Different applications may be failing to communicate to a server and it is sometimes nessessary to check to see if the server is listening on a port and that the client can communicate to the server on that port.
When possible first determine if the port has a listener on the server you want to connect to. To do this run the following: Netstat -an | find "<port number>"
The on line one you can see a TCP listener for 0.0.0.0 on port 10443. This is what you want to see. The ip can be 0.0.0.0 or any of the local ip addresses.
Once you have confirmed that the server is listening on the port you can then go to a client and use one of the following methods to check to see if the port is open over the network.
Method 1: Powershell script
This method is recommended because other application like telnet can have their specific type of communication blocked rather than just their port.
If the test is successful it will return "True" if unsuccessfull there will be a red error and report that "the target machine actively refusted it"
(Optional) If needed you can go to the target machine and use the following powershell command to start a listener (only do this if a service is not already listening on the port, verify with 'netstat -an' command):
Once the test is complete run the following command to stop the listener.
Method 2: Telnet client
Using the telnet client can be used if powershell is not available or telnet is already enabled on the machine. The main drawback to using telnet is that you can get a false negative result because some routers can specifically block telnet traffic even if the port is open.
Follow these steps to test a TCP connection with telnet
Open a command prompt
Use the following Syntax:
telnet <Destination IP> <port number>
telnet 192.168.2.100 10443
If the screen clears and goes dark then the port is open and telnet is attempting to establish a connection. If the port is closed then a message saying "Could not open connection to the host, on port <port number>: Connect failed.
If you get a telnet is not recognized as an internal command error then it is likely not enabled. To enable the telnet client:
Go to the Control Panel > Programs and Features > Turn Windows features on or off
Check Telnet Server and Telnet Client
Click OK to have the features installed.
Open a new command prompt and try again
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