Network+ IPv4 subnetting: host counts and network boundaries
For a conventional IPv4 subnet, the prefix length identifies network bits and the remaining bits identify hosts. With h host bits, the usual host count is 2 to the power h minus two, reserving network and broadcast addresses. This conventional formula has exceptions such as /31 point-to-point links. Determine the exact task: finding a network, a broadcast address, or the smallest subnet for a host requirement.
How to read the scenario
Do not confuse the number of total addresses with usable hosts. Check that the proposed subnet starts on a valid prefix boundary.
Identify the required outcome, the evidence already provided, and the limits on the technician’s action. Compare every option against those details before deciding. Record why the closest alternative does not meet the stated need.
Original practice example
A technician reviews IPv4 addresses before building an internal LAN. Which TWO addresses belong to RFC 1918 private address space? Select TWO.
- 172.20.4.9
- 10.24.8.1
- 172.40.4.9
- 8.8.8.8
Show the answer and explanation
172.20.4.9; 10.24.8.1
RFC 1918 includes 10.0.0.0/8 and 172.16.0.0/12; 172.40.4.9 and 8.8.8.8 are outside those ranges.
Study questions
Which objective does this guide support?
N10-009, objective 1.7. This independent guide supports original practice and does not replace the full official objectives.
What should I watch for in a scenario?
Do not confuse the number of total addresses with usable hosts. Check that the proposed subnet starts on a valid prefix boundary.
Source and version
CompTIA official N10-009 objectives, objective 1.7. Verified November 5, 2026. Use the exam code when choosing study materials; similarly named certifications can have different objectives.