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Knowledge document #606

Cannot establish connections using the Teredo protocol

You cannot use the FRITZ!Box's internet connection to establish connections using the Teredo protocol. As a result, you cannot use Windows Remote Assistance via Easy Connect or establish DirectAccess connections, for example.

Cause

  • For security reasons, the FRITZ!Box blocks UDP port 3544 when an IPv6 internet connection is active. This means that applications cannot use the Teredo protocol to access the internet; they are therefore also unable to bypass the FRITZ!Box's firewall and establish their own IPv6 connections using Teredo instead of using the FRITZ!Box's existing IPv6 connection. Thus, the FRITZ!Box complies with standardized recommendations for home network devices (RFC 6169 Section 3.1.3).

    Note:Teredo (RFC 4380) is an IPv6 tunneling mechanism devised to facilitate the transition from IPv4 to its successor IPv6. Teredo encapsulates IPv6 data packets from Windows computers within IPv4 data packets and transmits these to a Teredo server from Microsoft. This server then forwards the IPv6 data packets to their actual destination.

There are several ways to solve the problem, depending on whether the application can only be used with or also used without Teredo.

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

1 Configuring an application for use without Teredo

  1. Configure the application so that it uses the FRITZ!Box's IPv6 connection instead of Teredo. Refer to the manufacturer for information on how to use the application without Teredo, for example consult the manual.

2 Disabling the Teredo filter in the FRITZ!Box

If the application can only be used with the Teredo protocol, disable the Teredo filter in the FRITZ!Box:

  1. Click "Internet" in the FRITZ!Box user interface.
  2. Click "Filter" in the "Internet" menu.
  3. Click on the "Lists" tab.
  4. Click "Global Filter Settings" to display all of the settings.
  5. Disable the option "Teredo filter enabled".
  6. Click "Apply" to save the settings.
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