Using OpenDNS on Your Fon Router

There is large interest in OpenDNS, and I happen to be a fan of it myself.  Sadly, Fon routers, when connected directly to a modem and using DHCP, use the ISP's DNS servers and don't allow you to override those settings.  Fortunately, there is a loophole in older Fon firmware that allows you to enable a BusyBox shell (so you can connect to it via SSH).  This is actually a security hole and shouldn't be a good thing at all, but hey, I'm kind of glad it exists.  Anyways, let's get started.

Enable SSH access to your Fon router by following these instructions.  Be sure to enable permanent SSH access, as it'll be very useful later.  When your Fonera updates to newer firmware that doesn't allow code injections, SSH will still be enabled.  Be sure to leave your network cable unplugged until after you enable SSH permanently or you might form some gray hairs.

Now, in a shell, let's create a startup script that overrides the ISP's DNS settings after the network is initialized.  Type the following:

vi /etc/init.d/S45opendns

Now, in the vi window, paste this (press i to insert text):

echo "nameserver 208.67.222.222" > /etc/resolv.conf
echo "nameserver 208.67.220.220" >> /etc/resolv.conf

This will "blank" /etc/resolv.conf and load it with the OpenDNS settings.  Save and exit vi (press the esc key then type :x).

Now, to make the file executable type:

chmod +x /etc/init.d/S45opendns

You're all done!  OpenDNS settings will be persistent across reboots.  You can activate the settings now without having to reboot by simply running your new script:

/etc/init.d/S45opendns

If DHCP renewals cause your new nameserver settings to be overwritten to the ISP's, you can create a cron job that runs every few minutes (you can pick a time based on your ISP's DHCP lease time):

Type crontab -e in the terminal window.  When vi opens, insert the following line at the end:

15 * * * * /etc/init.d/S45opendns

This will run your new script every 15 minutes, so there will never be more than a 15-minute period where you will not be using OpenDNS.

That should be all you need to get you going. If you're using more advanced features of OpenDNS, you can use DNS-O-Matic on your Fon to keep OpenDNS informed of IP changes. Comment below with your experiences.