In OS X it is possible to assign more than one IP address to a single ethernet card. You might use this for instance if you wanted to use one IP as an external (public) IP and another as an internal-only secure IP for admin or whatever your needs are.
I was trying to do this via the Terminal in the same way it is done in other Unix variants. That method is:
% ifconfig eth0:2 192.168.1.132 upHowever, it's even easier in OS X. I cannot take credit for discovering this though - it is listed in an article at AFP548.
Let's say you currently have your machine IP set to 192.168.1.100 and you want to add a virtual IP address of 192.168.1.101 so both IP's point to your machine.
- Open Network Preferences pane.
- Selct "Active Network Ports" from the "Show" pull-down menu. Highlight your ethernet interface and hit the duplicate button.
- Configure the NEW ethernet interface with IP 192.168.1.101 and the other items as desired. The article at AFP548 states you should use netmask 255.255.255.255 or you will run into trouble. I ignored that and used my standard 255.255.255.0 and other items the same as my original IP.