The answer is tunnel mode, because it encrypts the entire IP packet, including the original header, and then wraps it in a new IP header for routing between VPN gateways. This is essential for site-to-site VPNs where the original source and destination addresses must be concealed, as the new header allows the encrypted packet to traverse the public internet securely. On the CompTIA Network+ N10-009 exam, this concept tests your understanding of IPsec modes in the context of VPN configurations—tunnel mode is always used for gateway-to-gateway connections, while transport mode only encrypts the payload, leaving the original header exposed. A common trap is confusing the two: remember that tunnel mode builds a new tunnel around the whole packet, whereas transport mode rides inside the existing header. For a quick memory tip, think “Tunnel = Totally new wrapper,” meaning the entire original packet gets sealed inside a fresh IP envelope.
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 engineer is configuring a site-to-site VPN between two branch offices. The requirement is to encrypt all traffic between the two networks using IPsec. Which IPsec mode should be used to encrypt the entire IP packet including the original header?
Why wrong: Transport mode encrypts only the payload, not the original IP header, so it is not suitable for site-to-site VPNs where the entire packet must be hidden.
B
Tunnel mode
Tunnel mode encapsulates the entire original IP packet with a new header, encrypting everything. This is the standard mode for site-to-site IPsec VPNs.
C
AH only
Why wrong: AH provides authentication but no encryption, so it does not meet the encryption requirement.
D
ESP only
Why wrong: ESP provides encryption but can be used in either transport or tunnel mode. The question asks which mode encrypts the entire packet including the header; that is tunnel mode, not just using ESP.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Tunnel mode
Tunnel mode is the correct choice because it encrypts the entire original IP packet, including the original header, and then encapsulates it within a new IP header. This is required for site-to-site VPNs where the original source and destination IP addresses must be hidden or protected, and the new header is used for routing between the two VPN gateways.
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.
✗
Transport mode
Why it's wrong here
Transport mode encrypts only the payload, not the original IP header, so it is not suitable for site-to-site VPNs where the entire packet must be hidden.
✓
Tunnel mode
Why this is correct
Tunnel mode encapsulates the entire original IP packet with a new header, encrypting everything. This is the standard mode for site-to-site IPsec VPNs.
Related concept
Read the scenario before looking for a memorised answer.
✗
AH only
Why it's wrong here
AH provides authentication but no encryption, so it does not meet the encryption requirement.
✗
ESP only
Why it's wrong here
ESP provides encryption but can be used in either transport or tunnel mode. The question asks which mode encrypts the entire packet including the header; that is tunnel mode, not just using ESP.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between Transport and Tunnel modes by asking which mode encrypts the entire packet, and candidates mistakenly choose Transport mode because they confuse 'encrypting the payload' with 'encrypting the entire packet', or they think AH provides encryption.
Detailed technical explanation
How to think about this question
In IPsec Tunnel mode, the entire original IP datagram (header and payload) is encrypted and encapsulated within a new IP packet with a new IP header, typically with ESP providing encryption and optional authentication. The new IP header contains the addresses of the VPN gateways, allowing the original packet to traverse the public internet securely. This mode is defined in RFC 4301 and is the standard for site-to-site VPNs, whereas Transport mode is more commonly used for end-to-end communications between hosts, such as in a remote access VPN scenario.
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: Tunnel mode — Tunnel mode is the correct choice because it encrypts the entire original IP packet, including the original header, and then encapsulates it within a new IP header. This is required for site-to-site VPNs where the original source and destination IP addresses must be hidden or protected, and the new header is used for routing between the two VPN gateways.
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.
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Question Discussion
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