Assign IP address script

Our school district uses DHCP to assign IP addresses to computers. We reserve IP addresses in the range 230-255 in each subnet so we can statically assign IP addresses to our network printers. For example, in subnet 80 we have the following addresses set aside for printers:

10.121.80.230, 10.121.80.231,.......,10.121.80.255

We have 10 different subnets on campus.

I have a database that keeps track of all our printers. I have a checkbox in one of my layouts labeled Networked. I have a script attached to this checkbox that I would like to do the following:

- When it is clicked and becomes checked I want the next available IP address in the subnet to be assigned to this printer. In other words, if we currently have subnet 12 with no networked printers and then we network one of them, I click the checkbox and this printer gets assigned 10.121.12.230. This assignment happens within Filemaker, we would still go to the printer and assign the address manually trough the printers interface. The second printer networked would automatically get 10.121.12.231. The first three octets (10.121.12) are easy to figure out. Every printer gets 10.121 and the subnet can be pulled from my Rooms database that keeps track of subnets for each room. How do I get Filemaker to dish out the last octet (230, 231, 232, etc)?

- When a networked printer is taken out of service, I want to click the Network checkbox to uncheck it and return its IP address to the pool of available addresses. For example, I already have the following addresses used:

10.121.12.230

10.121.12.231

10.121.12.232

10.121.12.233

I then take the printer with IP address 10.121.12.231 out of service. I want its IP address returned to the available pool AND be the next address assigned to a networked printer in this subnet.

Any ideas? I have thought of a few but none seem particularly elegant

Dave