- 21 – FTP
File Transfer Protocol (FTP) is a standard network protocol used to transfer files from one host to another host over a TCP-based network, such as the Internet. FTP is built on a client-server architecture and uses separate control and data connections between the client and server. Authentication is accomplished through the use of a clear-text sign-in protocol and is not considered to be secure.
File Transfer Protocol first establishes, then maintains a control connection throughout the session over TCP port 21. Then a second connection is opened over TCP port 20 for data transfer.
RFC 959 - File Transfer Protocol
- 23 – TELNET
Short for Telecommunications network, TELNET is a text based interface protocol that provides an insecure remote access to other computers. Telnet uses a command line interface and can be accessed in Windows from the Start menu by clicking <Start>, <Run>, then by typing: telnet (somesite) 23. Port number 23 is the default port used by telnet, but is usually optional and often not required.
TELNET typically uses TCP port 23.
RFC 854 - TELNET Protocol Specification
- 25 – SMTP
Simple Mail Transfer Protocol (SMTP) is a reliable and efficient mail transport and delivery protocol that is capable of transporting outgoing email across multiple networks. SMTP requires a reliable data stream channel for transmission.
SMTP typically uses TCP port 25
RFC 5321 - Simple Mail Transfer Protocol
- 53 – DNS
The Domain Name System (DNS) is a hierarchical naming system for computers, services, or any resource connected to the Internet or a private network. Internet and TCP utilities such as telnet, FTP, and SMTP use DNS to translate computer host and domain names to their corresponding IP addresses. DNS allows you to type recognizable names into your Web browser and your computer will automatically find that address on the Internet. Address information is stored in several locations in a hierarchical structure.
- 80 – HTTP
Hypertext Transfer Protocol (HTTP) is an application-level protocol used to request and deliver web pages between a server and browser. HTTP is the foundation of data communication for the World Wide Web.
HTTP is typically implemented using TCP port 80.
RFC 2616 - Hypertext Transfer Protocol
- 110 – POP3
Post Office Protocol (POP3) is a simple, standardized application-layer protocol used for retrieving incoming email from a remote mail server over a TCP/IP connection and saving to a local device. A POP3 server listens on well-known port TCP/110.
POP3 mail retrieval typically uses TCP port 110 by default but may vary depending on provider.
RFC 1939 - Post Office Protocol - Version 3
- 143 – IMAP
Internet message access protocol (IMAP) is one of the two most prevalent Internet standard protocols for e-mail retrieval, the other being the Post Office Protocol (POP). Virtually all modern e-mail clients and mail servers support both protocols as a means of transferring e-mail messages from a server. IMAP is a client/server protocol in which e-mail is received and held by your Internet server and downloaded from the server by request. Imap permits the manipulation of remote mailboxes as though they were local, and works well with slower modem connections.
RFC 3501 - Internet Message Access Protocol
- 443 – HTTPS
Hypertext Transfer Protocol Secure (HTTPS) is a combination of Hypertext Transfer Protocol (HTTP) with SSL/TLS protocol. It provides encrypted communication and secure identification of a network web server. HTTPS connections are often used for payment transactions on the World Wide Web and for sensitive transactions in corporate information systems. HTTPS uses port 443 by default.
HTTPS is a lower level Application Layer protocol that typically uses TCP port 443 by default.
RFC 2818 - HTTP Over TLS
- 3389 – RDP
