Alternate Network Configurations with OS X

I have to configure or test routers fairly often. Usually I don't need to actually hook them up to the Internet; having a local connection is enough. Almost always the setup involves configuring a client for DHCP and having the new router supply that.

However, that's slightly inconvenient as normally my MacBook is set to a static IP. Switching to DHCP to work on a router means wiping that information out and then having to re-enter it when I'm done. That's at least mildly annoying, but there are at least two simple ways to deal with this.

The first is the more complex and I really can't think of any reason why you'd want to do it this way, but I'll mention it just in case. What you'd do is create another instance of the Ethernet interface. You can do that either by choosing "Duplicate Service" while highlighting the normal Ethernet connection or by clicking the "+" and adding a new Ethernet connection.

Click on the gear icon (arrow in image is pointing at it) to make that service "Inactive" normally. When you want to use it, make the static Ethernet inactive and this one active.

Locations

There's a far easier way. I created a new "Location" called "routers":

When I need to switch to work on a router, I just choose the "router" location and plug in. I can do that from the main Apple menu or from the Network Configuration in System Preferences. Either way, I'm instantly switched to the DHCP configuration I need and can instantly switch back when I'm done.