TELNET (TELe-NETwork) is a network protocol In computing, a protocol is a set of rules which is used by computers to communicate with each other across a network. A protocol is a convention or standard that controls or enables the connection, communication, and data transfer between computing endpoints. In its simplest form, a protocol can be defined as the rules governing the syntax, used on the Internet The Internet is a global system of interconnected computer networks that use the standard Internet Protocol Suite to serve billions of users worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks of local to global scope that are linked by a broad array of electronic and or local area networks A local area network is a computer network covering a small physical area, like a home, office, or small groups of buildings, such as a school, or an airport. The defining characteristics of LANs, in contrast to wide area networks (WANs), include their usually higher data-transfer rates, smaller geographic area, and lack of a need for leased to provide a bidirectional interactive text-oriented communications facility via a virtual terminal A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system. Early terminals were inexpensive devices but very slow compared to punch cards or paper tape for input, but as the technology improved and video displays were introduced, connection. User data is interspersed in-band with TELNET control information in an 8-bit byte oriented data connection over the Transmission Control Protocol The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite (the other being Internet Protocol, or IP), so the entire suite is commonly referred to as TCP/IP. Whereas IP handles lower-level transmissions from computer to computer as a message makes its way (TCP).

Telnet was developed in 1969 beginning with RFC 15, extended in RFC 854, and standardized as Internet Engineering Task Force The Internet Engineering Task Force develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standards bodies and dealing in particular with standards of the TCP/IP and Internet protocol suite. It is an open standards organization, with no formal membership or membership requirements. All participants and managers are (IETF) Internet Standard STD 8, one of the first Internet standards.

Historically, telnet provided access to a command-line interface A command-line interface is a mechanism for interacting with a computer operating system or software by typing commands to perform specific tasks. This text-only interface contrasts with the use of a mouse pointer with a graphical user interface (GUI) to click on options, or menus on a text user interface (TUI) to select options. This method of (usually, of an operating system An operating system is the software on a computer that manages the way different programs use its hardware, and regulates the ways that a user controls the computer. Operating systems are found on almost any device that contains a computer with multiple programs—from cellular phones and video game consoles to supercomputers and web servers. Some) on a remote host. Most network equipment and operating systems An operating system is the software on a computer that manages the way different programs use its hardware, and regulates the ways that a user controls the computer. Operating systems are found on almost any device that contains a computer with multiple programs—from cellular phones and video game consoles to supercomputers and web servers. Some with a TCP/IP stack The Internet Protocol Suite is the set of communications protocols used for the Internet and other similar networks. It is named from two of the most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were the first two networking protocols defined in this standard. Today's IP networking support a Telnet service for remote configuration (including systems based on Windows NT Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was originally designed to be a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement consumer versions of). Because of security issues with Telnet, its use for this purpose has waned in favor of SSH Secure Shell or SSH is a network protocol that allows data to be exchanged using a secure channel between two networked devices. Used primarily on GNU/Linux and Unix based systems to access shell accounts, SSH was designed as a replacement for Telnet and other insecure remote shells, which send information, notably passwords, in plaintext,.

The term telnet may also refer to the software that implements the client part of the protocol. Telnet client applications are available for virtually all computer platforms In computing, a platform describes some sort of hardware architecture or software framework , that allows software to run. Typical platforms include a computer's architecture, operating system, programming languages and related runtime libraries or graphical user interface. Telnet is also used as a verb In syntax, a verb, from the Latin verbum meaning word, is a word that conveys action (bring, read, walk, run, murder), or a state of being (exist, stand). In most languages, verbs are inflected (modified in form) to encode tense, aspect, mood and voice. A verb may also agree with the person, gender, and/or number of some of its arguments, such as. To telnet means to establish a connection with the Telnet protocol, either with command line client or with a programmatic interface. For example, a common directive might be: "To change your password, telnet to the server, login and run the passwd command." Most often, a user will be telnetting to a Unix-like A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification server system or a network device such as a router and obtain a login prompt to a command line text interface or a character-based full-screen manager.

The Internet Protocol Suite The Internet Protocol Suite is the set of communications protocols used for the Internet and other similar networks. It is named from two of the most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were the first two networking protocols defined in this standard. Today's IP networking
Application Layer Application Layer is a term used in categorizing protocols and methods in architectural models of computer networking. Both the OSI model and the Internet Protocol Suite define application layers

BGP The Border Gateway Protocol is the core routing protocol of the Internet. It maintains a table of IP networks or 'prefixes' which designate network reachability among autonomous systems (AS). It is described as a path vector protocol. BGP does not use traditional Interior Gateway Protocol (IGP) metrics, but makes routing decisions based on path, · DHCP The Dynamic Host Configuration Protocol is a computer networking protocol used by hosts (DHCP clients) to retrieve IP address assignments and other configuration information · DNS The Domain Name System is a hierarchical naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participants. Most importantly, it translates domain names meaningful to humans into the numerical (binary) identifiers · FTP File Transfer Protocol is a standard network protocol used to copy a file from one host to another over a TCP/IP-based network, such as the Internet. FTP is built on a client-server architecture and utilizes separate control and data connections between the client and server applications, which solves the problem of different end host · GTP GPRS Tunnelling Protocol is a group of IP-based communications protocols used to carry General Packet Radio Service (GPRS) within GSM and UMTS networks · HTTP The Hypertext Transfer Protocol is an Application Layer protocol for distributed, collaborative, hypermedia information systems · IMAP The Internet Message Access Protocol is one of the two most prevalent Internet standard protocols for e-mail retrieval, the other being the Post Office Protocol (POP). Virtually all modern e-mail clients and mail servers support both protocols as a means of transferring e-mail messages from a server · IRC Internet Relay Chat is a form of real-time Internet text messaging (chat) or synchronous conferencing. It is mainly designed for group communication in discussion forums, called channels, but also allows one-to-one communication via private message as well as chat and data transfers via Direct Client-to-Client · LDAP The Lightweight Directory Access Protocol, or LDAP , is an application protocol for querying and modifying data using directory services running over TCP/IP · Megaco Megaco is an implementation of the Media Gateway Control Protocol architecture for controlling Media Gateways on Internet Protocol (IP) networks and the public switched telephone network (PSTN). The general base architecture and programming interface was originally described in RFC 2805 and the current specific Megaco definition is ITU-T · MGCP MGCP is an implementation of the Media Gateway Control Protocol architecture for controlling Media Gateways on Internet Protocol networks and the public switched telephone network (PSTN). The general base architecture and programming interface is described in RFC 2805 and the current specific MGCP definition is RFC 3435 (obsoleted RFC 2705). It is · NNTP The Network News Transfer Protocol is an Internet application protocol used for transporting Usenet news articles (netnews) between news servers and for reading and posting articles by end user client applications. Brian Kantor of the University of California, San Diego and Phil Lapsley of the University of California, Berkeley authored RFC 977, · NTP The Network Time Protocol is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. NTP uses UDP on port 123 as its transport layer. It is designed particularly to resist the effects of variable latency by using a jitter buffer. NTP also refers to a reference software implementation that · POP In computing, the Post Office Protocol is an application-layer Internet standard protocol used by local e-mail clients to retrieve e-mail from a remote server over a TCP/IP connection. POP and IMAP (Internet Message Access Protocol) are the two most prevalent Internet standard protocols for e-mail retrieval. Virtually all modern e-mail clients and · RIP The Routing Information Protocol is a dynamic routing protocol used in local and wide area networks. As such it is classified as an interior gateway protocol (IGP). It uses the distance-vector routing algorithm. It was first defined in RFC 1058 (1988). The protocol has since been extended several times, resulting in RIP Version 2 (RFC 2453). Both · RPC Remote procedure call is an Inter-process communication technology that allows a computer program to cause a subroutine or procedure to execute in another address space (commonly on another computer on a shared network) without the programmer explicitly coding the details for this remote interaction. That is, the programmer would write essentially · RTP The Real-time Transport Protocol defines a standardized packet format for delivering audio and video over the Internet. It was developed by the Audio-Video Transport Working Group of the IETF and first published in 1996 as RFC 1889, and superseded by RFC 3550 in 2003 · RTSP The Real Time Streaming Protocol is a network control protocol designed for use in entertainment and communications systems to control streaming media servers. The protocol is used to establish and control media sessions between end points. Clients of media servers issue VCR-like commands, such as play and pause, to facilitate real-time control of · SDP The Session Description Protocol is a format for describing streaming media initialization parameters in an ASCII string. The IETF published the original specification as an IETF Proposed Standard in April 1998, and subsequently published a revised specification as an IETF Proposed Standard as RFC 4566 in July 2006 · SIP The Session Initiation Protocol is an IETF-defined signaling protocol, widely used for controlling multimedia communication sessions such as voice and video calls over Internet Protocol (IP). The protocol can be used for creating, modifying and terminating two-party (unicast) or multiparty (multicast) sessions consisting of one or several media · SMTP Simple Mail Transfer Protocol is an Internet standard for electronic mail (e-mail) transmission across Internet Protocol (IP) networks. SMTP was first defined in RFC 821 (STD 15) (1982), and last updated by RFC 5321 (2008) which includes the extended SMTP (ESMTP) additions, and is the protocol in widespread use today. SMTP is specified for · SNMP Simple Network Management Protocol is a UDP-based network protocol. It is used mostly in network management systems to monitor network-attached devices for conditions that warrant administrative attention. SNMP is a component of the Internet Protocol Suite as defined by the Internet Engineering Task Force (IETF). It consists of a set of standards · SOAP SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks. It relies on eXtensible Markup Language as its message format, and usually relies on other Application Layer protocols (most notably Remote Procedure Call (RPC) and · SSH Secure Shell or SSH is a network protocol that allows data to be exchanged using a secure channel between two networked devices. Used primarily on GNU/Linux and Unix based systems to access shell accounts, SSH was designed as a replacement for Telnet and other insecure remote shells, which send information, notably passwords, in plaintext, · Telnet · TLS/SSL Transport Layer Security and its predecessor, Secure Socket Layer (SSL), are cryptographic protocols that provide security for communications over networks such as the Internet. TLS and SSL encrypt the segments of network connections at the Transport Layer end-to-end · XMPP Extensible Messaging and Presence Protocol (formerly named Jabber) is an open, XML-based protocol originally aimed at near-real-time, extensible instant messaging (IM) and presence information (e.g., buddy lists), but now expanded into the broader realm of message-oriented middleware. It was developed by the Jabber open-source community in 1999 ·

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Transport Layer In computer networking, the Transport Layer is a group of methods and protocols within a layered architecture of network components within which it is responsible for encapsulating application data blocks into data units suitable for transfer to the network infrastructure for transmission to the destination host, or managing the reverse

TCP The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite (the other being Internet Protocol, or IP), so the entire suite is commonly referred to as TCP/IP. Whereas IP handles lower-level transmissions from computer to computer as a message makes its way · UDP The User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol (IP) network without requiring prior communications to set up special transmission · DCCP The Datagram Congestion Control Protocol is a message-oriented Transport Layer protocol. DCCP implements reliable connection setup, teardown, ECN, congestion control, and feature negotiation. DCCP was published as RFC 4340, a proposed standard, by the IETF in March, 2006. RFC 4336 provides an introduction. Linux had an implementation of DCCP first · SCTP In computer networking, the Stream Control Transmission Protocol is a Transport Layer protocol, serving in a similar role as the popular protocols Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). It provides some of the same service features of both: it is message-oriented like UDP and ensures reliable, in-sequence transport · RSVP The Resource ReSerVation Protocol , described in RFC 2205, is a Transport layer protocol designed to reserve resources across a network for an integrated services Internet. "RSVP does not transport application data but is rather an Internet control protocol, like ICMP, IGMP, or routing protocols" - RFC 2205. RSVP provides receiver- · ECN ·

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Contents

History and standards

Telnet is a client-server protocol, based on a reliable connection-oriented transport. Typically this protocol is used to establish a connection to Transmission Control Protocol (TCP) port number 23, where a Telnet server application (telnetd) is listening. Telnet, however, predates TCP/IP and was originally run over Network Control Program (NCP) protocols.

Before March 5, 1973, Telnet was an ad-hoc protocol with no official definition.[1] Essentially, it used an 8-bit channel to exchange 7-bit ASCII data. Any byte with the high bit set was a special Telnet character. On March 5, 1973, a Telnet protocol standard was defined at UCLA[2] with the publication of two NIC documents: Telnet Protocol Specification, NIC #15372, and Telnet Option Specifications, NIC #15373.

Because of "negotiable options" protocol architecture, many extensions were made for it, some of which have been adopted as Internet standards, IETF documents STD 27 through STD 32. Some extensions have been widely implemented and others are proposed standards on the IETF standards track (see below).

Security

This section does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be and removed. (April 2010)

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 servers made encrypted alternatives much more of a necessity.

Experts in computer security, such as SANS Institute, 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 the Secure Shell (SSH) protocol, first released in 1995. SSH provides much of the 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 Transport Layer Security (TLS) security and Simple Authentication and Security Layer (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.

Telnet 5250

IBM 5250 or 3270 workstation emulation is supported via custom telnet clients, TN5250/TN3270, and IBM servers. 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.

Telnet data

All data octets except \377 are transmitted over the TCP transport as is. Therefore, a Telnet client application may also be used to establish an interactive raw TCP session, and it is commonly believed that such session which does not use the IAC (\377 character, or 255 in decimal) is functionally identical.[citation needed] This is not the case, however, because there are other network virtual terminal (NVT) rules, such as the requirement for a bare carriage return character (CR, ASCII 13) to be followed by a NULL (ASCII 0) character, that distinguish the telnet protocol from raw TCP sessions.[clarification needed] On the other hand, many systems now possess true raw TCP clients, such as netcat or socat on UNIX and PuTTY on Windows, which also can be used to manually "talk" to other services without specialized client software. Nevertheless, Telnet is still sometimes used in debugging network services such as SMTP, IRC, HTTP, FTP or POP3 servers, to issue commands to a server and examine the responses, but of all these protocols only FTP really uses Telnet data format.

Another difference of Telnet from a raw TCP session is that Telnet is not 8-bit clean by default. 8-bit mode may be negotiated, but high-bit-set octets may be garbled until this mode was requested, and it obviously will not be requested in non-Telnet connection. The 8-bit mode (so named binary option) is intended to transmit binary data, not characters though. The standard suggests the interpretation of codes \000–\176 as ASCII, but does not offer any meaning for high-bit-set data octets. There was an attempt to introduce a switchable character encoding support like HTTP has,[3] but nothing is known about its actual software support.

Current status

As of mid-2010, the Telnet protocol itself has been mostly superseded for remote login. Telnet is popular in various application areas:

Also note that Telnet is a component of FTP protocol. FTP control data are transmitted in Telnet format, although some software implements it incorrectly.

Related RFCs

Telnet clients

See also

References

  1. ^ RFC 318 - documentation of old ad-hoc telnet protocol
  2. ^ RFC 495 - Announcement of Telnet protocol
  3. ^ RFC 2066: TELNET CHARSET Option
  4. ^ Article: GSW UTS Team Services Retrieved 2009-12-15

External links

Categories: Application layer protocols | Clear text protocols | Internet history | Internet protocols | Internet standards | Network-related software | Remote administration software | Unix network-related software

 

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Can dos batch files be used to script and read from telnet to a file?
Q. I'd like to know if I can script telnet in dos so it makes a connection and continues through the batch file while feeding commands to telnet and receiving output and parsing?
Asked by und3r53v3n - Mon Aug 10 09:59:00 2009 - - 1 Answers - 0 Comments

A. It would be difficult to do in DOS because it is aimed more at handling files. You would also have to automate a seperate program (telnet.exe) You might want to have a look at the Perl scripting language. www.perl.org It is a scripting language that includes libraries for telnet. If you are prepared to invest the time to learn Perl then you can use it for a number of different server/PC administration/web tasks. This is a sample for the telnet: Perl tutorial(s)
Answered by mark r - Mon Aug 10 14:48:13 2009

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