My IPv6 setup

For my latest ugly hack, I wanted to give any/every machine in the house a globally-routable IPv6 address, and I didn’t want to have to babysit the setup every time the router’s IPv4 address changed.

I actually already had 6to4 up and running on one machine (but failing these two requirements) since this post a couple of years ago. To extend it, I’ve borrowed heavily from Michael Wensley’s howto, but used a different approach which I find more readable. (Danger, automatic modification of config files ahead…)

The idea here is for one machine on your network to set up a tunnel to your nearest 6to4 relay, thereby receiving an IPv6 prefix of the form 2002:wwxx:yyzz::/48, which it can then share among the other hosts by autoconfiguration using radvd. The machine on which you do this doesn’t have to be your router, but it will be the gateway for all IPv6 traffic, so pick something that’s usually powered on. Don’t pick a machine on which you want to run Steam, because you’ll want it to be the router’s DMZ destination, and Steam bizarrely refuses to run in a DMZ. It also doesn’t tell you that this is the problem. Yes, I did find this out the hard way. :-)

Having chosen a machine, add something like this tun6to4 stanza in /etc/interfaces, but replace abc with the internal address of this machine, and replace both instances of wwxx:yyzz with your router’s current external IPv4 address, in hex. A quick converter:

echo |sed 's/\./ /g' |xargs printf %02x%02x:%02x%02x\\n

Before bringing that interface up, be sure this machine has a firewall for both IPv4 and IPv6, because you’re about to have some shiny new globally reachable attack surface of your very own. :-) This should involve

ip6tables -P INPUT DROP; ip6tables -P FORWARD DROP

(or words to that effect) and poking holes as needed. There must be far better examples around, but this is the general idea. When you’re ready, set your router’s DMZ setting (or whatever it calls the machine to which to pass inbound traffic by default) to this machine. You actually only need IP protocol 41, but I don’t expect any home router can be that specific. :-) Run ifup tun6to4. You can now try ping6 (or browsing there).

Sharing the fun with the rest of the house isn’t any harder: apt-get install radvd and use this /etc/radvd.conf or something similar (replace wwxx:yyzz again). When you restart radvd, machines should begin to acquire IPv6 addresses in this subnet. If not, see what they say to sysctl -a |grep accept_ra and dmesg. Note that my firewall example above deliberately prevents inbound traffic to them until you add something like the commented FORWARD line.

Now for the ugly hack to update all of this. It’s quite simple, just substituting the prefix as necessary. You’ll need to edit it for your particular router; you may need to authenticate and might not find the IP at its root URL for example. Your firewall arrangements may also differ. Here it is:, and you’ll want to add this to /etc/crontab, perhaps every few minutes (if the IP hasn’t changed, it exits without writing anything).

Happy hacking. :-)