Maybe the apps are selecting the wrong 'local address', i.e. using the  
external address as if it were a loopback address.

I think I've even seen that.

On 3 Jan 2008, at 08:17, Bill Kelly wrote:

> Rubyists,
>
> If any of you having a "not-always-on" internet connection would
> be willing to try my test program on your systems, I'd be most
> grateful:
>
> http://tastyspleen.net/~billk/ruby/loopback-test/
>
> Years ago, some colleagues and I learned that some operating
> systems can attempt to dial out to establish an internet connection,
> even when a program is only trying to do inter-process communication
> using the IP stack over loopback (localhost).  I am hoping that this
> has changed in the intervening years.
>
> The purpose of this test is to discover whether your OS can handle
> UDP and TCP activity on localhost, without the OS trying to dial
> your modem and establish an internet connection.
>
> The program performs two tests.  UDP over loopback, and TCP over
> loopback.  Before the tests, you are asked to verify that your
> system is currently NOT connected to the internet.  After the tests,
> the program gives the option to automatically submit the results
> via email, or explains how to submit the results manually.
>
> No personal information will be gathered during this test, and a
> summary of the results will be made available to everyone.
>
> Here's hoping all tests come back negative!
>
> Thanks very much for your help!
>
> Regards,
>
> Bill
>
>
>