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  • difference between CIDR VLSM

    I need some help to understand the real difference between CIDR and VLSM...

    Without CIDR, the company would be able to get only an entire network of type A (16.7 million hosts), B (65 thousand hosts) or C (over 250 hosts). With CIDR, the company will be assigned only as many addresses as it absolutely requires...and than a company can use VLSM subnet the network using the IP range that is assigned.

    But what is the problem that doesn't permit to use VLSM, from a point of view of an ISP, to give to a company a neccessary range of ip address.....it's impossible to use it, for technical reason..or not?...

  • #2
    Re: difference between CIDR VLSM

    See this thread http://forums.petri.com/showthread.php?t=9855

    David Davis knows his networking stuff so you can trust his answer.
    Regards,
    Jeremy

    Network Consultant/Engineer
    Baltimore - Washington area and beyond
    www.gma-cpa.com

    Comment


    • #3
      Re: difference between CIDR VLSM

      I read the entire post.....it's really good but doesn't explain the difference.....
      for example
      bother, cidr and vlsm send subnet message on router's update and so, why isp can't use VLSM instead of CIDR?...there'is a specific reason?...
      after that also with vlsm we can use subnet different from /8 /16 /24, so we can't speek anymore about class A,B or C...


      I know tha i made some mistake in my reasoning...but i don't know where...


      if an ISP give asome block of IP ADDRESS with CIDR, may i apply VLSM on CIDR BLOCK?

      Comment


      • #4
        Re: difference between CIDR VLSM

        Originally posted by giobaxx View Post
        for example
        bother, cidr and vlsm send subnet message on router's update and so, why isp can't use VLSM instead of CIDR?...there'is a specific reason?...
        Now I'm consused as to what you're talking about.
        CIDR and VLSM are concepts. Routers need to be able to support these concepts if you are to use them. If a router supports one then it supports both.
        CIDR refers to assigning any size mask to a network regardless of it's class. VLSM refers to increasing (subnetting) or decreasing (supernetting) the mask bits in relation to the IP class.

        I don't know what you mean by "cidr and vlsm send subnet message on router's".
        Regards,
        Jeremy

        Network Consultant/Engineer
        Baltimore - Washington area and beyond
        www.gma-cpa.com

        Comment


        • #5
          Re: difference between CIDR VLSM

          There are no differences because you do not compare the two.

          VLSM allows you to subnet a subnet...

          Here's a great explanation

          http://www.trainsignaltraining.com/c...sm/2008-04-08/

          Comment


          • #6
            Re: difference between CIDR VLSM

            Great find Garen!!

            ALso VLSM - http://www.google.com.au/search?hl=e...le+Search&meta=

            Top of the list - http://www.vlsm-calc.net/

            So, CIDR v VLSM = 6 of one, half a dozen of the other.
            1 1 was a racehorse.
            2 2 was 1 2.
            1 1 1 1 race 1 day,
            2 2 1 1 2

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