Adding IP Addresses
From Mac OS X Server FAQ
There are three ways to configure additional IP addresses in Mac OS X Server. First is to use the Network preference pane to duplicate the desired port (this also works in mac os x client), the second way is to use the /etc/IPAliases file, and the third is to use the networksetup command line tool, which mimics the functionality of the Network preference pane, but from the command line.
