CISSP Communication and Network Security Practice Question
In IPsec, which protocol provides both authentication and encryption for the packet payload, but does not encrypt the IP header?
⚠ Common exam trap
A common pitfall in CISSP is confusing ESP and AH: ESP provides encryption and optionally authentication, while AH provides authentication only. ESP encrypts the payload but leaves the IP header unencrypted; AH authenticates the entire packet (including header) but provides no encryption. Candidates often mistakenly choose AH when encryption is required.
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) provides both authentication and encryption for the packet payload, while leaving the IP header unencrypted. This allows intermediate routers to process the packet normally, as the header remains in plaintext, but the payload is protected for confidentiality and integrity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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IKE (Internet Key Exchange)
Why it's wrong here
IKE (Internet Key Exchange) is a crucial component of the IPSec suite, primarily responsible for establishing Security Associations (SAs) and negotiating cryptographic keys between peers. It operates in two phases to authenticate the communicating parties and set up the necessary parameters for secure communication. However, IKE itself does not encrypt or authenticate the actual user data traffic; it merely sets the stage for data protection protocols.
- ✗
ISAKMP (Internet Security Association and Key Management Protocol)
Why it's wrong here
ISAKMP (Internet Security Association and Key Management Protocol) provides the architectural framework and procedures for establishing, modifying, and deleting Security Associations (SAs) in IPSec. It defines the payload types and exchanges used by key management protocols like IKE to negotiate security parameters. While fundamental to IPSec's operation by defining how SAs are managed, ISAKMP is a signaling protocol and does not directly provide data confidentiality or integrity for user traffic.
- ✓
ESP (Encapsulating Security Payload)
Why this is correct
Encapsulating Security Payload (ESP) is an IPSec protocol specifically designed to provide both confidentiality and integrity for data packets. It achieves confidentiality through encryption of the data payload and provides integrity and authentication through a Message Authentication Code (MAC) or digital signature. ESP can operate in either transport mode, encrypting only the payload, or tunnel mode, encrypting the entire original IP packet, making it the correct choice for both services.
- ✗
AH (Authentication Header)
Why it's wrong here
The Authentication Header (AH) protocol within IPSec is specifically designed to provide connectionless data integrity and data origin authentication for IP packets. It calculates a cryptographic checksum over the entire IP packet, including immutable fields of the IP header, to detect any unauthorized modifications. Crucially, AH does not offer any confidentiality services, meaning it explicitly does not encrypt the data payload, making it unsuitable when encryption 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
Security Governance and Principles
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
Encryption
Encryption is the process of converting readable data into a secret code to prevent unauthorized access.
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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.