Cisco IOS Sub Interface Command

R1#configuration terminal
R1(config)#interface fastethernet 0/0
R1(config-if)#ip address 10.2.1.1 255.255.255.0
R1(config-if)#interface 0/0.1
R1(config-if)#ip address 10.1.4.1 255.255.255.252

Helpful link
http://comtech247.net/2011/12/19/cisco-configuration/