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Knowledge document #1083

Cannot access the FRITZ! home network using port sharing

Although port sharing is configured, you cannot access devices in the home network of the FRITZ!Box, for example a NAS system, a web server, or remote maintenance server from the internet.

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

Note:All instructions on configuration and settings given in this guide refer to the latest FRITZ!OS for the FRITZ!Box.

1 FRITZ!Box is not accessible on the internet

Devices in the home network of the FRITZ!Box can only be accessed if the FRITZ!Box has an IPv6 or IPv4 address that is reachable on the internet and the device that is accessing it can reach this IP address.

Access via IPv4

For IPv4 internet access, the FRITZ!Box must obtain a public IPv4 address from the internet service provider. Access over IPv4 is not possible if the FRITZ!Box receives a private IPv4 address.

You can find out whether the FRITZ!Box has a public or private IPv4 address using the guide Identifying the address range of the IPv4 address for the internet connection.

Access via IPv6

For IPv6 internet access, both the FRITZ!Box and the device that is to access the FRITZ!Box must be connected to the internet over IPv6. If only the FRITZ!Box receives an IPv6 address but the other device is not connected to the internet via IPv6, IPv6 internet access is not possible.

You can call up the menu "Internet > Online Monitor" in the FRITZ!Box user interface to determine whether the FRITZ!Box is connected to the internet via IPv6.

You can test whether the device that is to access the FRITZ!Box is connected to the internet over IPv6 by calling up www.test-ipv6.com or www.ipv6-test.com on the device.

2 Setting up port sharing in the FRITZ!Box

The following step is only necessary if the device or server service uses PCP (Port Control Protocol) or UPnP (Universal Plug and Play) to open the ports it requires in the FRITZ!Box itself:

Note:If static port sharing is not configured for a device or application in the FRITZ!Box, in some cases other devices or applications may be able to configure the necessary port sharings for themselves using PCP or UPnP.

  1. If the devices or server services are accessible via a URI scheme (Uniform Resource Identifier) like https:// or ftp://, set up MyFRITZ! accesses for them.
  2. If the devices or server services are not accessible via a URI scheme (for example remote maintenance or VPN servers) or are to be accessed independently of MyFRITZ!, set up static port sharing for them.

3 Checking externally assigned ports

The FRITZ!Box may not always be able to open the desired ports, for example because the same port is already released for a different device or, with automatic port sharing via PCP, the internet service provider did not release the desired port:

  1. Click "Internet" in the FRITZ!Box user interface.
  2. Click "Permit Access" in the "Internet" menu.
  3. Click on the "Port Sharing" tab.
  4. Check whether the desired ports for IPv4 or IPv6 are displayed for the respective device by "Port Assigned Externally".
  5. If external ports other than the ones you want are displayed for sharing, use the ports displayed here to access the device or server service.

4 Do not disconnect automatically

  1. Click "Internet" in the FRITZ!Box user interface.
  2. Click "Account Information" in the "Internet" menu.
  3. Click "Change connection settings".
  4. Enable the option "Maintain permanently (recommended for flat rates)". If the option is not shown, the FRITZ!Box is already permanently connected to the internet.
  5. Click "Apply" to save the settings.

5 Configuring parental controls to allow internet access

You cannot access devices in the home network over the internet if the FRITZ!Box parental controls restrict the device's internet access. Therefore, make sure that the respective devices are allowed to access the internet:

  1. Click "Internet" in the FRITZ!Box user interface.
  2. Click "Filter" in the "Internet" menu.
  3. Click on the "Parental Controls" tab.
  4. Check whether internet use has been restricted for the device you want to access.
  5. If internet use has been restricted or blocked for the device, configure the parental controls for the device so that it has unrestricted internet access.

6 Disabling the NetBIOS filter

The following step is only necessary if you want to access shared files and printers in the home network over the internet and your internet service provider does not block TCP and UDP ports 139 and 445 that are used for this:

Important:For security reasons, the FRITZ!Box and some internet service providers (for example in the cable and mobile networks) block access from the internet to the ports used for file and printer sharing ("NetBIOS Filter"). Therefore, only disable the NetBIOS filter in the FRITZ!Box if a firewall is set up on each of the devices.

  1. Click "Internet" in the FRITZ!Box user interface.
  2. Click "Filter" in the "Internet" menu.
  3. Click on the "Lists" tab.
  4. Disable the option "NetBIOS filter enabled". If the option is not displayed, enable the Advanced View first.
  5. Click "Apply" to save the settings.

7 Configuring the device's firewall

If the server service or application is installed on a device with its own firewall (for example Windows firewall), the firewall must also be configured:

  1. Configure the device's firewall according to the manufacturer's instructions so that the server service or application can be accessed.

Now the FRITZ!Box is fully configured so that the FRITZ!Box or devices or server services in the FRITZ!Box home network can be accessed over the internet. If the issue persists, inappropriate settings or errors in the relevant application or device may be the cause.

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