How can I check what application block my connection?

Hi,

I'm having a problem with some users, my vb tools always check at the splash screen a response from a server with a simple:

Dim MyResult as string = oWebclient.DownloadString("www.mydomain.com/page.php")

This actually works for most users but in some clients the firewalls I think they block this call or bypass or something like that, I found that after telling the user to turn off the firewall everything works ok, now I have some users that according to them they don't have a firewall or they already disable and still they have the problem.

You can see from the image the error message they receive, so my question is do you know any kind of free tool that I can send to the user to maybe log what program or whatever is blocking the program to connect?

http://www.estaciona.com/error.bmp

Thanks for your time!

Diego

That error message does not seem like it would be thrown on that line of code. You are right it is probably a firewall blocking you. Just because a user says they don't have a firewall does not mean they aren't using one. I know a lot of end users who have no idea that the windows firewall is enabled.

You should never recommend to people to disable their firewalls, you should have them add an exception for your program if they want to use it.

If you are truly getting an error connecting to a website, there might not be much you can do. It could be a router or firewall blocking the outbound connection. Especially in business environments most connections on nonstandard ports will be blocked.

The error screen that you posted seems as if the program is trying to connect to the local computer on port 81. A firewall would definitely put a stop to that kind of connection.

Hi,

Yes you are right about that, and yes I only tell the user to disabled the firewall to prove it and then add the program to the trust list.

Why do you think is trying to connect to a 81 port? and also that address is not my domain ip off course is kind of a gateway ip?

And yes I'm 100% sure that the error appear from that line of code.

If your application is not trying to connect on port 81, then I would guess the user has a proxy server running on port 81. The reason I know it is port 81 is that in your error message it states an unreachable network at "127.0.0.1:81". The 81 is the port. So it is trying to connect to the local machine on port 81.

is there any workaounrd for this? something that I don't care how the user connect to the internet, if I use the webclient should not be using the lan settings of internet explorer? even if a proxy server is set there? is kind of hard to explain the user all this.

I can't say for sure that the user is using a proxy, and some organizations only let you connect through a proxy, but according to the documentation you can override the proxy to not use one by using the GetEmptyWebProxy call:

http://msdn.microsoft.com/en-us/libr...xy(VS.80).aspx
http://msdn.microsoft.com/en-us/libr...xy(VS.80).aspx

Thanks it's a good start for my research.