CCNA Network Infrastructure and Connectivity Practice Question
A host is configured as 172.16.20.190/26. Which range contains the usable host addresses for that subnet?
⚠ Common exam trap
A frequent exam trap is selecting an answer range that includes the network or broadcast address as usable hosts. For example, option B lists 172.16.20.128 to 172.16.20.191, which incorrectly includes the network (.128) and broadcast (.191) addresses. These addresses are reserved and cannot be assigned to hosts. Another trap is excluding valid host addresses or including addresses from adjacent subnets, as seen in options C and D. Misidentifying subnet boundaries or forgetting to exclude reserved addresses causes these errors, leading to incorrect subnetting 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
✓
172.16.20.129 to 172.16.20.190
A /26 uses blocks of 64 addresses. In practical terms, the fourth-octet ranges are 0–63, 64–127, 128–191, and 192–255. Since 190 falls inside the 128–191 block, the network address is .128 and the broadcast address is .191. That leaves .129 through .190 as the usable range. This is a strong test of whether you can identify the correct block and then exclude the reserved boundary addresses correctly.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
172.16.20.129 to 172.16.20.190
Why this is correct
This is correct because .128 is the network and .191 is the broadcast.
- ✗
172.16.20.128 to 172.16.20.191
Why it's wrong here
This is wrong because those include the reserved network and broadcast addresses.
When this WOULD be correct
If the question asked for the range of all IP addresses within the subnet, including the network and broadcast addresses, then option B would be correct, as it would encompass the entire range from 172.16.20.128 to 172.16.20.191.
- ✗
172.16.20.130 to 172.16.20.191
Why it's wrong here
This is wrong because it excludes one valid host and includes the broadcast address.
When this WOULD be correct
If the question specified a subnet mask of /25 instead of /26, the usable host range would be 172.16.20.129 to 172.16.20.254, making option C correct as it would then include valid host addresses within that range.
- ✗
172.16.20.193 to 172.16.20.254
Why it's wrong here
This is wrong because that range belongs to the next subnet block.
When this WOULD be correct
If the question specified a different subnet, such as 172.16.20.192/26, then option D would be correct, as it would represent the usable host addresses within that subnet range.
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.
✓172.16.20.129 to 172.16.20.190Correct answer▾
Why this is correct
This is correct because .128 is the network and .191 is the broadcast.
✗172.16.20.128 to 172.16.20.191Wrong answer — click to see why▾
Why this is wrong here
Option B is incorrect because it includes the network address (172.16.20.128) and the broadcast address (172.16.20.191) for the subnet, which are not usable host addresses.
★ When this WOULD be the correct answer
If the question asked for the range of all IP addresses within the subnet, including the network and broadcast addresses, then option B would be correct, as it would encompass the entire range from 172.16.20.128 to 172.16.20.191.
Why candidates choose this
Candidates may choose this option because it closely resembles the correct range and includes the last usable address, leading to confusion between usable and total address ranges in subnetting.
✗172.16.20.130 to 172.16.20.191Wrong answer — click to see why▾
Why this is wrong here
Option C is incorrect because it includes the address 172.16.20.191, which is the broadcast address for the subnet 172.16.20.128/26, making it unusable for hosts.
★ When this WOULD be the correct answer
If the question specified a subnet mask of /25 instead of /26, the usable host range would be 172.16.20.129 to 172.16.20.254, making option C correct as it would then include valid host addresses within that range.
Why candidates choose this
Candidates may choose option C due to confusion about subnet boundaries, mistakenly thinking that the broadcast address can be included in the usable range, especially if they miscalculate the subnet mask.
✗172.16.20.193 to 172.16.20.254Wrong answer — click to see why▾
Why this is wrong here
Option D is incorrect because the specified range (172.16.20.193 to 172.16.20.254) falls outside the subnet defined by 172.16.20.190/26, which only includes addresses from 172.16.20.128 to 172.16.20.191.
★ When this WOULD be the correct answer
If the question specified a different subnet, such as 172.16.20.192/26, then option D would be correct, as it would represent the usable host addresses within that subnet range.
Why candidates choose this
Candidates might choose this option due to a misunderstanding of subnetting boundaries, mistakenly believing that addresses beyond the subnet's defined range could still be valid host addresses.
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
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Related to this question
Learn chapter
IPv4 Addressing and Address Classes
Key term
Network address
A network address is a unique identifier that allows devices to find and communicate with each other on a computer network.
Key term
Subnet
A subnet is a logical subdivision of an IP network, created by partitioning a larger network address space using subnet masks.
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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.