FRITZ!Box 3390 Service - Knowledge Base

FRITZ!Box 3390 Service
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Cannot access FRITZ!Box home network using port sharing

Although port sharing is configured, you cannot access the FRITZ!Box or devices (for example NAS systems) or web servers, remote maintenance servers, and other server services in your home network from the Internet.

Important:Some of the settings described here are only displayed if the advanced view is enabled in the user interface. The configuration procedure and notes on functions given in this guide refer to the latest FRITZ!OS.

Simply proceed as described below. After each measure, check whether the issue persists.

1 Checking whether a public IP address was obtained

You can only use the conventional Internet Protocol v4 (IPv4) to access the FRITZ!Box or devices in the home network from the Internet if the FRITZ!Box establishes its own connection to the Internet using a modem (for example a DSL or cable modem), and your Internet service provider assigns the FRITZ!Box an IPv4 address from the public address range:

Important:The FRITZ!Box is only accessible over IPv6 when used on a DS-Lite ("Dual-Stack Lite") connection, and not over IPv4. When DS-Lite is active, the status "IPv4 over DS Lite" is displayed under "Connections" on the "Overview" page of the FRITZ!Box user interface.

  1. Check the address range of the IPv4 address that the Internet service provider assigned to the FRITZ!Box.
  2. If the FRITZ!Box obtained a public IPv4 address, proceed with the following section.
    • You cannot access the FRITZ!Box, devices, or server services in the home network over the Internet if the FRITZ!Box obtained a private IPv4 address.

2 Setting up port sharing in the FRITZ!Box

Setting up static port sharing

The following step is only necessary if the device or server service uses 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 UPnP.

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, then 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" or "Port Forwarding" 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 button (Edit) 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 that you can use port 81 to open its user interface.

3 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 would like to access.
  5. If Internet access has been restricted or blocked for the device, configure the parental controls for the device so that it has unrestricted Internet access.

4 Disabling the NetBIOS filter

The following step is only necessary if you would like to use the SMB or CIFS protocol to establish connections to devices in the FRITZ!Box home network (for example in order to access shared files or printers over the Internet):

ATTENTION!The FRITZ!Box filters TCP and UDP ports 139 and 445 ("NetBIOS filter") because they are often used to attack computers and these ports are normally not required for communication in the Internet. Only disable the NetBIOS filter if a firewall is set up on each of the computers.

  1. Click "Internet" in the FRITZ!Box user interface.
  2. Click "Filters" in the "Internet" menu.
  3. Click on the "Lists" tab.
  4. Disable the option "NetBIOS filter enabled".
  5. Click "Apply" to save the settings.

5 Configuring the computer's firewall

If the server service or application is installed on a computer with its own firewall (for example Windows firewall), you must also configure the firewall:

  • Configure the computer's firewall according to the manufacturer's instructions so that the server service or application can be accessed from the FRITZ!Box home network.

Now the FRITZ!Box is completely configured so that the FRITZ!Box or devices or server services in the FRITZ!Box home network can be accessed over the Internet.

Note:If the issue persists, inappropriate settings or errors in the relevant application or device may be the cause.