I have a need to have lots of internal SSL sites, so I need lots of internal IPs. With some helpful advice here on this site, I learned I can change my subnet mask to raise the limit of hosts that I have.
I've got my statically-configured servers changed over from 255.255.255.0 to 255.255.0.0. But my DHCP-enabled computers all get the subnet mask automatically from my DHCP server. The DHCP server itself is now on 255.255.0.0. But when I renew the lease on a DHCP-enabled client, it still gets the subnet mask 255.255.255.0. I want them all to get 255.255.0.0 automatically.
Note: I would like all of my computers to be able to talk to each other. So I would like them all to have the 255.255.0.0 subnet mask. However, I do not need to increase my DHCP scope (as far as I know). I am fine with it handing out only IPs within 192.168.0.x. I just want those computers that it serves to be able to communicate with the computers who have IPs such as 192.168.60.1.
If I right-click my Scope in DHCP (I have only one DHCP server with one scope), I can see the start and end IP addresses are currently 192.168.0.1 and 192.168.0.254 respectively (and I have an exclusion range defined elsewhere). However, subnet mask is grayed out. I suppose there is a distinction, though. The subnet mask here likely defines the subnet mask of the range I am defining, which I don't think I need to change. I just want the DHCP server to hand out the newly increased subnet mask to clients that are asking for DHCP service.
So how do I tell my DHCP server "Hey man, we do things differently now. Tell people the subnet mask is 255.255.0.0." I tried saying it out loud but the server was unresponsive.
Update: I am going to re-create the scope as suggested. You are probably all correct but I will set an answer after I confirm that it works. Or confirm that it would probably work but I am too stupid to get it to work. :)
Update 2: I have a new Windows Server 2008 R2 Server that I am migrating services to. I took this opportunity to install the DHCP role over there and create the new scope on that server instead. When I added the role, the setup wizard was very clear about which IPs were part of the first scope you were creating, and what would get served as the subnet mask. I simply followed the directions. I then authorized the new DHCP service, and De-Authorized the old one. Everything is great now.
Even though I had many DHCP reservations, the whole process only took a half hour. I would have spent as much time fiddling with an import/export process.