RFC 736

RFC 736: Telnet SUPDUP Option 🎀

Okay bestie, this one is from the Network Working Group 🦋. Mark Crispin (SU-AI) wrote it on 31 October 1977, and it's filed under NIC 42213 ✨. The header doesn't list a category, and it doesn't say it obsoletes or updates anything, so there's no drama there 💅.

1. Command name and code ✨

The name and number, no cap 🧚

SUPDUP               21

2. Command meanings 💖

Each of these is its own command with its own vibe, so read closely 🙈

IAC WILL SUPDUP

The sender of this one is asking permission to use the SUPDUP display protocol, or confirming that it's going to use it 🌸

IAC WON'T SUPDUP

The sender refuses to use the SUPDUP protocol. Not it 💅

IAC DO SUPDUP

The sender is either asking the receiver to use SUPDUP, or giving the receiver permission to use it 👑

IAC DON'T

The sender is demanding that the receiver not use the SUPDUP protocol. Hard no 💀

3. Default 🌈

The starting vibe is that neither side has opted in:

WON'T SUPDUP

DON'T SUPDUP

So basically, the SUPDUP display protocol is not in use ✨

4. Motivation for the option 🍓

After RFC 734 dropped, Mark got asked to design a TELNET option for SUPDUP service 🫶. This option lets a host offer SUPDUP service on the normal TELNET socket (27 octal) instead of 137 (octal), which is the normal SUPDUP ICP socket 🔥.

5. Description of the option 💜

A user TELNET program that wants the SUPDUP display protocol instead of NVT terminal service should send IAC DO SUPDUP. If the server is down to use SUPDUP, it should reply with IAC WILL SUPDUP. Otherwise it should refuse with IAC WONT SUPDUP 🦋

For hosts that normally offer SUPDUP terminal services, the server can send IAC WILL SUPDUP upon ICP, and then the user can accept or refuse ✨

Once the SUPDUP option is in effect, no more TELNET negotiations are allowed. They're meaningless now, because SUPDUP has its own facilities for everything that's needed 💅 So octal 377 becomes an ordinary transmitted character (in this case an invalid %TD code) instead of an IAC 🙈

Once both sides have mutually accepted the SUPDUP option, the SUPDUP negotiation goes ahead as described in RFC 734 🎀 Iconic, periodt 🌈