FRITZ!Box 3390 Service - Knowledge Base

FRITZ!Box 3390 Service
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FRITZ!Box reports "The port sharing cannot be created or enabled"

You cannot set up port sharing in the FRITZ!Box. When you try to create a port sharing, one of the following error messages is displayed:

  • "Port sharing cannot be configured or enabled, because there is already a corresponding port sharing setting."
  • "Port sharing cannot be configured or enabled because the rules conflict with an internal rule."
  • "Port sharing cannot be created or enabled, because the port is already in use for remote maintenance (HTTPS) (Internet / Permit Access / FRITZ!Box Services)."
  • "Port sharing cannot be created or enabled because internet access to your storage media over FTP/FTPS is enabled (Internet / Permit Access / FRITZ!Box Services)."


  • The FRITZ!Box prevents you from creating port sharings for TCP or UDP ports that have already been shared as well as from sharing the IP protocols ESP and GRE more than once. It is not possible to share the same port or the IP protocol ESP or GRE more than once in NAT routers like the FRITZ!Box.

    Note:The FRITZ!Box checks all incoming and outgoing data packets and automatically rejects unwanted data from the internet (Stateful Packet Inspection). The FRITZ!Box uses the NAT (Network Address Translation) mechanism to check incoming data and determine which port it is addressed to, which IP protocol it is transporting, and which device it should be forwarded to. If ports or IP protocols are shared more than once, it is no longer clear which device the data is intended for.

1 Ports used by the FRITZ!Box

The FRITZ!Box itself uses some ports to provide functions such as internet telephony. Here we give you an overview of ports that are typically opened by FRITZ!Box services:

Note:You can find a list of all the ports being used by your FRITZ!Box in the user interface under "Diagnostics > Security".

  • TCP port 21 (internet access to storage media via FTP/FTPS)
  • TCP port 443 (MyFRITZ! or internet access to the user interface via HTTPS)
  • UDP ports 500 and 4500 (VPN)
  • TCP and UDP port 5060 (internet telephony)
  • UDP ports 7078-7109 (internet telephony)
  • TCP port 8089 (automatic configuration over TR-069)

2 Using a different port

If internet applications (for example chat software or online games) or several computers, game consoles or other devices connected to the FRITZ!Box require the same TCP or UDP port for incoming connections from the internet, configure the devices or applications so that they all use different ports:

Important:IP protocols ESP and GRE can only be shared for one device. There is no workaround for these IP protocols.

  1. Configure the device or application so that it does not use the same ports to accept connections from the internet that are used by the FRITZ!Box, other devices, or other applications.

    Important:If you use the same application on several computers, assign different ports for incoming connections in the application on each computer.

  2. Set up port sharings in the FRITZ!Box for the new ports you configured in the device or application.

Now all of the devices or applications for which you set up port sharing can accept connections from the internet.