Thursday, 8 November 2012

Port Numbers: Common and Well Known Port Numbers

Port Numbers: Common and Well Known Port Numbers

A port is associated with an IP address of the host. A port is identified for each address and protocol by a 16-bit number, commonly known as the port number. The port number, added to a computer's IP address, completes the destination address for a communications session. That is, data packets are routed across the network to a specific destination IP address, and then, upon reaching the destination computer, are further routed to the specific process bound to the destination port number.

Communication Protocols using Port Number

There are mainly two communication protocols which use port numbers:

1. TCP ( Transmission Control Protocol)
2. UDP ( User Datagram Protocol)

Transport Layer protocols, such as the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP), specify a source and destination port number in their packet headers. A port number is a 16-bit unsigned integer, thus ranging from 1 to 65535.

Port Number Conflicts

Common application failures, sometimes called port conflicts, occur when multiple programs attempt to bind to the same port numbers on the same IP address using the same protocol.

Port Forwarding

Port forwarding allows remote computers to connect to a specific computer or service within a private local-area network. Network administrators may need to set up port forwarding to allow the port numbers of specific applications to pass through a firewall. Network programmers sometimes need to specify port numbers in their code, such as in socket programming.

Common and Well Known Port Numbers

The port numbers are divided into three ranges:

1. Well Known Ports
2. Registered Ports
3. Dynamic or Private Ports

1. Well Known Ports: The well-known ports are those from 0 through 1023. For example:

1. Port 20 & 21: File Transfer Protocol (FTP)
2. Port 22: Secure Shell (SSH)
3. Port 23: Telnet remote login service
4. Port 25: Simple Mail Transfer Protocol (SMTP)
5. Port 53: Domain Name System (DNS) service
6. Port 80: Hypertext Transfer Protocol (HTTP) used in the World Wide Web
7. Port 110: Post Office Protocol (POP3)
8. Port 119: Network News Transfer Protocol (NNTP)
9. Port 143: Internet Message Access Protocol (IMAP)
10. Port 161: Simple Network Management Protocol (SNMP)
11. Port 443: HTTP Secure (HTTPS)

2. Registered Ports: The registered ports are those from 1024 through 49151.

3. Dynamic or Private Ports: The dynamic or private ports are those from 49152 through 65535.

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