/etc/radvd.conf

interface eth0
{
        AdvSendAdvert on;
        AdvLinkMTU 1280;
        MinRtrAdvInterval 3;
        MaxRtrAdvInterval 10;
        prefix 2001:5c0:8fff:fffe::/128
        {
                AdvOnLink on;
                AdvAutonomous on;
                AdvRouterAddr on;
        };
        prefix ::/64
        {
                AdvOnLink off;
                AdvAutonomous on;
                AdvRouterAddr on;
                Base6to4Interface ppp0;
                AdvPreferredLifetime 20;
                AdvValidLifetime 30;
        };
};