CCNA Network Infrastructure and Connectivity Practice Question
A branch LAN requires 50 usable IPv4 host addresses. What is the most efficient subnet mask that provides at least 50 usable hosts?
⚠ Common exam trap
Read the requirement carefully. Cisco often uses subtle wording like 'most efficient' or 'industry standard' to eliminate technically correct but non-optimal answers.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
/26
A /26 provides 64 total addresses and 62 usable host addresses, which is the smallest subnet mask (largest prefix length) that fits 50 hosts, making it the most efficient choice.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
/27
Why it's wrong here
A /27 has 5 host bits, yielding 2^5 = 32 total addresses, minus 2 = 30 usable. That falls short of the 50 required, so it cannot support the branch LAN's addressing needs even before considering any reserved addresses.
When this WOULD be correct
In a different scenario where a branch LAN only requires up to 30 usable IPv4 host addresses, a question could ask for the smallest prefix that meets this requirement. In that case, /27 would be the correct answer.
- ✓
/26
Why this is correct
A /26 prefix has 6 host bits, so 2^6 = 64 total addresses, minus 2 for network and broadcast gives 62 usable hosts. This exactly satisfies the requirement of 50 usable addresses with headroom for future growth, and is the smallest prefix that meets the need, avoiding unnecessary address waste.
- ✗
/25
Why it's wrong here
A /25 has 7 host bits, giving 2^7 - 2 = 126 usable hosts. While this does meet the 50-host requirement, it is not the optimal choice because it allocates more than double the necessary address space, consuming a larger block from the overall IPv4 allocation than a /26 would.
When this WOULD be correct
If the exam question specified a need for at least 50 usable addresses but allowed for additional addresses for future growth, then /25 would be the correct choice, as it provides ample room for expansion while still meeting the minimum requirement.
- ✗
/24
Why it's wrong here
A /24 has 8 host bits, yielding 256 total addresses and 254 usable hosts. This is the traditional 'full subnet' often used by default, but for a branch LAN needing only 50 hosts it is significantly over-provisioned, wasting 204 usable addresses and reducing the number of subnets that can be carved from the same address space.
When this WOULD be correct
In a scenario where a question specifies a need for a larger subnet to accommodate future growth or additional devices, such as requiring 200 usable addresses, option D (/24) would be the correct choice. This would be appropriate if the network is expected to expand significantly.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓/26Correct answer▾
Why this is correct
A /26 prefix has 6 host bits, so 2^6 = 64 total addresses, minus 2 for network and broadcast gives 62 usable hosts. This exactly satisfies the requirement of 50 usable addresses with headroom for future growth, and is the smallest prefix that meets the need, avoiding unnecessary address waste.
✗/27Wrong answer — click to see why▾
Why this is wrong here
A /27 subnet provides only 30 usable host addresses, which is insufficient for the requirement of 50 usable addresses. Therefore, it does not meet the needs of the branch LAN.
★ When this WOULD be the correct answer
In a different scenario where a branch LAN only requires up to 30 usable IPv4 host addresses, a question could ask for the smallest prefix that meets this requirement. In that case, /27 would be the correct answer.
Why candidates choose this
Candidates may choose /27 due to a misunderstanding of subnetting calculations, mistakenly believing that it provides enough addresses or confusing it with a similar option that does meet the requirement.
✗/25Wrong answer — click to see why▾
Why this is wrong here
Option C: /25 provides 126 usable addresses, which exceeds the requirement of 50 usable addresses. However, it is not the smallest prefix that meets the requirement.
★ When this WOULD be the correct answer
If the exam question specified a need for at least 50 usable addresses but allowed for additional addresses for future growth, then /25 would be the correct choice, as it provides ample room for expansion while still meeting the minimum requirement.
Why candidates choose this
Candidates may choose /25 because they misinterpret the requirement as needing a larger subnet for potential future devices, mistakenly believing that a larger prefix is always better for accommodating growth.
✗/24Wrong answer — click to see why▾
Why this is wrong here
Option D, /24, provides 256 total addresses, which exceeds the requirement of 50 usable addresses. However, it is not the smallest prefix that meets the requirement, as /26 provides 64 addresses, which is sufficient and more efficient.
★ When this WOULD be the correct answer
In a scenario where a question specifies a need for a larger subnet to accommodate future growth or additional devices, such as requiring 200 usable addresses, option D (/24) would be the correct choice. This would be appropriate if the network is expected to expand significantly.
Why candidates choose this
Candidates may choose option D because they recognize that /24 offers a large number of addresses and may mistakenly believe that more addresses are always better, overlooking the need for efficiency in subnetting.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
Go deeper
Related to this question
Learn chapter
Troubleshoot: ACL Wildcard Mask Error
Key term
Prefix length
A prefix length is the number of bits in a subnet mask that identifies the network portion of an IP address, written after a slash (e.g., /24).
Key term
Subnet
A subnet is a logical subdivision of an IP network, created by partitioning a larger network address space using subnet masks.
About these practice questions
This 200-301 question is part of Courseiva's 1,450-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.