Transparent SOCKS5 proxy for linux using dual stack IPv4 and IPv6

As I understand the problem, radvd just controls the internal link. Leave forwarding on for all links. For the low end broadband interface make sure that the following settings are configured:

echo 2 > /proc/sys/net/ipv6/conf/<nic>/accept_ra
echo 1 > /proc/sys/net/ipv6/conf/<nic>/accept_ra_pinfo
echo 1 > /proc/sys/net/ipv6/conf/<nic>/autoconf

See also ip-sysctl.txt

Can't remember where I found this solution, but here it is

In /etc/bind/named.conf.local:

// disable lookup over IPv6
server ::/0 {
        bogus yes;
};

It then pretends that IP addresses in the IPv6 range are non reachable and does it with IPv4 instead.