Setup 6to4 and radvd with dynamic IPv4 address

gistfile1.ebuild

#!/bin/bash
IPv4=`ip a | sed -n '/eth0/,$p' | grep '^[[:space:]]*inet' | head -n 1 | sed -r 's/^[[:space:]]*inet[[:space:]]+([[:digit:].]+).*$/\1/'`
prefix=` echo $IPv4 | tr '.' '\n' | sed '1iobase=16'| bc | sed 's/^.$/0\0/'| tr -d '\n' | sed 's/^..../\0:/'`

cat >/etc/radvd.conf << EOF
interface eth1
{
        AdvSendAdvert on;

        prefix 2002:$prefix:100::/64
        {
        };
};
interface eth2
{
        AdvSendAdvert on;

        prefix 2002:$prefix:1000::/64
        {
        };
};
EOF

ip tunnel add tun6to4 mode sit remote any local $IPv4
ip link set dev tun6to4 up
ip -6 addr add 2002:$prefix::1/16 dev tun6to4
ip -6 route add 2000::/3 via ::192.88.99.1 dev tun6to4 metric 1

ip -6 addr add 2002:$prefix:100::1/64 dev eth1
ip -6 addr add 2002:$prefix:1000::1/64 dev eth2

ip6tables -A INPUT -i tun6to4 -j from-internet

sysctl net.ipv6.conf.all.forwarding=1

/etc/init.d/radvd start