The answer is nslookup, the command-line tool used to query DNS servers and verify hostname-to-IP resolution. When a user can reach internal servers by IP address but not by hostname, while other computers on the same subnet work correctly, the problem is almost certainly DNS-related rather than a network connectivity issue. The nslookup command for DNS resolution directly tests whether the computer’s configured DNS server is responding and returning the correct records, isolating the fault to the DNS client or server configuration. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding of basic network troubleshooting—a common trap is to reach for ping or ipconfig first, but those tools won’t reveal a misconfigured or unresponsive DNS server. Remember the memory tip: “Names fail? nslookup to the rescue.”
220-1101 Networking Tools Practice Question
This 220-1201 practice question tests your understanding of networking tools. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A technician is troubleshooting a user's computer that can reach internal servers by IP address but not by hostname. Other computers on the same subnet work correctly. Which tool should the technician use to check the computer's DNS resolution?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
nslookup
The nslookup command queries DNS servers to resolve hostnames to IP addresses. Since internal IPs work but names don't, the issue is likely DNS-related, and nslookup can test whether the computer's DNS server is responding correctly.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Ping
Why it's wrong here
Ping can test connectivity but does not directly diagnose DNS resolution issues.
✗
ipconfig /flushdns
Why it's wrong here
Flushing the DNS cache may help if the cache is corrupted, but it does not test DNS server functionality.
✓
nslookup
Why this is correct
nslookup queries the configured DNS server to resolve a hostname, allowing the technician to see if DNS is working.
Netstat shows active connections and listening ports, not DNS resolution details.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Trap categories for this question
Command / output trap
Netstat shows active connections and listening ports, not DNS resolution details.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 220-1201 question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 220-1201 subnetting questions on CIDR, address ranges, and subnet selection.
Networking Tools — This question tests Networking Tools — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: nslookup — The nslookup command queries DNS servers to resolve hostnames to IP addresses. Since internal IPs work but names don't, the issue is likely DNS-related, and nslookup can test whether the computer's DNS server is responding correctly.
What should I do if I get this 220-1201 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 220-1201 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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