ANS-C01 Network Implementation Practice Question
A company is setting up a Site-to-Site VPN connection to AWS. The customer gateway device is behind a NAT device that performs address translation. Which tunnel option must be enabled to ensure the VPN tunnel establishes correctly?
⚠ Common exam trap
The ANS-C01 exam often tests the misconception that IKEv2 alone solves NAT traversal, but in reality, NAT-T is a separate mechanism that must be enabled or negotiated regardless of the IKE version, and simply using IKEv2 does not automatically enable UDP encapsulation for ESP traffic.
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)
When a customer gateway device is behind a NAT device, the NAT device modifies the IP addresses and potentially the UDP ports in the IPsec packet headers. Standard IPsec (ESP) does not work through NAT because ESP is a Layer 4 protocol with no port numbers. NAT Traversal (NAT-T) solves this by encapsulating IPsec packets inside UDP (typically port 4500), allowing the NAT device to perform address translation without breaking the VPN tunnel.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Perfect Forward Secrecy (PFS)
Why it's wrong here
A security feature for keying, not related to NAT.
- ✓
NAT Traversal (NAT-T)
Why this is correct
Required to encapsulate IPsec in UDP to pass through NAT.
- ✗
Dead Peer Detection (DPD)
Why it's wrong here
Used to detect if the peer is alive, not for NAT.
- ✗
IKEv2
Why it's wrong here
A version of IKE, but not specifically for NAT traversal.
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.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services 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 ANS-C01 exam.