The answer is to add the API VM NICs to the destination application security group. This is correct because when the web tier can resolve the API subnet by name but traffic is still blocked, the issue lies in the network security group (NSG) rules not matching the intended destination. An application security group (ASG) allows you to group VM NICs logically, and the NSG rule must reference the correct ASG as the destination; without the API VM NICs added to ASG-API, the rule sees an empty group and falls back to the default deny rule, blocking the traffic. On the AZ-104 exam, this scenario tests your understanding of how ASGs differ from traditional IP-based NSG rules—a common trap is assuming DNS resolution alone guarantees connectivity, when in fact the NSG rule must explicitly include the destination ASG membership. Remember the tip: “DNS gets you the name, but ASG gets you the flow.”
AZ-104 Implement and Manage Virtual Networking Practice Question
This AZ-104 practice question tests your understanding of implement and manage virtual networking. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Exhibit
NSG rule summary:
Rule 1: Allow-Web-To-Api, Source=ASG-Web, Destination=ASG-Api, Port=8443, Action=Allow, Priority=300
ASG membership:
- WebVM01 NIC = ASG-Web
- WebVM02 NIC = ASG-Web
- ApiVM01 NIC = none
- ApiVM02 NIC = none
Observed result: Connections from WebVM01 to ApiVM01 on TCP 8443 fail.
Based on the exhibit, the web tier can reach the API subnet by name, but the traffic is still blocked. What should the administrator do?
NSG rule summary:
Rule 1: Allow-Web-To-Api, Source=ASG-Web, Destination=ASG-Api, Port=8443, Action=Allow, Priority=300
ASG membership:
- WebVM01 NIC = ASG-Web
- WebVM02 NIC = ASG-Web
- ApiVM01 NIC = none
- ApiVM02 NIC = none
Observed result: Connections from WebVM01 to ApiVM01 on TCP 8443 fail.
A
Add the API VM NICs to the destination application security group.
The allow rule is written for ASG-Api as the destination, but the exhibit shows that no API NICs are currently members of that ASG. Because NSG rules only match when both source and destination ASG membership is present, traffic will be blocked until the API VM NICs are added to ASG-Api.
B
Increase the priority number of the allow rule so it is evaluated earlier.
Why wrong: A higher priority number is evaluated later, not earlier, so this would make the rule less likely to match first.
C
Replace the ASG with a service endpoint on the API subnet.
Why wrong: Service endpoints are unrelated to NSG source and destination matching between virtual machine tiers.
D
Remove the web VMs from ASG-Web because ASGs block traffic by default.
Why wrong: ASGs do not block traffic by themselves; they are grouping objects used by NSG rules to match sets of NICs.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add the API VM NICs to the destination application security group.
The correct answer is A because the web tier can resolve the API subnet's name, but traffic is still blocked. This indicates that the network security group (NSG) rules are not correctly configured to allow traffic from the web VMs (in ASG-Web) to the API VMs (in ASG-API). By adding the API VM NICs to the destination application security group (ASG), the NSG rule that references ASG-API as the destination will match the API VMs, allowing the traffic. Without this, the NSG rule may be referencing an empty or incorrect destination, causing the traffic to be denied by the default deny rule.
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.
✓
Add the API VM NICs to the destination application security group.
Why this is correct
The allow rule is written for ASG-Api as the destination, but the exhibit shows that no API NICs are currently members of that ASG. Because NSG rules only match when both source and destination ASG membership is present, traffic will be blocked until the API VM NICs are added to ASG-Api.
Related concept
Read the scenario before looking for a memorised answer.
✗
Increase the priority number of the allow rule so it is evaluated earlier.
Why it's wrong here
A higher priority number is evaluated later, not earlier, so this would make the rule less likely to match first.
✗
Replace the ASG with a service endpoint on the API subnet.
Why it's wrong here
Service endpoints are unrelated to NSG source and destination matching between virtual machine tiers.
✗
Remove the web VMs from ASG-Web because ASGs block traffic by default.
Why it's wrong here
ASGs do not block traffic by themselves; they are grouping objects used by NSG rules to match sets of NICs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse name resolution with network connectivity, assuming that if a VM can resolve another VM's name via DNS, traffic must be allowed, but NSG rules are evaluated independently of DNS resolution.
Detailed technical explanation
How to think about this question
Application security groups (ASGs) allow you to group virtual machines and define network security policies based on those groups, without needing to manage explicit IP addresses. When an NSG rule references an ASG as the destination, the rule is applied to all NICs that are members of that ASG. Under the hood, Azure translates the ASG membership into a set of IP addresses and updates the NSG flow rules accordingly. A common real-world scenario is when VMs are added or removed from an ASG dynamically (e.g., via Azure Policy or automation), and the NSG rules automatically adjust without manual intervention.
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 the API VM NICs to the destination application security group. — The correct answer is A because the web tier can resolve the API subnet's name, but traffic is still blocked. This indicates that the network security group (NSG) rules are not correctly configured to allow traffic from the web VMs (in ASG-Web) to the API VMs (in ASG-API). By adding the API VM NICs to the destination application security group (ASG), the NSG rule that references ASG-API as the destination will match the API VMs, allowing the traffic. Without this, the NSG rule may be referencing an empty or incorrect destination, causing the traffic to be denied by the default deny rule.
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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