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