The Mathematical Reality of IP Addressin in IPv4...

Eric Germann ekgermann at
Thu Aug 26 21:45:39 UTC 1999

At 10:43 AM 8/26/99 -0700, bmanning at wrote:
>> What this proposal appears to be proposing is to permit NON-CONTIGUOUS
>> netmasks such as:
>> Or, in binary:
>>  1111111111 10000000 01111111 00000000
>> Thus, the network number would actually consist of all 8 bits of octet
>> one, the first bit of octet two, the last 7 bits of octet 3 and none of
>> octed four.
>Non-contigious masks were allowed up until the CIDR era... :)

As an exercise in insanity, when I teach my TCP/IP course, I use the
following example /

and ask the students to find the subnet address, first usable node, last
usable node and broadcast address for each subnet.  Takes them about three
hours and then they appreciate the recommendation that all subnet bits be
contiguous.  What it does do very well is hammer home how these things
actually work in terms of varying the host bits and network bits :)


  Eric Germann                                        CCTec
  ekgermann at                                 Van Wert, OH 45891                                Ph:  419 968 2640
  ICQ:  41927048                                      Fax: 419 968 2641
         Network Design, Connectivity & System Integration Services 
                     A Microsoft Solution Provider

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