Creating custom subnets to divide IP addresses is achieved using which technique?

• A. Variable Length Subnet Masking (VLSM)
• B. CIDR
• C. Subnet Masking
• D. Default Subnetting

Answer: (A)

Using different subnet masks to carve a network into several subnets of different sizes allows you to tailor each subnetwork to its actual needs. This technique, Variable Length Subnet Masking, lets you borrow varying numbers of host bits from each subnet so some subnets can be larger and others smaller within the same address block. The benefit is efficient use of IPv4 space—you don’t waste addresses by forcing all subnets to the same size.

In practice, you might take a single /24 and split it into subnets with /25, /26, and /27 masks to fit groups that need roughly 126, 62, and 30 hosts, respectively. CIDR provides the overall framework for using non-classful prefixes like these, but the specific method of creating subnets of differing sizes inside a given block is VLSM. Subnet masking is the general concept of applying a mask to determine network versus host bits, but the “custom” sizing comes from VLSM. Default (classful) subnetting would require fixed, uniform sizes and wouldn’t meet the goal of customizing each subnet’s capacity.