220-1101 Networking Practice Question
A user reports that they cannot access any websites using their web browser, but they can successfully ping external IP addresses such as 8.8.8.8. Other users on the same network are able to browse the internet normally. The technician checks the workstation's IP configuration and finds the following: IP 192.168.1.50, subnet mask 255.255.255.0, default gateway 192.168.1.1, DNS server 192.168.1.1. The technician can ping 192.168.1.1 successfully. Which of the following is the MOST likely cause?
⚠ Common exam trap
Test-takers frequently assume a successful ping to an external IP means the internet is fully functional, overlooking that DNS is a separate service required for name resolution, and that a misconfigured or unresponsive DNS server will break web browsing while leaving IP-level connectivity intact.
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
✓
DNS server not responding or misconfigured
The user can ping external IP addresses (e.g., 8.8.8.8) and the default gateway (192.168.1.1), confirming that IP routing and the gateway are functional. However, they cannot resolve domain names to IP addresses, which is a classic symptom of DNS failure. Since the DNS server is set to 192.168.1.1 (likely the gateway) and other users on the same network can browse normally, the issue is isolated to this workstation's DNS configuration or the DNS service on that server not responding to this specific client.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Incorrect subnet mask
Why it's wrong here
An incorrect subnet mask would cause the host to misclassify the default gateway as being on a remote network, prompting it to send ARP requests for the gateway's IP address instead of its MAC address. Since the technician successfully pinged the default gateway, the mask must be correctly identifying that the gateway is on the local subnet, so this is not the cause.
- ✗
Incorrect default gateway
Why it's wrong here
An incorrectly configured default gateway would either point to an unreachable or non-existent address, making a ping to it fail, or point to a valid but non-routing host that would never forward traffic onward. Because the technician can ping the default gateway, and users are able to reach external IP addresses directly, the gateway is correctly set and functioning as the routing hop, ruling this out.
- ✓
DNS server not responding or misconfigured
Why this is correct
The browser relies on DNS to translate domain names like www.example.com into IP addresses. Since IP-based communication (such as pinging an external IP) works but name resolution fails, the DNS server is either unreachable, not responding, or returning incorrect results; a corrupted DNS cache could also cause this symptom, but the root cause is DNS configuration. This precisely matches the symptom of 'cannot access websites' while general network connectivity remains intact.
- ✗
Firewall blocking web traffic (port 80/443)
Why it's wrong here
A firewall blocking web traffic on ports 80/443 would typically drop or reject HTTP/HTTPS connections while still allowing ICMP pings to external IPs. However, this would affect all users subject to that firewall rule, not just one workstation; since other users on the same network are able to browse successfully, a firewall is an unlikely cause, and the issue is better explained by a client-specific DNS failure.
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
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