How to preserve DHCP server settings when migrating from Lion Server to Mountain Lion Server?

Solution 1:

The situation is actually simpler than some references make it seem. As Apple states:

If you enabled DHCP (only) in Server Admin in Lion Server, your configuration will be preserved when you upgrade or migrate to OS X Server (Mountain Lion).

Moreover, the Server app now provides a (very limited, but sufficient) user interface for controlling DHCP.

Solution 2:

I'm confused.

This is from ML server. Next, as I understand it, you CAN NOT run Internet sharing WITH DHCP turned on. You do one or the other. If you turn on Internet Sharing it will supersede the DHCP configuration.