How do you go about getting UDP packets through network address translation? If a client tries to connect to my server, and they''re using NAT, the UDP packets from my server never reach the client. TCP packets arrive just fine. I''ve even tried "connect"ing the UDP port from the server to the client, but still no go.

The client needs to set up some port forwarding rules on the NAT server (or router, whatever you''re using.)

There''s got to be a way around that. I know for a fact that for instance pcAnywhere uses UDP and it goes through NAT just fine with no routing.

Nope. The client can transmit to the server, but there needs to be a forwarding rule for the server to send to the client.

If you''re running an application level firewall or proxy that''s a different story, but plain old NAT needs forwarding rules.

There is an emerging standard for controlling NAT gateways. Its called UPNP and the interface for doing so is available in WindowsXP and no earlier versions of Windows. I don''t know about linux.

Here''s a link to a reference in msdn
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ics/unat_ref_79gu.asp

To use this functionality you will need the latest platform sdk from microsoft(nice large download).

Some other information is available on www.upnp.com

Good luck if you want to use this stuff. Its VERY new and therefore the documentation and availability sucks.

Sorry.... the earlier reference is to www.upnp.org not .com

Not to be argumentative, but I don''t understand why this is so. At my day job, there''s at least 5 engineers here that all use pcAnywhere to "go home", and our office uses NAT. So, if it required port forwarding, only one of us could use the program, right?

Or am I misunderstanding something?

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Original post by Dr Pain
Not to be argumentative, but I don''t understand why this is so. At my day job, there''s at least 5 engineers here that all use pcAnywhere to "go home", and our office uses NAT. So, if it required port forwarding, only one of us could use the program, right?

Or am I misunderstanding something?

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What kind of NAT/Firewall software are you running there?

According to Symantec, you need to set up port forwarding and fiddle with default pcAnywhere ports when you have multiple hosts in a network.

I don''t know what we''re using, and our IT guy is out today.
I''ll find out on Monday.

But regardless of what they''re running, my client/server app does not work from my office, but pcAnywhere does. Is it possible they''re doing some kind of magic on the NAT for pcAnywhere''s specific ports to allow multiple connections (or any connections at all)?

Perhaps I should try switching my app''s port number to the same as pcAnywhere''s and see what happens.

It''s very possible that the router''s smart enough to figure this out. There are even a few home routers on the market now that have application awareness for things like MS Netmeeting (another UDP app you could test in your setup.)

It''s also possible that some PcAnywhere programmer threw in a TCP backup for this situation.