Netstat and Finding Processes/Apps

Windows:
In this example you can see the One Drive is using port 443.

C:\>netstat -aon | findstr "443"
  TCP    192.168.1.40:7443      52.173.26.181:443      ESTABLISHED     10252

C:\>tasklist | findstr /c:"10252"
OneDrive.exe                 10252 Console                    1     37,240 K

Use the “/V” parameter to get the user info.

MacOS/Unix/Linux:
In this example you can see the Java is using port 636.

root kc-hpux:/ # lsof -i tcp:636
COMMAND   PID USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
java    25697 root  323u  IPv4 0xe000000711c43d00    0t572  TCP dclwprd1:55776->dc1.cordero.me:636 (ESTABLISHED)
java    25697 root  324u  IPv4 0xe0000006ef12f080      0t0  TCP dclwprd1:55777->dc2.cordero.me:636 (SYN_SENT) 

If you want to see just all the ESTABLISHED connection for a given port:

C:\>netstat -aon | findstr "443" | findstr "ESTABLISHED"
  TCP    192.168.1.40:1062    104.26.8.142:443       ESTABLISHED     7492
  TCP    192.168.1.40:1086    192.168.10.222:443     ESTABLISHED     7492
  TCP    192.168.1.40:1105    40.97.190.18:443       ESTABLISHED     12928
  TCP    192.168.1.40:1110    40.97.190.18:443       ESTABLISHED     12928