by Darius Kazemi, December 5 2019

In 2019 I'm reading one RFC a day in chronological order starting from the very first one. More on this project here. There is a table of contents for all my RFC posts.

Multiplexed Telnet

RFC-339 is titled “MLTNET: A 'Multi Telnet' Subsystem for Tenex”. It's authored by Robert Thomas of BBN and dated May 5, 1972.

The technical content

MLTNET lets a user log in to multiple ARPANET Hosts at one time. It's useful if you need to coordinate behavior between Hosts: you need the program on Host A to do this, and then you need the program on Host B to do that.

Basically, you start off in Local Mode and open your connections to various remote sites. Here you can associate helpful names for these sites as shortcuts and query the remote site to make sure that it's still online. Then you enter a command TALK <sitename> and it switches to Remote Mode, where you're connected to that site in a Telnet-like way. You issue your commands, and then back out of Remote Mode into Local Mode, where you connect to another remote Host of your choosing.


It makes sense that someone at BBN would need to coordinate jobs running on different ARPANET nodes. Presumably this use case came up while BBN was running tests across the network as a whole.

Further reading

Bob Thomas is probably best known for writing Creeper, which was arguably the first computer “worm” to spread across a network. It was not a malicious program per se. It would simply display the text “I'm the creeper: catch me if you can” to a user's terminal.

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About me

I'm Darius Kazemi. I'm an independent technologist and artist. I do a lot of work on the decentralized web with ActivityPub, including a Node.js reference implementation, an RSS-to-ActivityPub converter, and a fork of Mastodon, called Hometown. You can support my work via my Patreon.