The answer is to add an allow rule in the subnet NSG at priority 150 for TCP 8443 from WebASG to AppASG. This is correct because in Azure, subnet NSG rules are evaluated before NIC NSG rules for inbound traffic, and the subnet’s deny rule at priority 200 blocks TCP 8443 from VirtualNetwork to any destination, overriding the NIC’s allow rule regardless of its lower priority number. The subnet deny is processed first, so even a higher-priority NIC allow cannot bypass it; you must insert a more specific allow rule in the subnet NSG at a higher priority (e.g., 150) to explicitly permit the desired traffic while keeping the broader deny in place. On the AZ-104 exam, this scenario tests your understanding of NSG rule evaluation order and the common trap of assuming a NIC allow can override a subnet deny. Remember the mnemonic: subnet first, then NIC—a subnet deny always wins unless a higher-priority subnet allow says otherwise.
AZ-104 Implement and Manage Virtual Networking Practice Question
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 backend VM belongs to AppASG and listens on TCP 8443. The subnet NSG has a deny rule at priority 200 that blocks TCP 8443 from VirtualNetwork to any destination. The backend VM's NIC NSG has an allow rule at priority 100 for TCP 8443 from WebASG to AppASG. Web VMs in WebASG still cannot connect. What should you change to allow only the web tier while keeping other virtual network traffic blocked?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add an allow rule in the subnet NSG at priority 150 for TCP 8443 from WebASG to AppASG.
In Azure, network security group (NSG) rules are evaluated in priority order, and subnet NSG rules are evaluated before NIC NSG rules for inbound traffic. The subnet NSG has a deny rule at priority 200 that blocks TCP 8443 from VirtualNetwork to any destination, which overrides the NIC NSG allow rule because the subnet deny is evaluated first. To allow traffic from WebASG to AppASG while still blocking other virtual network traffic, you must add an allow rule in the subnet NSG at a higher priority (e.g., 150) than the deny rule, explicitly permitting TCP 8443 from WebASG to AppASG.
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.
✗
Move the NIC NSG allow rule to priority 50.
Why it's wrong here
That still does not overcome the subnet-level deny rule that is evaluated first.
✓
Add an allow rule in the subnet NSG at priority 150 for TCP 8443 from WebASG to AppASG.
Why this is correct
This places a more specific allow ahead of the subnet deny, so only the intended tier is permitted.
Related concept
Read the scenario before looking for a memorised answer.
✗
Replace the subnet deny rule with a rule for the AzureLoadBalancer service tag.
Why it's wrong here
AzureLoadBalancer is for load balancer probes, not for restricting east-west application traffic.
✗
Remove the backend VM from AppASG and allow traffic by subnet only.
Why it's wrong here
That does not solve the priority conflict and reduces rule precision and manageability.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume NIC NSG rules can override subnet NSG rules due to higher priority, but in Azure, subnet NSG rules are evaluated before NIC NSG rules for inbound traffic, so a subnet deny will always block traffic regardless of NIC allow rules.
Detailed technical explanation
How to think about this question
Azure NSG rules are processed in priority order (lowest number first) for both inbound and outbound traffic, and subnet NSG rules are always evaluated before NIC NSG rules for inbound traffic. This means a subnet-level deny rule at priority 200 will block traffic even if a NIC-level allow rule exists at a higher priority (lower number), because the subnet rule is evaluated first. In a real-world scenario, this layered security model is critical for defense-in-depth, where subnet NSGs enforce broad policies and NIC NSGs provide fine-grained per-instance controls, but subnet-level denies can override NIC-level allows if not carefully prioritized.
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 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this AZ-104 question in full detail.
Implement and Manage Virtual Networking — This question tests Implement and Manage Virtual Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add an allow rule in the subnet NSG at priority 150 for TCP 8443 from WebASG to AppASG. — In Azure, network security group (NSG) rules are evaluated in priority order, and subnet NSG rules are evaluated before NIC NSG rules for inbound traffic. The subnet NSG has a deny rule at priority 200 that blocks TCP 8443 from VirtualNetwork to any destination, which overrides the NIC NSG allow rule because the subnet deny is evaluated first. To allow traffic from WebASG to AppASG while still blocking other virtual network traffic, you must add an allow rule in the subnet NSG at a higher priority (e.g., 150) than the deny rule, explicitly permitting TCP 8443 from WebASG to AppASG.
What should I do if I get this AZ-104 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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