RFC1122                       INTRODUCTION                  October 1989


1.  INTRODUCTION

   This document is one of a pair that defines and discusses the
   requirements for host system implementations of the Internet protocol
   suite.  This RFC covers the communication protocol layers:  link
   layer, IP layer, and transport layer.  Its companion RFC,
   "Requirements for Internet Hosts -- Application and Support"
   [INTRO:1], covers the application layer protocols.  This document
   should also be read in conjunction with "Requirements for Internet
   Gateways" [INTRO:2].

   These documents are intended to provide guidance for vendors,
   implementors, and users of Internet communication software.  They
   represent the consensus of a large body of technical experience and
   wisdom, contributed by the members of the Internet research and
   vendor communities.

   This RFC enumerates standard protocols that a host connected to the
   Internet must use, and it incorporates by reference the RFCs and
   other documents describing the current specifications for these
   protocols.  It corrects errors in the referenced documents and adds
   additional discussion and guidance for an implementor.

   For each protocol, this document also contains an explicit set of
   requirements, recommendations, and options.  The reader must
   understand that the list of requirements in this document is
   incomplete by itself; the complete set of requirements for an
   Internet host is primarily defined in the standard protocol
   specification documents, with the corrections, amendments, and
   supplements contained in this RFC.

   A good-faith implementation of the protocols that was produced after
   careful reading of the RFC's and with some interaction with the
   Internet technical community, and that followed good communications
   software engineering practices, should differ from the requirements
   of this document in only minor ways.  Thus, in many cases, the
   "requirements" in this RFC are already stated or implied in the
   standard protocol documents, so that their inclusion here is, in a
   sense, redundant.  However, they were included because some past
   implementation has made the wrong choice, causing problems of
   interoperability, performance, and/or robustness.

   This document includes discussion and explanation of many of the
   requirements and recommendations.  A simple list of requirements
   would be dangerous, because:

   o    Some required features are more important than others, and some
        features are optional.




 



RFC1122                       INTRODUCTION                  October 1989