- A
Querying public BGP route databases and looking up the organization's autonomous system (AS) number
BGP databases contain announced IP prefixes for AS numbers. By finding the target's ASN, the tester can see all public IP ranges associated with the organization.
- B
Performing a DNS zone transfer against the target's authoritative DNS servers
Why wrong: DNS zone transfers are active reconnaissance and are usually disabled on public DNS servers. Even if successful, they reveal hostnames and IPs, but not necessarily internal ranges.
- C
Using Shodan to search for devices from the target organization
Why wrong: Shodan indexes internet-facing devices; internal ranges are typically not shown. This technique is useful for external exposure but not for enumerating internal IP ranges.
- D
Sending ARP requests on the local network segment to discover hosts
Why wrong: ARP scanning is an active technique that requires being on the internal network. It is not passive reconnaissance.
Quick Answer
The answer is querying public BGP route databases using the organization’s autonomous system (AS) number. This technique is effective because BGP route databases like RADB or ARIN store all IP prefixes that an organization announces to the internet, and by passively looking up the target’s ASN, you can map their public-facing IP ranges without sending a single packet to their network. On the CompTIA PenTest+ PT0-002 exam, this question tests your understanding of passive reconnaissance versus active scanning—a common trap is confusing this with active tools like traceroute or whois lookups that still involve direct queries. The key distinction is that BGP databases are third-party repositories of routing data, making the discovery entirely passive. A helpful memory tip: “BGP is the internet’s phonebook—look up the ASN, find the numbers, never dial the target.”
PT0-002 Practice Question: Information Gathering and Vulnerability Scanning
This PT0-002 practice question tests your understanding of information gathering and vulnerability 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 penetration tester is performing passive reconnaissance on a target organization. The tester wants to identify internal IP address ranges used by the organization without interacting directly with their network. Which of the following techniques would be most effective for this purpose?
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
Querying public BGP route databases and looking up the organization's autonomous system (AS) number
Querying public BGP route databases (e.g., RADB, ARIN) using the organization's AS number allows a tester to retrieve IP prefixes announced by the target. This is passive reconnaissance because it uses publicly available routing data without sending any packets to the target's network, making it ideal for identifying internal IP ranges from an external perspective.
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.
- ✓
Querying public BGP route databases and looking up the organization's autonomous system (AS) number
Why this is correct
BGP databases contain announced IP prefixes for AS numbers. By finding the target's ASN, the tester can see all public IP ranges associated with the organization.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Performing a DNS zone transfer against the target's authoritative DNS servers
- ✗
Using Shodan to search for devices from the target organization
Why it's wrong here
Shodan indexes internet-facing devices; internal ranges are typically not shown. This technique is useful for external exposure but not for enumerating internal IP ranges.
- ✗
Sending ARP requests on the local network segment to discover hosts
Why it's wrong here
ARP scanning is an active technique that requires being on the internal network. It is not passive reconnaissance.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the distinction between passive and active reconnaissance, and the trap here is that candidates confuse DNS zone transfers (which are active and often restricted) with passive DNS lookups, or assume Shodan is always passive when it actually relies on active scanning data from the past.
Trap categories for this question
Command / output trap
Shodan indexes internet-facing devices; internal ranges are typically not shown. This technique is useful for external exposure but not for enumerating internal IP ranges.
Detailed technical explanation
How to think about this question
BGP route databases store AS-to-prefix mappings from global routing tables; by querying the target's ASN via whois or tools like bgp.he.net, a tester can obtain all IP blocks the organization advertises. This technique is effective because organizations often announce their entire IP space to the internet, including ranges used internally, and the data is publicly available without triggering any alerts. A subtle behavior is that some organizations may use private ASNs or non-announced ranges, but public BGP data still covers the majority of routable internal subnets.
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 security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this PT0-002 question test?
Information Gathering and Vulnerability Scanning — This question tests Information Gathering and Vulnerability Scanning — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Querying public BGP route databases and looking up the organization's autonomous system (AS) number — Querying public BGP route databases (e.g., RADB, ARIN) using the organization's AS number allows a tester to retrieve IP prefixes announced by the target. This is passive reconnaissance because it uses publicly available routing data without sending any packets to the target's network, making it ideal for identifying internal IP ranges from an external perspective.
What should I do if I get this PT0-002 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: Jun 30, 2026
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