curl -v telnet://target ip address:desired port number
When the vCenter Server Appliance connects successfully or fails, you see output similar to:
GOOD output
root@vc7 [ ~ ]# curl -v telnet://127.0.0.1:22
* Rebuilt URL to: telnet://127.0.0.1:22/
* Trying 127.0.0.1...
* TCP_NODELAY set
* Connected to 127.0.0.1 (127.0.0.1) port 22 (#0)
SSH-2.0-OpenSSH_7.8
^C
root@vc7 [ ~ ]# curl -v telnet://127.0.0.1:23
* Rebuilt URL to: telnet://127.0.0.1:23/
* Trying 127.0.0.1...
* TCP_NODELAY set
* connect to 127.0.0.1 port 23 failed: Connection refused
* Failed to connect to 127.0.0.1 port 23: Connection refused
* Closing connection 0
curl: (7) Failed to connect to 127.0.0.1 port 23: Connection refused