156-315.81.20 Advanced VPN Design Practice Question
An administrator is configuring a VPN between a Check Point R81 Security Gateway and a third-party vendor's gateway. The third-party gateway uses a single IP address for both IKE and IPsec traffic, but the Check Point gateway is behind a NAT device that translates its public IP. The administrator wants to ensure the VPN tunnel establishes successfully. Which Check Point feature should be enabled on the Check Point gateway?
⚠ Common exam trap
It's easy for candidates to confuse NAT Traversal with other VPN features like DPD or PFS, which are often configured together but serve different purposes and do not solve NAT-related connectivity issues.
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
✓
NAT Traversal (NAT-T)
NAT Traversal (NAT-T) is required when a VPN gateway is behind a NAT device. It encapsulates IPsec ESP packets in UDP, allowing them to pass through NAT. The other options are unrelated to NAT traversal: DPD monitors peer availability, PFS enhances key security, and Tunnel Sharing optimizes tunnel usage. Only NAT-T addresses the address translation issue that prevents the tunnel from establishing.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
NAT Traversal (NAT-T)
Why this is correct
NAT Traversal (NAT-T) enables IPsec traffic to pass through NAT devices by encapsulating ESP packets in UDP. It allows the Check Point gateway to detect NAT and use UDP port 4500 for IKE and IPsec. This is essential when the gateway is behind a NAT device, as without NAT-T the third-party gateway would not be able to establish the tunnel due to IP address mismatches and ESP protocol limitations.
- ✗
IPsec Dead Peer Detection (DPD)
Why it's wrong here
Dead Peer Detection is used to detect if a VPN peer is no longer responding and to tear down the tunnel. While useful for maintaining tunnel health, it does not solve the NAT traversal problem. DPD operates after the tunnel is established and does not enable the initial IKE negotiation to pass through NAT, so it would not help in this scenario.
- ✗
Perfect Forward Secrecy (PFS)
Why it's wrong here
Perfect Forward Secrecy ensures that a session key derived from a set of long-term keys will not be compromised if one of the long-term keys is compromised. It is a security enhancement for key exchange but does not address NAT traversal. Enabling PFS would not help the tunnel establish through a NAT device, as the fundamental issue is IP address translation, not key compromise.
- ✗
VPN Tunnel Sharing
Why it's wrong here
VPN Tunnel Sharing allows multiple subnets to share a single IPsec tunnel, reducing the number of tunnels. It is an optimization feature and does not affect NAT traversal. In this scenario, the problem is that the Check Point gateway is behind NAT, so tunnel sharing would not resolve the inability to establish the initial IKE negotiation or the ESP traffic through the NAT device.
Visual reference
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.
About these practice questions
This 156-315.81.20 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 156-315.81.20 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 156-315.81.20 exam.