Tried to increase DCHP Address range, but now getting error messages

Sounds like you've got some growing pains in your organization.

You could do it with a couple of Class C networks (say 192.168.200.x and 192.168.201.x) but you'll need to address routing issues between the subnets. I'd look at converting the whole thing over to a Class B or even a Class A instead.

Say, using the Class B subnet, 172.16.0.1, with a netmask of 255.255.252.0 would give you 1022 useable addresses (or with a netmask of 255.255.248.0, 2046 useable addresses) but you would also need to update your DNS, any static IP addresses on your network, gateways, etc.

Definitely going to be a bit more work than plugging in a few numbers. Depending on the size of your organization, it may be worthwhile to bring in an experienced consultant to help with the change.

Used Server Admin DCHP > Starting iP Address: 192.168.200.5, Ending IP Address (was 192.168.200.250) changed this to 192.168.205.250

The address pool you specify has to be valid for your network.

If your server's network is using a 255.255.255.0 subnet mask (check System Preferences -> Network) then the entire range of available addresses for your network runs from 192.168.200.1 through 192.168.200.254. That includes all the addresses available for statically-configured devices (e.g. your server, router, etc.) as well as all DHCP clients.

When you set the upper range to 192.168.205.252 you've exceeded the upper limit, and that's why the server is reporting an error.

You'll have to look at your network to see if there's enough space in your 192.168.200.0/255.255.255.0 network. If there isn't (e.g. you need more than 254 addresses) then you'll need to change your subnet mask to give yourself more addresses, but that has other repercussions - i.e. you'll have to re-configure every device on your network to match.

It *might* be possible to configure an additional LAN on your server, using a second subnet, but the validity of this solution depends on what other devices you have that you need to connect.

If you want more than 254 devices on your network you have two options:

1) expand your current subnet. Instead of using a 255.255.255.0 subnet mask, use 255.255.252.0.

This will change the range of your IP addresses from 192.168.200.0 - 192.168.0.255 to 192.168.200.0 - 192.168.203.255. In other words, you grow from a total of 256 addresses to 1024 addresses. That should be enough for your needs, but you can go even larger if you need.

However, this will involve reconfiguring every device (including your router and your printer) to have the new subnet mask - their IP addresses don't need to change, just the subnet mask). For DHCP-based clients this shouldn't be a big deal - reconfigure your DHCP server to hand out the right subnet and the next time those machines connect they'll get the right settings.

2) The other option is to add a second private LAN using a different range of IP addresses. In some ways this is simpler - you don't need to reconfigure existing devices - but you may run into issues if devices on the new subnet need to talk to a device on the existing subnet (e.g. your printer). I generally would not recommend this path unless you prefer to segregate your clients for some reason.