Access private IP through WAN interface from LAN?

RouterOS Beginner Basics
2

Simple Answers are

  • isolate the L2 connection from GPON-Module port, via Switch to MT-4011 in a VLAN to use the physical port-connection between Switch and MT as trunk ports, or
  • just use a second port on the MT-4011 for the 192.168.1.0/24 connection/route

…also configure Firewall according to your level of security (externality/internality of 192.168.1.0/24 net).

For setting up VLANs, read this: http://forum.mikrotik.com/t/using-routeros-to-vlan-your-network/126489/1