I assume that the following message that I got when I tried this test is a good one: THE EQUIPMENT AT THE TARGET IP ADDRESS DID NOT RESPOND TO OUR UPnP PROBES! (That's good news!) That was behind CenturyLink's modem (older and very old DSL setup with low speed). Behind that there is a router, and there are a few ports that are forwarded through both routers to one box. But reverse SSH tunnels are my jam.