Arevos

Unfortunately, if you're behind a NAT, people cannot connect directly to you. If port forwarding is out of the question, you need to have a third party that acts as the middleman. Your computer connects to the third party, and the remote accessor connects to the third party, which then connects the two streams. This is how Skype manages to work through NATs; it routes VoIP streams through other Skype users that are not behind NATs, encrypting the voice data so it can only be read by the intended recepient.

It's worth saying that only people behind routers will have a problem. Those connected direct to the net through a DSL/Dialup/whatever modem will be able to listen for incoming connections.

Sane

Do you think using some fancy os calls could forward a port systematically (and permanently) through a router. Or will it always be different depending on the router, ISP, etc?

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Ooble

I would murder the guy that came up with a way to do that. I like having only certain ports forwarded - it's a great blockade against "crackers" if they can't even get close.

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Cerulean

I think it will entirely depend on the router. My router, for example, is configurable through a web-interface. I know of no central API for playing with this and think it would be a very big security issue if there was one.
Your best choice is that which Arevos mentioned - going through a third party. A central server would be the nicest, though may cause too much strain if many people start using your application, and it would also be a lot slower than a direct connection (which is why MSN file transfers go so slow, for example).
You might just want to consider a friendly section in your installation wizard which will see if they can be connected to from outside - if they can't, this friendly graphical screen will tell them to forward a port, with details on how to do so with the most widespread routers.

Ooble

Same here - I type 192.168.2.1 into my web browser, and I get a pretty HTML interface. P2P routing would be the most effective, but also the hardest way of doing it, and it would slow things down a little.

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zorin

Well the way things work for me is if I go to 192.168.2.1 in my web browser I see the settings for my wireless router. You have to go to Firewall>Virtual Server, then you can specify what ports to forward to your computer and which to block ect... I think this should do it fine. I had a problem with an application not being able to send on certain ports, so I forwarded a few of them

Sane

The problem with the third party server is it's not permanent, or reliable. Since it would have to be one of my computers, and there's no way that could stay on __forever__.

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zorin

Then maybe you could set up an Application Gateway to allow certain ports at all times, and I think you can even choose to have it password protected. This should defentily work and allow your program to work with full functionallity

Ooble

Well, it could be any computer that has the service running... that's quite a few, if this thing takes off...

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