With NAT you may need STUN, TURN, ICE, and probably a few more acronyms: * https://en.wikipedia.org/wiki/STUN https://en.wikipedia.org/wiki/STUN * https://en.

With NAT you may need STUN, TURN, ICE, and probably a few more acronyms: * https://en.wikipedia.org/wiki/STUN https://en.wikipedia.org/wiki/STUN * https://en.wikipedia.org/wiki/Traversal_Using_Relays_around_NAT https://en.wikipedia.org/wiki/Traversal_Using_Relays_around_... * https://en.wikipedia.org/wiki/Interactive_Connectivity_Establishment https://en.wikipedia.org/wiki/Interactive_Connectivity_Estab... Not sure if that's more or less complicated than already knowing your IP address and 'just' using UPnP/PCP: * http://upnp.org/specs/arch/UPnP-arch-AnnexAIPv6-v1.pdf http://upnp.org/specs/arch/UPnP-arch-AnnexAIPv6-v1.pdf * https://en.wikipedia.org/wiki/Port_Control_Protocol https://en.wikipedia.org/wiki/Port_Control_Protocol