Assigned Numbers
RFC 900

Document Type RFC - Historic (June 1984; No errata)
Obsoleted by RFC 923
Obsoletes RFC 870
Last updated 2013-03-02
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Network Working Group                                        J. Reynolds
Request for Comments: 900                                      J. Postel
                                                                     ISI
Obsoletes RFCs:  870, 820,                                     June 1984
790, 776, 770, 762, 758, 755,
750, 739, 604, 503, 433, 349
Obsoletes IENs:  127, 117, 93

                            ASSIGNED NUMBERS

Status of this Memo

   This memo is an official status report on the numbers used in
   protocols in the ARPA-Internet community.

Introduction

   This Network Working Group Request for Comments documents the
   currently assigned values from several series of numbers used in
   network protocol implementations.  This RFC will be updated
   periodically, and in any case current information can be obtained
   from Joyce Reynolds.  The assignment of numbers is also handled by
   Joyce.  If you are developing a protocol or application that will
   require the use of a link, socket, port, protocol, network number,
   etc., please contact Joyce to receive a number assignment.

      Joyce Reynolds
      USC - Information Sciences Institute
      4676 Admiralty Way
      Marina del Rey, California  90292-6695

      Phone: (213) 822-1511

      ARPA mail: JKREYNOLDS@USC-ISIF.ARPA

   Most of the protocols mentioned here are documented in the RFC series
   of notes.  The more prominent and more generally used are documented
   in the "Internet Protocol Transition Workbook" [31] or in the old
   "ARPANET Protocol Handbook" [32] prepared by the NIC.  Some of the
   items listed are undocumented.  Further information on protocols can
   be found in the memo "Official Protocols" [83].

   In all cases the name and mailbox of the responsible individual is
   indicated.  In the lists that follow, a bracketed entry, e.g.,
   [31,iii], at the right hand margin of the page indicates a reference
   for the listed protocol, where the number cites the document and the
   "iii" cites the person.  Whenever possible, this "iii" is a NIC
   Ident.

Reynolds & Postel                                               [Page 1]



Assigned Numbers                                                 RFC 900
Network Numbers

                        ASSIGNED NETWORK NUMBERS

   The network numbers listed here are used as internet addresses by the
   Internet Protocol (IP) [31,71].  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 3 forms or classes.

      The first type of address, or class A, has a 7-bit network number
      and a 24-bit local address.  The highest-order bit is set to 0.
      This allows 128 class A networks.

                           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 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0|   NETWORK   |                Local Address                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                             Class A Address

      The second type of address, class B, has a 14-bit network number
      and a 16-bit local address.  The two highest-order bits are set to
      1-0.  This allows 16,384 class B networks.

                           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 0|           NETWORK         |          Local Address        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                             Class B Address

      The third type of address, class C, has a 21-bit network number
      and a 8-bit local address.  The three highest-order bits are set
      to 1-1-0.  This allows 2,097,152 class C networks.

                           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 1 0|                    NETWORK              | Local Address |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                             Class C Address

      Note:  No addresses are allowed with the three highest-order bits
      set to 1-1-1.  These addresses (sometimes called "class D") are
      reserved.

Reynolds & Postel                                               [Page 2]



Assigned Numbers                                                 RFC 900
Network Numbers

   One commonly used notation for internet host addresses divides the
   32-bit address into four 8-bit fields and specifies the value of each
   field as a decimal number with the fields separated by periods.  This
   is called the "dotted decimal" notation.  For example, the internet
   address of USC-ISIF.ARPA in dotted decimal is 010.002.000.052, or
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