RFC 790 (rfc790) - Page 2 of 15

Assigned numbers

Alternative Format: Original Text Document
< Previous
Next >

RFC 790                                                   September 1981
                                                        Assigned Numbers
Network Numbers


                        ASSIGNED NETWORK NUMBERS

   This list of network numbers is used in the internet address [33].
   The Internet Protocol (IP) uses a 32 bit address 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, or class a, of address has a 7-bit network number
      and a 24-bit local address.  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, or class b, of address has a 14-bit network
      number and a 16-bit local address.  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, or class c, of address has a 21-bit network number
      and a 8-bit local address.  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

   One notation for internet host addresses commonly used 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.  For
   example, the internet address of ISIF is 010.020.000.052.

   This notation will be used in the listing of assigned network


Postel
< Previous
Next >