Common port numbers

For students who studying in computer network should know and familiar in port numbers used networking system. I would like to introduce some port numbers that are useful for computer students.

Main article: List of TCP and UDP port numbers

The Internet Assigned Numbers Authority (IANA) is responsible for the global coordination of the DNS Root, IP addressing, and other Internet protocol resources. This includes the registration of commonly used port numbers for well-known Internet services. The concept of port numbers was established by the early developers of the ARPANET(Advance Research Project Agency Network) in informal cooperation of software authors and system administrators.

The port numbers are divided into three ranges: the well-known ports, the registered ports, and the dynamic or private ports. The well-known ports are those from 0 through 1023. Examples include:

• 20 & 21: File Transfer Protocol (FTP)
• 22: Secure Shell (SSH)
• 23: Telnet remote login service
• 25: Simple Mail Transfer Protocol (SMTP)
• 53: Domain Name System (DNS) service
• 80: Hypertext Transfer Protocol (HTTP) used in the World Wide Web
• 110: Post Office Protocol (POP3)
• 119: Network News Transfer Protocol (NNTP)
• 143: Internet Message Access Protocol (IMAP)
• 161: Simple Network Management Protocol (SNMP)
• 443: HTTP Secure (HTTPS)

The registered ports are those from 1024 through 49151. IANA maintains the official list.The dynamic or private ports are those from 49152 through 65535. One common use is for ephemeral ports.

The term port number was not yet used at this time. It was preceded by the use of the term socket number  in the early development stages of the network. A socket number for a remote host was a 40-bit quantity. The first 32 bits were similar to today's IPv4 address, but at the time the most-significant 8 bits were the host number. The least-significant portion of the socket number (bits 33 through 40) was an entity called Another Eightbit Number, abbreviated AEN, today's port number.

On March 26, 1972, Vint Cerf and Jon Postel called for documenting the then current usages and establishing a socket number catalog in RFC 322. Network administrators were asked to submit a note or place a phone call, "describing the function and socket numbers of network service programs at each HOST".

The 256 values of the AEN were divided into the following ranges:

• 0 through 63: network-wide standard functions
• 64 through 127: host-specific functions
• 128 through 239: reserved for future use
• 240 through 255: any experimental function

The Telnet service received the first official assignment of the value 1. In detail, the first set of assignments was:

1. Telnet

3  File transfer

5  Remote job entry

7  Echo

9  Discard

In the early ARPANET, the AEN was also called a socket name, and was used with the Initial Connection Protocol (ICP), a component of the Network Control Program (NCP) NCP was the forerunner of the modern Internet protocols. Today the terminology service name is still closely connected with port numbers, the former being text strings used in some network functions to represent a numerical port number.

 I will try later to post “well – known ports”.

Reference:wikipedia