need help subnetting a Class B address

Discussion in 'OT Technology' started by Stilgar1973, May 7, 2009.

  1. Stilgar1973

    Stilgar1973 New Member

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    This is for my Net+ class. working with subnetting came hard to me when I did the CCNA class (no didn't pass the exam) and now it is still not sinking in like I wish it would.

    I think I have it figured out. If someone that knows what they are talking about can tell me if I am on the correct track and if not offer me a hand I would very much appreciate it.

    The question:

    IP address: 165.125.0.0 you need 12 subnets. The subnet mask is 255.255.240.0 this is done borrowing 4 bits.

    I am going to list what I got as the first 2 subnets and there host addresses. If you agree, then I have it figured out and don't need any help. If I am missing something, it will show up here:

    Subnet 1: 165.125.16.1 through 165.125.16.254
    Subnet 2: 165.125.32.1 through 165.125.32.254

    Thanks for your help.
     
  2. Stilgar1973

    Stilgar1973 New Member

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    I am looking at this and my mind is just twisting.

    Why am I only assaigning host addresses to the 4th octet? Why can't host addreses start at the last 4 bits of the 3rd octet?

    God. This makes nothing but sense when we discuss it in class, but the next day blammmmmmmmm it is all confusing.
     
  3. Limp_Brisket

    Limp_Brisket New Member

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    i'm no expert on subnetting, but i would think if you used all your host bits it would be more like this:

    subnet 1: 165.125.0.1 - 165.125.15.255
    subnet 2: 165.125.16.1 - 165.125.31.255
    subnet 3: 165.125.32.1 - 165.125.47.255

    and so on
     
  4. this is right. you are using the 15 at a time from the third octet b/c the last four bits are turned on when the number is 240
    128 64 32 16 8 4 2 1
    n n n n y y y y
     
  5. Stilgar1973

    Stilgar1973 New Member

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    I mucked around with it for a while and found my mistakes.

    My instructor keeps telling me that when you work with subnetting working stuff out in binary makes it all a lot more clear.

    So I mucked around with 'anding' the ip address and the subnet address for about 20 minutes and it all became clear to me.
    I eventualy came up with the answers you have.

    Thanks for the help.
     
  6. 7960

    7960 New Member

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    once you get it, the worst thing you can do is go looking for an "easier" way. the easiest way is the way you know and that requires the least amount of memorization.
     

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