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 192.168.178.1-255 and get static ip adresses inside this range too, and have no internet acess.

i use LEDE 17.01.4

See: https://lede-project.org/docs/user-guide/network_configuration