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hardmultiple choiceObjective-mapped

What prefix length corresponds to the subnet mask 255.255.255.224?

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

/26

This is wrong because /26 would correspond to 255.255.255.192.

B

Best answer

/27

This is correct because 255.255.255.224 represents 27 network bits.

C

Distractor review

/28

This is wrong because /28 would correspond to 255.255.255.240.

D

Distractor review

/29

This is wrong because /29 would correspond to 255.255.255.248.

Common exam trap

Common exam trap: answer the scenario, not the keyword

A frequent exam trap is confusing the subnet mask 255.255.255.224 with masks like 255.255.255.192 or 255.255.255.240 because their decimal values are numerically close. Candidates often misinterpret the number of network bits by focusing on decimal values instead of binary representation. This leads to selecting /26 or /28 instead of the correct /27. Misreading this can cause incorrect subnetting decisions, impacting IP address allocation and routing. Understanding binary conversion of subnet masks is essential to avoid this mistake and correctly identify the prefix length in Cisco subnetting questions.

Technical deep dive

How to think about this question

Subnetting is a fundamental networking concept that divides a larger IP network into smaller, manageable subnetworks. The subnet mask determines which portion of an IP address refers to the network and which part refers to hosts. In IPv4, subnet masks are often expressed in dotted-decimal notation (e.g., 255.255.255.224) or as a prefix length (e.g., /27), indicating the number of bits used for the network portion. The subnet mask 255.255.255.224 corresponds to a prefix length of /27 because the first three octets (255.255.255) contribute 24 bits, and the fourth octet (224) in binary is 11100000, adding 3 more bits to the network portion. This totals 27 bits for the network and subnet combined, leaving 5 bits for host addressing. Cisco devices and CCNA exams require fluency in converting between these notations to understand network segmentation and address allocation. A common exam trap is confusing similar subnet masks with close prefix lengths, such as mistaking 255.255.255.224 (/27) for 255.255.255.192 (/26). This happens because the decimal values are close, but the binary representation differs significantly. Practically, using the correct prefix length ensures accurate subnetting, proper IP address allocation, and effective routing in Cisco networks, which is critical for network design and troubleshooting.

KKey Concepts to Remember

  • The subnet mask 255.255.255.224 uses 27 bits for the network portion, combining 24 bits from the first three octets and 3 bits from the fourth octet.
  • Subnet masks define how IP addresses are divided between network and host portions, which is critical for routing and address allocation in Cisco networks.
  • Cisco devices interpret subnet masks in both dotted-decimal and prefix length formats, requiring network engineers to convert between these notations fluently.
  • A /27 prefix length allows for 32 IP addresses per subnet, with 30 usable host addresses after reserving network and broadcast addresses.
  • Misinterpreting subnet masks by decimal value rather than binary leads to common exam mistakes, especially confusing /26, /27, and /28 subnet masks.
  • Correct subnetting ensures efficient IP address utilization and proper routing behavior in Cisco networks, which is essential for CCNA-level network design.
  • Subnetting questions test your ability to translate between binary, decimal, and prefix notation, a key skill for configuring VLANs, ACLs, and routing protocols.
  • Understanding subnet mask conversions helps prevent misconfiguration of interfaces and routing tables, which can cause connectivity issues in Cisco environments.

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

Related 200-301 practice-question pages

Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

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CCNA IPv6 practice questions

Practise IPv6 addressing, routes, neighbour discovery and common IPv6 exam traps.

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?

The subnet mask 255.255.255.224 uses 27 bits for the network portion, combining 24 bits from the first three octets and 3 bits from the fourth octet.

What is the correct answer to this question?

The correct answer is: /27 — The subnet mask 255.255.255.224 corresponds to /27. In plain language, the first three octets contribute 24 network bits, and 224 in binary is 11100000, which contributes 3 more network bits. That gives a total of 27 network bits. This is a common prefix-conversion question because it checks whether you can move between dotted-decimal masks and prefix lengths confidently.

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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