VLSM= variable length subnet mask supposedly TCP/IP version6 It is used in W2K and I am trying to learn it but it is confusing. With it you can borrow bits from an existing subnet and subnet the subnet. This way if you needed 40 subnets, if you borrowed enough to get 32 addresses,you could subnet the subnets to make up the other 8 needed. Instead of having to borrow enough to make 64 and waste the other 24.