N10-009 Question 322
Single answer5.5 Given a scenario, use the appropriate tool or protocol to solve networking issues.A network administrator receives reports that users in a branch office can reach internal resources by IP address, but they cannot browse external websites by name. The users can successfully ping 8.8.8.8, but attempts to access www.example.com fail. The administrator needs to quickly verify whether the problem is caused by DNS name resolution rather than general IP connectivity. Which tool should the administrator use first?
- A
dig
- B
traceroute
- C
arp
- D
netstat
Show answer and explanation
Correct answer: A
Explanation
The key detail is that users can reach external resources by IP address but not by hostname. That pattern typically indicates a DNS issue rather than a routing, switching, or general internet connectivity problem. A DNS query tool such as dig is the most appropriate first step because it allows the administrator to test whether a hostname resolves and what DNS server is responding. In many environments, nslookup may also be available and used for similar purposes, but dig is a standard DNS troubleshooting tool and is well suited to verify resolution failures. Best practice in network troubleshooting is to isolate the failure domain by confirming whether the issue is at Layer 3 connectivity or application/name resolution. Vendor and standards-based DNS documentation consistently treats direct query tools like dig as primary utilities for validating DNS responses, timeouts, and authoritative or recursive behavior.
- A. Correct.
Correct. dig is a DNS query tool used to test name resolution directly against configured or specified DNS servers. In this scenario, users can reach an external IP address but cannot resolve hostnames, which strongly suggests a DNS issue. Running dig for a known hostname would quickly confirm whether DNS queries are failing or returning incorrect results.
- B. Incorrect.
Incorrect. traceroute is used to identify the path packets take across a network and where latency or routing failures occur. Since the users can already reach an external IP address, basic Layer 3 connectivity exists. traceroute would not be the best first tool to confirm a DNS resolution problem.
- C. Incorrect.
Incorrect. arp displays and manages IP-to-MAC address mappings on the local network segment. This is useful for troubleshooting local subnet communication issues, duplicate IPs, or missing Layer 2 resolution, but it does not test DNS hostname resolution.
- D. Incorrect.
Incorrect. netstat is used to view network connections, listening ports, interface statistics, and routing information depending on the platform and switches used. While it can help identify local connection states, it does not directly test whether a hostname can be resolved by DNS.