This program is an example for programmatically creating and deleting 
a vlan interface in Mac OS X and FreeBSD. 
You can also use ifconfig and ipconfig commandds to create a vlan interface 
and assign an IP address to it.
Creating a vlan interface:   ifconfig vlan100 create
Binding the created interface to a parent interface and assign vlan id: 
ifconfig vlan100 vlan 100 vlandev en0
Assigning an IP address using DHCP: ipconfig set vlan100