In OS X Server (Mountain Lion) DHCP is used by the NetInstall service to provide startup information to NetInstall and NetBoot clients.

DHCP is also used by Internet Sharing (in the Sharing Pane of System Preferences) to provide addresses to clients on the private network that are using the server's Internet connection.

Only one of these two services can be used at one time. If you turn on NetInstall, do not turn on Internet Sharing. If you turn on Internet Sharing, you cannot turn on NetInstall.

If you previously enabled NAT and DHCP in Server Admin in Lion Server, your configuration will not be preserved when you upgrade or migrate to OS X Server (Mountain Lion). You can restore the default NAT and DHCP configuration by disabling then enabling Internet Sharing in System Preferences.

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).

If you enabled DHCP in Mac OS X Server v10.6, your configuration will be preserved when you upgrade or migrate to OS X Server (Mountain Lion).

Additional Information

DHCP settings can be customized by creating or editing the /etc/bootpd.plist file. For instructions, please see man bootpd.

Important: You can use a custom bootp configuration alongside NetInstall, but not alongside Internet Sharing. Any custom changes to /etc/bootpd.plist will be overwritten if you enable Internet Sharing in the Sharing pane of System Preferences.