Requirements for Internet gateways
RFC 1009

Document Type RFC - Historic (June 1987; No errata)
Obsoleted by RFC 1812
Obsoletes RFC 985
Last updated 2013-03-02
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Network Working Group                                          R. Braden
Request for Comments: 1009                                     J. Postel
Obsoletes: 985                                                       ISI
                                                               June 1987

                   Requirements for Internet Gateways

Status of this Memo

   This document is a formal statement of the requirements to be met by
   gateways used in the Internet system.  As such, it is an official
   specification for the Internet community.  Distribution of this memo
   is unlimited.

   This RFC summarizes the requirements for gateways to be used between
   networks supporting the Internet protocols.  While it was written
   specifically to support National Science Foundation research
   programs, the requirements are stated in a general context and are
   applicable throughout the Internet community.

   The purpose of this document is to present guidance for vendors
   offering gateway products that might be used or adapted for use in an
   Internet application.  It enumerates the protocols required and gives
   references to RFCs and other documents describing the current
   specifications.  In a number of cases the specifications are evolving
   and may contain ambiguous or incomplete information.  In these cases
   further discussion giving specific guidance is included in this
   document.  Specific policy issues relevant to the NSF scientific
   networking community are summarized in an Appendix.  As other
   specifications are updated this document will be revised.  Vendors
   are encouraged to maintain contact with the Internet research

1.  Introduction

   The following material is intended as an introduction and background
   for those unfamiliar with the Internet architecture and the Internet
   gateway model.  General background and discussion on the Internet
   architecture and supporting protocol suite can be found in the DDN
   Protocol Handbook [25] and ARPANET Information Brochure [26], see
   also [19, 28, 30, 31].

   The Internet protocol architecture was originally developed under
   DARPA sponsorship to meet both military and civilian communication
   requirements [32].  The Internet system presently supports a variety
   of government and government-sponsored operational and research
   activities.  In particular, the National Science Foundation (NSF) is
   building a major extension to the Internet to provide user access to

Braden & Postel                                                 [Page 1]

RFC 1009 - Requirements for Internet Gateways                  June 1987

   national supercomputer centers and other national scientific
   resources, and to provide a computer networking capability to a large
   number of universities and colleges.

   In this document there are many terms that may be obscure to one
   unfamiliar with the Internet protocols.  There is not much to be done
   about that but to learn, so dive in.  There are a few terms that are
   much abused in general discussion but are carefully and intentionally
   used in this document.  These few terms are defined here.

      Packet      A packet is the unit of transmission on a physical

      Datagram    A datagram is the unit of transmission in the IP
                  protocol.  To cross a particular network a datagram is
                  encapsulated inside a packet.

      Router      A router is a switch that receives data transmission
                  units from input interfaces and, depending on the
                  addresses in those units, routes them to the
                  appropriate output interfaces.  There can be routers
                  at different levels of protocol.  For example,
                  Interface Message Processors (IMPs) are packet-level

      Gateway     In the Internet documentation generally, and in this
                  document specifically, a gateway is an IP-level
                  router.  In the Internet community the term has a long
                  history of this usage [32].

   1.1.  The DARPA Internet Architecture

      1.1.1.  Internet Protocols

         The Internet system consists of a number of interconnected
         packet networks supporting communication among host computers
         using the Internet protocols.  These protocols include the
         Internet Protocol (IP), the Internet Control Message Protocol
         (ICMP), the Transmission Control Protocol (TCP), and
         application protocols depending upon them [22].

         All Internet protocols use IP as the basic data transport
         mechanism.  IP [1,31] is a datagram, or connectionless,
         internetwork service and includes provision for addressing,
         type-of-service specification, fragmentation and reassembly,
         and security information.  ICMP [2] is considered an integral

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