N10-009 Question 114
Single answer1.7 Given a scenario, use appropriate IPv4 network addressing.A network administrator is redesigning the addressing scheme for a branch office. The office has 5 departments with the following host requirements: Sales needs 50 hosts, Engineering needs 26 hosts, HR needs 12 hosts, Finance needs 10 hosts, and Management needs 6 hosts. The administrator has been assigned the 192.168.10.0/24 network and wants to use VLSM to minimize wasted addresses while ensuring each department has enough usable host addresses. Which of the following subnet assignments is the MOST appropriate?
- A
Sales: 192.168.10.0/26, Engineering: 192.168.10.64/27, HR: 192.168.10.96/28, Finance: 192.168.10.112/28, Management: 192.168.10.128/29
- B
Sales: 192.168.10.0/27, Engineering: 192.168.10.32/27, HR: 192.168.10.64/28, Finance: 192.168.10.80/28, Management: 192.168.10.96/29
- C
Sales: 192.168.10.0/25, Engineering: 192.168.10.128/28, HR: 192.168.10.144/29, Finance: 192.168.10.152/29, Management: 192.168.10.160/30
- D
Sales: 192.168.10.0/26, Engineering: 192.168.10.64/26, HR: 192.168.10.128/27, Finance: 192.168.10.160/28, Management: 192.168.10.176/28
Show answer and explanation
Correct answer: A
Explanation
The best answer is the one that uses variable-length subnet masking to match subnet sizes as closely as possible to host requirements while preserving valid subnet boundaries. For IPv4 subnetting, usable hosts are calculated as 2^(host bits) - 2. Therefore: 50 hosts requires a /26 (62 usable), 26 hosts requires a /27 (30 usable), 12 and 10 hosts each require /28s (14 usable), and 6 hosts requires a /29 (6 usable). Best practice in VLSM is to allocate the largest subnets first and then continue assigning smaller subnets from the remaining address space to avoid overlap and fragmentation. This approach aligns with standard IPv4 subnetting practices covered in CompTIA Network+ objectives and general RFC-based IPv4 addressing principles.
- A. Correct.
Correct. This allocation properly applies VLSM by assigning the smallest subnet that still meets each department's host requirement. A /26 provides 62 usable addresses for Sales, which satisfies 50 hosts. A /27 provides 30 usable addresses for Engineering, which satisfies 26 hosts. Each /28 provides 14 usable addresses, enough for HR and Finance. A /29 provides 6 usable addresses, exactly enough for Management. The subnets are also correctly aligned on valid network boundaries and do not overlap.
- B. Incorrect.
Incorrect. Sales is assigned a /27, which provides only 30 usable addresses, not enough for 50 hosts. The rest of the subnetting pattern appears plausible, which makes this a realistic distractor, but the first subnet alone makes the design invalid.
- C. Incorrect.
Incorrect. Sales is assigned a /25, which does provide enough addresses, but it wastes a large number of addresses and does not meet the goal of minimizing wasted space with VLSM. Additionally, Management is assigned a /30, which provides only 2 usable addresses, far short of the required 6 hosts.
- D. Incorrect.
Incorrect. All departments would have enough addresses, but this design is inefficient and does not best minimize address waste. Engineering only needs 26 hosts, yet a /26 gives 62 usable addresses. HR needs 12 hosts but receives a /27 with 30 usable addresses. While technically functional, it is not the MOST appropriate VLSM-based design.