Question 1mediummultiple choice
Full question →- A
DHCP
Why wrong: DHCP uses UDP ports 67 and 68.
- B
SNMP
SNMP uses UDP ports 161 (agent) and 162 (manager).
- C
TFTP
Why wrong: TFTP uses UDP port 69.
- D
DNS
Why wrong: DNS uses UDP port 53.
Question 327 of 1,010
Quick Answer
The answer is SNMP (Simple Network Management Protocol) because port 161/udp is its default listening port for receiving management queries like GET and SET requests from SNMP managers, as defined in RFC 1157. When you run an Nmap UDP scan with `-sU` targeting ports 161 and 162, an open result on 161/udp strongly indicates an SNMP agent is active, while port 162/udp is reserved for SNMP traps. On the Certified Ethical Hacker CEH exam, this question tests your ability to map common UDP ports to their services—a frequent topic in the scanning and enumeration domain. A common trap is confusing SNMP with other UDP services like DNS (port 53) or TFTP (port 69), so remember that SNMP is the only major service using port 161. For a quick memory tip: think "SNMP = Simple Network Management Protocol, and 161 is the one for management queries."
CEH Footprinting, Reconnaissance and Scanning Practice Question
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.
A security analyst runs `nmap -sU -p 161,162 10.0.0.1` and receives output showing port 161/udp is open. Which service is MOST likely running on this port?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
✓
SNMP
Port 161/udp is the default port for SNMP (Simple Network Management Protocol) used by SNMP agents to receive management queries (GET, SET) from SNMP managers. The `-sU` flag performs a UDP scan, and the open result on 161/udp strongly indicates an SNMP service is listening, as defined in RFC 1157.
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.
- ✗
DHCP
- ✓
SNMP
- ✗
TFTP
- ✗
DNS
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse SNMP's port 161 with SNMP trap port 162 or misattribute it to other UDP-based services like DHCP or TFTP, but the scan specifically targets 161, which is exclusively SNMP.
Detailed technical explanation
How to think about this question
SNMPv2c and SNMPv3 use port 161 for agent communication and port 162 for trap messages from agents to managers. A common real-world scenario is that an open SNMP port with default community strings (e.g., 'public') can expose extensive system information (interfaces, processes, routing tables) via MIB walks, making it a high-value reconnaissance target.
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 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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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Footprinting, Reconnaissance and Scanning — study guide chapter
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FAQ
Questions learners often ask
What does this CEH question test?
Footprinting, Reconnaissance and Scanning — This question tests Footprinting, Reconnaissance and Scanning — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: SNMP — Port 161/udp is the default port for SNMP (Simple Network Management Protocol) used by SNMP agents to receive management queries (GET, SET) from SNMP managers. The `-sU` flag performs a UDP scan, and the open result on 161/udp strongly indicates an SNMP service is listening, as defined in RFC 1157.
What should I do if I get this CEH question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on CEH
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. During a security assessment, a tester uses `nmap -sU 192.168.1.1`. What type of scan does this command perform?
easy- ✓ A.UDP scan
- B.TCP SYN scan
- C.Ping sweep
- D.OS fingerprinting
Why A: The `-sU` flag in Nmap explicitly instructs the tool to perform a UDP scan. This sends UDP packets to the target ports and analyzes responses (or lack thereof) to determine if a UDP port is open, closed, or filtered. Unlike TCP, UDP is connectionless, so the scan relies on ICMP unreachable messages or lack of response to infer port status.
Last reviewed: Jun 24, 2026
This CEH practice question is part of Courseiva's free EC-Council certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CEH exam.
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