Requirements for Internet Hosts - Application and Support
RFC 1123

Document Type RFC - Internet Standard (October 1989; Errata)
Updates RFC 952, RFC 822
Also known as STD 3
Last updated 2013-07-24
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Network Working Group                    Internet Engineering Task Force
Request for Comments: 1123                             R. Braden, Editor
                                                            October 1989

       Requirements for Internet Hosts -- Application and Support

Status of This Memo

   This RFC is an official specification for the Internet community.  It
   incorporates by reference, amends, corrects, and supplements the
   primary protocol standards documents relating to hosts.  Distribution
   of this document is unlimited.

Summary

   This RFC is one of a pair that defines and discusses the requirements
   for Internet host software.  This RFC covers the application and
   support protocols; its companion RFC-1122 covers the communication
   protocol layers: link layer, IP layer, and transport layer.

                           Table of Contents

   1.  INTRODUCTION ...............................................    5
      1.1  The Internet Architecture ..............................    6
      1.2  General Considerations .................................    6
         1.2.1  Continuing Internet Evolution .....................    6
         1.2.2  Robustness Principle ..............................    7
         1.2.3  Error Logging .....................................    8
         1.2.4  Configuration .....................................    8
      1.3  Reading this Document ..................................   10
         1.3.1  Organization ......................................   10
         1.3.2  Requirements ......................................   10
         1.3.3  Terminology .......................................   11
      1.4  Acknowledgments ........................................   12

   2.  GENERAL ISSUES .............................................   13
      2.1  Host Names and Numbers .................................   13
      2.2  Using Domain Name Service ..............................   13
      2.3  Applications on Multihomed hosts .......................   14
      2.4  Type-of-Service ........................................   14
      2.5  GENERAL APPLICATION REQUIREMENTS SUMMARY ...............   15

Internet Engineering Task Force                                 [Page 1]



RFC1123                       INTRODUCTION                  October 1989

   3.  REMOTE LOGIN -- TELNET PROTOCOL ............................   16
      3.1  INTRODUCTION ...........................................   16
      3.2  PROTOCOL WALK-THROUGH ..................................   16
         3.2.1  Option Negotiation ................................   16
         3.2.2  Telnet Go-Ahead Function ..........................   16
         3.2.3  Control Functions .................................   17
         3.2.4  Telnet "Synch" Signal .............................   18
         3.2.5  NVT Printer and Keyboard ..........................   19
         3.2.6  Telnet Command Structure ..........................   20
         3.2.7  Telnet Binary Option ..............................   20
         3.2.8  Telnet Terminal-Type Option .......................   20
      3.3  SPECIFIC ISSUES ........................................   21
         3.3.1  Telnet End-of-Line Convention .....................   21
         3.3.2  Data Entry Terminals ..............................   23
         3.3.3  Option Requirements ...............................   24
         3.3.4  Option Initiation .................................   24
         3.3.5  Telnet Linemode Option ............................   25
      3.4  TELNET/USER INTERFACE ..................................   25
         3.4.1  Character Set Transparency ........................   25
         3.4.2  Telnet Commands ...................................   26
         3.4.3  TCP Connection Errors .............................   26
         3.4.4  Non-Default Telnet Contact Port ...................   26
         3.4.5  Flushing Output ...................................   26
      3.5.  TELNET REQUIREMENTS SUMMARY ...........................   27

   4.  FILE TRANSFER ..............................................   29
      4.1  FILE TRANSFER PROTOCOL -- FTP ..........................   29
         4.1.1  INTRODUCTION ......................................   29
         4.1.2.  PROTOCOL WALK-THROUGH ............................   29
            4.1.2.1  LOCAL Type ...................................   29
            4.1.2.2  Telnet Format Control ........................   30
            4.1.2.3  Page Structure ...............................   30
            4.1.2.4  Data Structure Transformations ...............   30
            4.1.2.5  Data Connection Management ...................   31
            4.1.2.6  PASV Command .................................   31
            4.1.2.7  LIST and NLST Commands .......................   31
            4.1.2.8  SITE Command .................................   32
            4.1.2.9  STOU Command .................................   32
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