Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A host is configured with 192.168.10.129/25. Which subnet contains that host?
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
192.168.10.0/25
This is wrong because .129 is not in the lower /25 block.
B
Distractor review
192.168.10.64/25
This is wrong because /25 boundaries do not start at .64.
C
Best answer
192.168.10.128/25
This is correct because .129 is in the upper /25 block.
D
Distractor review
192.168.10.192/25
This is wrong because /25 boundaries start only at .0 and .128 within a /24.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is misidentifying the subnet boundaries for a /25 mask within a /24 network. Candidates often mistakenly believe that subnets start at .64 or .192, confusing /25 with other subnet sizes like /26 or /27. This leads to selecting incorrect subnets such as 192.168.10.64/25 or 192.168.10.192/25, which are invalid because /25 only divides the /24 into two halves starting at .0 and .128. This misunderstanding causes errors in subnet identification and can result in wrong routing or access decisions in real networks.
Technical deep dive
How to think about this question
Subnetting divides a larger network into smaller, manageable segments called subnets by borrowing bits from the host portion of an IP address. In this question, a /25 subnet mask means 25 bits are used for the network portion, leaving 7 bits for hosts. This splits a traditional Class C /24 network (256 addresses) into two equal subnets, each containing 128 addresses. The first subnet ranges from 192.168.10.0 to 192.168.10.127, and the second from 192.168.10.128 to 192.168.10.255. To determine which subnet contains a given IP address, you compare the address against the subnet boundaries defined by the mask. Since the host IP is 192.168.10.129 with a /25 mask, it falls just above 192.168.10.128, placing it in the second subnet block (192.168.10.128/25). This is a fundamental subnetting skill tested in CCNA, requiring quick recognition of subnet boundaries within a /24 network. A common exam trap is confusing the starting points of /25 subnets within a /24 block. Some may incorrectly assume subnets start at .64 or .192, but /25 splits only at .0 and .128. Understanding these fixed boundaries prevents misclassification of IP addresses. Practically, this knowledge ensures correct subnet assignment, which is critical for routing, access control, and network segmentation in Cisco environments.
KKey Concepts to Remember
- A /25 subnet mask divides a Class C /24 network into two equal subnets, each containing 128 IP addresses.
- Subnet boundaries for a /25 mask within a /24 network start only at .0 and .128, never at .64 or .192.
- To determine an IP's subnet, compare the host address against subnet ranges defined by the subnet mask.
- The first /25 subnet covers IPs from .0 to .127, and the second covers .128 to .255 within the same /24 block.
- Incorrectly assuming subnet boundaries for /25 leads to selecting invalid subnets and failing subnet identification.
- Cisco devices use subnet masks to route traffic correctly by matching IP addresses to their subnet ranges.
- Understanding subnet boundaries is essential for configuring VLANs, ACLs, and routing protocols in Cisco networks.
- Subnetting skills tested in CCNA require quick recognition of subnet ranges to ensure accurate network segmentation.
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.
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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?
A /25 subnet mask divides a Class C /24 network into two equal subnets, each containing 128 IP addresses.
What is the correct answer to this question?
The correct answer is: 192.168.10.128/25 — A /25 divides the /24 into two blocks: 0–127 and 128–255. In practical terms, 192.168.10.129 belongs to the upper half, so the containing subnet is 192.168.10.128/25. This is a simple subnet-boundary question, but it is designed to confirm that you can identify the correct half of the /24 quickly and 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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