hi, I hope that someone will help me. Is a strange Question. My network works correctly separating the IPs of the WAN (which is 

in truth the main LAN) from a SUB-LAN, if I ping the addresses in the WAN from the LAN side everything works fine, I reach and manage the devices. But if I'm on the WAN side and I try to reach the devices it doesn't work. This is obvious because normally it should work just like that ... but if I want to reach the LAN from the WAN, is there a way?
I'm not talking about using NAT, I ask you if there is a more "transparent" way for the network that is connected to the WAN port to reach the devices on the LAN. In essence, it is about breaking the broadcast domain between two networks, leaving the devices to talk to each other anyway. 
Is there another TPlink device I have to use? something like TL-SG3428, using VLAN ... but I know as creat the VLAN, but I don't know how reach the goal to permit a communication between them... 
It someone that can solve this incredible (for me) trouble?