Quick Answer
The answer is that a Network Security Group (NSG) blocking inbound TCP 3389 is the most likely Azure-side cause when an RDP connection is blocked by NSG rules. This is correct because an NSG acts as a stateful firewall at the subnet or network interface level, and even if the VM is healthy and its guest OS firewall permits RDP, the NSG silently drops packets that do not match an explicit allow rule for inbound traffic on port 3389 from the internet. On the AZ-104 exam, this scenario tests your understanding of Azure network security layers, often appearing as a distractor where candidates mistakenly blame the VM’s guest firewall or public IP configuration. A common trap is forgetting that NSG rules are evaluated before traffic reaches the VM, so a missing inbound rule for TCP 3389 will block RDP regardless of the guest OS settings. Memory tip: think of the NSG as the “bouncer at the door”—if it doesn’t have a rule to let RDP in, no one gets past the lobby.
This AZ-104 practice question tests your understanding of implement and manage virtual networking. 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 Windows VM in Azure has a public IP address, but administrators on the internet cannot connect by using Remote Desktop. You confirm that the VM is running and the guest firewall allows RDP. What is the most likely Azure-side 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.
The NSG does not allow inbound TCP 3389
An NSG deny or missing allow rule on TCP 3389 will block RDP access.
The storage account uses LRS
Why wrong: Storage redundancy does not affect RDP connectivity to a VM.
Azure Advisor is not enabled
Why wrong: Azure Advisor provides recommendations and does not gate VM connectivity.
The VM is in an availability set
Why wrong: Being in an availability set does not prevent Remote Desktop access.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The NSG does not allow inbound TCP 3389
The most likely Azure-side cause is that a Network Security Group (NSG) associated with the VM's subnet or network interface is blocking inbound traffic on TCP port 3389 (RDP). Even if the VM is running and the guest OS firewall allows RDP, an NSG rule must explicitly permit inbound TCP 3389 from the internet (or a specific source) for Remote Desktop connections to succeed. Without such a rule, the NSG silently drops the packets before they reach the VM.
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.
The NSG does not allow inbound TCP 3389
Why this is correct
An NSG deny or missing allow rule on TCP 3389 will block RDP access.
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 storage account uses LRS
Why it's wrong here
Storage redundancy does not affect RDP connectivity to a VM.
Azure Advisor is not enabled
Why it's wrong here
Azure Advisor provides recommendations and does not gate VM connectivity.
The VM is in an availability set
Why it's wrong here
Being in an availability set does not prevent Remote Desktop access.
Common exam traps
The trap here is that candidates often assume the guest OS firewall is the only barrier for RDP, overlooking that Azure's NSG acts as a separate, mandatory network-level filter that must explicitly allow inbound TCP 3389 from the internet.
Detailed technical explanation
NSGs are stateful firewalls that filter traffic at the subnet or NIC level using priority-ordered rules. By default, an NSG denies all inbound traffic unless an explicit allow rule exists. For RDP from the internet, you need a rule with source 'Any' or 'Internet', destination port '3389', protocol 'TCP', and action 'Allow'. A common subtlety is that the NSG's default deny rule (rule 65000) will block RDP if no higher-priority allow rule is present, even if the VM's guest firewall is configured correctly.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
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
Implement and Manage Virtual Networking — This question tests Implement and Manage Virtual Networking — Read the scenario before looking for a memorised answer..
The correct answer is: The NSG does not allow inbound TCP 3389 — The most likely Azure-side cause is that a Network Security Group (NSG) associated with the VM's subnet or network interface is blocking inbound traffic on TCP port 3389 (RDP). Even if the VM is running and the guest OS firewall allows RDP, an NSG rule must explicitly permit inbound TCP 3389 from the internet (or a specific source) for Remote Desktop connections to succeed. Without such a rule, the NSG silently drops the packets before they reach the VM.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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