CAS-004 Security Engineering Practice Question
A security administrator is configuring IPsec VPN between two sites. The data transmitted includes sensitive financial records. The administrator wants to ensure both confidentiality and integrity of the data, and also wants to authenticate the source. Which IPsec protocol and mode should 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 in tunnel mode
ESP (Encapsulating Security Payload) provides both confidentiality and integrity (optionally authentication). AH only provides integrity and authentication but not confidentiality. Transport mode encrypts only the payload, while tunnel mode encrypts the entire IP packet. For site-to-site VPN, tunnel mode is typically used.
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 in tunnel mode
Why this is correct
ESP provides encryption and integrity, and tunnel mode encrypts the entire packet, suitable for site-to-site VPN.
- ✗
AH in tunnel mode
Why it's wrong here
AH does not provide encryption.
- ✗
ESP in transport mode
Why it's wrong here
Transport mode does not encrypt the original IP header, which may expose internal IP addresses.
- ✗
AH in transport mode
Why it's wrong here
AH does not provide encryption, so confidentiality is not ensured.
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CAS-005 practice question is part of Courseiva's free CompTIA 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 CAS-005 exam.