TELNET control information

Question

A TELNET connection is a Transmission Control Protocol (TCP)
connection used to transmit data with interspersed TELNET control
information.

So, what's the TELNET control information? Can you get an example?

score 1 · Accepted Answer · answered Dec 26 '13 at 00:50

1

Control information is sent using sequences beginning with the IAC code. See the section titled TELNET COMMAND STRUCTURE in the RFC.

answered Dec 26 '13 at 00:50

Barmar

Thanks for your answer! But I have one doubt: Does it mean that client-server communication via telnet is just TCP session? – Dec 26 '13 at 01:12
Yes, what else would it be? – Barmar Dec 26 '13 at 02:31
_With the current set-up, only the IAC need be doubled to be sent as data_ Why when I sent from TCP server to telnet client 2 bytes of ASCII like this `255,55,55` only last 55 ASCII byte will return to client? – Dec 26 '13 at 03:05
1

IAC control sequences aren't sent to the terminal, they're processed by the TELNET program internally. – Barmar Dec 26 '13 at 03:08
What part of "off-topic" is confusing to you? Are you programming a TELNET client or server? If so, please post a question about the code. But I'm not sure why you would bother, it's mostly obsolete. SSH is the common remote login protocol these days. – Barmar Dec 26 '13 at 03:09

score 0 · Answer 2 · answered Dec 26 '13 at 00:52

0

Telnet control information varies form setting the terminal type, to allowing read-ahead. Including setting window size and turning on/off of echo.

answered Dec 26 '13 at 00:52

Scary Wombat

2 Answers2