The answer is to configure Azure Firewall application rules using FQDN tags to allow traffic to the SaaS endpoint. This is correct because FQDN tags let you specify a fully qualified domain name for a SaaS service, such as Microsoft 365 or Salesforce, and Azure Firewall dynamically resolves that FQDN to the current set of IP addresses, automatically handling frequent IP changes without requiring manual updates. On the Microsoft Cybersecurity Architect exam, this scenario tests your understanding of how to secure outbound traffic when traditional network rules based on static IPs fail—a common trap is confusing FQDN tags with service tags, which only apply to Azure platform services, not external SaaS endpoints. Remember the key distinction: FQDN tags are for external SaaS with dynamic IPs, while service tags are for Azure-internal endpoints. A useful memory tip is “FQDN for foreign SaaS, service tags for Azure’s own paths.”
SC-100 Design security solutions for infrastructure Practice Question
This SC-100 practice question tests your understanding of design security solutions for infrastructure. 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.
Your company uses Azure Firewall to secure outbound traffic from a hub virtual network that contains multiple spoke virtual networks. You need to implement a solution that allows traffic from specific spoke VMs to reach a specific external SaaS endpoint, while blocking all other outbound traffic. The SaaS endpoint uses a dynamic set of IP addresses that change frequently. What should you do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure Azure Firewall application rules using FQDN tags to allow traffic to the SaaS endpoint.
Option B is correct because using Azure Firewall with fully qualified domain name (FQDN) tags allows you to allow traffic to a specific SaaS endpoint by its FQDN, even if IP addresses change dynamically. Option A is wrong because network rules based on IP addresses cannot handle dynamic IP changes. Option C is wrong because service tags are used for Azure services, not external SaaS endpoints. Option D is wrong because Azure Firewall Manager is for managing multiple firewalls, not for solving dynamic IP filtering.
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.
✗
Configure Azure Firewall network rules to allow traffic to the SaaS endpoint's current IP range.
Why it's wrong here
IP ranges change frequently, making this rule ineffective and requiring constant updates.
✗
Deploy Azure Firewall Manager and enable threat intelligence-based filtering.
Why it's wrong here
Threat intelligence filtering blocks known malicious traffic, but does not allow specific SaaS endpoints.
✗
Use Azure Firewall service tags to allow traffic to the SaaS endpoint.
Why it's wrong here
Service tags are for Azure services, not external SaaS endpoints.
✓
Configure Azure Firewall application rules using FQDN tags to allow traffic to the SaaS endpoint.
Why this is correct
FQDN tags allow filtering by domain name, handling dynamic IP changes automatically.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this SC-100 question in full detail.
Identify which SC-100 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Design security solutions for infrastructure — This question tests Design security solutions for infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure Azure Firewall application rules using FQDN tags to allow traffic to the SaaS endpoint. — Option B is correct because using Azure Firewall with fully qualified domain name (FQDN) tags allows you to allow traffic to a specific SaaS endpoint by its FQDN, even if IP addresses change dynamically. Option A is wrong because network rules based on IP addresses cannot handle dynamic IP changes. Option C is wrong because service tags are used for Azure services, not external SaaS endpoints. Option D is wrong because Azure Firewall Manager is for managing multiple firewalls, not for solving dynamic IP filtering.
What should I do if I get this SC-100 question wrong?
Identify which SC-100 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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