Quick Answer
The answer is 10.10.10.128. This is correct because a /25 subnet mask (255.255.255.128) borrows one bit from the host portion, creating two subnets each with 128 addresses: the first block spans 10.10.10.0 to 10.10.10.127, and the second from 10.10.10.128 to 10.10.10.255. Since the host address 10.10.10.130 falls in the second block, its network address is the first address of that block, 10.10.10.128. On the CCNA 200-301 v2 exam, this type of subnet-boundary question tests your ability to quickly map a host to its prefix block without binary conversion—a skill essential for efficient troubleshooting and design. A common trap is forgetting that the network address is always the first address in the range, not the host’s own address. For a quick memory tip, think of the /25 mask as a “split in half”: the magic number is 128, so any host address above 128 belongs to the upper half, and the network address is that multiple of 128.
This 200-301 practice question tests your understanding of network infrastructure and connectivity. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. A key principle to apply: a /25 subnet mask divides a Class C network into two subnets, each containing 128 IP 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 is configured with 10.10.10.130/25. What is the network address of its subnet?
10.10.10.0
Why wrong: This is wrong because .130 is not in the lower 0–127 /25 block.
10.10.10.64
Why wrong: This is wrong because /25 does not create boundaries at 64.
10.10.10.128
This is correct because .130 falls in the upper /25 block starting at .128.
10.10.10.255
Why wrong: This is wrong because .255 is the broadcast address of that /25, not the network address.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
10.10.10.128
A /25 divides the address space into two blocks of 128 addresses. In plain language, the ranges are 0–127 and 128–255. Since the host ends in 130, it belongs to the 128–255 half. That means the network address is 10.10.10.128. This is a common subnet-boundary question because it tests whether you can map a host address into the correct prefix block quickly and confidently.
Key principle: A /25 subnet mask divides a Class C network into two subnets, each containing 128 IP addresses.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
10.10.10.0
Why it's wrong here
This is wrong because .130 is not in the lower 0–127 /25 block.
When this WOULD be correct
If the question asked for the network address of a host configured with 10.10.10.130/24, then 10.10.10.0 would be the correct answer, as it represents the network address for that subnet mask.
10.10.10.64
Why it's wrong here
This is wrong because /25 does not create boundaries at 64.
When this WOULD be correct
If the question asked for the first usable IP address of the subnet 10.10.10.64/26, then option B would be correct, as 10.10.10.64 would be the network address for that subnet.
10.10.10.128
Why this is correct
This is correct because .130 falls in the upper /25 block starting at .128.
Related concept
A /25 subnet mask divides a Class C network into two subnets, each containing 128 IP addresses.
10.10.10.255
Why it's wrong here
This is wrong because .255 is the broadcast address of that /25, not the network address.
When this WOULD be correct
If the question asked for the broadcast address of the subnet 10.10.10.128/25, then 10.10.10.255 would be the correct answer, as it is the last address in that subnet range.
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 upper /25 block starting at .128.
Why this is wrong here
10.10.10.0 is the network address of the 10.10.10.0/25 subnet (range 0-127), but the host IP 10.10.10.130 is not in that range. The /25 mask creates two subnets: 10.10.10.0/25 and 10.10.10.128/25, and .130 belongs to the latter.
★ When this WOULD be the correct answer
If the question asked for the network address of a host configured with 10.10.10.130/24, then 10.10.10.0 would be the correct answer, as it represents the network address for that subnet mask.
Why candidates choose this
Students might assume that any IP starting with 10.10.10.x belongs to the 10.10.10.0 network, forgetting that the subnet mask determines the boundary. The .0 address is a common network address for /24, but with /25, the network address changes.
Why this is wrong here
10.10.10.64 is not a valid network address for any /25 subnet derived from 10.10.10.0/24. A /25 subnet has a block size of 128, so the network addresses are multiples of 128: 0 and 128. 64 is a multiple of 64, which would be a /26 boundary, not /25.
★ When this WOULD be the correct answer
If the question asked for the first usable IP address of the subnet 10.10.10.64/26, then option B would be correct, as 10.10.10.64 would be the network address for that subnet.
Why candidates choose this
Students often confuse subnet boundaries for different prefix lengths. For example, a /26 has boundaries at multiples of 64, so 10.10.10.64 is a valid network for /26. This option tempts those who misapply the /26 boundary to a /25 question.
Why this is wrong here
10.10.10.255 is the broadcast address for the 10.10.10.128/25 subnet, not the network address. The broadcast address is the last address in the subnet (all host bits set to 1), while the network address is the first address (all host bits set to 0).
★ When this WOULD be the correct answer
If the question asked for the broadcast address of the subnet 10.10.10.128/25, then 10.10.10.255 would be the correct answer, as it is the last address in that subnet range.
Why candidates choose this
Students often confuse the broadcast address with the network address because both are special addresses in a subnet. The .255 address is a common broadcast address for /24 subnets, but for a /25, the broadcast is 10.10.10.255 only if the subnet is 10.10.10.0/25; here the subnet is 10.10.10.128/25.
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 /24 or mistake the broadcast address for the network address.
Detailed technical explanation
Subnetting is a fundamental concept in IP networking that divides a larger network into smaller, manageable subnetworks. The subnet mask determines how the IP address is split between the network and host portions. In this question, the /25 mask means the first 25 bits represent the network portion, leaving 7 bits for host addresses. This creates two equal-sized subnets within the original Class C range, each with 128 addresses. The /25 subnet mask (255.255.255.128) splits the 10.10.10.0 network into two subnets: 10.10.10.0/25 and 10.10.10.128/25. The first subnet covers IP addresses from 10.10.10.0 to 10.10.10.127, and the second subnet covers 10.10.10.128 to 10.10.10.255. Since the host IP is 10.10.10.130, it falls within the second subnet range, making 10.10.10.128 the correct network address. A common exam trap is confusing the subnet boundaries or misinterpreting the broadcast address as the network address. For example, 10.10.10.255 is the broadcast address for the 10.10.10.128/25 subnet, not the network address. Understanding how subnet masks define network and broadcast addresses helps avoid this mistake and ensures accurate subnet identification in Cisco networking scenarios.
Key takeaway
A /25 subnet mask divides a Class C network into two subnets, each containing 128 IP 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 a Class C network into two subnets, each containing 128 IP 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 a Class C network into two subnets, each containing 128 IP addresses..
The correct answer is: 10.10.10.128 — A /25 divides the address space into two blocks of 128 addresses. In plain language, the ranges are 0–127 and 128–255. Since the host ends in 130, it belongs to the 128–255 half. That means the network address is 10.10.10.128. This is a common subnet-boundary question because it tests whether you can map a host address into the correct prefix block quickly and confidently.
Review a /25 subnet mask divides a Class C network into two subnets, each containing 128 IP addresses., then practise related 200-301 questions on the same topic to reinforce the concept.
A /25 subnet mask divides a Class C network into two subnets, each containing 128 IP addresses.
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A router interface is configured with 192.0.2.97/28. What is the network address of the subnet?
hardWhy B: A /28 uses blocks of 16 addresses. The block containing .97 runs from .96 through .111, so .96 is the network address.
Last reviewed: May 17, 2026
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