FRITZ!Box WLAN 3270: Customize DNS Servers

I finally had enough with my providers DNS mishandling, so I decided to change the DNS servers, preferably on the router level, since we have multiple clients connected. Alas, the Fritz!Box 3270 doesn’t support this; or, more specifically, it doesn’t expose the functionality in the UI.

As described in a number of places, you can actually do this by editing a config file on the box, which you can do by enabling telnetd first, which AVM is nice enough to let you do, either through dialing a magic number, or, if your particular box doesn’t have a phone socket, by uploading a prepared fake-firmware, which is easy because they don’t need to be signed.

This is just to confirm that this process indeed works with the 3270 as well.

Step 1: Enable telnetd. Here’s one of the better pages explaining this. Short version: the custom image really is just a .tar file, containing a /var/install script with the content /usr/sbin/telnetd -l /sbin/ar7login.

Step 2 (optional): Make it permanent. I had to hurry somewhat, because the box rebooted on my after like a minute or two of asking me on the web interface after the image upload (and getting no response). telnet fritz.box and echo ‘/usr/sbin/telnetd -l /sbin/ar7login’ > /var/flash/debug.cfg did the trick.

Step 3: Configure custom DNS servers. I followed the steps outlined here. Yes, that link worked just fine a couple days ago, now the entry seems to be gone, so let me replicate the steps here:

  • While in telnet, open the file we need to edit: nvi /var/flash/ar7.cfg
  • Search for “overwrite”: /overwrite. There are multiple occurances, the correct one is the one wrapped in the target { } with name=”internet”.
  • Change both values to your preferred servers. You need to press i to enter insert mode.
  • Leave the insert mode with ESC and save and exit with :wq.
  • Reboot, through the web interface, or by typing reboot.

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