How to configure sub-interfaces for layer 3 switches

Enter the global configuration mode of the switch: configure terminal
Create a sub-interface and specify the physical interface and sub-interface number to use. For example, create a sub-interface Fa0/1.1, using the physical interface FastEthernet0/1, with sub-interface number 1: interface FastEthernet0/1.1
Configure Internet Protocol Address and Subnet Mask for Subinterfaces: IP address < Subnet Mask >
Configure the VLAN to which the sub-interface belongs (if required): encapsulation dot1q
Activate sub-interface: no shutdown
Exit sub-interface configuration mode: exit
Repeat the above steps to configure the other sub-interfaces that need to be configured.
Save configuration: write memory