ANS-C01 Network Management and Operations Practice Question
A network engineer is setting up an AWS Site-to-Site VPN connection. The customer gateway device is behind a NAT device that performs PAT. The VPN tunnel fails to come up. What is the most likely cause?
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
✓
The NAT device is not forwarding UDP 500 and UDP 4500 traffic.
IPsec requires UDP ports 500 and 4500, which must be forwarded through the NAT device. Option A is incorrect because tunnel options such as DPD and encryption algorithms do not need to match exactly for the tunnel to come up. Option B is incorrect because disabling DPD does not prevent tunnel establishment; it only affects detection of peer failure. Option C is incorrect because route propagation does not affect the establishment of the VPN tunnel itself; it affects routing of traffic once the tunnel is up.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The tunnel options (DPD, encryption algorithms) must match exactly.
Why it's wrong here
They should match, but NAT is the more likely issue.
- ✗
Dead peer detection (DPD) is disabled.
Why it's wrong here
DPD is for monitoring, not initial tunnel setup.
- ✗
The VPN connection does not have route propagation enabled.
Why it's wrong here
Route propagation is for routing, not tunnel establishment.
- ✓
The NAT device is not forwarding UDP 500 and UDP 4500 traffic.
Why this is correct
IPsec requires these ports for IKE and 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.