How to Allow Only HTTP and HTTPS Traffic to Specific FQDNs Using Azure Firewall Application Rules
Your company uses Azure Firewall to filter outbound traffic from a virtual network. You need to allow only HTTP and HTTPS traffic to specific FQDNs, while blocking all other outbound traffic. Which Azure Firewall rule type should you use?
Quick Answer
The answer is application rules, because Azure Firewall application rules are specifically designed to allow outbound HTTP and HTTPS traffic to fully qualified domain names (FQDNs) while blocking all other outbound traffic. Unlike network rules, which filter by IP addresses and ports, application rules inspect the Host header in HTTP/HTTPS requests, enabling granular control over which FQDNs are permitted. On the Microsoft Cybersecurity Architect exam, this concept tests your understanding of Azure Firewall rule types and their appropriate use cases, often appearing in scenario-based questions where you must distinguish between network, NAT, threat intelligence, and application rules. A common trap is confusing network rules for FQDN filtering, but remember that network rules cannot filter by domain name—only by IP and port. For a quick memory tip: think “app rules for apps” since application rules handle application-layer protocols like HTTP and HTTPS, while network rules handle lower-layer traffic.
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
✓
Application rule
Application rules in Azure Firewall allow filtering outbound traffic based on fully qualified domain names (FQDNs) for HTTP and HTTPS protocols. Option A is wrong because NAT rules only perform destination network address translation, not FQDN filtering. Option C is wrong because threat intelligence rules are used to block traffic from known malicious IP addresses, not for allowing FQDNs. Option D is wrong because network rules filter traffic based on IP addresses, ports, and protocols, not FQDNs.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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NAT rule
Why it's wrong here
NAT rules perform destination network address translation for inbound traffic to published services; they cannot filter outbound FQDN-based HTTP/HTTPS traffic. NAT rules are the correct choice when publishing internal servers to the internet via the firewall's public IP.
- ✓
Application rule
Why this is correct
Application rules filter outbound traffic by FQDN and HTTP/HTTPS protocol, satisfying the requirement to permit only those destinations while denying everything else. Network rules cannot inspect FQDN-based HTTP/HTTPS traffic, as they operate at IP and port level, so they cannot meet the FQDN constraint.
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Threat intelligence rule
Why it's wrong here
Threat intelligence rules act on Microsoft's feed of known malicious IPs and FQDNs, not on your own allow-list of destinations. They cannot express "permit only these FQDNs". Application rules are the correct choice for filtering outbound HTTP/HTTPS by FQDN; threat intelligence mode is for alerting or denying traffic to known-bad endpoints.
- ✗
Network rule
Why it's wrong here
Network rules filter by IP address, port and protocol, and cannot match FQDNs, so they cannot restrict traffic to named destinations. It is tempting because network rules handle HTTP and HTTPS ports, but application rules with FQDN tags are required for domain-based filtering.
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Same concept, more angles
1 more way this is tested on SC-100
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Variation 1. A company uses Azure Firewall to protect their virtual network. They need to allow outbound HTTPS traffic to a specific external website while blocking all other outbound traffic. What should they configure?
easy- ✓ A.Add an Application Rule with the destination FQDN of the website.
- B.Add a Network Rule with the destination IP address and port 443.
- C.Add a Threat Intelligence rule to allow the website's domain.
- D.Add a DNAT Rule to translate the traffic to the website's IP.
Why A: Application Rules filter outbound traffic based on FQDN (e.g., *.contoso.com). Option B is wrong because Network Rules filter based on IP addresses/ports, not FQDNs. Option C is wrong because Threat Intelligence rules block known malicious IPs/FQDNs, not allow specific ones. Option D is wrong because DNAT rules are for inbound traffic.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SC-100 practice question is part of Courseiva's free Microsoft 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 SC-100 exam.