Port (software)

Basic explanation

If you digest data processing badly, regard the ports as Doors giving access to your operating system (Windows, Mac OS, Linux, Solaris…). To function, a program must have access to your operating system (for example for the plays with acceleration 3D/2D, of the software of photo final improvement, etc), and must thus open doors to be able to enter your operating system. When you leave the program, the door does not need more to be open. The security issues occur when certain programs forget to close again these known as doors (the " Ports "), or even quite simply when the badly controlled configuration of the computer opens ports without any utility. That gives place to data-processing security breaches, because if a door is not closed again, no matter who can borrow it…

Utility

Thanks to this abstraction, one can carry out several software waiters on the same machine, and even simultaneously of the software customers and waiters, which is frequent on the Operating systems Multitâche S and Multiutilisateur S.

Attribution of the ports

For each port, a number is allotted to him, which is coded on 16 bits, which implies that there exists a maximum of 65.536 ports ( $2^ {16}$ ) per computer.

The attribution of the ports is made by the Operating system, on request for an application. The latter can ask so that the operating system allot any port to him, provided that it is not already allotted. The application can then use it as good seems to him.

When software customers want to dialog with a server software, also called service, it needs to know the port listened by this last. The ports used by the services having to be known by the customers, the principal service types use ports which known as are reserved. By convention, they are all those ranging between 0 and 1.023 included and their use by a server software often requires that Ci is carried out with Rights of access particular. The services using these ports are called the Well-Known Services (the most known services).

On a machine of the type UNIX, the file /etc/services recalls the list of these famous services, of which most known and most useful are in particular the ports:

21, for the file-swapping via ftp
22, for the access at protected Shell Secure Shell
23, for port telnet
25, for the sending of a Email via a waiter dedicated smtp
80, for the consultation of a waiter HTTP by the means of a navigator Web
110, for the recovery of its email via POP
143, for the recovery of its email via IMAP

(IMAP is equipped with functionalities more advanced than POP, to see the respective articles for more details)

443, for the protected Web servers HTTPS

It should however be noted that conventions above can not be respected provided that the customer and the waiter are coherent between them and that the new selected number is not already used in addition. The majority of the communication software give access this adjustment what is useful in certain cases.

See too

List of the software ports
material Port

External bonds

corresponding ports and services
a base of data to find the description of a port TCP and UDP
Ports and services (Source of the base of data: IANA)

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