Important RFCs: Telnet RFCs

Telnet Options

Good Telnet clients are difficult to program, but the Telnet protocol spec (RFC 854) is an almost dainty 15 pages. Part of the reason is that the Telnet protocol itself is not that powerful. (The other reason has to do with terminal emulation, but that's another issue entirely.) Instead, most of Telnet's power is in its extensible architecture, and over the past two decades, it has been extended again and again.

Today's Telnet clients must support a minimum of six additional Telnet options to be considered "standard," and your users will want even more options supported. So, below is a table summarizing the currently-acknowledged Telnet options along with links to their respective RFCs.

	RFC	Extension Name
	RFC 856 (STD 27)	Binary Transmission
	RFC 857 (STD 28)	Echo
	RFC 858 (STD 29)	Suppress Go-Ahead
	RFC 859 (STD 30)	Status
	RFC 860 (STD 31)	Timing Mark
	RFC 861 (STD 32)	Extended Options List
	RFC 726	Remote Controlled Transmission and Echoing
	RFC 652	Output Carriage-Return Disposition
	RFC 653	Output Horizontal Tabstops
	RFC 654	Output Horizontal Tab Disposition
	RFC 655	Output Formfeed Disposition
	RFC 656	Output Vertical Tabstops
	RFC 657	Output Vertical Tab Disposition
	RFC 658	Output Linefeed Disposition
	RFC 698	Extended ASCII
	RFC 727	Logout
	RFC 735	Byte Macro
	RFC 1043	Data Entry Terminal
	RFC 736	SUPDUP
	RFC 749	SUPDUP Output
	RFC 779	Send Location
	RFC 1091	Terminal Type
	RFC 885	End of Record
	RFC 927	TACACS User Identification
	RFC 933	Output Marking
	RFC 946	Terminal Location Number
	RFC 1041	Telnet 3270 Regime
	RFC 1053	X.3 PAD
	RFC 1073	Negotiate About Window Size
	RFC 1079	Terminal Speed
	RFC 1372	Remote Flow Control
	RFC 1184	Linemode
	RFC 1096	X Display Location
	RFC 1572	Environment
	RFC 1647	TN3270 Enhancements