This 200-301 practice question tests your understanding of network infrastructure and connectivity. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. A key principle to apply: a subnet mask defines which bits of an IP address represent the network and which represent hosts by setting network bits to 1 and host bits to 0.. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
What prefix length corresponds to the subnet mask 255.255.255.248?
/28
Why wrong: This is wrong because /28 would correspond to 255.255.255.240.
/29
This is correct because 255.255.255.248 equals 29 network bits.
/30
Why wrong: This is wrong because /30 would correspond to 255.255.255.252.
/27
Why wrong: This is wrong because /27 would correspond to 255.255.255.224.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
/29
The mask 255.255.255.248 corresponds to /29. In practical terms, the first three octets provide 24 network bits, and the value 248 in the last octet is 11111000 in binary, which contributes 5 more network bits. That gives a total prefix length of 29. This is a standard dotted-decimal to prefix conversion question. It matters because subnetting often requires you to move comfortably between both forms.
Key principle: A subnet mask defines which bits of an IP address represent the network and which represent hosts by setting network bits to 1 and host bits to 0.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
/28
Why it's wrong here
This is wrong because /28 would correspond to 255.255.255.240.
When this WOULD be correct
In a different question, if asked what prefix length corresponds to a subnet mask of 255.255.255.240, option A would be correct, as that subnet mask corresponds to a /28 prefix length, allowing for 16 IP addresses.
/29
Why this is correct
This is correct because 255.255.255.248 equals 29 network bits.
Related concept
A subnet mask defines which bits of an IP address represent the network and which represent hosts by setting network bits to 1 and host bits to 0.
/30
Why it's wrong here
This is wrong because /30 would correspond to 255.255.255.252.
When this WOULD be correct
In a different question, if asked for the prefix length of a subnet mask of 255.255.255.252, which corresponds to /30, option C would be correct, as it would accurately reflect the number of usable addresses in that subnet.
/27
Why it's wrong here
This is wrong because /27 would correspond to 255.255.255.224.
When this WOULD be correct
In a different question asking for the prefix length of a subnet mask of 255.255.255.224, option D would be correct, as that subnet mask corresponds to a /27 prefix length, allowing for 30 usable IP addresses.
Option-by-option analysis
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.
Why this is correct
This is correct because 255.255.255.248 equals 29 network bits.
Why this is wrong here
The subnet mask 255.255.255.240 corresponds to a /28 prefix length, not /29. This mask has 28 network bits, leaving 4 host bits, which yields 14 usable hosts per subnet.
★ When this WOULD be the correct answer
In a different question, if asked what prefix length corresponds to a subnet mask of 255.255.255.240, option A would be correct, as that subnet mask corresponds to a /28 prefix length, allowing for 16 IP addresses.
Why candidates choose this
Students often confuse the prefix lengths for common subnet masks. Since /28 is close to /29, they might mistakenly think that 255.255.255.248 is /28 without calculating the binary representation.
Why this is wrong here
The subnet mask 255.255.255.252 corresponds to a /30 prefix length, not /29. A /30 mask has 30 network bits and only 2 host bits, providing 2 usable addresses, typically used for point-to-point links.
★ When this WOULD be the correct answer
In a different question, if asked for the prefix length of a subnet mask of 255.255.255.252, which corresponds to /30, option C would be correct, as it would accurately reflect the number of usable addresses in that subnet.
Why candidates choose this
Both /29 and /30 are used for small subnets, and students may confuse the number of host bits. Since /30 is a common mask for WAN links, they might incorrectly assume 255.255.255.248 is /30.
Why this is wrong here
The subnet mask 255.255.255.224 corresponds to a /27 prefix length, not /29. A /27 mask has 27 network bits and 5 host bits, providing 30 usable hosts per subnet.
★ When this WOULD be the correct answer
In a different question asking for the prefix length of a subnet mask of 255.255.255.224, option D would be correct, as that subnet mask corresponds to a /27 prefix length, allowing for 30 usable IP addresses.
Why candidates choose this
Students may misremember the binary pattern for /27 and /29. Since both masks have the last octet as a non-standard value, they might incorrectly associate 248 with /27 without proper calculation.
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?”
Common exam traps
Be careful not to confuse the binary values of subnet masks. Ensure you understand how to convert between dotted-decimal and CIDR notation.
Detailed technical explanation
Subnetting is a fundamental concept in IP networking that divides a larger 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. The prefix length, also known as CIDR notation, expresses the subnet mask as the number of bits set to 1 in the mask. For example, a subnet mask of 255.255.255.248 means the first 29 bits are network bits, leaving 3 bits for host addresses. To determine the prefix length from a subnet mask, convert each octet to binary and count the consecutive 1 bits from left to right. In 255.255.255.248, the first three octets (255.255.255) each have 8 bits set to 1, totaling 24 bits. The last octet, 248, in binary is 11111000, which adds 5 more bits set to 1. Adding these gives a prefix length of /29. This prefix length is critical in Cisco networking for configuring interfaces, routing protocols, and access control lists that rely on subnet boundaries. A common exam trap is confusing similar subnet masks with close prefix lengths, such as /28 (255.255.255.240) or /30 (255.255.255.252). These masks differ by the number of host bits and available addresses. Misidentifying the prefix length can lead to incorrect subnetting, causing routing or addressing errors in Cisco devices. Understanding the binary representation and practicing conversions helps avoid this mistake and ensures accurate subnet configuration in CCNA scenarios.
Key takeaway
A subnet mask defines which bits of an IP address represent the network and which represent hosts by setting network bits to 1 and host bits to 0.
Real-world example
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
Review a subnet mask defines which bits of an IP address represent the network and which represent hosts by setting network bits to 1 and host bits to 0., then practise related 200-301 questions on the same topic to reinforce the concept.
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FAQ
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — A subnet mask defines which bits of an IP address represent the network and which represent hosts by setting network bits to 1 and host bits to 0..
The correct answer is: /29 — The mask 255.255.255.248 corresponds to /29. In practical terms, the first three octets provide 24 network bits, and the value 248 in the last octet is 11111000 in binary, which contributes 5 more network bits. That gives a total prefix length of 29. This is a standard dotted-decimal to prefix conversion question. It matters because subnetting often requires you to move comfortably between both forms.
Review a subnet mask defines which bits of an IP address represent the network and which represent hosts by setting network bits to 1 and host bits to 0., then practise related 200-301 questions on the same topic to reinforce the concept.
A subnet mask defines which bits of an IP address represent the network and which represent hosts by setting network bits to 1 and host bits to 0.
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Last reviewed: Apr 12, 2026
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