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subnetting formula

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  • subnetting formula


    Can someone remind the formula or point in the right direction how to in easy way subnet class A, just need to find specific subnet for example to estimate what will be subnet 420 or 500. Need the shortcut to in easy way find X subnet to do VLSM on them.

    as that one is not very clear for me and can not understand this one:
    Nth subnet = (N - 1) / (2^s) = X.Y

    N is the subnet you wish to find
    S is the number of subnet bits in the "interesting" octet
    X = the new number for the 2nd octet
    Y * 256 = the number in the interesting octet


  • #2
    Re: subnetting formula

    I would generally use this

    In general though I would typically start with a Class C subnet and for each borrowed bit from the 3rd octet I would double my available range. Class C give you a useable range of 254 hosts, 0-255 where 0 is your network and 255 is your broadcast.

    In the instance you have provided your subnet mask will be to give you 511 useable hosts.

    I don't have a formula that I use and I have no idea really how I do it.

    Try here


    • #3
      Re: subnetting formula

      Subnet Calculator rules
      A recent poll suggests that 6 out of 7 dwarfs are not happy