N10-009 Question 308
Single answer5.3 Given a scenario, troubleshoot common issues with network services.Users in a branch office report that they can access internal file shares by IP address, but they cannot open the company intranet by its URL or browse external websites by name. A technician verifies that the WAN link is up, the default gateway is reachable, and Internet access works when using public IP addresses directly. The DHCP scope was recently updated. Which of the following is the MOST likely cause of this issue?
- A
The DHCP scope is distributing incorrect DNS server addresses to clients
- B
The DHCP scope lease time is too short, causing frequent renewals
- C
The default gateway on client systems is configured with the wrong subnet mask
- D
The branch switch has a duplex mismatch on its uplink port
Show answer and explanation
Correct answer: A
Explanation
This scenario tests troubleshooting of common network services, specifically DNS and DHCP interaction. When users can reach services by IP address but not by hostname or URL, the standard troubleshooting conclusion is a DNS problem. The clue that the DHCP scope was recently updated strongly suggests that the DNS server option delivered by DHCP was misconfigured. In IPv4 environments, DHCP commonly supplies DNS server information to clients along with IP address, subnet mask, and default gateway. Best practice is to verify the client configuration with tools such as ipconfig /all, confirm the assigned DNS servers, and then test name resolution with nslookup or dig. This aligns with standard operational guidance for DNS and DHCP troubleshooting documented by Microsoft, ISC DHCP references, and common enterprise networking best practices.
- A. Correct.
Correct. The symptoms point directly to a name resolution problem, not a general connectivity problem. Users can reach resources by IP address, which shows Layer 3 connectivity is functioning, but they cannot reach hosts by URL or hostname. Because the DHCP scope was recently changed, the most likely issue is that clients are receiving the wrong DNS server addresses or unusable DNS settings through DHCP option configuration.
- B. Incorrect.
Incorrect. A short DHCP lease can increase renewal traffic and administrative overhead, but it does not typically cause a consistent inability to resolve internal and external hostnames while IP-based connectivity continues to work. This option is plausible because the issue began after a DHCP change, but the symptom pattern is specifically DNS-related, not lease-duration-related.
- C. Incorrect.
Incorrect. If the default gateway or subnet-related addressing were wrong, clients would usually have broader connectivity problems, such as failing to reach remote networks at all. In this scenario, users can reach internal resources and Internet hosts by IP address, which indicates routing is operational enough for end-to-end communication. A subnet mask issue would not selectively break hostname resolution in this way.
- D. Incorrect.
Incorrect. A duplex mismatch can cause poor performance, late collisions, retransmissions, and intermittent connectivity issues, but it would not specifically prevent hostname resolution while allowing reliable access by IP address. This distractor reflects a common troubleshooting tendency to suspect physical-layer problems, but the scenario isolates the failure to a network service: DNS.