Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A host with address 10.0.0.130/25 needs to identify its subnet. Which subnet is correct?
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
10.0.0.0/25
This is wrong because the 0/25 block covers 0 through 127, not 130.
B
Distractor review
10.0.0.64/25
This is wrong because /25 boundaries do not increment by 64.
C
Best answer
10.0.0.128/25
This is correct because 130 falls in the 128 through 255 range.
D
Distractor review
10.0.0.192/25
This is wrong because /25 boundaries begin at 0 and 128, not 192.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is misinterpreting the /25 subnet boundaries as increments of 64 or 192 instead of 128. Candidates often mistakenly select 10.0.0.64/25 or 10.0.0.192/25 because they confuse subnet increments or forget that /25 splits the address space exactly in half. This error leads to choosing an incorrect subnet that does not actually contain the host IP 10.0.0.130. Understanding that /25 creates two subnets of 128 addresses each, starting at 0 and 128, is critical to avoid this mistake.
Technical deep dive
How to think about this question
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.
KKey Concepts to Remember
- A /25 subnet mask divides an IP address range into two equal subnets, each containing 128 addresses including network and broadcast addresses.
- Subnet boundaries for a /25 mask occur at 0 and 128 in the fourth octet, defining the two subnets 10.0.0.0/25 and 10.0.0.128/25.
- To identify the correct subnet for a host IP, compare the host's fourth octet against the subnet boundaries determined by the mask.
- Cisco devices use subnet masks like /25 to segment networks and route traffic correctly within the assigned subnet ranges.
- Incorrectly assuming subnet increments of 64 or 192 for a /25 mask leads to common mistakes in subnet identification.
- The network address is always the first address in the subnet range, and the broadcast address is the last, which helps define subnet boundaries.
- Subnetting knowledge is essential for configuring IP addressing and routing in Cisco networks, ensuring efficient network segmentation.
- Understanding binary subnetting principles helps avoid exam traps and improves accuracy in subnet calculations during the CCNA exam.
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 an IP address range into two equal subnets, each containing 128 addresses including network and broadcast addresses.
What is the correct answer to this question?
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.
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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