Prior to "upgrading" to Mountain Lion Server, I used OS X Server as my DHCP server. The purpose of the configuration I had was to provide MAC filtering, assigning static leases based on hardware MAC addresses. In Server, I had sets of address ranges and specified static leases for all the hardware on my network. This worked fine for years, but since updating to Mountain Lion, though all of my settings appear to have been migrated successfully, my server now issues "dynamic" IP addresses to hardware for which I have set static addresses. These addresses are not only wrong, they duplicate addresses that I have configured statically (for hardware that is off or out of the building at the time). Moreover, any attempt to correct this by setting the correct IP address manually at the client, results in loss of WAN access for that client.
Server's static mapping of IP addresses was a key element of my security set up that is now thwarted by whatever Mountain Lion Server is doing (or not doing).
Why does Server issue dynamic leases for MAC addresses for which I have set static IP addresses? Is there some setting that I've missed — that was not automatically migrated — that will prevent Server from issuing dynamic DHCP leases?
Update: This is getting worse, rather than better. Server seems to pay no attention to the "static" entries in the list of clients, and uses the IP addresses there for whatever client it feels like, completely disregarding the MAC addresses specified for those static addresses. Worse, it issues as dynamic IP addresses that are intended for specific MAC addresses, thus "using them up", so that they become unavailable for the machines to which they have been configured. This is completely scrambling my network. For the time being, Server continues to assign most addresses correctly, but gradually (with no apparent pattern) it is scrambling more and more of my network. Eventually I'll loose the ability to administer the network, which depends on my admin machine having the correct IP address (which I've had to force using
sudo ipconfig set en0 INFORM ..; using a manual assignment in Network Preferences doesn't work reliably).