The computer's port address mean? The data output ports such as printers

Answers:1   |   LastUpdateAt:2012-07-30 06:37:57  

Asked at 2012-07-28 13:44:02
The computer's port address mean? The data output ports such as printers
Answer1ExistentialistAnswered at 2012-07-30 06:37:57
PC "port" is the English port of the meaning of the translation can be considered as the exchange of computer communication with the outside world exports. An area of ​​the port, also known as the hardware interface, such as USB ports, serial ports and so on. Software generally refers to a connection-oriented port network services and connectionless services, the communication protocol of the port, is an abstract software architecture, even if some data structures and I / S buffer (input and basic output). Network can be named and addressed the communication port is an operating system can allocate resources. For the network OSI (Open Systems Interconnection Reference Model, OpenSystemInterconnectionReferenceModel) shows seven protocols transport layer and network layer, transport layer, the biggest difference is that the ability to provide the communication process, network communication includes not Only the final address of the host address, also include a description of the identification of species. So the TCP / IP port proposed protocol can be considered as an identifier of the communication process of the network. Applications (commonly known as running in memory: process) with a port through the system call to connect (union, the union), the transport layer is passed to the data port is received by the appropriate process, distributing process corresponding transport layer data output from the port. In the implementation of TCP / IP, port operations similar to general I / O operations, the process of a port for the local equivalent of the only E / S file, you can use normal read and write is similar the file descriptor Each port has a port number of the descriptors integers called, to distinguish different port. Because TCP / IP protocols of the transport layer TCP and UDP are two completely separate the two software modules, so that each port is independent of each other. If a TCP port 255, UDP port can also have a 255, two do not conflict. Port, there are two basic methods of distribution: the first is called the global distribution of centralized distribution, a recognized authority by the central, according to the uniform distribution of user needs, and the results are made public, and second is a local distribution, also known as dynamic linking, this process has to access the service from the transport layer, an application to the local operating system, the only operating system returns the local port number, the process and then through the appropriate system calls, and the port itself up (connecting link). TCP / IP port of the distribution of a combination of the two previous methods, the port number is divided into two parts, a small amount as a port reserved for the overall allocation for the service process. Each server has a global standard recognized by the mouth of the port name known, even on different machines, the port number are the same. It remains a free port, to be distributed locally. TCP and UDP states that the port is less than 256 can be used as reserved ports. By port number can be divided into 3 groups: (1) recognizes the port (WellKnownPorts): 0 to 1023, which are closely linked (binding) in some services. These ports are usually clear that some sort of communications services agreement. For example: HTTP communications port 80 is always in fact. (2) The registered ports (RegisteredPorts): From 1024 to 49151. They are more or less forced some services. There are many services that bind to these ports, these ports are used for many other purposes. For example: Many systems handling dynamic ports around 1024. (3) Dynamic and / or private ports (Dynamicand / orPrivatePorts): 49152 to 65535. In theory, these ports should not be assigned to the service. In fact, machines are usually dynamic assignment of ports 1024 onwards. There are exceptions: SUN RPC ports from 32768. System administrators can "redirect" port: A common technique is to redirect a port to another address. For example, the default HTTP port is 80, many people will redirect to another port like 8080. If this is changed, to access this article should use this address (Of course, this is just a theoretical example.) Redirection to hide the default port recognized , reducing the rate of destruction. Therefore, if someone is the default port of attack you must be a recognized port scan. Most of the similarities with the port redirection port of origin, for example, changes in most of HTTP port 80: 81,88,8000,8080,8888. POP port as the original 110, they are often redirected to 1100. Is selected, there are many statistics on the number of special significance, as 1234,23456,34567. Many people have other reasons to choose the number of strange, 42,69,666,31337. Recently, more and more remote control Trojans (RemoteAccessTrojans, rats) through the same default port. If NetBus defaults to port 12345. BlakeR.Swopes there is a reason to use port forwarding on UNIX systems, if you want to listen on ports below 1024 requires root privileges. If you do not have root privileges, but wants to open web services, you need to install in a major port. Also, some ISP firewall blocks the low end
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