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How to work out subnetting, classes A, B & C

Discussion in 'General Cisco Certifications' started by griffin84, May 15, 2012.

  1. griffin84

    griffin84 New Member

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    I made some rules for my own thought process when looking at subnetting and I think they make sense (at least so far they do), do these make sense to you's??

    Thanks
     

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    Last edited by a moderator: May 16, 2012
    Certifications: Hnd IT Support, Hnc IT support, Mcdst, A+
    WIP: Bsc Networking
  2. soundian

    soundian Gigabyte Poster

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    Writing it out in binary until I understand the difference between network and host.
    Then it's all 2's

    Ah, you still seem to be confused even after using binary.
    Erm....
     
    Last edited: May 15, 2012
    Certifications: A+, N+,MCDST,MCTS(680), MCP(270, 271, 272), ITILv3F, CCENT
    WIP: Knuckling down at my new job
  3. griffin84

    griffin84 New Member

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    Could you explain?..
    Please
     
    Certifications: Hnd IT Support, Hnc IT support, Mcdst, A+
    WIP: Bsc Networking
  4. Coupe2T

    Coupe2T Megabyte Poster

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    I couldn't make sense out of what you have written there. Not sure what you are doing exactly and your working out seems odd.

    Do the rules work? Have you tested them? I can't follow your thought process as you have it written down but if it works for you then it works for you. You need to test it though against some real problems and see if you get the right answers.
     
    Certifications: ECDL, Does that Count!?!
  5. soundian

    soundian Gigabyte Poster

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    Turns out it was me that was confused.
    That's a really complicated way of working things out. For instance, step 2.3 is superfluous, use the 'increment' that you calculate in 2.4 and subtract that from 256 (not 255, there are 256 possible numbers in 8 bits, 1-255 AND 0). I'd also avoid using vertical lines like that, when doing it by hand they may look far too much like a one to avoid the occasional mistake.


    You really don't need to do all the binary stuff to work out how many network bits you need to borrow from the host bits, just count up 2,4,8,16,32,64,128....(which equates to 1 bit, 2 bits, 3 bits, 4 bits etc) until you hit the first number that is above the required number of networks.You start at two because 1 bit can have two values, 0 or 1.
     
    Certifications: A+, N+,MCDST,MCTS(680), MCP(270, 271, 272), ITILv3F, CCENT
    WIP: Knuckling down at my new job

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