Every Windows server or client provides TCP ports through which a TCP connection can be established. Even if a server still responds to a ping, it is possible that a connection is no longer possible on those TCP ports. Checking the TCP ports periodically is a good way to determine if a server is working properly.

How can I find open TCP ports of a server?

(Here we refer to the device that makes TCP ports available as a "server". This can also be a Windows client, a router or switch or any other device that communicates via TCP/IP in the network).

Option 1: netstat command on the Windows client
With the command netstat -a from the command line, you can see which connections are currently established. This allows you to see on which TCP ports the client is communicating with the servers. If, for example

TCP 10.5.1.12 CRM-SERVER:9001 LISTENING

is displayed, you know that your own client is talking to the CRM-SERVER on TCP port 9001.

Option 2: netstat command on the Windows server
You can see the connections on the server in the same way - if you have administrative access to the server. Simply enter netstat -a in a command prompt.

Option 3: PortCheck from the client
The free mini command line tool PortCheck.exe can be used to check a server for open ports from the client. Basically, you can use it to query individual ports, but you can also use the command

PortCheck MyServer 1-50000 or
PortCheck MyServer knownports

to check entire ranges. TCP ports that are displayed here in green are responding.

Checking the known ports in Windows 11 - Port 22 (SSH) answers

>>> Change to the TCP Port check PowerShell page