RFCs

Implemented

  • RFC 727, “Telnet Logout Option,” Apr 1977.
  • RFC 779, “Telnet Send-Location Option”, Apr 1981.
  • RFC 854, “Telnet Protocol Specification”, May 1983.
  • RFC 855, “Telnet Option Specifications”, May 1983.
  • RFC 856, “Telnet Binary Transmission”, May 1983.
  • RFC 857, “Telnet Echo Option”, May 1983.
  • RFC 858, “Telnet Suppress Go Ahead Option”, May 1983.
  • RFC 859, “Telnet Status Option”, May 1983.
  • RFC 860, “Telnet Timing mark Option”, May 1983.
  • RFC 885, “Telnet End of Record Option”, Dec 1983.
  • RFC 1073, “Telnet Window Size Option”, Oct 1988.
  • RFC 1079, “Telnet Terminal Speed Option”, Dec 1988.
  • RFC 1091, “Telnet Terminal-Type Option”, Feb 1989.
  • RFC 1096, “Telnet X Display Location Option”, Mar 1989.
  • RFC 1123, “Requirements for Internet Hosts”, Oct 1989.
  • RFC 1184, “Telnet Linemode Option (extended options)”, Oct 1990.
  • RFC 1372, “Telnet Remote Flow Control Option”, Oct 1992.
  • RFC 1408, “Telnet Environment Option”, Jan 1993.
  • RFC 1571, “Telnet Environment Option Interoperability Issues”, Jan 1994.
  • RFC 1572, “Telnet Environment Option”, Jan 1994.
  • RFC 2066, “Telnet Charset Option”, Jan 1997.

Not Implemented

  • RFC 861, “Telnet Extended Options List”, May 1983. describes a method of negotiating options after all possible 255 option bytes are exhausted by future implementations. This never happened (about 100 remain), it was perhaps, ambitious in thinking more protocols would incorporate Telnet (such as FTP did).
  • RFC 927, “TACACS User Identification Telnet Option”, describes a method of identifying terminal clients by a 32-bit UUID, providing a form of ‘rlogin’. This system, published in 1984, was designed for MILNET by BBN, and the actual TACACS implementation is undocumented, though partially re-imagined by Cisco in RFC 1492. Essentially, the user’s credentials are forwarded to a TACACS daemon to verify that the client does in fact have access. The UUID is a form of an early Kerberos token.
  • RFC 933, “Output Marking Telnet Option”, describes a method of sending banners, such as displayed on login, with an associated ID to be stored by the client. The server may then indicate at which time during the session the banner is relevant. This was implemented by Mitre for DOD installations that might, for example, display various levels of “TOP SECRET” messages each time a record is opened – preferably on the top, bottom, left or right of the screen.
  • RFC 946, “Telnet Terminal Location Number Option”, only known to be implemented at Carnegie Mellon University in the mid-1980’s, this was a mechanism to identify a Terminal by ID, which would then be read and forwarded by gatewaying hosts. So that user traveling from host A -> B -> C appears as though his “from” address is host A in the system “who” and “finger” services. There exists more appropriate solutions, such as the “Report Terminal ID” sequences CSI + c and CSI + 0c for vt102, and ESC + z (vt52), which sends a terminal ID in-band as ASCII.
  • RFC 1041, “Telnet 3270 Regime Option”, Jan 1988
  • RFC 1043, “Telnet Data Entry Terminal Option”, Feb 1988
  • RFC 1097, “Telnet Subliminal-Message Option”, Apr 1989
  • RFC 1143, “The Q Method of Implementing .. Option Negotiation”, Feb 1990
  • RFC 1205, “5250 Telnet Interface”, Feb 1991
  • RFC 1411, “Telnet Authentication: Kerberos Version 4”, Jan 1993
  • RFC 1412, “Telnet Authentication: SPX”
  • RFC 1416, “Telnet Authentication Option”
  • RFC 2217, “Telnet Com Port Control Option”, Oct 1997

Additional Resources

These RFCs predate, or are superseded by, RFC 854, but may be relevant for study of the telnet protocol.

  • RFC 97 A First Cut at a Proposed Telnet Protocol
  • RFC 137 Telnet Protocol.
  • RFC 139 Discussion of Telnet Protocol.
  • RFC 318 Telnet Protocol.
  • RFC 328 Suggested Telnet Protocol Changes.
  • RFC 340 Proposed Telnet Changes.
  • RFC 393 Comments on TELNET Protocol Changes.
  • RFC 435 Telnet Issues.
  • RFC 513 Comments on the new Telnet Specifications.
  • RFC 529 A Note on Protocol Synch Sequences.
  • RFC 559 Comments on the new Telnet Protocol and its Implementation.
  • RFC 563 Comments on the RCTE Telnet Option.
  • RFC 593 Telnet and FTP Implementation Schedule Change.
  • RFC 595 Some Thoughts in Defense of the Telnet Go-Ahead.
  • RFC 596 Second Thoughts on Telnet Go-Ahead.
  • RFC 652 Telnet Output Carriage-Return Disposition Option.
  • RFC 653 Telnet Output Horizontal Tabstops Option.
  • RFC 654 Telnet Output Horizontal Tab Disposition Option.
  • RFC 655 Telnet Output Formfeed Disposition Option.
  • RFC 656 Telnet Output Vertical Tabstops Option.
  • RFC 657 Telnet Output Vertical Tab Disposition Option.
  • RFC 658 Telnet Output Linefeed Disposition.
  • RFC 659 Announcing Additional Telnet Options.
  • RFC 698 Telnet Extended ASCII Option.
  • RFC 701 August, 1974, Survey of New-Protocol Telnet Servers.
  • RFC 702 September, 1974, Survey of New-Protocol Telnet Servers.
  • RFC 703 July, 1975, Survey of New-Protocol Telnet Servers.
  • RFC 718 Comments on RCTE from the TENEX Implementation Experience.
  • RFC 719 Discussion on RCTE.
  • RFC 726 Remote Controlled Transmission and Echoing Telnet Option.
  • RFC 728 A Minor Pitfall in the Telnet Protocol.
  • RFC 732 Telnet Data Entry Terminal Option (Obsoletes: RFC 731)
  • RFC 734 SUPDUP Protocol.
  • RFC 735 Revised Telnet Byte Macro Option (Obsoletes: RFC 729, RFC 736)
  • RFC 749 Telnet SUPDUP-Output Option.
  • RFC 818 The Remote User Telnet Service.

The following further describe the telnet protocol and various extensions of related interest: