N10-009 Question 323
Single answer5.5 Given a scenario, use the appropriate tool or protocol to solve networking issues.A network administrator is troubleshooting reports that users can reach internal web applications but cannot browse external websites by name. Users can successfully ping 8.8.8.8, but attempts to open www.example.com fail from multiple workstations. The administrator wants to verify whether the issue is caused by DNS name resolution rather than general IP connectivity. Which tool should the administrator use first?
- A
nslookup
- B
tracert
- C
netstat
- D
arp
Show answer and explanation
Correct answer: A
Explanation
The key troubleshooting clue is that users can ping an external IP address such as 8.8.8.8 but cannot access external sites by hostname. That pattern strongly suggests DNS resolution is failing while basic network connectivity remains functional. Best practice in troubleshooting is to isolate the problem domain before investigating deeper layers. Using nslookup first allows the administrator to test whether DNS queries succeed, which DNS server is being used, and whether the expected records are returned. This aligns with standard TCP/IP troubleshooting methodology and common vendor documentation from Microsoft, BIND, and other DNS implementations, all of which recommend validating name resolution separately from connectivity when symptoms point to DNS-specific failures.
- A. Correct.
Correct. nslookup is specifically designed to query DNS servers and verify name resolution. In this scenario, users can reach an external IP address directly, which indicates basic IP connectivity is working. Since access by hostname fails, the most appropriate first step is to use nslookup to test whether DNS records can be resolved and whether the configured DNS server is responding properly.
- B. Incorrect.
Incorrect. tracert helps identify the path packets take to a destination and where routing delays or failures occur. While useful for diagnosing Layer 3 path problems, it does not directly test DNS resolution beyond possibly resolving names during the trace. Because the scenario already shows that IP connectivity to the internet exists, tracert is not the best first tool.
- C. Incorrect.
Incorrect. netstat displays local network connections, listening ports, interface statistics, and routing information depending on the switches used. It is useful for checking whether a host has active sessions or whether a service is listening, but it does not directly validate DNS name lookups for external websites.
- D. Incorrect.
Incorrect. arp is used to view and manage the local Address Resolution Protocol cache, which maps IPv4 addresses to MAC addresses on the local network segment. ARP is relevant to local subnet communication, not internet DNS resolution. A candidate might choose this if confusing name resolution with address resolution, but ARP does not resolve hostnames.