It follows standard cidr rules. for example, I am using 255.255.254.0 to allow for more than 255 access points on the ap-management interfaces. If you need options like dhcp reservations,etc. you may want to use an external server.
I am concerned because, in configuration guide of controller is show;
"Internal DHCP Server
The controllers contain an internal DHCP server. This server is typically used in branch offices that do not already have a DHCP server. The wireless network generally contains 10 access points or fewer, with
the access points on the same IP subnet as the controller. The internal server provides DHCP addresses to wireless clients, direct-connect access points, appliance-mode access points on the management interface, and DHCP requests that are relayed from access points. Only lightweight access points are supported."
I like use the controller as dhcp server, but I'm concern if controller support a number of 50 APs for example.
obs: excuse for the orthographic mistakes, my English is not so good.
Yes, 50 will be the limit. Hopefully you have more than 1 controller. I put half my dhcp scope on one controller and the other half on another. I have 4 controllers with @ 24 APs balanced across all. This way, if I lose a controller, the APs will have a controller to roll to. I also have ap-management interfaces per controller and flip-flop the primary controller port on each. Also, my dhcp scope for APs is 5+ days, so if I lose a controller with part of the dhcp scope, I have time to bring it up on another controller