I'm using several AirPort Extremes to create a wireless network for a large amount of devices. One AirPort is advertised to support 50 devices, so I'm using 4 AirPorts currently for 200 devices.
My setup consists of 1 AirPort in DHCP and NAT mode, and the remaining AirPorts in Bridge mode.
Now, I'd like to extend the network capacity to 400-ish devices.
One issue I see is that AirPort Utility only supports setting DHCP ranges within a /24 subnet, meaning that there is a maximum of around 250 devices possible.
It is important that all devices share the same subnet, because the used application requires UDP broadcasts to communicate with other peers.
It is also important that roaming (i.e. moving around in the room and reconnecting to other base stations without disconnects) is possible. This works fine with my 4 AirPort setup so far.
What is the preferred way to create a larger than default subnet (e.g. /23) using Apple AirPort Extreme?