Internet numbers
RFC 997

Document Type RFC - Unknown (March 1987; No errata)
Obsoleted by RFC 1020, RFC 1117
Updates RFC 990
Last updated 2013-03-02
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Network Working Group                                        J. Reynolds
Request for Comments:  997                                     J. Postel
                                                                     ISI
Obsoletes RFCs: 990, 960, 943, 923, 900,                      March 1987
870, 820, 790, 776, 770, 762, 758,
755, 750, 739, 604, 503, 433, 349
Obsoletes IENs:  127, 117, 93

                            INTERNET NUMBERS

Status of this Memo

   This memo is an official status report on the network numbers used in
   the Internet community.  Distribution of this memo is unlimited.

Introduction

   This Network Working Group Request for Comments documents the
   currently assigned network numbers and gateway autonomous systems.
   This RFC will be updated periodically, and in any case current
   information can be obtained from Hostmaster.

      Hostmaster
      DDN Network Information Center
      SRI International
      333 Ravenswood Avenue
      Menlo Park, California  94025

      Phone: 1-800-235-3155

      ARPA mail: HOSTMASTER@SRI-NIC.ARPA

   Most of the protocols used in the Internet are documented in the RFC
   series of notes.  Some of the items listed are undocumented.  Further
   information on protocols can be found in the memo "Official
   ARPA-Internet Protocols" [24].  The more prominent and more generally
   used are documented in the "DDN Protocol Handbook" [11] prepared by
   the NIC.  Other collections of older or obsolete protocols are
   contained in the "Internet Protocol Transition Workbook" [12], or in
   the "ARPANET Protocol Transition Handbook" [13].  For further
   information on ordering the complete 1985 DDN Protocol Handbook,
   contact the Hostmaster.

   In the entries below, the name and mailbox of the responsible
   individual is indicated.  The bracketed entry, e.g., [nn,iii], at the
   right hand margin of the page indicates a reference for the listed
   protocol, where the number ("nn") cites the document and the letters
   ("iii") cites the person.  Whenever possible, the letters are a NIC
   Ident as used in the WhoIs (NICNAME) service.

Reynolds & Postel                                               [Page 1]



Internet Numbers                                                 RFC 997
Introduction

   The convention in the documentation of Internet Protocols is to
   express numbers in decimal and to picture data in "big-endian" order
   [31].  That is, fields are described left to right, with the most
   significant octet on the left and the least significant octet on the
   right.

   The order of transmission of the header and data described in this
   document is resolved to the octet level.  Whenever a diagram shows a
   group of octets, the order of transmission of those octets is the
   normal order in which they are read in English.  For example, in the
   following diagram the octets are transmitted in the order they are
   numbered.

                                    
    0                   1                   2                   3   
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       1       |       2       |       3       |       4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       5       |       6       |       7       |       8       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       9       |      10       |      11       |      12       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Transmission Order of Bytes

   Whenever an octet represents a numeric quantity the left most bit in
   the diagram is the high order or most significant bit.  That is, the
   bit labeled 0 is the most significant bit.  For example, the
   following diagram represents the value 170 (decimal).

                                    
                            0 1 2 3 4 5 6 7 
                           +-+-+-+-+-+-+-+-+
                           |1 0 1 0 1 0 1 0|
                           +-+-+-+-+-+-+-+-+

                          Significance of Bits

   Similarly, whenever a multi-octet field represents a numeric quantity
   the left most bit of the whole field is the most significant bit.
   When a multi-octet quantity is transmitted the most significant octet
   is transmitted first.

Reynolds & Postel                                               [Page 2]



Internet Numbers                                                 RFC 997
Network Numbers

                             NETWORK NUMBERS

   The network numbers listed here are used as internet addresses by the
   Internet Protocol (IP) [11,21].  The IP uses a 32-bit address field
   and divides that address into a network part and a "rest" or local
   address part.  The division takes 4 forms or classes.

      The first type of address, or class A, has a 7-bit network number
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