Telnet ppt
- 1. Topic: TELNET Protocol By Sunilkumarsingh Kumpawat Master of Library and Information Science Sem-1 Dept. of Library and Information Science Maharaja Sayajirao University of Baroda
- 2. content i. Meaning ii. How it Works? iii.What is mean by NVT? iv.What is NVT Character Sets? v. TELNET Options vi.TELNET Options Negotiations vii.TELNET Mode of Operation viii.Symmetry ix.User’s Interference x. Security Issue xi.Conclusion xii.References
- 3. Meaning • Telnet (Terminal Networks) is a networking protocol and software program used to access remote computers and terminals over the Internet or a TCP/IP computer network. • Telnet was conceived in 1969 and standardized as one of the first Internet standards by the Internet Engineering Task Force (IETF). • It can be use Programs and data from other Computers if they are into the same LAN (Local Area Network). Telnet protocol is available on port number 23 of the host machine. • Telnet sends all messages in clear text and has no specific security mechanisms. Thus, in many applications and services, Telnet has been replaced by Secure Shell (SSH).
- 4. How it works? Telnet works on two logins • Local Login • Remote Login Local Login When a user logs into a local time-sharing system, it is called local login. As a user types at a terminal or at a workstation running a terminal emulator, the keystrokes are acceptsed by the terminal driver. The terminal driver passes the characters to the operating system. The operating system, in turn, interprets the combination of characters and invokes the desired application program or utility.
- 5. Conti. • Remote Login When a user wants to access an application program or utility located on a remote machine, he or she performs remote login. Here the TELNET client and server programs come into use. The user sends the keystrokes to the terminal driver where the local operating system accepts the characters but does not interpret them. The characters are sent to the TELNET client, which transforms the characters to a universal character set called Network Virtual Terminal (NVT) characters and delivers them to the local TCP/IP stack.
- 6. What is mean by NVT? • The mechanism to access a remote computer is complex. This is because every computer and its operating system accept a special combination of characters as tokens. For example, the end-of-file token in a computer running the DOS operating system is Ctrl+z, while the UNIX operating system recognizes Ctrl+d. • TELNET solves this problem by defining a universal interface called the Network Virtual Terminal (NVT) character set. Via this interface, the client TELNET translates characters (data or commands) that come from the local terminal into NVT form and delivers them to the network. The server TELNET, on the other hand, translates data and commands from NVT form into the form acceptable by the remote computer.
- 7. NVT Cont. • NVT Character Set NVT uses two sets of characters, one for data and one for control. Both are 8-bit bytes. Data Characters: For data, NVT normally uses what is called NVT ASCII (American Standard Code for Information Interchange). This is an 8-bit character set in which the seven lowest order bits are the same as US ASCII and the highest order bit is 0.
- 8. NVT Cont. Control Characters: To send control characters between computers (from client to server or vice versa), NVT uses an 8-bit character set in which the highest order bit is set to 1. Lists some of the control characters and their meanings.
- 9. TELNET Options • TELNET lets the client and server negotiate options before or during the use of the service. Options are extra features available to a user with a more sophisticated terminal.
- 10. TELNET Options Negotiations • To use any of the options mentioned in the previous Slide first requires option negotiation between the client and the server. Four control characters are used for this purpose; Enabling an Option: Some options can only be enabled by the server, some only by the client, and some by both. An option is enabled either through an offer or a request. Offer to Enable The offering party sends the WILL command, which means “Will I enable the option?” The other party sends either the DO command, which means “Please do,” or the DONT command, which means “Please don’t.” Request to Enable The requesting party sends the DO command, which means “Please do enable the option.” The other party sends either the WILL command, which means “I will,” or the WONT command, which means “I won’t.”
- 11. Cont. Disabling an Option: An option that has been enabled can be disabled by one of the parties. An option is disabled either through an offer or a request. Offer to Disable The offering party sends the WONT command, which means “I won’t use this option anymore.” The answer must be the DONT command, which means “Don’t use it anymore.” Request to Disable The requesting party sends the DONT command, which means “Please don’t use this option anymore.” The answer must be the WONT command, which means “I won’t use it anymore.”
- 12. TELNET Modes of Operation Most TELNET implementations operate in one of three modes: default mode, character mode, or line mode. Default Mode: The default mode is used if no other modes are invoked through option negotiation. In this mode, the echoing is done by the client. The user types a character and the client echoes the character on the screen (or printer) but does not send it until a whole line is completed. Character Mode: In the character mode, each character typed is sent by the client to the server. The server normally echoes the character back to be displayed on the client screen. Line Mode: A new mode has been proposed to compensate for the deficiencies of the default mode and the character mode. In this mode, called the line mode, line editing (echoing, character erasing, line erasing, and so on) is done by the client.
- 13. Symmetry • One interesting feature of TELNET is its symmetric option negotiation in which the client and server are given equal opportunity. This means that, at the beginning of connection, it is assumed that both sides are using a default TELNET implementation with no options enabled. • If one party wants an option enabled, it can offer or request. The other party has the right to approve the offer or reject the request if the party is not capable of using the option or does not want to use the option. This allows for the expansion of TELNET. A client or server can install a more sophisticated version of TELNET with more options. • When it is connected to a party, it can offer or request these new options. If the other party also supports these options, the options can be enabled; otherwise, they are rejected.
- 14. User’s Interference The normal user does not use TELNET commands as defined above. Usually, the operating system (UNIX, for example) defines an interface with user-friendly commands. Note that the interface is responsible for translating the user-friendly commands to the previously defined commands in the protocol.
- 15. Security Issue TELNET suffers from security problems. Although TELNET requires a login name and password (when exchanging text), often this is not enough. A microcomputer connected to a broadcast LAN can easily eavesdrop using snooper software and capture a login name and the corresponding password (even if it is encrypted)
- 16. Conclusion To conclude in simple words the TELNET is used for remote login of the computer and features like TELNET Options, Negotiation & Commands and symmetry were used for smooth run in the default or line or character mode.
- 18. References 1. Telnet(TN).(2020).Techopedia.Com.https://www.techopedia.com/definition/2457/telnet-tn retrieved on 16th Dec. 2020 2. Dhillon, G. (2013). Remote Login: TELNET and SSH. Https://Gursimrandhillon.Wordpress.Com. https://gursimrandhillon.files.wordpress.com/2013/09/telnet-and-ssh.pdf, retrieved on 22nd Jan. 2021 3. Slideshare (2017, May 5). Telnet presentation. Slideshare.Com. https://www.slideshare.net/travel_affair/telnet- presentation, retrieved on 17th Dec. 2020.