There are 65,535 possible port numbers, although not all are in common use. Some of the most used ports, along with their associated networking protocol, are: Ports 20 and 21:       File Transfer Protocol (FTP). FTP is for transferring files between a client and a server. Port 22:                      Secure Shell (SSH). SSH is one of many tunneling protocols that create secure network connections. Port 25:                      Simple Mail Transfer Protocol (SMTP). SMTP is used for email. Port 53:                    Domain Name System (DNS). DNS is an essential process for the modern Internet, it matches human-readable domain names to machine-readable IP addresses, enabling users to load websites and applications without memorizing a long list of IP addresses. Port 80:                      Hypertext Transfer Protocol (HTTP). HTTP is the protocol that makes the World Wide Web possible. Port 123:               Network Time Protocol (NTP). NTP allows computer clocks to sync with each other, a process that is essential for encryption. Port 179:             Border Gateway Protocol (BGP). BGP is essential for establishing efficient routes between the large networks that make up the Internet Port 443:                HTTP Secure (HTTPS). HTTPS is the secure and encrypted version of HTTP. All HTTPS web traffic goes to port 443. Port 500:                   Internet Security Association and Key Management Protocol (ISAKMP), which is part of the process of setting up secure IPsec connections. Port 3389:                 Remote Desktop Protocol (RDP). RDP enables users to remotely connect to their desktop computers from another device.