how to create virtual network in OS X 10.9

ifconfig lo0 alias 172.16.123.1 will add an alias IP 172.16.123.1 to the loopback adapter

sudo ifconfig en1 alias 172.16.123.1

ifconfig lo0 -alias 172.16.123.1 will remove it

sudo ifconfig en1 -alias 172.16.123.1

Reference: 

http://stackoverflow.com/questions/87442/virtual-network-interface-in-mac-os-x