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  1. 05-13-2010, 06:34 PM #1
    bigdessert
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    Default When to use /8, /24, /32 etc IP Adressing 101

    This may be a rather dumb question, but I have not used this kind of addressing until I started using untangle.

    What would be the cases to use:

    192.168.1.0/8
    192.168.1.0/24
    192.168.1.0/32
    etc.

    Consider this an IP addressing 101, I know this type of naming has a "name" but cannot remember it off the top of my head.

    Thanks for putting up with a big dummy...
  2. 05-13-2010, 06:37 PM #2
    pirateghost
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    Default

    this one explains subnets pretty well.
    http://en.wikipedia.org/wiki/Subnetwork
  3. 05-13-2010, 07:46 PM #3
    mrunkel
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    Default

    If you realize that these are all binary numbers, then it makes more sense:

    The /n = netmask with n number of 1's.

    255 = in binary is 11111111

    255.0.0.0 = 1111111100000000000000000000 or 8 ones = /8
    255.255.255.0 = 1111111111111111111100000000 or 24 ones = /24
    255.255.255.255 = 1111111111111111111111111111 or 32 ones = /32

    The reason people switched from the 255.0.0.0 nomenclature to the /8 is because with the advent of classless internet numbers a whole lot of new subnet masks starting showing up. How many bits in the address field in at 255.255.252.0? or 255.255.255.248? It's much easier to look at /23 (255.255.252.0) and know that you have 9 bits in the address field since an IP address is 32 bits long.
    m.
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  4. 05-13-2010, 09:00 PM #4
    Solignis
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    Default

    wow just this thread brings back CCNA Level 1.

    Ah the horrors.

    Also if you are lazy like me, download solarwinds ip subnet calculator.

    In my cisco class my teacher made us subnet on paper, it sucked.
    “Most good programmers do programming not because they expect to get paid or get adulation by the public, but because it is fun to program.” - Linus Torvalds
  5. 05-14-2010, 05:55 AM #5
    mozerd
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    Default Cidr

    Quote Originally Posted by bigdessert View Post
    Consider this an IP addressing 101, I know this type of naming has a "name" but cannot remember it off the top of my head.
    CIDR - Classless Inter Domain Routing
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