Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A network requires at least 500 usable host addresses in one IPv4 subnet. Which prefix is the smallest that meets the requirement?
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
/24
This is wrong because a /24 provides only 254 usable host addresses.
B
Best answer
/23
This is correct because a /23 provides 510 usable host addresses.
C
Distractor review
/22
This is wrong because /22 would work but is larger than necessary.
D
Distractor review
/25
This is wrong because a /25 provides only 126 usable host addresses.
Common exam trap
Common exam trap: answer the scenario, not the keyword
The main exam trap is choosing a /22 subnet because it obviously supports more than 500 hosts, but it is larger than necessary. This mistake wastes IP address space and shows a lack of understanding of subnet sizing. Candidates often overlook that a /23 subnet already provides 510 usable hosts, which is sufficient. Selecting a /22 may seem safe but fails to demonstrate efficient subnetting skills, which Cisco exams emphasize. Avoid this trap by carefully calculating usable hosts and matching the smallest subnet that meets the requirement.
Technical deep dive
How to think about this question
Subnetting is a fundamental concept in IPv4 networking that divides a larger network into smaller subnetworks, each identified by a network prefix. The prefix length, expressed as a slash followed by a number (e.g., /24), determines how many bits are used for the network portion versus the host portion of the address. The number of usable host addresses in a subnet is calculated as 2^(32 - prefix length) minus 2, accounting for the network and broadcast addresses which cannot be assigned to hosts. To determine the smallest prefix that supports at least 500 usable hosts, you must find the subnet mask that provides at least 502 total addresses (500 hosts plus network and broadcast). A /24 subnet provides 256 total addresses (254 usable), which is insufficient. A /23 subnet doubles the address space to 512 total addresses, yielding 510 usable hosts, which meets the requirement efficiently without excessive waste of IP space. Larger subnets like /22 provide more addresses than needed, which is less optimal. A common exam trap is to select a /22 subnet because it clearly supports more than 500 hosts, but this wastes IP addresses and is not the smallest valid subnet. Cisco exams test your ability to optimize subnetting for host requirements. Practically, using the smallest subnet that meets host needs conserves IP address space and simplifies network management, especially in environments with limited IPv4 address availability.
KKey Concepts to Remember
- Subnetting divides an IPv4 network into smaller subnets by allocating bits to the network and host portions of the address.
- The number of usable host addresses in a subnet equals 2^(32 - prefix length) minus 2, accounting for network and broadcast addresses.
- A /24 subnet provides 254 usable host addresses, which is insufficient for networks requiring at least 500 hosts.
- A /23 subnet provides 510 usable host addresses, making it the smallest subnet prefix that satisfies a 500-host requirement.
- Selecting a subnet larger than necessary, such as /22, wastes IP address space and is inefficient for network design.
- Cisco exams test your ability to optimize subnet size based on host requirements rather than simply choosing a subnet that works.
- Network and broadcast addresses cannot be assigned to hosts, so they must be excluded when calculating usable host counts.
- Efficient subnetting conserves IPv4 address space and simplifies network management, especially in large or segmented networks.
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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Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
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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?
Subnetting divides an IPv4 network into smaller subnets by allocating bits to the network and host portions of the address.
What is the correct answer to this question?
The correct answer is: /23 — To support at least 500 usable hosts, the subnet must provide at least 502 total addresses when the network and broadcast addresses are included. In plain language, that means 256 total addresses in a /24 are not enough, so the next larger power-of-two block is required. A /23 provides 512 total addresses and 510 usable host addresses, which satisfies the requirement while remaining the smallest valid option. This is a classic host-capacity question because it checks whether you can work backward from a required usable host count and choose the smallest prefix that works without wasting more space than necessary.
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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