156-215.81.20 Security Policy and NAT Practice Question
A security administrator is configuring NAT for a network where internal users need to access external web servers. The administrator wants to hide the internal IP addresses behind a single public IP address. However, some internal users report that they cannot access certain websites that require multiple simultaneous connections from the same source IP. What is the most likely cause of this issue?
⚠ Common exam trap
The trap here is assuming that Hide NAT with a single IP can handle unlimited concurrent connections, when in fact port exhaustion can occur.
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 Hide NAT rule is using a single IP address, and the port pool is exhausted.
Hide NAT using a single public IP relies on port address translation, which has a finite number of ports. When many internal users initiate multiple simultaneous connections, the available ports can be exhausted, leading to failures for new connections. This is a scalability limitation of Hide NAT with a single IP. Using a pool of public IPs or configuring multiple IP addresses can mitigate this issue.
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 Hide NAT rule is using a single IP address, and the port pool is exhausted.
Why this is correct
Hide NAT with a single public IP uses port address translation, which has a limited number of ports (approximately 64,000 per IP). If many internal users make multiple simultaneous connections to the same external service, the available ports can be exhausted, causing connection failures. This is a common issue when using a single IP for Hide NAT.
- ✗
The external web servers are blocking the public IP address due to too many connections.
Why it's wrong here
While external servers might block an IP after excessive connections, the more immediate and common cause in a Hide NAT scenario is local port exhaustion. The question states that some users cannot access certain websites, which is consistent with port exhaustion on the gateway.
- ✗
The Hide NAT rule is not applied to the correct interface.
Why it's wrong here
If the Hide NAT rule were applied to the wrong interface, it would likely affect all outbound traffic, not just certain websites. The symptom of specific websites failing while others work points to a resource limitation rather than an interface misconfiguration.
- ✗
The internal users are using a proxy server that is not configured for NAT.
Why it's wrong here
A proxy server misconfiguration would typically cause broader access issues or affect all users behind the proxy, not just those making multiple simultaneous connections. The scenario does not mention a proxy, and the symptom is specific to multiple connections.
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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