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What: |
How: |
What is Telnet?
Telnet is the way you can access someone else's computer, assuming they have given you permission. (Such a computer is frequently called a host computer.) More technically, Telnet is a user command and an underlying TCP/IP protocol for accessing remote computers. The Web or HTTP protocol and the FTP protocol allow you to request specific files from remote computers, but not to actually be logged on as a user of that computer. For some types of tasks, you will need to use telnet to access a remote computer.
A very simple analagy of telnet compared to ftp or http would be like stopping at a stop-and-go convenience store. FTP would be like going to the window and asking the clerk for a certain item. The clerk would go get the item and give it to you. Every item you asked for, the clerk would get it for you and bring it to the window and give it to you because you were not allowed to enter the store and get it yourself. On the other hand, with telnet if you were authorized you could go right into the store yourself and get items that you want. You could even read a book or use the restroom while you were in the store. Host computers have to be more particular who they let telnet into their domain. The more rights one has, the more potential damage they could cause.
The administrator of the host computer can give a remote user as many or as
few rights as they choose. Most people logging on will not have every
right possible - giving all rights to the ordinary user would be very dangerous!
It would be quite easy to bring the system to a halt. The general user
that telnets into a host computer probably will only be allowed a certain amount
of disk space, only be able to access certain directories, only be able to execute
certain programs, and will be restricted to a limited amount of memory.
By enforcing these restrictions there is not very much chance that a remote
user could do any serious damage to the system or other users.
When was Telnet First
Established?
The first standards for telnet were set forth in 1980 in RFC764.
However, in May of 1983 it was revised in RFC854.
These standards set conformity for the telnet protocol. RFC855
set the standards for the options that may be used in telnet. Before any options
can be used the two communicating computers must agree on them. This is done
via a request and the computer receiving the request has the choice to use the
option or not and sends information back to the sending computer acknowledging
or denying its request.
Who Uses Telnet?
In the earlier days of Internet computing, just about everyone who wanted to access the Internet would use telnet. Usually you would telnet to a UNIX-based host. Once logged in you could use lynx, which was an internet browser. Telnet does not support graphics, so all applications were text based. Newsgroups that could also be accessed by telneting into a host computer. There was no hotmail.com or Eudora either! All email was text based, so telnet was used quite a lot for that also. A lot of libraries had card catalogs that could be accessed with a telnet application.
That was then, this is now! Just about everything that was accessed by telnet is now available via a Web page. You can still access Web pages using telnet and a text-based browser; however, with all of the graphics and tables and frames on most Web pages you would sure miss a lot.
So is telnet history? Absolutely not! It is still used by a number of people. One very important use of telnet today is by service personnel. So many of today's machines and equipment are controled by computers. Quite often service personnel can telnet to this equipment without ever leaving their home or office. This means that quite often they are able to fix a problem that is caused by software on the computer controlled equipment. This is a very good use of telnet. It saves time and money for all concerned. Service personnel usually do not have any restrictions when they telnet under these circumstances. Telnet is almost like being right there next to the computer.
Internet servers are often administered by telnet. That way, one administrator sitting at a workstation can administer many of an organization's servers without having to move from one to another. He just telnets to whichever server needs attention, enters his administrator code and password, and does what's needed: adds users, clears out unwanted files, formats new disks, installs new software, troubleshoots problems, and whatever is needed. If there is trouble while the administrator is at home, he may be able to solve the problems by telneting from a home computer - as long as the server operating system and telnet function is running.
Web servers may also be accessed via telnet by the Webmaster for various purposes. Though much can be handled by a good Web site management program or FTP, she may need to do something that is only allowed through telnet - such as giving permission to a new Web designer to save her files on the server.
How
To Use Telnet In Windows Telnet is a client-server application. That means the user runs a client program and a host runs (surprise!) server software. Most operating systems have telnet clients among their utilities - including UNIX, VAX-VMS, and Mac-OS.
Microsoft Windows also comes with a telnet program. This program is installed when you install the Dialup Networking, but Windows does not put a menu selection or an icon on the desktop for the telnet application. The easiest way of running it is to click the Start menu, then Run, type telnet and press OK.
Unfortunately, the telnet program that comes with Windows is not able to transfer files between your computer and the host. There are very good third party applications that are shareware or even freeware. One such application is called Tera Term and it is free. This application has provisions for many different types of file transfer with many other features thrown in. Below is a screen shot of the Tera Term telnet application. You must fill in the host computer that you want to telnet to. The port setting on this program defaults to port 23, which is usually the excepted port for telnet. Some host computers choose to use a different port for one reason or another. If this is true just type in the port you wish to use.
| *****************************************************************************
* This is the University of Michigan information technology environment. * You must be authorized to use these resources. As an authorized user, by * your use of these resources, you have implicitly agreed to abide by the * highest standards of responsibility to your colleagues -- the students, * faculty, staff, and external users who share this environment. You are * required to comply with all University policies, state, and federal laws * concerning appropriate use of information technology. Non-compliance is * considered a serious breach of community standards and may result in * disciplinary or legal action. ***************************************************************************** UNIX(r) System V Release 4.0 (moonpatrol.gpcc.itd.umich.edu) login:
strieter |
After entering your login name and password you are all ready to start your telnet session. Of course, you will need to be familiar with the operating system of the host computer! (If you are thrown into a UNIX system and need a quick guide, you may find "UNIX Summary: A Survival Guide," module Q02cu, helpful.)
When you are done with your telnet session, you log out and the host's telnet server will disconnect you.
If you would like to download Tera Term or its source code, you may use one of these links:
How to Use
Telnet in DOSAt one time not so very long ago all applications for a PC were made for DOS.
DOS did not have a TCP/IP protocol built into it like the modern day Windows
does. However, running telnet in DOS was and still is possible. There
are dialers that can be used in a DOS envirement. These applications can
obtain an internet connection with service providers, or dial to a modem directly
connected to a host computer. These DOS applications will "terminate
and stay resident" (TSR). There are telnet applications that can
communicate with these TSRs. These application for DOS are not very popular
anymore and are sometimes very hard to configure for the average computer user.
For those of you who like model Ts and old 16 bit processors, we have found
a Web page with software for using telnet in DOS! Most of the software was designed
to run on DOS 5.00 and may not work on the DOS that is supplied with Windows
9x.
How to use
telnet in UNIX1) At the UNIX $ prompt, type
telnet hostname or IP address
for example:
$ telnet cidermill.wccnet.org
$ telnet 198.111.176.7
Or
1) At the UNIX $ prompt, type telnet
$ telnet
You will be presented with the telnet> prompt.
2) Type open hostname (where hostname is the name of the host you
wish to connect to).
telnet> open cidermill.wccnet.org
To end a UNIX telnet session:
1) Log off from the remote system you have connected to.
2) Telnet will automatically terminate and return you to the UNIX $ prompt.
3) Or if you used the second method (using the open command), you
will be returned to the telnet> prompt,
and you should type quit to leave telnet,
or use the open command to make another connection.
| joust%
telnet telnet> open login.itd.umich.edu Trying 141.211.2.153... Connected to seawolf.gpcc.itd.umich.edu. Escape character is '^]'. ******************************************************************************
UNIX(r)
login:
|
Telnet CommandsNote: These commands are not completely standardized. They work as shown if you are using the UNIX C shell, Korn shell, TC shell or BASH shell. Most of them work the same in other telnet clients, but there will be exceptions. (What the computer types is in color; what you type is in white.)
| To ... | Do this ... |
| Connect to a remote system | telnet>open remote_system_name |
| Suspend a telnet connection and return to the telnet prompt | Ctrl ] |
| Close a connection to a remote system |
Ctrl
] |
| Suspend telnet and work on the local system (UNIX only) | telnet>z |
| Resume the use of telnet (UNIX only) |
prompt%fg |
| End the telnet session | telnet>quit |
| To display a list of telnet commands | telnet> ? |
| To get an explanation of a command | telnet> help name_of_command |
Here is a list of telnet commands and explanations as shown by a UNIX
? command:
| joust%
telnet telnet> ? Commands may be abbreviated. Commands are: close
close current connection |
You can learn more on telnet commands at www.nacse.org.
Audience: This is for people who need a basic idea of telnet and its uses. You need minimal computer understanding for this topic, but to use telnet requires familiarity with command-based operating systems.
Objectives: After you study this web page, you will be able:
1) To define what
telnet is all about.
2) To use telnet in windows, dos, and UNIX environment.
3) To start telnet and end the session.
Click here to review: 
About this document...
Module NA40c: This
document is part of a modular instruction series in Computer Information Systems.
For more information, see the overview
or the list of modules in this series, NA "Network Application". This document
has been used in the following classes: