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Technically, the internet is, in the main, a TCP/IP and a UDP/IP network. Both the TCP element - Transmission Control Protocol - and the UDP - User Datagram Protocol - elements amongst other things work upon the notion that hosts (i.e. computers) can offer services, such as a web-server or email service, through a designated port. Other computers can ask to use such services, by sending an appropriate message to an appropriate port. By way of example (and stripping out some detail of the handshaking that goes on), when a web page is retrieved from a webserver, the client computer will typically send a get request to Port 80 of a computer running a webserver. The server will capture and act on the message received through its Port 80, and send back an HTML page to the client.
Different services, by convention, use different port numbers, such as:
and, in fact, there can be anything up to 65,536 distinct Ports on a single machine. (And note, too, that a single Port can, generally, handle multiple simultaneous transactions - so a webserver can "talk" to many different users at the same time.)
Port scanners scan a computer and report on two things:
The information in a Port Scan has many legitimate uses; not least in checking machines to see that Ports are not left open without good reason. However port scanning can also be used to those who would do harm to or abuse another computer. Ports are places where data can enter the computer, and be run by a process on the computer. Many exploits depend upon finding open ports and sending to them strings of data that cause the computer operating system to malfunction in a predictable way (called a buffer overflow) that can be exploited, for instance to load more software which enables other tasks to be undertaken.
Running a port scan without permission is seen as unethical and most Internet Service Providers disallow it in their Acceptable Use Policies.
NmapNmap is free port scanning software distributed by Insecure. Org and designed to detect open ports on a target computer, determine which services are running on those ports, and infer which operating system the computer is running (this is also known as f is one of the leading open source software port scanners, and is supplied with most LinuxThis article is about Linux-based operating systems, GNU/Linux, and related topics. See Linux kernel for the kernel itself. See Linux (washing powder) for the Swiss brand of washing powder. Tux, a plump penguin, is the official Linux mascot Linux is the n and UNIX distributions; it is also available for Microsoft WindowsImage use policy. Microsoft Windows is a range of commercial operating environments for personal computers. The range was first introduced by Microsoft in 1985 and eventually has come to dominate the world personal computer market. All recent versions of operating system machines.| Politics | Business | Finance |
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