220-1102 Question 257
Single answerdigA Linux workstation can browse the internet by IP address, but users report that websites fail when they enter hostnames such as www.example.com. The technician suspects a DNS issue and wants to verify whether the configured DNS server can resolve the hostname. Which command would BEST test DNS resolution directly against a specific DNS server using dig?
- A
dig @192.168.1.53 www.example.com
- B
dig www.example.com /flushdns
- C
dig -release www.example.com 192.168.1.53
- D
dig www.example.com && ping 192.168.1.53
Show answer and explanation
Correct answer: A
Explanation
The best answer is "dig @192.168.1.53 www.example.com" because dig is commonly used on Linux and other UNIX-like systems to troubleshoot DNS. Specifying a server with @server lets the technician bypass the system's normal resolver path and query the suspected DNS server directly. This is a standard best practice when isolating DNS problems: first confirm network connectivity, then test name resolution against the intended DNS server. The dig manual documents the @server syntax for selecting the name server to query. In an A+ Core 2 troubleshooting scenario, this helps distinguish between a local resolver configuration issue, a DNS server failure, or a broader name resolution problem.
- A. Correct.
Correct. In dig, the @ symbol is used to specify the DNS server to query directly. Running "dig @192.168.1.53 www.example.com" sends a DNS lookup for the hostname to that server, which is exactly what the technician needs when validating whether a particular DNS server can resolve a name.
- B. Incorrect.
Incorrect. "/flushdns" is associated with Windows ipconfig, not dig. A candidate might choose this if they confuse DNS cache-clearing tools with DNS query tools. dig does not use this syntax and this command would not test name resolution against a DNS server.
- C. Incorrect.
Incorrect. "-release" is also associated with Windows ipconfig for releasing a DHCP lease, not with dig. This option mixes unrelated networking functions with DNS lookup syntax. It would not perform a valid DNS query.
- D. Incorrect.
Incorrect. This command does run a dig query followed by a ping to the DNS server, but it does not direct dig to use 192.168.1.53 as the DNS server. Instead, dig would use the system's default resolver configuration. A candidate might choose this because pinging the DNS server seems useful, but it does not answer the core question of whether that specific server can resolve the hostname.