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I have a Windows 2008 R2 server that will need to listen on a particular port (e.g. 1234) in order for an application upgrade to work, but currently the application doesn't have a listener service configured for port 1234.

Our firewall is managed by a third party, but I would like to check in advance that the port 1234 has been opened before I install the update. Is this possible?

I know I can telnet to the server on other listening ports, but as this server has no application listening to 1234 I can't be certain that it is in fact, open. Telnet results are inconsistent when connecting to ports that are apparently listening in netstat.

Is there anything I can do in Powershell or VB for instance, to set up a listener for port 1234 in advance of the upgrade to ensure it will go smoothly?

Many thanks in advance.

Potatan
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1 Answers1

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Anything that accepts traffic would work.

  1. Run some other service on port 1234 and see if you can connect to that.
  2. Use a network sniffer like WireShark on the server and see if you're getting connection attempts to port 1234.
  3. Install netcat on the server and tell it to listen to port 1234 then connect to that port on the firewall. If it connects, the port is open. (This is really the same as #1 but without an actual service.)
Brian White
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  • I am unable to download Netcat / Ncat for Windows as our corporate firewall is blocking it. I've managed to install Wireshark locally so I'll have a little play with that – Potatan Apr 30 '15 at 10:44
  • There's always the "sneaker-net" method. (i.e. floppy, cd-rw, usb key, etc.). – Brian White Apr 30 '15 at 12:45