September 1981


RFC:  791
Replaces:  RFC 760
IENs 128, 123, 111,
80, 54, 44, 41, 28, 26

                           INTERNET PROTOCOL

                         DARPA INTERNET PROGRAM
                         PROTOCOL SPECIFICATION



1.  INTRODUCTION

1.1.  Motivation(略)

1.2.  Scope(略)

1.3.  Interfaces(略)

1.4.  Operation

  The internet protocol implements two basic functions:  addressing and
  fragmentation.

  The internet modules use the addresses carried in the internet header
  to transmit internet datagrams toward their destinations.  The
  selection of a path for transmission is called routing.

  The internet modules use fields in the internet header to fragment and
  reassemble internet datagrams when necessary for transmission through
  "small packet" networks.

  The model of operation is that an internet module resides in each host
  engaged in internet communication and in each gateway that
  interconnects networks.  These modules share common rules for
  interpreting address fields and for fragmenting and assembling
  internet datagrams.  In addition, these modules (especially in
  gateways) have procedures for making routing decisions and other
  functions.

  The internet protocol treats each internet datagram as an independent
  entity unrelated to any other internet datagram.  There are no
  connections or logical circuits (virtual or otherwise).

  The internet protocol uses four key mechanisms in providing its
  service:  Type of Service, Time to Live, Options, and Header Checksum.

  The Type of Service is used to indicate the quality of the service
  desired.  The type of service is an abstract or generalized set of
  parameters which characterize the service choices provided in the
  networks that make up the internet.  This type of service indication
  is to be used by gateways to select the actual transmission parameters
  for a particular network, the network to be used for the next hop, or
  the next gateway when routing an internet datagram.

  The Time to Live is an indication of an upper bound on the lifetime of
  an internet datagram.  It is set by the sender of the datagram and
  reduced at the points along the route where it is processed.  If the
  time to live reaches zero before the internet datagram reaches its
  destination, the internet datagram is destroyed.  The time to live can
  be thought of as a self destruct time limit.

  The Options provide for control functions needed or useful in some
  situations but unnecessary for the most common communications.  The
  options include provisions for timestamps, security, and special
  routing.

  The Header Checksum provides a verification that the information used
  in processing internet datagram has been transmitted correctly.  The
  data may contain errors.  If the header checksum fails, the internet
  datagram is discarded at once by the entity which detects the error.

  The internet protocol does not provide a reliable communication
  facility.  There are no acknowledgments either end-to-end or
  hop-by-hop.  There is no error control for data, only a header
  checksum.  There are no retransmissions.  There is no flow control.

  Errors detected may be reported via the Internet Control Message
  Protocol (ICMP) [3] which is implemented in the internet protocol
  module.

(以下，略)

                               REFERENCES

[1]  Cerf, V., "The Catenet Model for Internetworking," Information
     Processing Techniques Office, Defense Advanced Research Projects
     Agency, IEN 48, July 1978.

[2]  Bolt Beranek and Newman, "Specification for the Interconnection of
     a Host and an IMP," BBN Technical Report 1822, Revised May 1978.

[3]  Postel, J., "Internet Control Message Protocol - DARPA Internet
     Program Protocol Specification," RFC 792, USC/Information Sciences
     Institute, September 1981.
RFC791原文