156-215.81.20 Security Policy and NAT Practice Question
A security administrator is configuring a NAT rule to hide internal users behind the gateway's external IP when accessing the Internet. The administrator wants to ensure that return traffic is correctly routed back to the internal users. Which configuration setting is essential for this to work?
⚠ Common exam trap
The trap here is thinking that routing alone handles return traffic, when in fact stateful NAT session tracking is the key mechanism.
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 gateway must maintain a NAT session table to map the translated connections back to the original source IPs.
Hide NAT relies on the gateway maintaining a stateful session table that tracks the translation of source IP and port. When return traffic arrives, the gateway uses this table to reverse the translation and forward packets to the correct internal host. Without this stateful mapping, return traffic would not be delivered, and connections would fail.
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 gateway must maintain a NAT session table to map the translated connections back to the original source IPs.
Why this is correct
When Hide NAT is applied, the gateway translates the source IP of outbound packets to its external IP and dynamically assigns a source port. It maintains a session table that records the original source IP and port, the translated IP and port, and the destination. Return traffic matching the translated connection is then un-NATed and forwarded to the correct internal host. This stateful mechanism is essential for Hide NAT to function.
- ✗
The Hide NAT rule must be configured with the 'Translate destination on client side' option.
Why it's wrong here
The 'Translate destination on client side' option is used for destination NAT, not source Hide NAT. For Hide NAT, the source translation is applied, and return traffic is automatically handled by the gateway's stateful inspection. This option is irrelevant for outbound Hide NAT and does not affect return traffic routing.
- ✗
The gateway must have a default route pointing to the Internet.
Why it's wrong here
A default route is necessary for the gateway to forward outbound traffic, but it does not ensure return traffic is routed correctly. Return traffic is handled by the gateway's NAT session table, which tracks the translation. The default route is a basic requirement but not the specific setting that ensures return traffic is un-NATed and forwarded to the internal users.
- ✗
The internal users must have a route to the gateway's external IP.
Why it's wrong here
Internal users typically have a default route pointing to the gateway's internal IP, not the external IP. They do not need a route to the external IP because their traffic is sent to the gateway, which then translates the source IP. The return traffic is handled by the gateway's NAT session table, not by routing on the internal users' part.
Visual reference
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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 Check Point exam blueprint
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