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Knowledge document #3600
FRITZ!Box 5491
This support document is available for the following products:

FRITZ!Box does not establish a fiber optic connection

Although the FRITZ!Box was configured for use with a fiber optic line, the FRITZ!Box does not establish a fiber optic connection. The message "Fiber interrupted" is displayed on the "Overview" page of the FRITZ!Box user interface. The message "Fiber cable not connected" may be displayed in the "Fiber Information" of the FRITZ!Box.

Simply proceed as described below. After each measure, check whether the problem is solved.

1 Making sure that the fiber optic connection is supported

  1. Check the documentation for your fiber optic connection or ask your internet service provider whether it is a passive fiber optic connection according to the standard G.984 (GPON). It is not possible to use the FRITZ!Box with an active fiber optic network (ITU-T G.652, AON).

2 Checking the cabling

  1. Remove all cable extensions and adapters between the FRITZ!Box and the fiber optic socket.
  2. Use an undamaged cable to connect the FRITZ!Box with the fiber optic socket. The fiber optic cable may not have any kinks or be damaged. For detailed information, refer to the quick guide included with the FRITZ!Box and the manual.

    Note:The FRITZ!Box has an SC/APC connector (wide connector, polished at an 8-degree angle). Depending on the fiber optic socket, you may need to use a fiber optic cable with an adapter. The fiber optic cable is not included in your FRITZ!Box package. 

3 Installing the latest FRITZ!OS for the FRITZ!Box

Install the latest version of FRITZ!OS because it contains improvements for different fiber optic connections that can resolve the error:

  1. Install the latest FRITZ!OS on the FRITZ!Box.

4 Unlocking your FRITZ!Box

If you purchased your FRITZ!Box from a retailer, your internet service provider may have to unlock it first:

  1. Call the customer service of your internet service provider and have them unlock the FRITZ!Box for your fiber optic connection, if necessary. Depending on the provider, you can either call their customer service or use an activation portal to activate it.
    • With some providers, the FRITZ!Box's "GPON Serial" is required to unlock it. You can find this information on the bottom of the device.