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I've wrote a .NET WCF service I put onto a Windows Server 2003 R2 server several months ago. I've not been able to work with it since, due to other job related responsbilities, but now am trying to get back to it. Back when I did work on it, it worked fine. However, now I'm getting an error message saying that I cannot make a connection to it, from my development machine. That the target machine is "actively refusing it". So I'm wondering if some update, or security patch, applied to the server may now be blocking the attempt. I'm trying to access this via TCP. How do I determine if the TCP port I'm trying to use, is open and listening, on the server?

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up vote 3 down vote accepted

Use "nmap" to scan the target machine for open ports.

But since you get an active refusal this sounds as if the local firewall on the w2k3r2 server has been activated.

A more simple method is a "telnet IP port" - since this is a TCP service you should get a blank screen or some ASCII-chars if the port is open and listening.

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I just tried the telnet command you gave. It did give me a blank screen, so I guess port is opened and being listened to on the server. However, I still am getting that error message. I'm guessing you're correct, that something on the server is blocking it. It doesn't look like Windows Defender is running, and at least poking around in Programs, I don't see anything. I'll ask around to see if anyone knows what might be installed on that server. –  Rod Jul 21 '11 at 15:23
    
Have you got command line access to the server? netstat -a -b -p tcp will show you what program (pid) is listening on what tcp-port. –  Nils Jul 21 '11 at 19:35
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