I have a setup of a laptop connected to a cellular IPv4 network (3G usb dongle) and PC connected to another IPv4/IPv6 network. Both have been configured to run as IPv6 routers and each has its IPv6 network. The laptop connects to the Internet via the 3G network with IPv4 address (private one and it is mostly changing) on one interface and has the other interface on AP mode providing its own private IPv6 network (2001:db8:444::/64). The PC connects to the Internet via the organization network with both public IPv4 and IPv6 addresses on one interface and has the other interface on AP mode providing its own private IPv6 network (2001:db8:222::/64). Both running Linux Ubuntu. Is it possible to get the two IPv6 network (2001:db8:222::/64 and 2001:db8:444::/64) to communicate over the IPv4 Internet? Is openvpn of any good in this case to get IPv6 traffic over IPv4-IPv4 tunnel? Thanks for helping in advance