Friday, 5 July 2013

Telnet



What is Telnet?
Telnet is a user command and an underlying TCP/IP protocol for accessing remote computers. Through Telnet, an administrator or another user can access someone else's computer remotely. On the Web, HTTP and FTP protocols allow you to request specific files from remote computers, but not to actually be logged on as a user of that computer. With Telnet, you log on as a regular user with whatever privileges you may have been granted to the specific application and data on that computer.
A Telnet command request looks like this (the computer name is made-up):
telnet the.libraryat.whatis.edu
The result of this request would be an invitation to log on with a userid and a prompt for a password. If accepted, you would be logged on like any user who used this computer every day.
Telnet is most likely to be used by program developers and anyone who has a need to use specific applications or data located at a particular host computer.
Related glossary terms: system administrator (sysadmin), ring, Internet, keystone jack, corporate area network (CAN), port, home server, LANDesk Client Manager (LDCM), HomeRF (home radio frequency), local access and transport area (LATA)

Telnet

Telnet is the main Internet protocol for creating a connection with a remote machine. It gives the user the opportunity to be on one computer system and do work on another, which may be across the street or thousands of miles away. Where modems are limited, in the majority, by the quality of telephone lines and a single connection, telnet provides a connection that's error-free and nearly always faster than the latest conventional modems.

Using Telnet

As with FTP (see section Anonymous FTP), the actual command for negotiating a telnet connection varies from system to system. The most common is telnet itself, though. It takes the form of:
telnet somewhere.domain
To be safe, we'll use your local system as a working example. By now, you hopefully know your site's domain name. If not, ask or try to figure it out. You'll not get by without it.
To open the connection, type
telnet your.system.name
If the system were wubba.cs.widener.edu, for example, the command would look like
telnet wubba.cs.widener.edu
The system will respond with something similar to
Trying 147.31.254.999...
Connected to wubba.cs.widener.edu.
Escape character is '^]'.
The escape character, in this example ^] (Control-]), is the character that will let you go back to the local system to close the connection, suspend it, etc. To close this connection, the user would type ^], and respond to the telnet> prompt with the command close. Local documentation should be checked for information on specific commands, functions, and escape character that can be used.

Telnet Ports

Many telnet clients also include a third option, the port on which the connection should take place. Normally, port 23 is the default telnet port; the user never has to think about it. But sometimes it's desirable to telnet to a different port on a system, where there may be a service available, or to aid in debugging a problem. Using
telnet somewhere.domain port
will connect the user to the given port on the system somewhere.domain. Many libraries use this port method to offer their facilities to the general Internet community; other services are also available. For instance, one would type
telnet martini.eecs.umich.edu 3000
to connect to the geographic server at the University of Michigan (see section Geographic Name Server). Other such port connections follow the same usage.

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