Primary TCP/IP Port Assignments and Descriptions

TCP/IP provides a total of 65,535 ports of which 1023 are considered to be well known ports. In reality the number of ports that are used by popular network clients and services comprises an even smaller subset of the well known group of ports. The following table lists the functions of this subset.

Port	Assigment	Description
20	FTP	File Transfer Protocol (Data) - The File Transfer protocol provides a mechanism for transferring specific files between network connected computer systems (usually a Linux or UNIX based system). Transfer is typically performed using the ftp client which provides a range of commands used to connect to a remote server for the purpose of uploading or downloading files. Most modern web browsers also have the ability to browse and download files located on a remote FTP server. FTP uses TCP (rather than UDP) to transfer files so is considered to be a highly reliable transport mechanism. FTP does not encrypt data and is not considered to be a secure file transfer protocol. The use of Secure Transport Protocol (SCP) and Secure File Transfer Protocol (SFTP) is strongly recommended in place of FTP.
21	FTP	File Transfer (Control) - Traditionally FTP has two ports assigned (port 20 and port 21). Port 20 was originally conisidered the data transfer port, while port 21 was assigned to communicate control information. In modern implementations port 20 is now rarely used, with all communication taking place on port 21.
22	SSH	Secure Shell - The Secure Shell is used to provide a secure, encypted, remote logon session to a remote host over a TCP/IP network. The original mechanism for remote access was the Telnet protocol. Because Telnet transmits data in plain text its use is now strongly discouraged in favor of the secure shell, which encrypts all communications, including log-in and password credentials. SSH also provides the mechanism by which files can be securely trandferred using the Secure Copy Protocol (SCP), and is also the basis for the Secure File Transfer Protocol (SFTP). SSH also replaces both the rsh and rlogin clients.
23	Telnet
25	SMTP - Simple mail Transfer Protocol
53	DNS - Domain Name Server
69	TFTP	Trivial File Transfer Protocol - TFTP is a strpped down version of the File Transfer Protocol (FTP). It has a reduced command-set and lacks authentication. The most significant feature of TFTP is that it uses UDP to transfer data. This results in extremely fast transfer speeds but, consequently, lacks data reliability. TFTP is typically used in network based booting for diskless workstations.
80	HTTP - Hypertext Text Transfer Protocol
110	POP3 - Post Office Protocol
119	NNTP - Network News Transfer Protocol
123	NTP - Network Time Protocol
143	IMAP4 - Internet Message Access Protocol, Version 4
161	SNMP	Simple Network Management Protocol - Provides a mechanism whereby network administrators are able to collect information about the devices (such as hubs, bridges, routers and switches) on a network. The SNMP protocol enables agents running on network devices to communicate their status to a central manager and, in turn, enables the manager to send new configuration parameters to the device agent. The agents can further be configured to notify the manager when certains events, known as traps, occur. SNMP uses UDP to send and receive data.
443	HTTPS - Hypertext Transfer Protocol Secure
2049	NFS - Network File System