[wwn_se]

Just forward the port?

[marcodiego]

I think that is only possible if a have control of the NAT/router, right?

[DarylZero]

If you have control of any IP address anywhere (doesn't have to be on your router), you can forward a port.

If you don't have any control of an IP address, you cannot be connected to through software that is not "special" (i.e., software that only uses IP to connect). As a matter of logic.

[npteljes]

UPnP has a protocol to handle that, but the router needs to support it and have it enabled.

[marcodiego]

That allows only outgoing connections, right?

I there a way for me, behind a NAT, to pass an address for someone to connect to a port open on my machine?

[DarylZero]

No, UPnP is for forwarding ports for incoming connections. NAT itself is for outgoing connections.

[marcodiego]

I think I understand what is proposed, but I wouldn't be too hopeful an ISP would allow that.

[DarylZero]

It's not up to the ISP. It's on your router. And most consumer home routers support it, or else a newer alternative like NAT-PMP, but you have to have to enable it in the router settings via web browser interface.

(You can also, in these settings, manually forward individual ports, or use DMZ to forward all ports to a single machine.)

Some ISPs don't even give you a real IPv4 address though (they use CGNAT). THEN you have no hope.