CCNA Network Infrastructure and Connectivity Practice Question
A host address is 192.168.90.33/28. Which address is the last usable host in the subnet?
⚠ Common exam trap
Cisco often tests the distinction between the broadcast address and the last usable host, tricking candidates who forget to subtract one from the broadcast address.
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
✓
192.168.90.46
The /28 subnet mask (255.255.255.240) gives a block size of 16 addresses. The network address for 192.168.90.33 is 192.168.90.32, so the broadcast address is 192.168.90.47. The last usable host is the broadcast address minus one, which is 192.168.90.46.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
192.168.90.46
Why this is correct
192.168.90.46 is the last usable host address in the /28 subnet that contains .33. A /28 prefix has a block size of 16, so the subnet boundaries are 192.168.90.32 and 192.168.90.47. The address .46 has all host bits set to 1 except the last one, making it the highest address that can be assigned to a device. The next address, .47, is the directed broadcast for this subnet.
- ✗
192.168.90.47
Why it's wrong here
192.168.90.47 is the broadcast address for the 192.168.90.32/28 subnet, not a usable host address. In a /28 subnet, the broadcast address is the last address in the range, with all host bits set to 1 (32 + 15 = 47). Sending traffic to this address reaches every host in the subnet, and it cannot be assigned to an interface. Therefore, it is incorrect to list it as the last usable host.
When this WOULD be correct
If the question asked for the last address in the subnet instead of the last usable host, option B would be correct, as the broadcast address for the subnet 192.168.90.32/28 is indeed 192.168.90.47.
- ✗
192.168.90.33
Why it's wrong here
192.168.90.33 is the first usable host address in the 192.168.90.32/28 subnet, not the last. Since the network address is .32, the first assignable address is .33. While it is a valid host address, the question specifically asks for the last usable address, which is .46. This option is a distractor for someone who confuses the first usable address with the last.
When this WOULD be correct
If the question asked for the first usable host address in the subnet 192.168.90.32/28, then option C would be correct, as it represents the first address available for assignment to a host.
- ✗
192.168.90.48
Why it's wrong here
192.168.90.48 is the network address of the next consecutive /28 subnet (192.168.90.48/28), not part of the subnet containing .33. The /28 block size is 16, so subnets increment by 16: .32, .48, .64, etc. Since .48 is immediately after the broadcast .47, it belongs to a different subnet and cannot be used as a host address in the 192.168.90.32/28 network. This option is incorrect because it lies outside the valid host range for the given address.
When this WOULD be correct
If the question asked for the first address in the next subnet after 192.168.90.32/28, then 192.168.90.48 would be the correct answer, as it represents the start of the subnet 192.168.90.48/28.
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.
✓192.168.90.46Correct answer▾
Why this is correct
192.168.90.46 is the last usable host address in the /28 subnet that contains .33. A /28 prefix has a block size of 16, so the subnet boundaries are 192.168.90.32 and 192.168.90.47. The address .46 has all host bits set to 1 except the last one, making it the highest address that can be assigned to a device. The next address, .47, is the directed broadcast for this subnet.
✗192.168.90.47Wrong answer — click to see why▾
Why this is wrong here
192.168.90.47 is the broadcast address for the subnet 192.168.90.32/28. Broadcast addresses cannot be assigned to hosts; they are used to send traffic to all hosts in the subnet.
★ When this WOULD be the correct answer
If the question asked for the last address in the subnet instead of the last usable host, option B would be correct, as the broadcast address for the subnet 192.168.90.32/28 is indeed 192.168.90.47.
Why candidates choose this
Students often confuse the last usable host with the broadcast address, especially when the subnet boundary is not obvious. The broadcast is one less than the next subnet's network address, and it's easy to mistakenly think it's usable.
✗192.168.90.33Wrong answer — click to see why▾
Why this is wrong here
192.168.90.33 is the first usable host in the subnet (network address .32 + 1). The question asks for the last usable host, not the first.
★ When this WOULD be the correct answer
If the question asked for the first usable host address in the subnet 192.168.90.32/28, then option C would be correct, as it represents the first address available for assignment to a host.
Why candidates choose this
A test-taker might see that .33 is a valid host and assume it is the last because it is close to the given address, without calculating the subnet range correctly.
✗192.168.90.48Wrong answer — click to see why▾
Why this is wrong here
192.168.90.48 is the network address of the next subnet (192.168.90.48/28). It is not part of the current subnet and cannot be used as a host address in the subnet containing .33.
★ When this WOULD be the correct answer
If the question asked for the first address in the next subnet after 192.168.90.32/28, then 192.168.90.48 would be the correct answer, as it represents the start of the subnet 192.168.90.48/28.
Why candidates choose this
Students may think that .48 is the last usable because it is numerically higher than .46, not realizing that subnet boundaries restrict the range. They might also confuse it with the broadcast address of the previous subnet.
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.