Question: What is port?

Ha! This port is not seaport, there is also a term called port in networking. This port is usually means the logical connection point used by server program to communicate with its client program. Each port is tagged with a number (0-65535).

As an example, I have a web server (test.com) that listens on port 80, so we can access the web server by typing http://test.com in web browser (client). The web browser sends the request data to server's port 80, the server will then send the data back to browser. Please note also the client program will also tie to source port (random number between 1025 – 65535) to communicate with server’s destination port.

Port numbers are ranged from 0 to 65535. Ports 0 to 1024 are reserved for common programs, such as http, telnet, ftp, whois, netbios, snmp, bgp, syslog, etc. You can also check out the latest IANA’s port list here.