Quick Answer
The most effective way to enforce HTTPS traffic only at the network perimeter firewall is to allow TCP port 443 and block TCP port 80. This works because HTTPS operates exclusively over port 443 with TLS encryption, while HTTP uses port 80 in cleartext; by explicitly denying port 80 at the firewall, you prevent any unencrypted web traffic from entering or leaving the network, directly enforcing the protocol restriction without relying on application-layer inspection. On the CISSP exam, this concept tests your understanding of network security controls in the Communication and Network Security domain, where a common trap is to assume that a proxy or deep packet inspection is required—when in fact a simple port-based rule is the most direct and effective perimeter enforcement. Remember the memory tip: “Block 80, allow 443—no HTTP, only HTTPS.”
This CISSP practice question tests your understanding of security operations. 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 company is deploying a new web application and needs to ensure that only HTTPS traffic is allowed. What is the MOST effective way to enforce this at the network perimeter?
Allow TCP port 443 only and block port 80.
Only allows HTTPS, rejecting all HTTP connections.
Configure the firewall to allow TCP port 80 and 443.
Why wrong: Allows both HTTP and HTTPS; does not enforce HTTPS-only.
Use a proxy server to decrypt all traffic.
Why wrong: Does not enforce HTTPS-only; it decrypts but does not block HTTP.
Block TCP port 443.
Why wrong: Blocks HTTPS, the desired protocol.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Allow TCP port 443 only and block port 80.
Blocking TCP port 80 and allowing only TCP port 443 at the network perimeter ensures that only HTTPS traffic can enter or leave the network. This is the most effective method because it directly enforces the protocol restriction at the firewall, preventing any HTTP traffic from bypassing encryption. Allowing both ports would permit unencrypted HTTP, while using a proxy or blocking port 443 would either add unnecessary complexity or deny legitimate HTTPS traffic.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Allow TCP port 443 only and block port 80.
Why this is correct
Only allows HTTPS, rejecting all HTTP connections.
Related concept
Read the scenario before looking for a memorised answer.
Configure the firewall to allow TCP port 80 and 443.
Why it's wrong here
Allows both HTTP and HTTPS; does not enforce HTTPS-only.
Use a proxy server to decrypt all traffic.
Why it's wrong here
Does not enforce HTTPS-only; it decrypts but does not block HTTP.
Block TCP port 443.
Why it's wrong here
Blocks HTTPS, the desired protocol.
Common exam traps
The trap here is that candidates may think allowing both ports 80 and 443 is acceptable for flexibility, but the question explicitly requires only HTTPS, so blocking port 80 is essential to enforce encryption at the perimeter.
Detailed technical explanation
HTTPS uses TLS over TCP port 443, while HTTP uses TCP port 80. Firewall rules based on destination port numbers are a stateless or stateful filtering mechanism that operates at Layers 3 and 4 of the OSI model. In a real-world scenario, an attacker could attempt to tunnel other protocols over port 443, but for basic enforcement of HTTPS-only traffic, port-based ACLs are the simplest and most effective perimeter control, as defined in RFC 2818 for HTTP over TLS.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
What to study next
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FAQ
Security Operations — This question tests Security Operations — Read the scenario before looking for a memorised answer..
The correct answer is: Allow TCP port 443 only and block port 80. — Blocking TCP port 80 and allowing only TCP port 443 at the network perimeter ensures that only HTTPS traffic can enter or leave the network. This is the most effective method because it directly enforces the protocol restriction at the firewall, preventing any HTTP traffic from bypassing encryption. Allowing both ports would permit unencrypted HTTP, while using a proxy or blocking port 443 would either add unnecessary complexity or deny legitimate HTTPS traffic.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This CISSP practice question is part of Courseiva's free ISC2 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 CISSP exam.
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