mediumMultiple Select
350-401 Practice Question: Which three statements about NAT traversal and…
Which three statements about NAT traversal and translation are true? (Choose three.)
⚠ Common exam trap
The trap is assuming NAT automatically rewrites application-layer embedded IPs (it does not — that is ALG/fixup territory) and confusing 'ip nat inside destination' (destination IP translation) with MAC translation.
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
✓
IPsec NAT traversal uses UDP encapsulation on port 4500 to allow ESP traffic to pass through a NAT device.
Option A is correct because IPsec NAT-T encapsulates ESP packets inside UDP datagrams sent to port 4500, which lets the NAT device track the flow and allows the encapsulated ESP traffic to traverse the NAT. Option B is correct because the ip nat outside source command performs translation on the source address of packets that arrive on the outside interface, typically used for outside-to-inside translation scenarios. Option C is correct because NAT can apply separate translation rules that modify both the source and destination IP addresses within the same packet, as with twice NAT or policy NAT configurations. Option D is not correct because standard NAT does not automatically translate IP addresses embedded in application-layer payloads; ALGs or application inspection are required for protocols like FTP or SIP. Option E is not correct because the ip nat inside destination command translates the destination IP address of packets entering the inside interface, not the destination MAC address.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
IPsec NAT traversal uses UDP encapsulation on port 4500 to allow ESP traffic to pass through a NAT device.
Why this is correct
NAT-T encapsulates ESP packets inside UDP datagrams on port 4500, allowing them to traverse NAT devices that cannot process ESP or handle PAT for protocol 50. This satisfies the stem's requirement by enabling IPsec traffic through NAT where raw ESP would be dropped.
- ✓
The ip nat outside source command translates the source IP address of packets arriving on the outside interface.
Why this is correct
The ip nat outside source command performs translation on packets entering the outside interface, rewriting their source address before forwarding. This is distinct from ip nat inside source, which translates source addresses of packets on the inside interface, and matches the statement's claim precisely.
- ✓
NAT can translate both source and destination IP addresses in the same packet for different translation rules.
Why this is correct
NAT translation rules operate independently on source and destination fields, so a single packet can have both addresses rewritten when separate rules match. This is distinct from port address translation, which alters port numbers, and confirms the statement's claim about simultaneous address translation.
- ✗
NAT automatically translates IP addresses embedded in application-layer payloads such as FTP or SIP.
Why it's wrong here
NAT operates at Layer 3 and does not inspect or rewrite IP addresses embedded in application payloads; FTP and SIP require ALGs or NAT traversal mechanisms to handle those. It tempts because embedded-address problems are real, but the fix is an application-layer gateway, not NAT itself.
- ✗
The ip nat inside destination command translates the destination MAC address of packets entering the inside interface.
Why it's wrong here
The ip nat inside destination command translates the destination IP address of inside-to-outside packets, not the destination MAC address, which NAT never rewrites. It tempts because destination translation is a genuine NAT function, but it operates on Layer 3 addresses, leaving MAC addresses untouched.
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
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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 Cisco exam blueprint
This 350-401 practice question is part of Courseiva's free Cisco 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 350-401 exam.