CISSP Communication and Network Security Practice Question
A network engineer is configuring an IPsec VPN in tunnel mode. Which IPsec protocol provides both authentication and encryption of the entire IP packet?
⚠ Common exam trap
A common pitfall is thinking AH (Authentication Header) provides encryption because it offers authentication, but AH only ensures integrity and origin authentication—it does not encrypt. For both authentication and encryption, ESP must be used.
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
✓
ESP (Encapsulating Security Payload)
ESP (Encapsulating Security Payload) in tunnel mode provides both authentication and encryption for the entire original IP packet, including the original header and payload. It encapsulates the packet with a new IP header and ESP trailer, ensuring confidentiality via encryption and integrity via authentication. This makes it the correct choice for a VPN requiring both security 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.
- ✓
ESP (Encapsulating Security Payload)
Why this is correct
ESP encapsulates the original IP packet and applies both confidentiality and integrity, encrypting the payload and authenticating it. AH only authenticates and cannot encrypt, so ESP is the protocol satisfying the requirement for authentication plus encryption of the entire packet.
- ✗
IKE (Internet Key Exchange)
Why it's wrong here
IKE handles key exchange, not packet protection.
- ✗
ISAKMP
Why it's wrong here
ISAKMP defines the framework for negotiating security associations and key exchange; it carries no packet encryption itself, so it cannot encrypt the entire IP packet. It is correct for setting up the tunnel, whereas ESP performs the authentication and encryption in tunnel mode.
- ✗
AH (Authentication Header)
Why it's wrong here
AH provides authentication and integrity only; it does not encrypt payloads, so it cannot satisfy the requirement for encryption of the entire IP packet. It is tempting because AH does authenticate the whole packet including the outer IP header, making it the right choice when integrity protection without confidentiality is required.
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
Go deeper
Related to this question
Learn chapter
Secure Network Architecture and Components
Key term
Authentication
Authentication is the process of verifying that someone or something is who or what it claims to be before granting access to a system or resource.
Key term
IPsec
IPsec is a suite of protocols used to secure Internet Protocol (IP) communications by encrypting and authenticating each IP packet in a data stream.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CISSP practice question is part of Courseiva's free ISC2 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 CISSP exam.