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 /25 subnet mask divides an IP address range into two equal subnets, each containing 128 addresses including network and broadcast addresses.. 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.
A host with address 10.0.0.130/25 needs to identify its subnet. Which subnet is correct?
10.0.0.0/25
Why wrong: This is wrong because the 0/25 block covers 0 through 127, not 130.
10.0.0.64/25
Why wrong: This is wrong because /25 boundaries do not increment by 64.
10.0.0.128/25
This is correct because 130 falls in the 128 through 255 range.
10.0.0.192/25
Why wrong: This is wrong because /25 boundaries begin at 0 and 128, not 192.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
10.0.0.128/25
A /25 uses blocks of 128 addresses. In plain language, that means the fourth-octet ranges are 0–127 and 128–255. Since the host address ends in 130, it belongs to the upper block, which means the subnet is 10.0.0.128/25. This kind of question is a staple of subnetting because it tests whether you can identify the correct subnet boundary from the prefix and host address. Once you recognize the /25 split, the answer becomes straightforward.
Key principle: A /25 subnet mask divides an IP address range into two equal subnets, each containing 128 addresses including network and broadcast addresses.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
10.0.0.0/25
Why it's wrong here
This is wrong because the 0/25 block covers 0 through 127, not 130.
When this WOULD be correct
If the question asked for the base address of the subnet that includes all addresses from 10.0.0.0 to 10.0.0.127, then option A would be correct as it represents the starting address of that subnet.
10.0.0.64/25
Why it's wrong here
This is wrong because /25 boundaries do not increment by 64.
When this WOULD be correct
In a question where the subnet mask is changed to /26 and the host address is specified as 10.0.0.130, option B (10.0.0.64/25) could be correct if the question asks for the subnet that includes addresses from 10.0.0.64 to 10.0.0.127. This would make it a valid subnet for a different host range.
10.0.0.128/25
Why this is correct
This is correct because 130 falls in the 128 through 255 range.
Related concept
A /25 subnet mask divides an IP address range into two equal subnets, each containing 128 addresses including network and broadcast addresses.
10.0.0.192/25
Why it's wrong here
This is wrong because /25 boundaries begin at 0 and 128, not 192.
When this WOULD be correct
This option would be correct if the question asked for the subnet of a host with an address in the range of 10.0.0.192 to 10.0.0.255, such as 10.0.0.200/25. In that case, 10.0.0.192/25 would accurately represent the subnet for that host.
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 130 falls in the 128 through 255 range.
Why this is wrong here
The subnet 10.0.0.0/25 covers addresses 10.0.0.0 through 10.0.0.127. Since 10.0.0.130 is outside this range, it cannot belong to this subnet. The host's address must be within the subnet's range.
★ When this WOULD be the correct answer
If the question asked for the base address of the subnet that includes all addresses from 10.0.0.0 to 10.0.0.127, then option A would be correct as it represents the starting address of that subnet.
Why candidates choose this
A student might assume that any address starting with 10.0.0.x belongs to the 10.0.0.0/24 network and forget that the /25 mask splits the /24 into two subnets. They may incorrectly think 10.0.0.0/25 includes all addresses from 0 to 255.
Why this is wrong here
The /25 prefix length has a subnet size of 128, so valid network addresses are multiples of 128 (0, 128, 256, etc.). 10.0.0.64 is not a multiple of 128, so it is not a valid /25 network address.
★ When this WOULD be the correct answer
In a question where the subnet mask is changed to /26 and the host address is specified as 10.0.0.130, option B (10.0.0.64/25) could be correct if the question asks for the subnet that includes addresses from 10.0.0.64 to 10.0.0.127. This would make it a valid subnet for a different host range.
Why candidates choose this
Students often confuse /25 with /26 (which has a 64-address block size) or /27 (32-address block). The number 64 is a common boundary for /26 subnets, leading to the mistaken belief that 10.0.0.64/25 is valid.
Why this is wrong here
The /25 prefix length creates subnets with a block size of 128, starting at 0, 128, 256, etc. 10.0.0.192/25 would be a valid subnet if the network started at 192, but 192 is not a valid /25 boundary because 192 is not a multiple of 128.
★ When this WOULD be the correct answer
This option would be correct if the question asked for the subnet of a host with an address in the range of 10.0.0.192 to 10.0.0.255, such as 10.0.0.200/25. In that case, 10.0.0.192/25 would accurately represent the subnet for that host.
Why candidates choose this
Students often confuse /25 boundaries with /26 boundaries (which increment by 64) or mistakenly think that any address ending in .192 could be a subnet start. The number 192 is a common subnet boundary for /26 or /27, leading to this error.
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 subnet mask with the number of addresses it covers. Always calculate the address range based on the subnet mask.
Detailed technical explanation
Subnetting divides a larger IP network into smaller, manageable segments called subnets by borrowing bits from the host portion of the address to create subnet masks. A /25 subnet mask means 25 bits are fixed for the network and subnet, leaving 7 bits for host addresses, resulting in two subnets within a Class A or Class C range. Each /25 subnet contains 128 IP addresses, including network and broadcast addresses. To determine which /25 subnet an IP address belongs to, you examine the fourth octet and compare it against the subnet boundaries. The two /25 subnets in the 10.0.0.0 network are 10.0.0.0/25 (addresses 0–127) and 10.0.0.128/25 (addresses 128–255). Since 10.0.0.130 falls between 128 and 255, it belongs to the 10.0.0.128/25 subnet. This method applies universally for subnetting with /25 masks in Cisco networking. A common exam trap is confusing subnet boundaries by incorrectly assuming increments of 64 or 192 for /25 masks, which actually split the address space into two equal halves of 128 addresses each. Practically, Cisco devices use this subnetting logic to route traffic correctly and assign IP addresses within the correct subnet, ensuring proper network segmentation and communication.
Key takeaway
A /25 subnet mask divides an IP address range into two equal subnets, each containing 128 addresses including network and broadcast addresses.
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 /25 subnet mask divides an IP address range into two equal subnets, each containing 128 addresses including network and broadcast addresses., 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 /25 subnet mask divides an IP address range into two equal subnets, each containing 128 addresses including network and broadcast addresses..
The correct answer is: 10.0.0.128/25 — A /25 uses blocks of 128 addresses. In plain language, that means the fourth-octet ranges are 0–127 and 128–255. Since the host address ends in 130, it belongs to the upper block, which means the subnet is 10.0.0.128/25. This kind of question is a staple of subnetting because it tests whether you can identify the correct subnet boundary from the prefix and host address. Once you recognize the /25 split, the answer becomes straightforward.
Review a /25 subnet mask divides an IP address range into two equal subnets, each containing 128 addresses including network and broadcast addresses., then practise related 200-301 questions on the same topic to reinforce the concept.
A /25 subnet mask divides an IP address range into two equal subnets, each containing 128 addresses including network and broadcast addresses.
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Last reviewed: May 17, 2026
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