The correct answer is the rule that sets the source interface to Outside, source to any, destination to 10.0.0.10, port 80, and action to allow. This is correct because HTTP traffic from the internet arrives on the outside interface, and the firewall rule must explicitly match that ingress interface while specifying the DMZ web server’s IP and port 80 to permit the traffic. On the CISSP exam, this tests your understanding of firewall rule construction and network segmentation, specifically how to craft a permit rule for inbound web traffic to a DMZ without exposing the internal network. A common trap is confusing the source interface with the destination interface or misplacing the web server on the inside interface, which would violate the principle of least privilege. Remember the memory tip: “Outside in, DMZ out”—for HTTP from the internet, the source interface is always the untrusted outside, and the destination is the DMZ host’s IP and port.
CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
A network engineer is configuring a firewall to allow HTTP traffic from the internet to a web server (10.0.0.10). The firewall has three interfaces: outside (ISP), DMZ (10.0.0.0/24), and inside (192.168.1.0/24). The web server is in the DMZ. Which rule is correct?
Option B is correct because HTTP traffic from the internet arrives on the outside interface, and the firewall rule must match the source interface (Outside), allow any source IP, and specify the destination IP (10.0.0.10) and port 80. This permits inbound web traffic to the DMZ web server while maintaining security boundaries.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
Source interface should be outside for incoming traffic.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the concept that firewall rules must specify the correct source interface (ingress zone) rather than just the source IP, leading candidates to mistakenly choose rules that match the destination but not the traffic's entry point.
Detailed technical explanation
How to think about this question
Stateful firewalls track connection state and enforce rules based on the interface where traffic enters; the source interface must match the ingress path. In a three-legged firewall design, the outside interface is typically the only one with a default route to the internet, and rules should explicitly permit only necessary services (e.g., TCP/80) to the DMZ. Misconfiguring the source interface can lead to asymmetric routing or complete traffic drop, as the firewall's security zones are tied to interface assignments.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
Communication and Network Security — This question tests Communication and Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Rule: Source interface Outside, Source any, Destination 10.0.0.10, Port 80, Action allow — Option B is correct because HTTP traffic from the internet arrives on the outside interface, and the firewall rule must match the source interface (Outside), allow any source IP, and specify the destination IP (10.0.0.10) and port 80. This permits inbound web traffic to the DMZ web server while maintaining security boundaries.
What should I do if I get this CISSP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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