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Telnet consists of two components: (1) the protocol itself and (2) the service component. The telnet protocol is a client-server protocol, based on a reliable connection-oriented transport. [2] This protocol is used to establish a connection to Transmission Control Protocol (TCP) port number 23 or 2323, where a Telnet server application is ...
The port numbers in the range from 0 to 1023 (0 to 2 10 − 1) are the well-known ports or system ports. [3] They are used by system processes that provide widely used types of network services. On Unix-like operating systems, a process must execute with superuser privileges to be able to bind a network socket to an IP address using one of the ...
The most common transport protocols that use port numbers are the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP); those port numbers are 16-bit unsigned numbers. A port number is always associated with a network address of a host, such as an IP address, and the type of transport protocol used for communication. It ...
[d] [76] [77] Port numbers are used to identify different services, and to allow multiple connections between hosts. [14] TCP uses 16-bit port numbers, providing 65,536 possible values for each of the source and destination ports. [17]
This article lists protocols, categorized by the nearest layer in the Open Systems Interconnection model.This list is not exclusive to only the OSI protocol family.Many of these protocols are originally based on the Internet Protocol Suite (TCP/IP) and other models and they often do not fit neatly into OSI layers.
For example, the HyperText Transfer Protocol uses server port 80 and Telnet uses server port 23. Clients connecting to a service usually use ephemeral ports, i.e., port numbers assigned only for the duration of the transaction at random or from a specific range configured in the application.
For an example, telnet can be configured as follows (line taken from a machine running AIX version 5.1): telnet stream tcp6 nowait root /usr/sbin/telnetd telnetd -a The first word, telnet, is the official name of the service. It is resolved using the system database to map port numbers and protocols to service names.
An ephemeral port is a communications endpoint of a transport layer protocol of the Internet protocol suite that is used for only a short period of time for the duration of a communication session. Such short-lived ports are allocated automatically within a predefined range of port numbers by the IP stack software of a computer operating system.