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Expert tips to solve port 3389 issues when end users gets blocked

Enterprise security expert, Michael Gregg answers a question regarding port 3389 issues when a user tries to open port 3389 RDP on their router to work from home, but hits a roadblock when the ISP blocks the port.

I have opened port 3389 RDP on my router so that I can access my work computer from home. However, I'm not yet

able to RDP my work computer from home since there is a proxy server through which all Internet traffic passes. When I do a port scan, port 3389 is open on the router but not on the proxy server. I have requested my ISP to open the port on the proxy server but he tells me that he is already using port 3389 for VoIP. What can I do? Please help.

This is a good question and a common problem in that ISP’s sometimes block ports that end users need. In these situations, there are a couple of things you can do. First, is to ask the ISP to unblock the port. In your case this that is not possible as the ISP states they are using the port for another application. That brings us to the second option. This option involves using a non-standard port.  It’s possible to get applications to function on non-standard ports. As an example, while HTTP uses port 80 by default there is nothing stopping us from instructing http to use another port such as 79. To use a non-standard port setup your router to forward this new port to the internal device you want to communicate with. As an example: 192.168.123.1:3388. Next, setup RDP to recognize the new port. You will need to edit the registry for this:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp] "PortNumber"=dword:00000d3c

The hex value of d3c set the port to 3388. I hope this helps!

More on this topic

To learn more about enterprise security, check out Michael Gregg’s answers to other enterprise security queries.

 

This was first published in April 2011

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