Two networks - same interface

Is it possible to put a switch on an RB411 and run the WAN and LAN side of the router on one physical interface? I’m still trying to find a solution for replacing the lost 133 board. I need that physical size but more than one ethernet port.
Thanks.

you can but its not recommended and makes things harder. Its also somewhat of a security problem. if you have a vlan capable switch then that would work just like multiple nics, you just assign vlans to the ports on the switch and create vlans on the mikrotik to match.