Setup iot network interface without internet acess

I want to setup an iot( internet of things) wifi.

so i created an new wifi network, setup wifi - security and attatched it to a new network calles iot.

but how to setup the new network interface - iot ?

my goal is that the connected iot devices can only reach the ip range and get static ip adresses inside this range too, and have no internet acess.

i use LEDE 17.01.4