Subnet Mask, Decimal, Slash Notation.

Discussion in 'Server Networking' started by Robert Bollinger, Oct 6, 2007.

  1. Hey Guys,

    I am hoping that you can assis me with this question, as i have hit a wall.
    I need to have this explained to me, this is in my 70-291 book on page 2-16.


    128.000.000.000 has a binary value of 10000000.00000000.00000000.00000000

    This is mask to binary conversion, i can memorize this all day but would
    rather understand how and WHY it works like the above example.

    How come a binary notation of 10000000 = 128? how is that done? why does it
    start at 128? and not at 1?

    HOw are the bit's determined and converted into a dotted.decimal address?

    i understand this: 32-bit ip addy is 4 groups of eight bits at different
    placements (starting) with 0-8 9-16 etc.

    theses are called octets which means eight or of eight. Wht i dont
    understand is as stated above.

    I am sorru of this is not clear but i am fried on this one.

    Please advise... Thank you.

    Robert
     
    Robert Bollinger, Oct 6, 2007
    #1
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  2. Robert Bollinger

    Bill Grant Guest

    An octet is eight bits. In binary, each column can only have the value of
    zero or one.

    So binary 10 = 2 decimal
    100 = 4
    1000=8
    10000=16
    100000=32
    1000000=64
    10000000=128
     
    Bill Grant, Oct 7, 2007
    #2
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  3. Bill thanks for your answer.

    Can you be more specific with more examples about that, i am kinda getting
    it but there is a difference between "I think I know" and "I have a clue" and
    "I really know, yes i can fix your network".
     
    Robert Bollinger, Oct 7, 2007
    #3
  4. Robert Bollinger

    jorgen Guest

    In our normal decimal system (base 10)

    1 is one
    10 is ten
    100 is hundred

    each time you put a zero in, the value goes up by a factor of 10. In the
    binary system (base 2) the value goes up by a factor of 2:

    1 is one
    10 is two
    100 is four
    ....
    10000000 is 128
    01000000 is 64
     
    jorgen, Oct 7, 2007
    #4
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