N10-009 Question 324
Single answerA network administrator is troubleshooting reports that users in a branch office can reach internet websites by IP address, but they cannot consistently reach internal applications by hostname. The issue appears intermittent and affects multiple VLANs. The administrator wants to verify whether the problem is related to DNS resolution rather than routing or basic IP connectivity, and wants the quickest command-line test from a client workstation to confirm this. 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 clue is that users can reach destinations by IP address but not reliably by hostname. That strongly indicates a DNS-related issue rather than a basic routing or connectivity problem. Best practice is to start with the most targeted tool that tests the suspected service directly. nslookup is commonly used on Network+ objectives to verify DNS resolution, confirm which DNS server is answering, and compare expected versus actual records. By contrast, tracert is for route analysis, netstat is for connection and socket information, and arp is for local IP-to-MAC mapping. Modern environments may also use dig for DNS testing on many UNIX/Linux systems, but from the listed choices, nslookup is the most appropriate first step. This aligns with standard vendor documentation and troubleshooting methodology: verify name resolution separately from connectivity when IP reachability is already confirmed.
- A. Correct.
Correct. nslookup is designed to query DNS servers and verify name resolution results from a client. In this scenario, users can reach resources by IP address, which suggests IP connectivity is working, but hostname-based access is failing intermittently. Using nslookup allows the administrator to directly test whether DNS records are being returned correctly and whether the configured DNS server is responding as expected.
- B. Incorrect.
Incorrect. tracert (or traceroute on non-Windows systems) helps identify the path packets take through the network and where latency or routing failures may occur. It is useful for diagnosing routing problems, but it does not directly test DNS record resolution in the way required by this scenario.
- C. Incorrect.
Incorrect. netstat displays information about active connections, listening ports, routing tables, and protocol statistics depending on the options used. While it can help identify whether a host has established sessions or whether certain ports are in use, it is not the best first tool to validate whether DNS name resolution is the cause of hostname access failures.
- D. Incorrect.
Incorrect. arp displays or manages the local ARP cache, which maps IPv4 addresses to MAC addresses on the local subnet. ARP is relevant to Layer 2/Layer 3 neighbor resolution, not DNS hostname resolution. Someone might choose this if they confuse hostname lookup issues with local address resolution problems.