RFC 1009 (rfc1009) - Page 2 of 55

Requirements for Internet gateways

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
                  network.

      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
                  routers.

      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




Braden & Postel