Seven Things a Student Must Know to Subnet

 Four Formulas:

1. # of theoretical subnets created   = 2 ^ (# bits borrowed)

 2.  # of usable subnets created           = [2 ^ (bits borrowed) ] – 2

 3. # of theoretical hosts per subnet  = 2^ (# bits remaining*)

 *bits remaining = total bits in host field – bits borrowed

 4.  # of usable hosts per subnet         = [2 ^ (# bits remaining)] – 2

 Three Definitions:

 5.  Network* address/identifier = network bits match the license number and host bits are all zeroes (0).

6.  Network* broadcast             =  network bits match the license number and the host bits are all ones (1).

7.  Subnet Mask                      =  network and subnet bits are all ones (1) and host bits are all zeroes (0).

*For subnet  addresses and broadcasts, the subnet bits are treated as network bits.  Remember:  we “borrowed” them to be part of the network field.