In your previous mail you wrote: If I assume correctly, these customers also have IPv4 Internet access, => your assumption is not correct if you add "usable for 6to4 relaying". Regards Francis.Dupont@enst-bretagne.fr PS: a notable fraction of IPv6 sites I know are in fact IPv6 only (i.e. no IPv4 or IPv4 managed by other with firewalls, etc).