220-1101 Networking Practice Question
A user reports that their workstation cannot access network resources. The technician runs ipconfig and sees the following: IP address: 192.168.1.100, Subnet mask: 255.255.255.0, Default gateway: 192.168.1.1. The technician pings 127.0.0.1 (success), pings 192.168.1.100 (success), but pinging 192.168.1.1 fails. Other workstations on the same subnet can ping the default gateway successfully. The cable is connected and the link light is on. Which of the following is the MOST likely cause?
⚠ Common exam trap
Many exam-takers assume a failed ping to the gateway is always a physical or firewall issue, but the fact that the workstation can ping its own IP and the loopback, while other devices on the same subnet can reach the gateway, points directly to an address conflict rather than a configuration or firewall problem.
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
✓
Duplicate IP address.
The workstation has a valid IP address and subnet mask, and the loopback (127.0.0.1) and its own IP (192.168.1.100) respond to ping, confirming the TCP/IP stack and network interface are working. The failure to ping the default gateway (192.168.1.1) while other workstations on the same subnet can reach it indicates a local issue. A duplicate IP address on the network would cause the workstation to receive no reply from the gateway because the gateway's ARP table may map the IP to another device's MAC address, or the duplicate device may respond with a conflicting ARP reply, preventing proper communication.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
DNS server is not configured.
Why it's wrong here
DNS is not required for ping when the destination is specified by IP address. Even if the DNS server were missing or misconfigured, ICMP echo requests to raw IP addresses (like the gateway) would still work, so this cannot be the root cause. The failure at Layer 2 or Layer 3—not at the application layer—persists regardless of DNS availability.
- ✗
Incorrect subnet mask.
Why it's wrong here
An incorrect subnet mask would usually prevent communication with any host outside the immediate subnet, but the workstation can ping its own IP and the gateway should be in the same subnet if mask is /24. If mask were wrong, the gateway might be considered remote.
- ✓
Duplicate IP address.
Why this is correct
A duplicate IP address can cause the switch to direct traffic to the wrong device, and the workstation may receive its own ARP replies or the gateway may have an incorrect ARP entry, preventing successful ping.
- ✗
Firewall on the workstation blocking ICMP.
Why it's wrong here
If a firewall were blocking ICMP, the ping to the gateway would fail, but other workstations can ping the gateway, indicating the gateway is reachable. However, the workstation can ping itself, so a local firewall blocking outbound ping could be possible, but duplicate IP is more likely given the scenario.
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.
Go deeper
Related to this question
Learn chapter
Default Gateway Configuration
Key term
Media Access Control
Media Access Control (MAC) is a sublayer of the Data Link Layer in networking that controls how devices on the same network share access to the physical medium and uniquely identifies each device with a hardware address.
Key term
TCP
TCP is a connection-oriented transport layer protocol that ensures reliable, ordered, and error-checked delivery of data between applications over IP networks.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 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 220-1101 exam.