omnitel.ie  the unofficial telnet fan club.

Telnet is more than fifty years old but is still
the quickest way to say hello to a port. We think that deserves a fan
site. Not affiliated with any protocol, standards body or router.

New here? Type join below to get your membership number.
Type help to see everything else.

$ cat history.txt
1969  Telnet is first described in RFC 15, written for the ARPANET.
1983  RFC 854 and RFC 855 set the standard still in use: the protocol
      itself, and how options are negotiated.
1995  Tatu Ylönen writes SSH after a password-sniffing attack on his
      university network. Encrypted logins start to replace telnet.
now   Telnet is gone from most servers. It lives on in old network
      gear, MUD games, and as a debugging tool.

$ man telnet
Port       23/tcp
Model      Network Virtual Terminal (NVT): a lowest-common-denominator
           terminal that every host and client agrees to emulate.
Escape     Byte 255 (IAC, "interpret as command") starts a command.
           The four verbs are WILL, WON'T, DO and DON'T.
Options    Client and server negotiate extras one at a time, such as
           ECHO (RFC 857) and SUPPRESS-GO-AHEAD (RFC 858).
Security   None. Usernames, passwords and every keystroke cross the
           network as plain text.

$ telnet example.com 80
Telnet is still handy for checking that a port answers. It opens a raw
TCP connection, so you can type a request by hand:

  $ telnet example.com 80
  GET / HTTP/1.0
  Host: example.com
  (press Enter twice)

You get back the server's headers and page. No browser, no library.
Many systems no longer ship a telnet client: it was dropped from macOS
in 2017 and is an optional feature on Windows. nc (netcat) does the
same job.

$ cat why-we-love-it.txt
* It is tiny. Open a connection and you are talking, no setup needed.
* It is honest. Everything you type is plain text you can read by eye.
* It is everywhere. Routers, switches, old servers and MUDs still
  answer on port 23.
* It is a time capsule. Its design dates from when the whole network
  fit on a few dozen machines.

$ ls hall-of-fame/
Jon Postel      Co-author of RFC 854 (with J. Reynolds), and long-time
                editor of the RFC series.
The ARPANET     Where telnet was born and first used.
MUD players     Kept telnet alive for decades, one dungeon at a time.
nc, a.k.a.      Telnet's modern cousin, for when the client is missing.
  netcat

$ ssh --why
Fans can be fond and still honest: use SSH for anything real.
It does everything telnet does, encrypts the whole session,
and checks that the machine you reach is the one you meant to reach.
If a device only offers telnet, keep it off the open internet and
off any network you don't control.