220-1101 Networking Practice Question
A technician is troubleshooting a network issue where a user's computer can access local resources but cannot reach any external websites. The technician runs ipconfig and sees that the computer has an IP address of 192.168.1.50, a subnet mask of 255.255.255.0, and a default gateway of 192.168.1.1. The technician can ping 192.168.1.1 successfully but cannot ping 8.8.8.8. Which of the following is the MOST likely cause?
⚠ Common exam trap
The trap here is assuming a DNS issue because the user cannot reach websites, but the technician pinged an IP address, bypassing DNS.
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 router is not performing NAT correctly.
The ability to ping the default gateway but not external IP addresses points to a failure in routing or NAT at the router. The router must perform NAT to translate private IPs to a public IP for internet access. If NAT is misconfigured or disabled, outbound packets may not be translated, and replies cannot return. DNS and subnet mask issues would present differently. The most likely cause is a NAT problem.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The DNS server is misconfigured.
Why it's wrong here
A DNS issue would prevent resolving domain names, but the technician cannot ping 8.8.8.8, which is an IP address. Pinging an IP does not rely on DNS. Therefore, DNS is not the cause of the inability to reach external IPs. The problem lies elsewhere in the network path.
- ✗
The subnet mask is incorrect.
Why it's wrong here
An incorrect subnet mask could cause local communication issues, but the computer can ping the gateway, indicating the subnet mask is likely correct. If the mask were wrong, the computer might not recognize the gateway as local. Since local pings work, the mask is not the problem. Therefore, this option is incorrect.
- ✓
The router is not performing NAT correctly.
Why this is correct
The computer can reach the local gateway but not external IPs. This suggests the router is not translating private IP addresses to a public IP for outbound traffic. Without NAT, external hosts cannot reply. The gateway responds locally, but traffic beyond it fails. Thus, a NAT malfunction is the most likely cause.
- ✗
The default gateway is incorrect.
Why it's wrong here
The technician successfully pinged the default gateway (192.168.1.1), so it is reachable and correctly configured. If the gateway were incorrect, the ping would fail. The issue is beyond the gateway, likely with routing or NAT. Thus, this is not the most likely cause.
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 and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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