> Can IPSec secure traffic on IPv6 being tunnelled over the IPv4 > networks, e.g. using 6to4 etc? Yes. 2401[bis] uses examples of IPv4 tunneled in IPv4 and IPv6 tunneled in IPv6 for ease of description, but the other two cases, IPv4 in IPv6 and IPv6 in IPv4 are also valid. IPsec can be used in all four scenarios, and IKEv2 can setup the appropriate SAs. Charlie