Telecommunication Network (Telnet)‏

• TELNET is a client-server protocol, based on a reliable connection-oriented transport .
• This protocol establishes a connection to TCP port 23, where a getty-equivalent program (telnetd) is listening.
• Telnet is a protocol for remote computing on the Internet. It allows a computer to act as a remote terminal on another machine, anywhere on the Internet. This means that when you telnet to a particular host and port, the remote computer (which must have a telnet server) accepts input directly from your computer (which must have a telnet client) and output for your session is directed to your screen
• To open a Telnet session, go to the UNIX command line or the Windows Run dialog box, and type telnet [hostname] enter your user name and password, or the access information you know the computer requires

telnet 192.168.1.1

 



TELNET for remote logins should be discontinued under all normal circumstances, for the following reasons:

• TELNET, by default, does not encrypt any data sent over the connection (including passwords), and so it is often practical to eavesdrop on the communications and use the password later for malicious purposes; anybody who has access to a router, switch, hub or gateway located on the network between the two hosts where TELNET is being used can intercept the packets passing by and obtain login and password information (and whatever else is typed) with any of several common utilities like tcpdump and Wireshark.
• Most implementations of TELNET have no authentication to ensure that communication is carried out between the two desired hosts and not intercepted in the middle.
• Commonly used TELNET daemons have several vulnerabilities discovered over the years.

With the release of SSH, which 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.Extensions to the TELNET protocol provide TLS security and SASL authentication that address the above issues. 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.
 



 

Advantages/Disadvantages of Telnet

Advantages

• Fast
• Cheap
• Can run on all computers

Disadvantages

• Only text and numbers displayed.
• no graphics
• no colors
• no mouse

How to run telnet command in CMD ?

Telnet is a protocol that enables you to connect to remote computers and local computers over a TCP/IP network, over TCP port 23. By default, Telnet is disabled in recent Windows environments.
To enable Telnet command line utilities in windows:

• Click Start > Control Panel.
• Click Programs and Features.
• Click Turn Windows features on or off.
• In the Windows Features dialog box, check the Telnet Client check box.
• Click OK. The system installs the appropriate files. This will take a few seconds to a minute.

To open a Telnet session:

• Click Start.
• Enter cmd in the Search field in the Start menu. A command prompt is displayed.
• Type telnet and press ENTER. The Telnet> prompt is displayed.