GCIH Scanning and Mapping Practice Question
During an incident response investigation, you need to identify all hosts on a subnet that are responding to ARP requests. You have administrative access to a Linux workstation on the same subnet and want to use Nmap to perform this discovery without sending any IP packets. Which Nmap option should you use?
⚠ Common exam trap
The trap here is assuming that any ping scan uses ARP; only -PR explicitly enables ARP ping, while other discovery probes use IP packets.
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
✓
-PR
The -PR option performs ARP ping, which sends ARP requests to discover hosts on the local subnet. ARP operates at layer 2 and does not use IP packets, satisfying the requirement. It is also the most reliable method on a local Ethernet segment because hosts must respond to ARP to communicate. The other options all send IP packets (ICMP, TCP SYN, or TCP ACK) and are not ARP-based.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
-PS
Why it's wrong here
-PS sends TCP SYN packets to specified ports, which are IP packets. It is used for host discovery when ICMP is blocked, but it does not use ARP and violates the requirement to avoid IP packets. It may also trigger firewall logs or IDS alerts, making it less stealthy than ARP.
- ✗
-PE
Why it's wrong here
-PE sends ICMP echo requests, which are IP packets. While ICMP can discover hosts, it is often blocked by firewalls and does not use ARP. In this scenario, the requirement is to avoid IP packets, so -PE is not appropriate. It also may miss hosts that block ICMP.
- ✓
-PR
Why this is correct
The -PR option enables ARP ping, which sends ARP requests to discover hosts on the local Ethernet subnet. It is the default discovery method for local targets and does not send IP packets. This is ideal for identifying live hosts on the same subnet quickly and reliably, as ARP is rarely filtered.
- ✗
-PA
Why it's wrong here
-PA sends TCP ACK packets to specified ports, which are IP packets. Like -PS, it does not use ARP and is not suitable when the goal is to avoid IP traffic. It is typically used to bypass stateless firewalls, but in this local subnet discovery scenario, ARP is the correct choice.
Visual reference
About these practice questions
This GCIH question is part of Courseiva's 322-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official GIAC exam blueprint
This GCIH practice question is part of Courseiva's free GIAC 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 GCIH exam.