- A
Run netstat on the server to see if the application is listening on the correct port.
Netstat shows listening ports and can confirm if the application is bound to the expected port.
- B
Ping the server from a client to test network connectivity.
Why wrong: Ping tests ICMP, not TCP port availability.
- C
Use nslookup to verify the server's hostname resolves correctly.
Why wrong: Nslookup is for DNS resolution, not port testing.
- D
Check the DHCP lease to ensure the client has a valid IP address.
Why wrong: DHCP is for IP assignment, not port connectivity.
Question 107 of 1,020
Using Netstat to Verify Listening Ports for CompTIA A+ 220-1201
This 220-1201 practice question tests your understanding of tcp & udp ports. 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 company deploys a new internal application that uses a custom TCP port. The application fails to connect from client workstations. A technician verifies that the server is running and the firewall allows outbound traffic. Which step should the technician take next to identify the port issue?
Quick Answer
The correct step is to run netstat on the server to verify that the application is listening on the expected TCP port. Netstat displays active network connections and listening ports, allowing the technician to confirm whether the service has bound to the correct port number and is ready to accept incoming connections. This directly addresses the failure scenario because the server may be running but not actually listening on the custom port due to a misconfiguration or service error. On the CompTIA A+ Core 1 220-1201 exam, questions like this test your ability to differentiate between connectivity tools: telnet tests reachability to an open port, ping checks ICMP (not TCP), and DNS resolves hostnames—none of which show listening services. A common trap is to jump to telnet first, but netstat must be used on the server side to verify the port is open and listening before testing from a client. Remember the mnemonic: “Netstat shows the state—listening or waiting.”
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Run netstat on the server to see if the application is listening on the correct port.
Option A is correct because the technician needs to verify that the application is actually listening on the expected custom TCP port. Running `netstat -an` on the server will show all listening ports and their states; if the application's port is not listed, the application may be bound to a different port or not started correctly, which is a common cause of connection failures even when the server is running and outbound traffic is allowed.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Run netstat on the server to see if the application is listening on the correct port.
Why this is correct
Netstat shows listening ports and can confirm if the application is bound to the expected port.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Ping the server from a client to test network connectivity.
- ✗
Use nslookup to verify the server's hostname resolves correctly.
Why it's wrong here
Nslookup is for DNS resolution, not port testing.
- ✗
Check the DHCP lease to ensure the client has a valid IP address.
Why it's wrong here
DHCP is for IP assignment, not port connectivity.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Some candidates may think that ping or general network connectivity tests are sufficient to diagnose port-specific issues, but the trap here is that ICMP and TCP operate at different layers, and only a port-level check like netstat can confirm whether the application is listening on the correct TCP port.
Detailed technical explanation
How to think about this question
The `netstat -an` command displays all active TCP and UDP connections and listening ports, including the listening state (LISTEN) for server sockets. In a real-world scenario, an application might be configured to listen on a different port than expected due to a misconfigured config file or a port conflict, and netstat reveals this discrepancy immediately. Additionally, using `netstat -anb` (on Windows) or `netstat -tlnp` (on Linux) can show the process ID or executable name, helping to identify which application is bound to which port.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 220-1201 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Visual reference
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 220-1201 question test?
TCP & UDP Ports — This question tests TCP & UDP Ports — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Run netstat on the server to see if the application is listening on the correct port. — Option A is correct because the technician needs to verify that the application is actually listening on the expected custom TCP port. Running `netstat -an` on the server will show all listening ports and their states; if the application's port is not listed, the application may be bound to a different port or not started correctly, which is a common cause of connection failures even when the server is running and outbound traffic is allowed.
What should I do if I get this 220-1201 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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