Scenario:

Procedures:

1. Add the VID (VLAN ID) to the port interface. In this example, the traffic will tag VLAN 2.

Console#configure
Console(config)#interface ethernet 1/1
Console(config-if)#switchport allowed vlan add 2 tagged
Console(config-if)#exit
Console(config)#interface ethernet 1/47
Console(config-if)#switchport allowed vlan add 2 tagged

2. Create a class map to classify the specified traffic. In this example, it will match to the traffic of CoS 0.

Console(config)#class-map CoS
Console(config-cmap)#match cos 0

Console#show class-map
Class Map match-any CoS
Description:
 Match CoS 0

3. Create a policy map and use the class command to configure policies for traffic which match the criteria defined in a class map. In this example, the value of CoS will be modified to "7" if the traffic match to the class map.

Console(config)#policy-map CoS-test
Console(config-pmap)#class CoS
Console(config-pmap-c)#set cos 7

Console#show policy-map
Policy Map CoS-test
Description:
 class CoS
  set CoS 7

4. Apply the policy map to the ingress or egress side of a particular interface. In this example, the policy map will be applied to ingress of port 1.

Console#configure
Console(config)#interface ethernet 1/1
Console(config-if)#service-policy ?
  input   Input direction
  output  Output  direction
Console(config-if)#service-policy input CoS-test

Console#show running-config interface ethernet 1/1
interface ethernet 1/1
 switchport allowed vlan add 2 tagged
 service-policy input CoS-test
!

Result:

When the switch received the packet of CoS "0" from port 1, this CoS will be modified to "7" then be sent out from the port 47.