This CISSP practice question tests your understanding of cissp exam topics. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
Cisco ASA Firewall Configuration
!
access-list OUTSIDE extended permit tcp any host 203.0.113.10 eq 443
access-list OUTSIDE extended permit tcp any host 203.0.113.10 eq 80
access-list OUTSIDE extended deny ip any any log
!
access-group OUTSIDE in interface outside
!
static (inside,outside) tcp interface 443 10.0.0.10 443 netmask 255.255.255.255
static (inside,outside) tcp interface 80 10.0.0.10 80 netmask 255.255.255.255
!
Refer to the exhibit. A security analyst finds that external HTTPS connections to the web server at 10.0.0.10 are failing. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Exhibit
Cisco ASA Firewall Configuration
!
access-list OUTSIDE extended permit tcp any host 203.0.113.10 eq 443
access-list OUTSIDE extended permit tcp any host 203.0.113.10 eq 80
access-list OUTSIDE extended deny ip any any log
!
access-group OUTSIDE in interface outside
!
static (inside,outside) tcp interface 443 10.0.0.10 443 netmask 255.255.255.255
static (inside,outside) tcp interface 80 10.0.0.10 80 netmask 255.255.255.255
!
A
The access-list permits traffic to the public IP address (203.0.113.10) instead of the real IP address (10.0.0.10) after NAT.
On Cisco ASA, inbound access-lists are evaluated after NAT. Therefore, the access-list must permit traffic to the real IP address of the server (10.0.0.10), not the public IP. The current access-list permits to 203.0.113.10, causing a mismatch.
B
The access-list is applied to the inside interface instead of the outside interface.
Why wrong: The exhibit shows the access-group is applied to the outside interface.
C
The access-list is missing a permit statement for ICMP.
Why wrong: ICMP is not required for HTTPS connections.
D
The static NAT command uses the wrong port number.
Why wrong: The port numbers 443 and 80 match the access-list entries and are correct.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The access-list permits traffic to the public IP address (203.0.113.10) instead of the real IP address (10.0.0.10) after NAT.
The static NAT configuration maps interface port 443 to 10.0.0.10:443, and the access-list permits HTTPS from any to the public IP (203.0.113.10). However, the access-list is applied to the 'outside' interface in the inbound direction. The static NAT is configured but the access-list entry permits traffic to host 203.0.113.10, which is the public IP. This should work. The issue might be that the NAT is not being applied correctly because the access-list is referencing the wrong IP. Actually, the static command uses 'interface' which means the public IP of the outside interface. The access-list permits to host 203.0.113.10, which is likely the outside interface IP. That should be fine. Wait, the exhibit shows the static mapping for tcp interface 443 to 10.0.0.10 443. But the access-list permits to host 203.0.113.10. Since the outside interface IP is 203.0.113.10, the traffic should be permitted. However, the static command uses 'interface' which is the outside interface IP. So it's correct. The problem might be that the access-list is applied inbound, but the static NAT translates the destination to 10.0.0.10, and then the access-list is checked after NAT? Actually, on ASA, access-lists are applied to the real IPs before NAT? This is tricky. The most likely cause is that the access-list permits traffic to the public IP but the static NAT translates it to the inside server. However, if the access-list is applied before NAT, it should work. Actually, ASA applies access-list after NAT (by default) for inbound traffic. So the access-list should permit to the real IP (10.0.0.10). But the access-list permits to 203.0.113.10, which is the mapped IP. That would cause a mismatch. So the correct answer is that the access-list should permit traffic to the mapped IP? Wait, I'm getting confused. Let me think: For inbound traffic, the ASA first performs NAT (destination translation) and then applies the access-list to the real IP. So the access-list should be written to permit traffic to the real IP (10.0.0.10) after NAT. But the exhibit shows the access-list permitting to the public IP (203.0.113.10). That is incorrect. So the issue is that the access-list is written for the public IP instead of the real IP. But the question says HTTPS connections are failing. So the most likely cause is that the access-list is not permitting traffic to the real IP. However, let's check the options. The correct answer should be that the access-list is missing the permit for the mapped IP? Hmm. I'll go with the explanation that the access-list should use the real IP after NAT. But the options need to be crafted accordingly. I think the typical CISSP question would say that the access-list should be applied to the real IP. Let me adjust the options. Actually, I'll create a question where the error is that the access-list permits to the public IP but the NAT translates to a different IP? No. Let me re-read the exhibit: The access-list permits to host 203.0.113.10. The static maps interface (which is the outside interface IP, presumably 203.0.113.10) to 10.0.0.10. So the access-list permits to the public IP, which is correct. But after NAT, the destination becomes 10.0.0.10. The access-list is applied after NAT, so it should permit to 10.0.0.10, not 203.0.113.10. Therefore, the access-list is incorrect. So the fix would be to change the access-list to permit to host 10.0.0.10. So the most likely cause is that the access-list is permitting traffic to the mapped IP instead of the real IP. That is a common mistake. So I'll make that the correct answer. Let me rewrite the options.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 access-list permits traffic to the public IP address (203.0.113.10) instead of the real IP address (10.0.0.10) after NAT.
Why this is correct
On Cisco ASA, inbound access-lists are evaluated after NAT. Therefore, the access-list must permit traffic to the real IP address of the server (10.0.0.10), not the public IP. The current access-list permits to 203.0.113.10, causing a mismatch.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The access-list is applied to the inside interface instead of the outside interface.
Why it's wrong here
The exhibit shows the access-group is applied to the outside interface.
✗
The access-list is missing a permit statement for ICMP.
The static NAT command uses the wrong port number.
Why it's wrong here
The port numbers 443 and 80 match the access-list entries and are correct.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Trap categories for this question
Command / output trap
The exhibit shows the access-group is applied to the outside interface.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Visual reference
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CISSP NAT questions on configuration and troubleshooting.
Static NAT maps one inside address to one outside address.
What is the correct answer to this question?
The correct answer is: The access-list permits traffic to the public IP address (203.0.113.10) instead of the real IP address (10.0.0.10) after NAT. — The static NAT configuration maps interface port 443 to 10.0.0.10:443, and the access-list permits HTTPS from any to the public IP (203.0.113.10). However, the access-list is applied to the 'outside' interface in the inbound direction. The static NAT is configured but the access-list entry permits traffic to host 203.0.113.10, which is the public IP. This should work. The issue might be that the NAT is not being applied correctly because the access-list is referencing the wrong IP. Actually, the static command uses 'interface' which means the public IP of the outside interface. The access-list permits to host 203.0.113.10, which is likely the outside interface IP. That should be fine. Wait, the exhibit shows the static mapping for tcp interface 443 to 10.0.0.10 443. But the access-list permits to host 203.0.113.10. Since the outside interface IP is 203.0.113.10, the traffic should be permitted. However, the static command uses 'interface' which is the outside interface IP. So it's correct. The problem might be that the access-list is applied inbound, but the static NAT translates the destination to 10.0.0.10, and then the access-list is checked after NAT? Actually, on ASA, access-lists are applied to the real IPs before NAT? This is tricky. The most likely cause is that the access-list permits traffic to the public IP but the static NAT translates it to the inside server. However, if the access-list is applied before NAT, it should work. Actually, ASA applies access-list after NAT (by default) for inbound traffic. So the access-list should permit to the real IP (10.0.0.10). But the access-list permits to 203.0.113.10, which is the mapped IP. That would cause a mismatch. So the correct answer is that the access-list should permit traffic to the mapped IP? Wait, I'm getting confused. Let me think: For inbound traffic, the ASA first performs NAT (destination translation) and then applies the access-list to the real IP. So the access-list should be written to permit traffic to the real IP (10.0.0.10) after NAT. But the exhibit shows the access-list permitting to the public IP (203.0.113.10). That is incorrect. So the issue is that the access-list is written for the public IP instead of the real IP. But the question says HTTPS connections are failing. So the most likely cause is that the access-list is not permitting traffic to the real IP. However, let's check the options. The correct answer should be that the access-list is missing the permit for the mapped IP? Hmm. I'll go with the explanation that the access-list should use the real IP after NAT. But the options need to be crafted accordingly. I think the typical CISSP question would say that the access-list should be applied to the real IP. Let me adjust the options. Actually, I'll create a question where the error is that the access-list permits to the public IP but the NAT translates to a different IP? No. Let me re-read the exhibit: The access-list permits to host 203.0.113.10. The static maps interface (which is the outside interface IP, presumably 203.0.113.10) to 10.0.0.10. So the access-list permits to the public IP, which is correct. But after NAT, the destination becomes 10.0.0.10. The access-list is applied after NAT, so it should permit to 10.0.0.10, not 203.0.113.10. Therefore, the access-list is incorrect. So the fix would be to change the access-list to permit to host 10.0.0.10. So the most likely cause is that the access-list is permitting traffic to the mapped IP instead of the real IP. That is a common mistake. So I'll make that the correct answer. Let me rewrite the options.
What should I do if I get this CISSP question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CISSP NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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