• For cos, enter the CoS value to which the DSCP values correspond.
The DSCP range is 0 to 63; the CoS range is 0 to 7.
Step 3
end Return to privileged EXEC mode.
Step 4
show mls qos maps dscp-to-cos Verify your entries.
Step 5
copy running-config startup-config (Optional) Save your entries in the configuration file.
