Subnet Numbers

Discussion in 'Technical' started by networkingnub, Jul 19, 2009.

  1. networkingnub

    networkingnub New Member

    I am kinda new to the whole subnetting thing. I am learning and as such came across this comment:

    The binary arithmetic involved in using CIDR block addressing is painful. It is much easier to start with another private network address space, say, and use the third byte to represent internal subnets:,,, and so on. Now you use the default ( or "classful") subnet mask of (or /24) and each subnet includes 254 host addresses. See how much easier it is to start with a Class B (/16) network, and split it into 254 Class Cs (/24)? Perhaps the designers of TCP/IP weren't so dumb after all when they chose to use byte boundaries in the initial network addressing scheme

    I am not sure I see how it is easier using the numbers with the example above.
  2. id10t

    id10t Member

    All correct, until you have a large area (think a open lab at a college) where you'll end up with more than 253 hosts on the network.

    For example, the big lab at the college I work for has 165 workstations. 20 of 'em are Macs, and have Parallels installed, so there are 20 more windows "computers".

    Then each windows machine has both vmware and virtualbox on it, so if a few classes worth of IT students are working on virtual stuff (the class I teach has one lab with each student using the physical machine and 5 virtual ones), you can quickly hit the 253 host limit.

    And yeah, its 253 hosts not 254 - you reserve one address (.0 usually) for the network, one for broadcast, and one for default gateway.

    So for us, our netmasks are (using various 172.16.xx network numbers)

  3. matey

    matey New Member

    Can you just use in situation like yours?
    and ?
    where you'll have limit?
    would there be a problem?

    I am not sure about this, I never really learned the bolts and nuts of the IP scheme.



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