What is a subnetting plan, and how would you design a hierarchical addressing scheme to reduce waste and optimize routing?

What is a subnetting plan, and how would you design a hierarchical addressing scheme to reduce waste and optimize routing?

• A. A subnetting plan partitions address space to fit subnet sizes; a hierarchical scheme uses core, distribution, and access subnets, with VLSM to minimize waste and enable route summarization.
• B. Subnetting plans are only for IPv4; IPv6 does not require planning.
• C. Hierarchical addressing increases waste; VLSM is not used.
• D. A subnetting plan means using a single /8 for all devices.

Answer: (A)

A subnetting plan is about organizing the address space so each subnet gets exactly what it needs, without wasting addresses. Designing a hierarchical addressing scheme means structuring the network into layers (for example, core, distribution, and access) so routing can be scalable and manageable. The two ideas fit together: you allocate subnet sizes using VLSM (variable-length subnet masks) to match required host counts for each subnet, and you place these subnets in a way that lets you summarize routes at higher-level routers. Why this is the best approach hinges on two benefits. First, VLSM lets you tailor each subnet to its actual needs, so small subnets don’t end up with oversized masks and large subnets don’t waste addresses. For example, a subnet needing 50 hosts can be allocated a /26 (which supports up to 62 hosts), while a smaller subnet needing 12 hosts might get a /28 (14 usable addresses). Second, a hierarchical design enables route summarization. By grouping subnets under common boundaries and advertising a single summary route from the distribution/core layer, you reduce the size of the routing table and improve routing performance, while still keeping traffic within the appropriate areas of the topology. IPv6 also uses subnetting and a hierarchical approach, so a blanket claim that planning isn’t needed is inaccurate. A single /8 plan would be extremely wasteful and impractical for real networks, and hierarchical addressing is intended to reduce waste and support efficient routing, not increase it.

A subnetting plan is about organizing the address space so each subnet gets exactly what it needs, without wasting addresses. Designing a hierarchical addressing scheme means structuring the network into layers (for example, core, distribution, and access) so routing can be scalable and manageable. The two ideas fit together: you allocate subnet sizes using VLSM (variable-length subnet masks) to match required host counts for each subnet, and you place these subnets in a way that lets you summarize routes at higher-level routers.

Why this is the best approach hinges on two benefits. First, VLSM lets you tailor each subnet to its actual needs, so small subnets don’t end up with oversized masks and large subnets don’t waste addresses. For example, a subnet needing 50 hosts can be allocated a /26 (which supports up to 62 hosts), while a smaller subnet needing 12 hosts might get a /28 (14 usable addresses). Second, a hierarchical design enables route summarization. By grouping subnets under common boundaries and advertising a single summary route from the distribution/core layer, you reduce the size of the routing table and improve routing performance, while still keeping traffic within the appropriate areas of the topology.

IPv6 also uses subnetting and a hierarchical approach, so a blanket claim that planning isn’t needed is inaccurate. A single /8 plan would be extremely wasteful and impractical for real networks, and hierarchical addressing is intended to reduce waste and support efficient routing, not increase it.