Quick Answer
The correct command is `nc -v <target> 25`. This works because the `-v` (verbose) flag forces Netcat to display connection details, including the service banner that the SMTP server sends immediately upon TCP handshake completion—typically a line like "220 smtp.example.com ESMTP". On the Certified Ethical Hacker CEH exam, this tests your understanding of banner grabbing as a reconnaissance technique; a common trap is omitting `-v` and assuming Netcat will show the banner by default, but without verbose mode the output is silent. Remember that SMTP port 25 always sends its banner unprompted, so the key is ensuring Netcat prints it. Memory tip: think "Verbose reveals the verse"—the `-v` flag is what makes the server's greeting visible.
This CEH practice question tests your understanding of footprinting, reconnaissance and scanning. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
During a security assessment, a tester uses Netcat to connect to a target's SMTP port and receive the service banner. Which command would achieve this?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
nc -z <target> 25
Why wrong: -z performs a zero I/O scan, which does not read banners.
nc -l -p 25
Why wrong: This puts Netcat in listening mode on port 25, not connecting to a target.
nc -u <target> 25
Why wrong: -u is for UDP, but SMTP uses TCP.
nc -v <target> 25
This connects to the target on port 25 and displays the banner.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
nc -v <target> 25
Option D is correct because the `-v` (verbose) flag in Netcat causes it to display connection details, including the service banner received from the target. When connecting to SMTP port 25, the server typically sends a banner (e.g., "220 smtp.example.com ESMTP") immediately upon TCP connection establishment, and `nc -v <target> 25` prints that banner to stdout, allowing the tester to read it.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
nc -z <target> 25
Why it's wrong here
-z performs a zero I/O scan, which does not read banners.
nc -l -p 25
Why it's wrong here
This puts Netcat in listening mode on port 25, not connecting to a target.
nc -u <target> 25
nc -v <target> 25
Why this is correct
This connects to the target on port 25 and displays the banner.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often confuse the `-v` flag with `-z` or `-u`, mistakenly thinking that a simple connection (without verbose) or a UDP scan would reveal the banner, but only `-v` ensures the received data is printed to the terminal.
Detailed technical explanation
SMTP banners are sent as part of the greeting handshake defined in RFC 5321, where the server sends a 220 response immediately after TCP connection establishment. The `-v` flag in Netcat enables verbose output, which includes the data received from the remote side; without it, `nc` would still receive the banner but not display it unless the user explicitly reads from the socket (e.g., with a separate `read`). In real-world assessments, banner grabbing via `nc -v` is a common first step to identify SMTP server software and version for vulnerability mapping.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the CEH 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.
What to study next
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Footprinting, Reconnaissance and Scanning — This question tests Footprinting, Reconnaissance and Scanning — Read the scenario before looking for a memorised answer..
The correct answer is: nc -v <target> 25 — Option D is correct because the `-v` (verbose) flag in Netcat causes it to display connection details, including the service banner received from the target. When connecting to SMTP port 25, the server typically sends a banner (e.g., "220 smtp.example.com ESMTP") immediately upon TCP connection establishment, and `nc -v <target> 25` prints that banner to stdout, allowing the tester to read it.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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