|  | 10.6 | Basics of Subnetting
| 10.6.2 | Subnetwork

Subnet addresses include the Class A, Class B, or Class C network portion, plus a subnet field and a host field. The subnet field and the host field are created from the original host portion for the entire network. The ability to decide how to divide the original host portion into the new subnet and host fields provides addressing flexibility for the network administrator. To create a subnet address, a network administrator borrows bits from the original host portion and designates them as the subnet field.

Figures and illustrate the hierarchical nature of subnet addresses.

To create a subnet address, a network administrator borrows bits from the host field and designates them as the subnet field. The minimum number of bits that can be borrowed is 2. If you were to borrow only 1 bit, to create a subnet, then you would only have a network number - the .0 network - and the broadcast number - the .1 network. The maximum number of bits that can be borrowed can be any number that leaves at least 2 bits remaining, for the host number. In this example of a Class C IP Address, bits from the host field for the subnet field have been borrowed.

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