220-1101 Question 443
Single answer5.5 Given a scenario, troubleshoot network issues.A technician is troubleshooting a desktop in a small office. The user reports that they can access shared folders on other PCs in the office, but they cannot open any websites. The technician verifies the link light is on and runs ipconfig, which shows the PC has an IPv4 address of 192.168.10.45, a subnet mask of 255.255.255.0, and no default gateway listed. Other devices on the same network can browse the internet normally. Which of the following is the MOST likely cause of the problem?
- A
The PC has an incorrect DNS server configured
- B
The PC is missing a default gateway configuration
- C
The switch port is operating at the wrong duplex setting
- D
The NIC has failed and must be replaced
Show answer and explanation
Correct answer: B
Explanation
This scenario tests practical network troubleshooting by distinguishing between local connectivity and external connectivity. A host uses its subnet mask to determine whether a destination is on the local network. For local destinations, it communicates directly. For remote destinations, it sends traffic to the default gateway, typically the router interface on the LAN. Since the PC can access shared folders on the same subnet, the NIC, cabling, and local switching are working. The absence of a default gateway in ipconfig is the clearest indicator of the issue. This aligns with standard TCP/IP troubleshooting practices used in Windows environments and documented in Microsoft networking guidance: verify IP address, subnet mask, default gateway, and DNS settings when diagnosing connectivity problems. In an A+ Core 1 context, this is a classic symptom of 'limited to local network access' caused by a missing or incorrect gateway.
- A. Incorrect.
This is incorrect. A DNS problem can prevent access to websites by name, but it would not explain why ipconfig specifically shows no default gateway. Also, a DNS issue would typically still allow testing internet connectivity by IP address if routing were working. The key symptom here is that the PC can reach local resources on the same subnet but cannot reach external networks, which points to a routing issue rather than name resolution.
- B. Correct.
This is correct. The default gateway is required for traffic destined for networks outside the local subnet, such as the internet. Because the PC can still access shared folders on other PCs in the office, local subnet communication is working. The missing default gateway prevents the host from forwarding traffic to external networks, making this the most likely cause.
- C. Incorrect.
This is incorrect. A duplex mismatch can cause slow performance, late collisions, retransmissions, and intermittent connectivity issues, but it would not normally result in a clean symptom where local subnet access works while all off-subnet access fails and ipconfig shows no default gateway. The configuration output directly indicates the more probable root cause.
- D. Incorrect.
This is incorrect. A failed NIC would usually cause broader connectivity issues, such as no link light, inability to obtain an IP address, or inability to communicate even with local devices. In this scenario, the NIC is functioning well enough to communicate on the local network, so replacement is not the most likely next conclusion.