Chapter 17 System Administration : VLANs : VLANs in NAT mode : Adding VLAN subinterfaces
  
Adding VLAN subinterfaces
A VLAN subinterface, also called a VLAN, is a virtual interface on a physical interface. The subinterface allows routing of VLAN tagged packets using that physical interface, but it is separate from any other traffic on the physical interface.
Adding a VLAN subinterface includes configuring:
Physical interface
IP address and netmask
VLAN ID
VDOM