How is a subnet defined?
Refer to "TCP/IP Network Administration" by Craig Hunt, O’Reilly & Associates, Inc.
Sectioning network communication by subnets.
A subnet is defined by applying a bit mask (subnet mask) to the IP address.
- If a bit is on in the mask, that equivalent bit in the address is interpreted as a network bit.
- If a bit in the mask is off, the bit belongs to the host part of the address.
The subnet is only known locally.