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How to close port 3020?

Dear Experts,

I have a Client / Server application that are communicating through port 3020.
PS: the application has to run on this port, so there is no option to change it.
In many times the server fails to listen on port 3020 and claims that the port is in use.

I wanted to check this so:
-Closed the Client and Server applications
-telnet 3020
-I find it replying to this command instead of failing to open connection

I need an application or a code snippet that closes explicitly this port 3020 so that I can run my Client / Server application smoothly over this port.

I am running Windows XP SP2, any ideas ?

Thanks very much,
Georges Antoun
1 Solution
Michael WorshamInfrastructure / Solutions ArchitectCommented:
I recommend downloading and running TCPView to see what is using port 3020 on the PC:

Then you can see what is actively taking over this port and look at disabling it.

Since it is probably your own app using that port, you need to make sure that only one instance runs at a time, otherwise you'll run into trouble. See http://support.microsoft.com/kb/243953 ("How to limit 32-bit applications to one instance in Visual C++")
evilrixSenior Software Engineer (Avast)Commented:
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evilrixSenior Software Engineer (Avast)Commented:
>> Is the port in a Time_WAIT state?
You can find this out by using the netstat command.
Proto  Local Address          Foreign Address        State
TCP    cenobite:3069          bu-in-f189.google.com:http  ESTABLISHED
TCP    cenobite:3218          ug-in-f19.google.com:http  TIME_WAIT <--------------------------------------EXAMPLE
TCP    cenobite:3460    ESTABLISHED
TCP    cenobite:3499          lm-in-f147.google.com:http  ESTABLISHED
TCP    cenobite:3501          ug-in-f19.google.com:http  ESTABLISHED

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trinitrotolueneDirector - Software EngineeringCommented:
are you registering a channel on that port?
Consider setting socket option SO_REUSEADDR, if the socket cannot be closed politely. Beware that this must have been set on the previous listener. You'll have to wait for TIME_WAIT otherwise, as evilrix pointed out.
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