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    Networking troubles


    I have a tough go about trying to subnet and can't seem to grasp the concept , here is one ouestion
    Chapter 5Guide to Networking Essentials (Gregory Tomsho)

    15. For a Class C network address 192.168.10.0 , which of the following subnet masks provides 32 subnets ??
    b.255.255.255.248
    but how ? ggrrrrr
    any help would be appreciated :-)Kris
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    Each time you borrow an additional bit in the subnet mask you cut the available range in half. A /24 subnet borrows 0 bits, therefor has a range of 256.

    Borrow 1 bit and it's TWO ranges of 128
    Borrow 2 bits and it's FOUR ranges of 64
    Borrow 3 bits and it's EIGHT ranges of 32
    ...

    Therefore your total address space is always the same. Take a pizza for example. If you make zero cuts you have a whole pizza. 1 cut and you have two halves. 2 cuts and you have Four quarters, 4 cuts (because you have to cut each half in half) you have 8 1/8ths and so on.
    Last edited by AdamPI; July 5th, 2012 at 10:10 AM.
    Adam TT
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    192.168.10.0
    255.255.255.248

    248 in Binary 11111000 = 2*5 = 32 Subnets( 5 bits on)
    2*3 - 2 = 6 Hosts per subnet (3 bits off)

    subtract 2 for subnet address and broadcast address.

    Valid subnets 256 - 248 = 8
    Hence 0,8,16,24................248

    0 to 255 >>> 256

    Source : CCNA SYBEX TODD LAMMLE

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