OSX: Have both a static and dynamic IP address at the same time – Mr. Joel Kemp

Here’s how you can set up OSX to have a DHCP IP address and a Static IP address at the same time. Some tutorials on configuring a static IP will tell you to change your network interface to a manual configuration, but although that works, it prevented me from also using the internet. Plus, you’d have to remember to switch back to DHCP configuration. There’s an easier way.

I’m using OSX Lion, but the instructions should hold for Mountain Lion and Snow Leopard – though the button locations may differ

1. Go to Preferences -> Network
2. Use the + icon down the bottom left to duplicate the desired interface (wifi, ethernet etc…)
3. Select the newly duplicated network interface
4. Click Advanced
5. Select TCP/IP from the dropdown list
6. From the Configure IPv4 menu, select the ‘Manually’ option.
7. Enter the desired, static IP address (ex: 192.168.1.110) in the IPv4 Address field.
8. Click OK
9. Click Apply

Now you have a DHCP address on the original interface and a static ip on the copy of the interface.

This was based on the tutorial here with the dual-interface approach described in the comments.