3. Describing Subnet Masks
Calculating The extended network number is defined by extending the default
Extended Network netmask (with ones) contiguously into the host number field. This
Numbers with extended netmask is often referred to as the subnet mask. Each
Subnet Masks host-number bit that is masked (using the logical AND operator)
becomes defined as a subnet number.
Network numbers can be calculated using four types of subnet
masks:
• Byte bound
• Nonbyte bound
• Variable length
• Permanent
Describing Subnet Masks
Byte-Bound The graphic illustrates the use of a byte-bound subnet mask
Subnet Masks (255.255.255.0) to extend the original network number.