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subnetting question

Discussion in 'Routing & Switching' started by slipned, May 10, 2012.

  1. slipned

    slipned Bit Poster

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    So, as Im studying this subnetting malarky am I right in thinking it really doesnt matter then what subnet mask you use with any class of address !


    for instance at the mo in a book im reading we have a class A address with a class C mask ie 10.1.1.1 255.255.255.0


    and a class B with a class C mask 172.16.1.1 255.255.255.0


    one is configured on a serial interface the other on a fa/0


    I just thought id learnt subnetting but now this has just threw me..


    So why would we use a class c mask on a class A and class B IP address????

    Am i right in thinking that if in my example of the original question of a class A ip address with a class C subnet mask,


    10.1.1.1 255.255.255.0 does this then mean that the range will be 10.1.1.1- 10.1.1.254? because having the 255.255.255 in the mask means the 10.1.1. must remain the same all the way through in this particular example?
     
  2. Cunningfox

    Cunningfox Byte Poster

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    Imo the best thing is to forget the Class A,B,C system it's old, it's used for teaching and not much else. You can use any subnet mask/network address combination. The important thing to remember is the private ranges for real world.

    So your last statement (below) is correct yes. Class is irrelevant subnet mask is relevant.

     
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  3. slipned

    slipned Bit Poster

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    Thank you so much for your your kind help... Really appreciated..
     
  4. soundian

    soundian Gigabyte Poster

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    As cunningfox says there is very little use for classes in the real world, but in his advice to you to forget classes, he forgot you were actually studying. Classes are useful until you reach the point in your studying where they aren't. I think that's the best way to sum them up.

    One thing he didn't explicitly cover: Why use a 255.255.255.0 mask with a 10.x.x.x address. Simple, keep the number of hosts down to a manageable level as all hosts in a subnet are part of the same collision domain.
     
    Last edited: May 10, 2012
    Certifications: A+, N+,MCDST,MCTS(680), MCP(270, 271, 272), ITILv3F, CCENT
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  5. slipned

    slipned Bit Poster

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    Thank you as well soundian. I get your point now about keeping the number of hosts down.... I really appreciate your help too.
     
  6. Telephasic

    Telephasic New Member

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    Hey. I'm sure you knew this but just to clarify - a subnet is a broadcast domain, unless it's all hooked into one hub it probably won't all be the same collision domain. ;)
     
  7. soundian

    soundian Gigabyte Poster

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    I've just seen this correction. Thanks Telephasic, a silly mistake on my part.
     
    Certifications: A+, N+,MCDST,MCTS(680), MCP(270, 271, 272), ITILv3F, CCENT
    WIP: Knuckling down at my new job

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