The answer is that the servers are on different subnets and require a router to communicate. This is because a /25 subnet mask (255.255.255.128) splits the 192.168.10.0/24 network into two distinct subnets: 192.168.10.0/25, which hosts addresses 1 through 126, and 192.168.10.128/25, which hosts addresses 129 through 254. Server A at .25 falls in the first subnet, while Server B at .200 falls in the second, so they cannot communicate directly without a router to forward traffic between them. On the CompTIA A+ Core 1 220-1201 exam, this question tests your ability to apply advanced subnetting to a real-world troubleshooting scenario, often catching test-takers who assume all addresses in the same classful range can talk without a gateway. A common trap is forgetting that a /25 changes the broadcast domain boundary at .128. Memory tip: think of the /25 as a “splitter”—the .128 line is the wall; if one host is below it and the other above, you need a router to knock it down.
220-1101 IP Addressing Practice Question
This 220-1201 practice question tests your understanding of ip addressing. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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 network administrator is troubleshooting a connectivity issue between two servers. Server A has IP 192.168.10.25/25, and Server B has IP 192.168.10.200/25. Server A can ping its default gateway (192.168.10.1) but cannot ping Server B. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The servers are on different subnets and require a router to communicate.
A /25 subnet mask (255.255.255.128) divides the 192.168.10.0/24 network into two subnets: 192.168.10.0/25 (hosts 1-126) and 192.168.10.128/25 (hosts 129-254). Server A (25) is on the first subnet, Server B (200) on the second. They need a router to communicate. This tests advanced subnetting.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Server A has a duplicate IP address.
Why it's wrong here
A duplicate IP would cause intermittent issues, but Server A can ping the gateway, indicating no conflict on its subnet.
✗
The subnet mask is incorrect on one of the servers.
Why it's wrong here
Both servers use /25, which is consistent; the issue is that they are on different subnets within the same /24 block.
✓
The servers are on different subnets and require a router to communicate.
Why this is correct
With a /25 mask, 192.168.10.25 is in the 0-126 range, and 192.168.10.200 is in the 128-254 range, placing them on different subnets.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Server A can ping the gateway, so the gateway is reachable; the issue is between the servers, not the gateway.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 220-1201 question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 220-1201 subnetting questions on CIDR, address ranges, and subnet selection.
IP Addressing — This question tests IP Addressing — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The servers are on different subnets and require a router to communicate. — A /25 subnet mask (255.255.255.128) divides the 192.168.10.0/24 network into two subnets: 192.168.10.0/25 (hosts 1-126) and 192.168.10.128/25 (hosts 129-254). Server A (25) is on the first subnet, Server B (200) on the second. They need a router to communicate. This tests advanced subnetting.
What should I do if I get this 220-1201 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 220-1201 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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