ps.
telnet SDF.org
just works...
Does this impact traffic for MUDs at all? I know several MUDs operate on nonstandard Telnet ports, but many still allow connection on port 23. Does this block end-to-end Telnet traffic, or does it only block attempts to access Telnet services on the backbone relays themselves?
Since Telnet is totally plain text that would absolutely be easy to do right?
MUDs use plaintext TCP protocols that are accessible to a wide range of clients.
The Telnet protocol is well-defined and not completely plaintext. There are in-band signaling methods and negotiations. Telnet is defined to live on 23/tcp as an IANA well-known, privileged, reserved port.
MUDs do none of this. You can usually connect to a MUD using a Telnet client, but most players hate the experience and often deride this method in favor of a dedicated, programmable client.
The fact that MUDs inhabit higher 4-digit ports is an artifact from their beginnings as unprivileged, user-run servers without a standardized protocol or an assigned “well-known port” presence. If you want your MUD to be particularly inaccessible, you could certainly run on port 23 now!
Most MUDs implement RFC 854, and a number of non-standard Telnet option subnegotiation protocols have been adopted for compression (MCCP2), out-of-band data transmission (ATCP, GMCP, ZMP), and even a mechanism for marking up the normal in-band content using XML-style tags out-of-band (MXP). These telopts build on the subnegotiation facility in standard Telnet, whose designers knew that the base protocol would be insufficient for many needs; there are a great number of IANA-controlled and standardized telopt codes that demonstrate this, and the MUD community has developed extensions using that same mechanism.
> You can usually connect to a MUD using a Telnet client, but most players hate the experience and often deride this method in favor of a dedicated, programmable client.
I think you are confusing "telnet" the program with "telnet" the protocol. I am speaking here of the protocol, defined at base in RFC 854, for which "telnet" the program is but one particularly common implementation. You look at any of those "dedicated, programmable clients" and they will contain an implementation of RFC 854, probably also an implementation of RFC 1143 (which nails down the rules of subnegotiation in order to prevent negotiation loops), and an implementation of the RFCs for several standard telopts as well as non-standardized MUD community telopts.
That said in this day and age, servers on the public network really ought to use SSH.
$ telnet smtp.example.co.uk 25
HELO me
MAIL FROM: gerdesj@example2.co.uk
RCPT TO: gerdesj@example.co.uk
DATA
A more "proper" tool for that is netcat -- I doubt SMTP supports the Telnet option negotiations subsystem. (I also doubt SMTP servers can interpret the full suite of Network Virtual Terminal (NVT) commands that the Telnet protocol supports.) There's clearly enough similarity between the two protocols that if you're just using it to transfer plaintext it will probably work out fine, but they are distinct protocols.
Never heard about https://jetmore.org/john/code/swaks/, thanks for the tip.
Who?
Where's the commit?
In this case the hero's name is apparently Simon Josefsson (maintainer).
Ah, someone beat me to it!
(OK, I know one ancient talker that uses it - but on a very non-standard port so a port 23 block wouldn't be relevant)
telnet towel.blinkenlights.nl https://www.youtube.com/watch?v=Mhcf6tc2jeQ
(Remember hearing about this many years ago and verified it still exists.)
adolph•51m ago
RupertSalt•18m ago