ASUS DSL-AC56U modem wizard is only for ADSL connection.
If you want to use ASUS DSL-AC56U modem for NBN with FTTP (fibre to the premises), then go to WAN section then on Transfer Mode select Ethernet WAN.
Make sure your network cable is connected on UNI-D1 (or active UNI-D port) back to the E-WAN port of the ASUS DSL-AC56U modem.Add a comment
The reason why it had been disconnecting every 4 or 5 minutes is because two different modems from two different locations were trying to authenticate at the same time, even though both modems are set to dynamic and there were no broadband username and password set to the modem.Add a comment
Go to modem/router configuration page and enable ICMP or Respond to ping on Internet WAN Port