> So far as I know there is no equivalent kludge to UPnP Port Forwarding that works reliably on that scale There's only Port Control Protocol, but almost no s

> So far as I know there is no equivalent kludge to UPnP Port Forwarding that works reliably on that scale There's only Port Control Protocol, but almost no sane ISP will ever enable it, because it can't really solve much and the security implications make people really uncomfortable. The big problem with carrier grade NAT is when you stick N people behind 1 IP, they can only have at most 65,536/N ports each. If you're a big city in India, say, and N=1000, that's 65 ports per person. Your ports-per-person is your ceiling on maximum simultaneous TCP sessions per person. 65 ports is barely enough for a few browser tabs to be open simultaneously, and god help you if you've got another layer of NAT at the household level (which you probably do) and you're splitting those 65 ports between 2 or 3 other people (which you probably are). Consequently, browsing the internet is a fraught process in a lot of places with carrier grade NAT. You can absolutely forget about P2P or anything else complex and port-hungry.