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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter20 Configuring QoS Configuring QoS
Configuring the DSCP Trust State on a Port Bordering Another QoS Domain
If you are administering two separate QoS domains between which you want to implement QoS features
for IP traffic, you can configure the switch ports bordering th e domains to a DSCP-tru sted state as shown
in Figure20-9. Then the receiving port accepts the DSCP-trusted value and avoids the classification
stage of QoS. If the two domains use different DSCP values, you can configure the
DSCP-to-DSCP-mutation map to translate a set of DSCP values to match the definition in the other
domain.
Figure20-9 DSCP-Trusted State on a Port Bordering Another QoS Domain
Beginning in privileged EXEC mode, follow these steps to configure the DSCP-trusted state on a port
and modify the DSCP-to-DSCP-mutation map. To ensure a consistent mapping strategy ac ross both QoS
domains, you must perform this procedure on the ports in bo th d omai ns:
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QoS Domain 1 QoS Domain 2
Set interface to the DSCP-trusted state.
Configure the DSCP-to-DSCP-mutation map.
IP traffic
Gigabit
Ethernet
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Gigabit
Ethernet
0/3
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 mls qos Enable QoS on the switch.
Step3 mls qos map dscp-mutation
dscp-mutation-name in-dscp to out-dscp Modify the DSCP-to-DSCP-mutation map.
The default DSCP-to-DSCP-mutation map is a null map, which maps
an incoming DSCP value to the same DSCP value.
For dscp-mutation-name, enter the mutation map name. You can
create more than one map by specifying a new name.
For in-dscp, enter up to eight DSCP values separated by spaces.
Then enter the to keyword.
For out-dscp, enter up to eight DSCP values separated by spaces.
The DSCP range is 0 to 63.
Step4 interface interface-id Enter interface configuration mode, and specify the interface to be
trusted.
Valid interfaces include physical interfaces.
Step5 mls qos trust dscp Configure the ingress port as a DSCP-trusted port.