CEH Footprinting, Reconnaissance and Scanning Practice Question
An analyst executes 'nmap -sU -p 161,162 10.0.0.1'. What is the primary purpose of this scan?
⚠ Common exam trap
Many exam-takers confuse `-sU` with TCP scans or assume the command scans all ports, but CEH specifically tests the understanding that `-sU` with `-p 161,162` targets SNMP over UDP, not general port enumeration or attacks.
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
✓
Discover SNMP services running on the target
The `-sU` flag instructs Nmap to perform a UDP scan, and the `-p 161,162` targets the default SNMP ports (UDP 161 for SNMP queries, UDP 162 for SNMP traps). This combination is specifically designed to discover SNMP services running on the target host, as SNMP operates exclusively over UDP. Option C is correct because the command's primary purpose is to probe for SNMP services.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Detect TCP services on the target
Why it's wrong here
The `nmap -sU` command explicitly specifies a UDP scan, which is designed to send UDP packets to target ports and analyze UDP responses. This scan type does not initiate TCP three-way handshakes or interact with TCP-based services in any manner. Therefore, it is fundamentally incapable of detecting TCP services, as it operates on a completely different network protocol layer.
- ✗
Enumerate all open ports on the target
Why it's wrong here
The command `nmap -sU -p 161,162` precisely limits the scope of the scan to only two specific UDP ports: 161 and 162. It does not include any other UDP ports, nor does it involve scanning any TCP ports. Consequently, this command cannot enumerate all open ports on the target system, as it intentionally targets only a minuscule subset of the available port range.
- ✓
Discover SNMP services running on the target
Why this is correct
The command `nmap -sU -p 161,162` specifically instructs Nmap to perform a UDP scan on ports 161 and 162. UDP port 161 is the well-known port for the Simple Network Management Protocol (SNMP) agent, used for management queries, while UDP port 162 is designated for SNMP trap messages, which are asynchronous notifications. Therefore, this scan is precisely configured to identify the presence and responsiveness of SNMP services and their associated trap listeners on the target.
- ✗
Perform a SYN flood attack
Why it's wrong here
Nmap is a network discovery and security auditing tool, not a utility for launching denial-of-service (DoS) attacks like a SYN flood. A SYN flood attack specifically targets TCP services by overwhelming them with a high volume of SYN requests without completing the handshake, aiming to exhaust connection resources. The `-sU` scan, however, sends UDP packets and does not involve TCP SYN packets at all, making it entirely distinct from a SYN flood.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.