ASM Community

The Problem:
It's a vexing issue for many users whose machines have Private (LAN) IP addresses (ie are behind some kind of NAT device such as a Router, or use 'ICS' to feed a Hub).
You can't accept incoming connections without configuring your NAT device (or Gateway machine).
That means you can't run Servers, and your p2p-based apps are forced to use only outgoing connections, which often equates to limited service.
Of course, the average user is simply not tech-savvy enough to set up port forwarding, and even if they are, they may be working in an environment where the local Administrator(s) are less than helpful.

The Solution:
There is a standard solution to all these problems, assuming that the Universal Plug and Play ports (udp 1900 and tcp 5000) are not firewalled within the LAN... and if they are, asking the Admin to allow UPnP ports inside the LAN doesn't sound as bad or dangerous as asking for specific ports to be forwarded so you can run a Server (say, in a public library).
It is possible to programatically set up Port Forwarding from any LAN machine.
This kind of support can be added to all Server applications such that they may automatically perform remote configuring of Port Forwarding apon the Gateway Machine, or alternatively, a separate application can be written to remotely view/edit/add forwarded ports, allowing any LAN machine to host Server apps :)

Homer, WHY are you telling us what we (may) already know?
This is just a Heads Up to announce that I've translated the NATUPNP header to OA32 format and will be writing a primitive engine as a reusable OA32 Object Module for public use.
I am essentially doing this to add this feature to my IOCP Server/Client Engine (which currently is used by my VOIP demo, and some other projects), but it is such a useful entity that I will keep it separate from that framework. I may end up enshrining it as a LIB or DLL to allow programmers everywhere to use it, but the initial goal will be OBJ.
Although this is COM/RPC stuff, I am designing this module in such a way as to hide all the ugly COM stuff so that the average OA32 user doesn't need to worry about any of that.

Have a nice day - Prug and Pray :)

Are you certain?
Try searching for "lan server port forward".
You'll find a lot of people run servers from behind NATs and across firewalls that would otherwise restrict them.

For UDP protocol exists http://en.wikipedia.org/wiki/UDP_hole_punching

However this is not useful to expose a server over the internet but still interesting :)

I forgot to tell, you can accept incomming conections with UPnP, at least on my network uTorrent maps the port on the ICS of my router PC and if I check the list of port forwardings I can see the automatically maped port there.

http://www.codeproject.com/internet/PortForward.asp

This demo (with C source) supports all the features I intend, but is rather ugly codewise.
Anyway, the binary demo provided allows for testing a built-in webserver.

UDP hole-punching is completely different from UPnP, but a useful technique in itself... and UPnP indeed does let you accept incoming connections. It's either b0rked in my router or the more recent µTorrent versions though :/

Homer, are you doing this to be able to do VoIP in a P2P fashion? Note that if you have a server in which clients connect to, then perhaps you should also give a try to the UDP hole-punching since it enables you to do P2P connections even if your NAT device doesn't supports UPnP nor manual port forwardings.