- A
The Azure Firewall in East US is not configured to allow traffic from West US to AAD DS.
Why wrong: AAD DS traffic does not go through the firewall; it's intra-region.
- B
The VNet peering between East and West US hubs is not properly configured with 'Allow forwarded traffic' enabled.
Why wrong: This would affect cross-region traffic, but AAD DS is local.
- C
The ExpressRoute circuit is down, causing traffic to be routed over the internet.
Why wrong: ExpressRoute is for on-premises, not for AAD DS authentication.
- D
The route table for the West US application spoke has a default route (0.0.0.0/0) pointing to the NVA, causing traffic to AAD DS to be sent across regions.
This forces traffic to the NVA, which may route it out of region or cause asymmetric routing.
Quick Answer
The answer is a misconfigured default route in the West US application spoke’s route table pointing to the network virtual appliance (NVA). This forces all outbound traffic, including authentication requests to the local Azure AD Domain Services (AAD DS) in the same region’s shared services spoke, to traverse the NVA and potentially cross regions via the hub peering, rather than staying within the local VNet. AAD DS requires low-latency, direct connectivity within the same region to function properly, so this routing misconfiguration breaks authentication. On the Microsoft Cybersecurity Architect exam, this scenario tests your understanding of how forced tunneling and custom routes can disrupt hub-spoke topology AAD DS authentication routing, often appearing as a trap where candidates overlook that a default route overrides local VNet peering. The key insight is that a 0.0.0.0/0 route to an NVA or firewall will hijack all traffic, even to local services, unless you add a more specific route for the AAD DS subnet. Memory tip: “Default route to NVA? Local AAD DS goes astray.”
SC-100 Design security for infrastructure Practice Question
This SC-100 practice question tests your understanding of design security 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.
A large enterprise is designing a secure infrastructure for a multi-region application deployment. They have a hub-spoke topology in two Azure regions (East US and West US) with VNet peering between the hubs. Each region has a shared services spoke containing Azure AD Domain Services (AAD DS) and management jump boxes. Application spokes in each region host VMs that need to authenticate to the local AAD DS. The company mandates that all traffic between regions must traverse a network virtual appliance (NVA) for inspection, except for Azure management traffic. They also require that all outbound internet traffic from application VMs goes through a single Azure Firewall in the East US hub. They have deployed ExpressRoute to on-premises. Currently, application VMs in West US cannot authenticate to the local AAD DS. 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.
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
The route table for the West US application spoke has a default route (0.0.0.0/0) pointing to the NVA, causing traffic to AAD DS to be sent across regions.
The most likely cause is that the route table for the West US application spoke has a default route (0.0.0.0/0) pointing to the NVA. This forces all outbound traffic, including traffic destined for the local AAD DS (which resides in the same region's shared services spoke), to be routed through the NVA and potentially across regions via the hub peering, rather than staying within the local VNet. Since AAD DS requires low-latency, direct connectivity within the same region, this misrouting prevents authentication.
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.
- ✗
The Azure Firewall in East US is not configured to allow traffic from West US to AAD DS.
Why it's wrong here
AAD DS traffic does not go through the firewall; it's intra-region.
- ✗
The VNet peering between East and West US hubs is not properly configured with 'Allow forwarded traffic' enabled.
Why it's wrong here
This would affect cross-region traffic, but AAD DS is local.
- ✗
The ExpressRoute circuit is down, causing traffic to be routed over the internet.
Why it's wrong here
ExpressRoute is for on-premises, not for AAD DS authentication.
- ✓
The route table for the West US application spoke has a default route (0.0.0.0/0) pointing to the NVA, causing traffic to AAD DS to be sent across regions.
Why this is correct
This forces traffic to the NVA, which may route it out of region or cause asymmetric routing.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the Azure Firewall or VNet peering is misconfigured, but the real issue is a routing override that forces local traffic through a non-local path, a classic 'asymmetric routing' or 'forced tunneling' pitfall in multi-region hub-spoke topologies.
Detailed technical explanation
How to think about this question
Azure AD Domain Services publishes a service endpoint IP within the same region's virtual network, and VMs authenticate via LDAP or Kerberos, which require direct network connectivity without hair-pinning through a firewall or NVA. When a default route (0.0.0.0/0) points to an NVA, Azure's system routes will send even local traffic to the NVA, which may then forward it across the hub peering to the other region, breaking the required low-latency path. This is a common misconfiguration in hub-spoke designs where forced tunneling is applied too broadly.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this SC-100 question test?
Design security for infrastructure — This question tests Design security for infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The route table for the West US application spoke has a default route (0.0.0.0/0) pointing to the NVA, causing traffic to AAD DS to be sent across regions. — The most likely cause is that the route table for the West US application spoke has a default route (0.0.0.0/0) pointing to the NVA. This forces all outbound traffic, including traffic destined for the local AAD DS (which resides in the same region's shared services spoke), to be routed through the NVA and potentially across regions via the hub peering, rather than staying within the local VNet. Since AAD DS requires low-latency, direct connectivity within the same region, this misrouting prevents authentication.
What should I do if I get this SC-100 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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.
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