The answer is that the peered VNet does not have 'Allow Azure Bastion Communication' enabled on the peering connection. This setting is essential because Azure Bastion operates as a platform-as-a-service resource that requires explicit permission to route its control and data plane traffic across a VNet peering link to reach the target VM. Without it, the Bastion service cannot establish the secure RDP or SSH session, even though the VM appears in the portal due to read-level visibility. On the Microsoft Cybersecurity Architect exam, this scenario tests your understanding of Azure Bastion's unique peering dependency, which is a common trap—candidates often assume that standard VNet peering alone is sufficient for all cross-VNet connectivity. A helpful memory tip is to think of Bastion as a guarded bridge: the peering is the road, but you still need to open the gate labeled "Allow Azure Bastion Communication" for traffic to cross.
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 company deploys Azure Bastion in a VNet. They want to allow a security engineer to connect to a Windows VM in a peered VNet using Azure Bastion. The engineer can see the VM in the portal but cannot connect. Which configuration is most likely missing?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The peered VNet does not have 'Allow Azure Bastion Communication' enabled on the peering connection.
Azure Bastion requires the 'Allow Azure Bastion Communication' setting to be enabled on the peering connection for the peered VNet. Without this, the Bastion service cannot route traffic to the target VM in the peered VNet, even though the VM is visible in the portal. This setting allows the Bastion's control plane and data plane to communicate across the peering link.
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 Bastion subnet size is /28.
Why it's wrong here
The required size is /26 or larger; a /28 would prevent deployment, not connectivity.
✓
The peered VNet does not have 'Allow Azure Bastion Communication' enabled on the peering connection.
Why this is correct
This setting must be enabled on both sides of the peering for Bastion to connect to VMs in the peered VNet.
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.
✗
The VM's subnet does not have an inbound NSG rule allowing RDP (3389) from the Azure Bastion subnet.
Why it's wrong here
Azure Bastion does not require inbound RDP rules on the VM subnet; it connects via private IP using the Bastion service.
✗
The VM does not have Azure AD authentication enabled.
Why it's wrong here
Azure Bastion supports local username/password or SSH keys; Azure AD authentication is optional.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume NSG rules on the VM subnet are the primary blocker, but Azure Bastion's peering requirement is a distinct, often-missed setting that controls cross-VNet connectivity.
Detailed technical explanation
How to think about this question
Azure Bastion uses a control plane channel over the Azure backbone to establish a secure RDP/SSH session, and the data plane traffic flows through the Bastion host's private IPs. The 'Allow Azure Bastion Communication' peering setting enables the necessary routing between the Bastion's subnet and the peered VNet's subnets; without it, the Bastion's private IPs cannot reach the target VM. In a real-world scenario, this setting is often overlooked when peering VNets for Bastion access, leading to connectivity failures despite correct NSG and subnet configurations.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this SC-100 question in full detail.
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 peered VNet does not have 'Allow Azure Bastion Communication' enabled on the peering connection. — Azure Bastion requires the 'Allow Azure Bastion Communication' setting to be enabled on the peering connection for the peered VNet. Without this, the Bastion service cannot route traffic to the target VM in the peered VNet, even though the VM is visible in the portal. This setting allows the Bastion's control plane and data plane to communicate across the peering link.
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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