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Subnetting Notes

Subnets

2n -2 = # of subnets n = # of masked bits

Hosts

2n -2 = # of hosts/subnet n = # of unmasked bits

Subnetting

  1. Once you have determined the subnet mask subtract the decimal number in the rightmost octet from 256.
  2. The result will is the subnet increment.
  3. Start with a subnet of zero (This one is not usable, however)
  4. Add the increment until you reach the value equaling the decimal number in the rightmost octet of the subnet mask. (This one is also unusable.)
  5. Count the subnet ID=s (do not include the first and last!). The result should be equal to (or perhaps a few more) than the number of subnets required.

 Example

You are given a network ID of 192.168.1.0. You are required to have two subnets with the maximum number of hosts per subnet. Calculate the subnet mask and the subnet ID=s necessary to achieve this.

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