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Knowledge document #1083

Cannot access FRITZ!Box home network using port sharing

Although port sharing is configured, you cannot access devices in the FRITZ!Box home network, 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 Public IP address required for access

You can only access devices in the FRITZ!Box home network over the internet if the FRITZ!Box obtains a public IPv4 address or an IPv6 address from your internet service provider when it connects to the internet.

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 obtains a private IPv4 address.

You can find out whether the FRITZ!Box obtained a public or private IPv4 address by following the steps in our 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 obtains 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

Setting up static sharing

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. Configure static port sharing in the FRITZ!Box for the devices or server services.

Deleting multiple port sharings for the same destination port

You cannot access different devices in the home network over the internet if packets being sent to the same port (destination port) on the FRITZ!Box are supposed to be forwarded to different IP addresses in the home network.

If several port sharings are configured for the same destination port, the first port sharing rule to be used deactivates all of the other port sharing rules for this destination port. Other port sharings are blocked from using this destination port until it has not been accessed for 15 minutes.

Example:
In the FRITZ!Box you configured port sharing from port 80 to port 80 for a web server, and port sharing from port 81 to port 80 for a NAS system. The web server cannot be reached if the NAS system is being accessed over the internet.

Use a different destination port for each port sharing. Otherwise you may not be able to or sometimes may not be able to access certain devices or server services:

  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. If several ports sharings are configured for the same destination port ("to Port") in the "List of Shared Ports":
    1. Configure the devices or server services to use a port that is not used by other devices in the FRITZ!Box home network.
    2. Click the (Edit) button next to all port sharings for the same destination port and enter a new port number for "to Port".

      Example:
      Configure port sharing from port 80 to port 80 for your web server. Configure port sharing from port 81 to port 81 for the user interface of your NAS system and adjust its settings so you can use port 81 to open its user interface.

3 Maintaining a permanent internet connection

  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.

4 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 "Filters" 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.

5 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.

6 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 to allow access to the server service or application from the FRITZ!Box home network.

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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