Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A host is configured with IP address 10.10.40.78/28. 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
10.10.40.48/28
This is wrong because that block ends at .63.
B
Best answer
10.10.40.64/28
This is correct because .78 falls inside the .64 through .79 range.
C
Distractor review
10.10.40.72/28
This is wrong because /28 boundaries do not start at .72.
D
Distractor review
10.10.40.80/28
This is wrong because that block begins above the host address.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is selecting a subnet that seems numerically close to the host IP but does not align with the actual subnet boundaries defined by the mask. For example, choosing 10.10.40.72/28 is incorrect because /28 subnets increment in blocks of 16, and 72 is not a valid subnet boundary. This mistake happens when candidates overlook the block size calculation and assume any number near the host IP is a valid network address. Understanding the block size and subnet increments is essential to avoid this pitfall.
Technical deep dive
How to think about this question
Subnetting is a fundamental concept in IP networking that divides a larger network into smaller, manageable subnetworks. A /28 subnet mask corresponds to 255.255.255.240, which means the last octet has 4 bits for host addressing, allowing for 16 IP addresses per subnet block. These addresses include the network address, usable host addresses, and the broadcast address. Understanding how to calculate subnet boundaries is critical for efficient IP address allocation and routing. To determine the subnet containing a specific IP address like 10.10.40.78/28, you calculate the block size by subtracting the subnet mask from 256, which yields 16. The subnets increment in blocks of 16 in the last octet: 0-15, 16-31, 32-47, 48-63, 64-79, and so forth. Since 78 falls between 64 and 79, the correct subnet is 10.10.40.64/28. This method ensures precise identification of the network address and prevents misconfiguration. A common exam trap is confusing subnet boundaries with arbitrary numbers that appear close to the host IP, such as 10.10.40.72/28, which is invalid because /28 subnets do not start at .72. Cisco exams test your ability to calculate subnet ranges accurately rather than relying on memorized or approximate values. Practically, correct subnetting ensures proper routing and prevents IP conflicts in a network environment.
KKey Concepts to Remember
- A /28 subnet mask creates subnets with 16 IP addresses each, including network and broadcast addresses.
- Subnet boundaries increment by the block size, which is calculated as 256 minus the subnet mask value in the relevant octet.
- The network address is the first IP in the subnet block, and the broadcast address is the last IP in that block.
- Hosts must fall within the usable IP range between the network and broadcast addresses of their subnet.
- Incorrect subnet selection often results from ignoring the block size and choosing arbitrary IP ranges.
- Cisco devices use subnet masks to determine network boundaries and route traffic appropriately.
- Understanding subnetting is critical for IP address management and avoiding address conflicts in Cisco networks.
- Subnetting questions test your ability to convert prefix lengths into block sizes and identify correct subnet ranges.
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.
Related practice questions
Related 200-301 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
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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 /28 subnet mask creates subnets with 16 IP addresses each, including network and broadcast addresses.
What is the correct answer to this question?
The correct answer is: 10.10.40.64/28 — A /28 subnet has a block size of 16. In simple terms, the fourth-octet ranges are 0–15, 16–31, 32–47, 48–63, 64–79, 80–95, and so on. Because 78 falls inside the 64–79 block, the network address for this host’s subnet is 10.10.40.64/28. This style of subnetting question checks whether you can move from prefix length to block size and then place the host into the correct range. The common mistake is choosing the nearest familiar-looking number instead of the actual block boundary.
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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