156-215.81.20 VPN Basics Practice Question
Which IKE Phase 2 proposal setting specifically ensures that session keys are not derived from the original long-term keys, protecting past sessions if a key is compromised?
⚠ Common exam trap
Candidates often confuse Phase 1 aggressive/main mode parameters with Phase 2 key derivation properties, forgetting that Perfect Forward Secrecy specifically protects past sessions using unique key exchanges.
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
✓
Perfect Forward Secrecy (PFS)
Perfect Forward Secrecy (PFS) is a property of key-agreement protocols that ensures a session key derived from a set of long-term keys will not be compromised if one of the long-term keys is compromised in the future. By forcing a new Diffie-Hellman exchange during Phase 2, the gateway ensures each session has unique, independent keying material, which is a best practice for high-security environments.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Main Mode
Why it's wrong here
Main Mode is an IKE Phase 1 negotiation mode that provides identity protection by encrypting the exchange. It does not provide forward secrecy for the data traffic SAs, as it only handles the initial authentication and setup of the management tunnel.
- ✓
Perfect Forward Secrecy (PFS)
Why this is correct
PFS triggers a new Diffie-Hellman key exchange during the Quick Mode (Phase 2) negotiation. This ensures that the keys used for encrypting the data traffic are mathematically independent of the initial master keys used for the tunnel, providing the required forward security.
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Aggressive Mode
Why it's wrong here
Aggressive mode is a faster negotiation method that does not protect the identity of the peers as effectively as Main Mode. It does not have any relationship with session key derivation or the forward security of the encrypted data packets.
- ✗
Anti-Replay Protection
Why it's wrong here
Anti-Replay is a security mechanism that prevents attackers from capturing and re-sending encrypted packets to disrupt the session. While it is a critical IPsec feature, it is unrelated to key derivation or the mathematical property of forward secrecy.
Quick reference
Asymmetric Encryption Algorithm Comparison
| Algorithm | Key Exchange | Signatures | Equivalent Security Key | Notes |
|---|---|---|---|---|
| RSA-3072 | Yes | Yes | 128-bit | Widely deployed; slow for bulk data |
| ECDSA P-256 | No | Yes | 128-bit | Fast signatures; standard TLS certs |
| ECDH / ECDHE | Yes | No | 128-bit | Perfect forward secrecy in TLS 1.3 |
| DH / DHE | Yes | No | 128-bit (3072-bit key) | Replaced by ECDHE in modern TLS |
| Ed25519 | No | Yes | ~128-bit | SSH keys, modern PKI |
About these practice questions
This 156-215.81.20 question is part of Courseiva's 210-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Check Point exam blueprint
This 156-215.81.20 practice question is part of Courseiva's free Check Point 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 156-215.81.20 exam.