How do I disable the FXS ports for my Billion VoIP modem /router?

By default, if you enable the FXS ports on the Billion 7401 - 7404 series router to be sip enabled, the router automatically forwards the port (5060) to its own IP address and an error will occur if you try to forward that port to the engin voicebox. This is because it is intended for the FXS ports to connect directly to a SIP provider. To overcome this issue, complete the following.

From a windows command prompt

  1. Type: 
    telnet 192.168.1.254
  2. Enter the username: admin and password: admin 
  3. Type: 
    voip set interfacename iplan
    (this changes it from the WAN to the LAN interface)
  4. Type: 
    system config save
  5. Type: 
    user logout
  6. Now you can add the NAT to point to the engin voicebox.