insmod ip_tunnel
insmod sit
sleep 4
radvd -C /tmp/radvd.conf stop
sleep 4 
IFC=`ifconfig vlan2`
WANIP="$(echo $IFC | sed 's/.*addr:\(.*\)Bcast.*/\1/')"
echo $WANIP
if [ -n "$WANIP" ]
then
        V6PREFIX=$(printf '2002:%02x%02x:%02x%02x' $(echo $WANIP | tr . ' '))
        ip tunnel add tun6to4 mode sit ttl 255 remote any local $WANIP
        ip link set tun6to4 mtu 1280
        ip link set tun6to4 up
        ip addr add $V6PREFIX:0::1/16 dev tun6to4
        ip addr add $V6PREFIX:1::1/64 dev br0
        ip -6 route add 2000::/3 via ::192.88.99.1 dev tun6to4
        kill -HUP $(cat /var/run/radvd.pid)
fi
radvd -C /tmp/radvd.conf start

Following startup script enables:
* install missing kernel modules
* install 6to4 tunnel for dd-wrt with kernel versions 3.x
* restarts radvd with a new config

6to4 for dd-wrt kernel 3.x

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