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220-1201 Practice Question: A network administrator is troubleshooting a…
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?
⚠ Common exam trap
The 220-1201 exam often tests the misconception that a /25 mask is simply a larger subnet that includes all addresses from .0 to .255, when in fact it creates two distinct subnets that require a router to communicate.
Answer choices
Why each option matters
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.
Server A (192.168.10.25/25) has a subnet mask of 255.255.255.128, placing it in the 192.168.10.0/25 subnet (range 0–127). Server B (192.168.10.200/25) is in the 192.168.10.128/25 subnet (range 128–255). These are different subnets, so Server A cannot reach Server B directly via Layer 2; a router (or Layer 3 switch) is required to forward traffic between them. The fact that Server A can ping its default gateway (192.168.10.1) confirms its IP and mask are correctly configured for its own subnet.
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
If Server A had a duplicate IP address, it would experience severe, intermittent connectivity problems due to Address Resolution Protocol (ARP) conflicts. The fact that Server A can successfully ping its default gateway reliably indicates that its IP address is unique and operational on its local subnet, ruling out a duplicate IP as the cause of communication failure with another server.
- ✗
The subnet mask is incorrect on one of the servers.
Why it's wrong here
While both servers are configured with a /25 subnet mask, which is consistent, the issue isn't an incorrect mask in the sense of a typo or misconfiguration. Instead, the /25 mask correctly divides the 192.168.10.0/24 network into two distinct subnets. The problem arises because the servers' assigned IP addresses fall into different segments defined by this mask, not because the mask itself is improperly applied or erroneous on one server.
- ✓
The servers are on different subnets and require a router to communicate.
Why this is correct
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's IP (192.168.10.25) falls within the first subnet, while Server B's IP (192.168.10.200) belongs to the second. Since they reside on different logical networks, a router is necessary to forward traffic between them, as direct layer 2 communication is not possible.
- ✗
The default gateway is misconfigured.
Why it's wrong here
If the default gateway were misconfigured on Server A, it would be unable to ping its gateway successfully, as the gateway address would be unreachable or incorrect for its subnet. The ability of Server A to ping its default gateway confirms that its gateway configuration is correct and the gateway device is operational, indicating the problem lies elsewhere in the network path between the two servers.
Visual reference
Quick reference
IPv4 Address Class Summary
| Class | First Octet Range | Default Mask | Networks | Hosts per Network |
|---|---|---|---|---|
| A | 1–126 | /8 (255.0.0.0) | 126 | 16,777,214 |
| B | 128–191 | /16 (255.255.0.0) | 16,384 | 65,534 |
| C | 192–223 | /24 (255.255.255.0) | 2,097,152 | 254 |
| D | 224–239 | N/A | Multicast groups | — |
| E | 240–255 | N/A | Reserved / experimental | — |
127.x.x.x is reserved for loopback. Modern networks use CIDR (classless) rather than classful addressing.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1201 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1201 exam.