-- telnet FAQ

I have the attention span of a newborn baby and only five minutes time. What is telnet?
The best way to understand telnet is to try it out. Click here or here, follow the instructions on the screen and play around a bit. If nothing happens, forget about it and read on.

What is telnet?
telnet is a protocol that allows you to log on to a remote computer through a local network or the internet to access a character - based service. The remote computer must run telnet server software, you will need telnet client software; both telnet client and sever must first agree on a terminal type to emulate. Of course, this doesn't really tell you anything, so read on.

What is the historical development of telnet?
To understand telnet, it is useful to know a little bit about recent computer history.
Before the advent of personal / desktop computers in the early Eighties, the most popular type of computer system were mainframes (a rather bulky and expensive type of computer) with a number of "dumb" terminals connected to it. These terminals consisted chiefly of a monochrome monitor that could only display characters (no graphics), and a keyboard.
The telnet protocol was defined around 1980 by Jan Postel. It enables modern desktop computers to emulate an old - fashioned dumb terminal to access terminal - based services over an intranet or on the internet via TCP / IP, or to log on to the system shell itself.

What is telnet actually good for?
The short answer: to connect to a remote computer and do one of four things:
  • to log on to the system shell as superuser,
  • to log on as regular user,
  • to access certain character - based, password - protected services,
  • to access anonymous, character - based services.
    The long answer: telnet allows you to log on to a remote computer; if this computer runs a command - line oriented operating system such as UNIX or VAX / VMS and you have the appropriate privileges, you can work in its shell.
    It is more likely, though, that you will want to use telnet to access certain password - protected services on your company or university network. Such as: e.mail, MUD (multi user dungeons, a type of adventure game for computer boffins), library and other types of catalogues, BBSs (bulletin board service, a bit like usenet), chat, etc. There are also some anonymous (publicly available) telnet services on the internet, but they are the exception.
    I will give you an example of a telnet service: the university I was studying at in the mid - Nineties used telnet to provide e.mail service using a Digital VAX / VMS mainframe to their pool of 486 / 586 PCs. Back then, MIME attachments and HTML - enhanced mail were not really an issue, so the character - based access to e.mail worked fine. Being able to have telnet access from outside the campus was also very useful since HTML based e.mail services such as Hotmail or GMX were not yet available.

    I want to try out telnet, what software do I need?
    You will probably not need any additional software. UNIces, Windows 95 / 98 and NT 4.0 (and most modern operating systems) already contain a telnet client.
    For example, you can start a telnet session by typing "telnet www.test.com" at the UNIX shell prompt or the MS DOS console under Windows. Or you can open a telnet session in a Netscape or Internet Explorer browser just like opening a website by typing "telnet://" instead of "http://"). See if this works on your system by clicking here (it is possible that you must first take some steps to "integrate" telnet into your browser, check what is says in your browser's helpfile).
    If you want to use a third - party client, such as the popular NCSA software, or if you are looking for a telnet client for an obscure OS, you should be able to find suitable software on the internet.
    If you are an America Online subscriber, type the keyword "Telnet".

    What else do I need?
    A valid telnet address, ID and password (if the site is non - anonymous). You should be aware that telnet can emulate many different terminal types, so you have to communicate to the server which terminal type you want to use. The default in the Macitosh and Windows world is VT100; if the characters in a telnet session appear to be scrambled, then you must set you telnet client to another terminal format (this entire terminal business is really a bit of a nuisance).

    What about Java telnet?
    You can use a Java applet to access telnet (or integrate a Java applet into your website if you are running a telnet server). This a great way to bridge old and new technologies, and to provide anonymous telnet access to a wider audience.
    You must take into consideration that only 32 bit operating systems can run Java, which rules out DOS or Windows 3.x. Also, telnet through Java is usually relatively slow.

    Are there any security issues with telnet?
    Strictly speaking, connecting your computer to the internet always means taking a risk on your privacy. To be on the safe side you should use up - to - date software.
    A telnet session usually starts with the server displaying information on its operating system; for example: "FreeBSD (www.address.com) (ttyp1)". That is valuable information for anyone trying to break into that particular server, and scanning software such as SATAN actually uses telnet to obtain it. So if you are adminstrating a telnet server, you should consider setting up your software so that OS information is obscured.

    What exactly does "character - based" mean?
    First of, it doesn't have to mean "dull" or "text - only". Especially MUD - sites tend to be surprisingly flashy.
    Not to be expected though, are pixel graphics, sounds, millions of colours, videos. And even though telnet can emulate relatively modern terminal types, which could at least display a few colours, for compatiblity purposes the terminal most often emulated is the ancient and monochrome VT100.

    What is the difference between telnet and rlogin?
    rlogin (remote login) is part of the "r - tools" (rlogin, rcp, rsh). Both telnet and rlogin are originally UNIX shell commands, even though there are now programs for other operating systems that provide the same functionality; both commands allow you to log in to a remote, command - line based system. telnet has done remarkaly well in the non - UNIX world, whereas rlogin is more associated with UNIX.
    telnet tends to be more flexible and easier to use. If you want to provide anonymous services to untrustworthy clients, then telnet will probably be your protocol of choice.

    What is the future of telnet?
    Actually, I think that there is no straightforward answer to this question. So here are a couple of answers:
    - telnet is one of the oldest internet services, and as a way to log on to a remote (UNIX) shell, it will probably not be replaced soon. In the Windows world though, there is competition from remote - access (or servicing or espionage) products Symantec's PCAnywhere or the infamous BackOrifice by l0pht Heavy Industries.
    - most internet users today will never use telnet. The telnet protocol is being superseded by more recent implementations of active network content, such as HyperText with CGI, Java, JavaScript, and Microsoft's Active Server Pages and Active-X.
    Which is not to say that telnet is obsolete. Aside from rlogin it is a unique method to remotely log on to a computer (mostly to a UNIX shell) over a network.
    - telnet is still a great way to provide certain interactive network services such as BBSs and library catalogues, which would not profit from greater flashiness anyway. For example, if you are already successfully running a telnet catalogue over the internet, there is little reason for doing away with telnet. And with a Java - telnet applet, telnet can now be provided to anyone surfing the net with a modern OS and browser.

    About this FAQ.
    I am not a telnet afficionado. I wrote this FAQ merely because I couldn't find a similar document on the internet that answers the questions I had on telnet in a concise and comprehensive way.
    If you have any criticism or suggestions please send me an e.mail.

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    telnet FAQ Page on Michael Barnikel's Website. © 7/2003.