Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A subnet uses the mask 255.255.255.224. How many usable host addresses does it provide?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Distractor review
14
This is wrong because 14 usable hosts would correspond to a /28, not a /27.
B
Best answer
30
This is correct because a /27 has 32 total addresses and 30 usable host addresses.
C
Distractor review
62
This is wrong because 62 usable hosts would correspond to a /26.
D
Distractor review
126
This is wrong because 126 usable hosts would correspond to a /25.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is selecting the number of total addresses instead of usable host addresses. Many candidates see 32 total addresses for a /27 subnet and mistakenly choose 32 or confuse it with 30 usable hosts. Another common error is mixing up subnet masks, such as confusing /27 with /26 or /28, which have different host counts. This mistake often happens because candidates remember block sizes but forget to subtract the network and broadcast addresses, which are not assignable to hosts. Understanding the difference between total and usable addresses is essential to avoid this trap.
Technical deep dive
How to think about this question
Subnetting is a fundamental concept in networking that divides a larger IP network into smaller, manageable segments called subnets. Each subnet uses a subnet mask to determine which portion of the IP address represents the network and which portion represents hosts. The subnet mask 255.255.255.224 corresponds to a /27 prefix length, meaning the first 27 bits are the network portion and the remaining 5 bits are for host addresses. The number of usable host addresses in a subnet is calculated by taking 2 to the power of the number of host bits and subtracting 2 for the network and broadcast addresses. For a /27 subnet mask, there are 5 host bits, so 2^5 equals 32 total addresses. Subtracting 2 leaves 30 usable host addresses. This calculation is critical for designing networks that require specific numbers of hosts per subnet. A common exam trap is confusing the subnet mask with similar masks like /26 or /28, which have different host counts. For example, a /26 mask provides 62 usable hosts, and a /28 provides 14. Misremembering these values or forgetting to subtract the network and broadcast addresses leads to incorrect answers. Practically, Cisco devices use this logic to allocate IP addresses efficiently and avoid address conflicts within subnets.
KKey Concepts to Remember
- A subnet mask defines how many bits of an IP address are used for the network versus the host portion, directly affecting subnet size.
- The subnet mask 255.255.255.224 corresponds to a /27 prefix, which means 27 bits are network bits and 5 bits are host bits.
- The number of usable host addresses in a subnet is calculated by 2 to the power of host bits minus 2, accounting for network and broadcast addresses.
- A /27 subnet provides 32 total addresses, but only 30 are usable for hosts because the first address is the network ID and the last is the broadcast address.
- Confusing total addresses with usable host addresses is a common mistake that leads to incorrect subnetting answers on the CCNA exam.
- Subnetting requires precise calculation of host bits and understanding reserved addresses to design efficient and functional IP networks.
- Cisco devices rely on correct subnetting to allocate IP addresses and route traffic properly within segmented networks.
- Memorizing common subnet masks and their usable host counts helps avoid errors and speeds up subnetting questions during the exam.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Related practice questions
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
A subnet mask defines how many bits of an IP address are used for the network versus the host portion, directly affecting subnet size.
What is the correct answer to this question?
The correct answer is: 30 — A mask of 255.255.255.224 corresponds to a /27 prefix. In plain language, that leaves 5 host bits available in the address, which creates 32 total addresses in each subnet. Two of those are reserved: one for the network address and one for the broadcast address. That leaves 30 usable host addresses. This is a classic subnetting question because it tests whether you can move from mask to prefix idea to host count without getting lost. Many learners remember the block size but forget to subtract the network and broadcast entries. The correct answer comes from that full logic chain: /27 means 32 total, and therefore 30 usable.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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