OK, so I have a subnet (192.168.11.0) that currently has all servers and clients on it. It's running out of addresses. So, I create a new subnet (192.168.12.0) and change my DHCP server (Fortigate ...

To connect some copiers or multi-function printers to a router, you may need to know the subnet mask value for the network. A subnet mask defines the value range of IP addresses used in a workgroup.