The correct answer is an IP spoofing attack. This is because packets arriving on the external interface with a source IP from the internal 10.0.0.0/8 range indicate the attacker is forging the source address to impersonate a trusted internal host, a classic sign of IP spoofing. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding of how attackers manipulate packet headers to bypass access control lists or exploit trust relationships based on source IP. A common trap is confusing this with a DDoS or replay attack, but the key clue is the internal IP appearing on the wrong interface. Remember the memory tip: if the source IP doesn’t belong on the interface it arrived from, think “spoofed source.”
N10-009 Network Security Practice Question
This N10-009 practice question tests your understanding of network security. 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 is reviewing firewall logs and sees many incoming packets with a source IP address that matches the internal IP range of the company (10.0.0.0/8) arriving on the external interface. Which type of attack is likely being attempted?
Why wrong: A Smurf attack uses ICMP echo requests with a spoofed source IP to broadcast addresses, causing amplification; the source IP is not necessarily internal.
B
IP spoofing attack
Correct. The attacker is spoofing the source IP address to appear as an internal host, trying to bypass firewall rules that may allow internal traffic without inspection.
C
SYN flood
Why wrong: A SYN flood sends many TCP SYN packets without completing handshakes, but the source IPs are often random, not specifically internal.
D
DNS amplification
Why wrong: DNS amplification uses open DNS resolvers to flood a target with large DNS responses; the source IPs are the resolvers, not internal addresses.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
IP spoofing attack
The correct answer is B because packets arriving on the external interface with a source IP address from the internal 10.0.0.0/8 range indicate that the attacker is forging (spoofing) the source address to impersonate an internal host. This is a classic IP spoofing attack, often used to bypass access control lists or to launch further attacks that rely on trust relationships based on source IP.
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.
✗
Smurf attack
Why it's wrong here
A Smurf attack uses ICMP echo requests with a spoofed source IP to broadcast addresses, causing amplification; the source IP is not necessarily internal.
✓
IP spoofing attack
Why this is correct
Correct. The attacker is spoofing the source IP address to appear as an internal host, trying to bypass firewall rules that may allow internal traffic without inspection.
Related concept
Read the scenario before looking for a memorised answer.
✗
SYN flood
Why it's wrong here
A SYN flood sends many TCP SYN packets without completing handshakes, but the source IPs are often random, not specifically internal.
✗
DNS amplification
Why it's wrong here
DNS amplification uses open DNS resolvers to flood a target with large DNS responses; the source IPs are the resolvers, not internal addresses.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the distinction between IP spoofing and other attacks by focusing on the specific packet characteristic (source IP matching internal range on an external interface) rather than the attack's goal or volume, leading candidates to confuse it with a Smurf or SYN flood attack.
Detailed technical explanation
How to think about this question
IP spoofing exploits the fact that IP routing is destination-based and does not inherently validate the source address. In the context of RFC 2827 (BCP 38), ingress filtering at the network edge should drop packets with source addresses that do not belong to the internal network, but if missing, an attacker can send packets that appear to originate from the internal 10.0.0.0/8 range, potentially bypassing ACLs that permit traffic from trusted subnets. Real-world scenarios include using spoofed internal IPs to exploit trust-based services like NFS or RSH, or to hide the true origin of an attack.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: IP spoofing attack — The correct answer is B because packets arriving on the external interface with a source IP address from the internal 10.0.0.0/8 range indicate that the attacker is forging (spoofing) the source address to impersonate an internal host. This is a classic IP spoofing attack, often used to bypass access control lists or to launch further attacks that rely on trust relationships based on source IP.
What should I do if I get this N10-009 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.
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 →
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. A network security analyst notices that the firewall is logging traffic on the external interface that has a source IP address of 10.0.1.5, which is within the internal network range. This is most likely the result of which type of attack?
medium
A.DNS poisoning
✓ B.IP spoofing
C.ARP poisoning
D.VLAN hopping
Why B: The firewall is logging traffic on its external interface with a source IP address from the internal RFC 1918 range (10.0.1.5). This indicates the source IP has been forged, because private IP addresses should never appear as source addresses on a public-facing interface. This is the classic signature of an IP spoofing attack, where the attacker modifies the source IP in the packet header to impersonate an internal host.
Last reviewed: Jun 30, 2026
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