Information AboutTelnet |
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TELNET ('''TEL'''ecommunication '''NET'''work) is a Network Protocol used on the Internet or Local Area Network (LAN) connections. It was developed in 1969 beginning with RFC#0015 and standardized as IETF STD 8 , one of the first Internet standards. The term ''telnet'' also refers to software which implements the client part of the protocol. TELNET clients have been available on most Unix systems for many years and are available for virtually all Platforms . Most network equipment and OS s with a TCP/IP Stack support some kind of TELNET service server for their remote configuration (including ones based on Windows NT ). Recently, Secure Shell has begun to dominate remote access for Unix-based machines. "To telnet" is also used as a Verb meaning to establish or use a TELNET or other interactive TCP connection, as in, "To change your password, telnet to the server and run the Passwd command". Most often, a user will be ''telneting'' to a unix-like server system or a simple network device such as a switch. For example, a user might "telnet in from home to check his mail at school". In doing so, he would be using a telnet client to connect from his computer to one of his servers. Once the connection is established, he would then log in with his account information and execute operating system commands remotely on that computer, such as ''ls'' or ''cd''. On many systems, the client may also be used to make interactive raw- TCP sessions, even when that option is not available, telnet sessions are equivalent to raw TCP as long as byte 255 never appears in the data. PROTOCOL DETAILS TELNET is a Client-server Protocol , based on a Reliable Connection-oriented transport. Typically this is TCP Port 23, although TELNET predates TCP/IP and was originally run on NCP . The protocol has many extensions, some of which have been adopted as Internet Standard s. IETF standards STD 27 through STD 32 define various extensions, most of which are extremely common. Other extensions are on the IETF Standards Track as proposed standards. SECURITY When TELNET was initially developed in 1969, most users of networked computers were in the computer departments of academic institutions, or at large private and government research facilities. In this environment, security was not nearly as much of a concern as it became after the bandwidth explosion of the 1990s . The rise in the number of people with access to the Internet, and by extension, the number of people attempting to Crack other people's Server s made encrypted alternatives much more necessary. Experts in Computer Security , such as SANS Institute , and the members of the Comp.os.linux.security Newsgroup recommend that the use of TELNET for remote logins should be discontinued under all normal circumstances, for the following reasons:
These security-related shortcomings have seen the usage of the TELNET protocol drop rapidly, especially on the public Internet , in favor of a the Ssh protocol, first released in 1995. SSH provides much functionality of telnet, with the addition of strong encryption to prevent sensitive data such as passwords from being intercepted, and Public Key authentication, to ensure that the remote computer is actually who it claims to be. As has happened with other early Internet protocols, extensions to the TELNET protocol provide TLS security and SASL authentication that address the above issues. However, most TELNET implementations do not support these extensions; and there has been relatively little interest in implementing these as SSH is adequate for most purposes. The main advantage of TLS-TELNET would be the ability to use certificate-authority signed server certificates to authenticate a server host to a client that does not yet have the server key stored. In SSH, there is a weakness in that the user must trust the first session to a host when it has not yet acquired the server key. Clients and servers designed to pass IBM 5250 data streams over Telnet generally do support SSL encryption, as SSH does not include 5250 emulation. Under OS/400, Port 992 is the default port for Secured Telnet. CURRENT STATUS As of the mid-2000s, while the TELNET protocol itself has been mostly superseded, TELNET clients are still used, often when diagnosing problems, to manually "talk" to other services without specialized client software. For example, it is sometimes used in Debug ging network services such as an SMTP , IRC or HTTP server, by serving as a simple way to send commands to the server and examine the responses. Though, other software such as ''nc'' ( Netcat ) or ''socat'' on Unix (or PuTTY on Windows) are finding greater favor with some system administrators for testing purposes, as they can be called with arguments to not send any terminal control Handshaking data. Also netcat does not distort the ÿ octet, which allows raw access to TCP socket, unlike any standard-compliant TELNET software. TELNET is still very popular in enterprise networks to access host applications, e.g. on IBM Mainframes . TELNET is also heavily used for MUD games played over the Internet, as well as Talker s, MUSH es, MUCK s, MOO es, and the resurgent BBS community. SEE ALSO
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