IPv6 with Hurricane Electric 6in4 tunnel on DD-WRT

Oct 23, 2010 4 min read solence Routers

My Asus WL500g Deluxe router is running an Eko build of DD-WRT, which comes with IPv6 support. They haven’t yet included it in the official releases for some reason. However, there is still no ISP offering native IPv6 here. It’s a shame. So some sort of tunnel is needed to finally equip my LAN with an IPv6 subnet.

I didn’t really trust those tunnel brokers, so I tried a 6to4 tunnel. There is a good tutorial and only a few scripts are needed to get it running. The problem was that my IPv4 address is dynamic and changes with every reconnect, which is also enforced every 24h. Unfortunately with 6to4 this also changes the IPv6 prefix since it includes the v4 address. That’s no fun and it also messes up the routing and clients using automatic address assignment. Ok, I need a tunnel broker.

My first try was SIXXS, which took like forever to get everything approved. After finishing the ‘paperwork’, my very own /48 subnet was ready. Some hours later I figured out how to run their proprietary aiccu client on my router. It basically worked, but the connection was slow and the client crashed again and again. The port for MIPS-based routers was from 2007 and I couldn’t find a more recent version. It was very disappointing. So hopefully Hurricane Electric will do better.

The tunnel request is pretty easy and instant. You don’t have to wait a week or two until everything is approved. There is no special software, so you have to rely on the tunneling features of your operating system, that is good. DD-WRT has no GUI to configure tunnels, so some scripts are necessary. The IPv6 tutorial for HE tunnels on DD-WRT is not very good, but I finally figured out how it works. To my surprise this solution is very stable and also very fast. The latency with IPv6 is sometimes even lower than with native IPv4. They must have a really good routing.

So here’s what needs to be done:

Get an Eko build running for IPv6 support. For my Asus router it’s the VINT build in V24_TNG.
Go to Administration and Management and under IPv6 Support, enable IPv6, Radvd and use the following for Radvd config:
```
interface br0 {
    MinRtrAdvInterval 3;
    MaxRtrAdvInterval 10;
    AdvSendAdvert on;
    prefix <Your subnet prefix>::/64 {
        AdvOnLink on;
        AdvAutonomous on;
    };
};
```
This enables Router advertisements, so all the clients can assign an address automatically. Note that this only works with /64 subnets. If you have an /48 subnet you can only use one /64 part of it. Make sure that br0 really is your LAN interface and replace it with the correct identifier otherwise.

Go to Commands under Administration and add the following Startup Script:

/usr/bin/wget 'http://ipv4.tunnelbroker.net/ipv4_end.php?
ipv4b=AUTO&pass=<your password as MD5 hash>&
user_id=<your user id>&tunnel_id=<your tunnel id>' -O -

if [ -n `ifconfig | grep 'he-ipv6'` ]
then
    insmod ipv6
    sleep 3
    ip tunnel add he-ipv6 mode sit remote <HE IPv4 tunnel endpoint> ttl 64
    ip link set he-ipv6 up
    ip addr add <your IPv6 tunnel endpoint>/64 dev he-ipv6
    ip route add ::/0 dev he-ipv6 metric 1
    ip -6 addr add <your router's IPv6 address>/64 dev br0
fi

radvd -C /tmp/radvd.conf &

I have an USB stick attached, and placed everything above in a script file. Makes it a little clearer. Make sure the wget call has no line breaks like displayed here (due to limited space). Add the following Firewall rules on the same page:

iptables -I INPUT 2 -p ipv6 -i br0 -j ACCEPT
iptables -I INPUT 2 -p ipv6 -i ppp0 -j ACCEPT

That’s it already. Reboot the router and IPv6 should work fine on the router itself and on clients which automatically assigned themselves addresses of the subnet announced by radvd.

For increased reliability, I also added a script which is run as a cron job every couple of minutes:

IP=<HE IPv6 tunnel endpoint>

RESULT=`ping6 -c 3 $IP | grep '64 bytes'`

if [ -n $RESULT ]
then
  /usr/bin/wget 'http://ipv4.tunnelbroker.net/ipv4_end.php?
  ipv4b=AUTO&pass=<your password as MD5 hash>&
  user_id=<your user id&tunnel_id=<your tunnel id>' -O -
fi

This tries to ping the tunnel endpoint of HE three times. If it fails, the website to update the IP address is called, because probably the IPv4 address changed without the Startup Script being run.