The answer is that the private DNS zone is not linked to VNet2. Even though clients in VNet2 can resolve the SQL server FQDN to the private IP—often due to Azure’s default DNS resolution or cached records—the actual private DNS zone ‘privatelink.database.windows.net’ is only linked to VNet1, so VNet2 does not have authoritative access to the zone’s records. This means the resolved IP may be stale or incorrect, and traffic from VNet2 to the private endpoint is not properly routed, causing connection failures despite apparent resolution. On the AZ-500 exam, this scenario tests your understanding that private DNS zone links are not inherited across VNet peering; you must explicitly link the zone to each peered VNet or configure a custom DNS server. A common trap is assuming that peering automatically propagates DNS resolution, but it does not—only network connectivity is established. Memory tip: “Peering links networks, not DNS zones—link the zone to every VNet that needs it.”
AZ-500 Secure networking Practice Question
This AZ-500 practice question tests your understanding of secure 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.
You deploy Azure Private Link for an Azure SQL Database. You create a private endpoint in VNet1 and configure a private DNS zone 'privatelink.database.windows.net' linked to VNet1. Clients in VNet2 (peered to VNet1) can resolve the SQL server FQDN to the private IP, but connections fail. 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.
Private endpoint is in a 'Failed' provisioning state.
Why wrong: If private endpoint were failed, it wouldn't have a private IP assigned.
B
VNet2 does not have a route to the private endpoint's subnet.
Why wrong: Peering provides connectivity; a specific route is not needed unless forced tunneling is used.
C
Azure SQL Database's firewall rules block traffic from the private endpoint.
Why wrong: Private endpoint bypasses SQL firewall; the firewall rules are for public endpoint.
D
The private DNS zone is not linked to VNet2.
For clients in a peered VNet to resolve the private endpoint's FQDN, the private DNS zone must be linked to that VNet or they must use a custom DNS that can resolve it.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The private DNS zone is not linked to VNet2.
Private DNS zones linked to VNet1 are not automatically resolvable from peered VNets unless the DNS zone is also linked to VNet2 or VNet2 is configured to use a custom DNS server that can resolve the zone. The clients in VNet2 may resolve to the private IP, but the firewall or NSG may block traffic. However, typical issue is DNS resolution not being propagated.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Private endpoint is in a 'Failed' provisioning state.
Why it's wrong here
If private endpoint were failed, it wouldn't have a private IP assigned.
✗
VNet2 does not have a route to the private endpoint's subnet.
Why it's wrong here
Peering provides connectivity; a specific route is not needed unless forced tunneling is used.
✗
Azure SQL Database's firewall rules block traffic from the private endpoint.
Why it's wrong here
Private endpoint bypasses SQL firewall; the firewall rules are for public endpoint.
✓
The private DNS zone is not linked to VNet2.
Why this is correct
For clients in a peered VNet to resolve the private endpoint's FQDN, the private DNS zone must be linked to that VNet or they must use a custom DNS that can resolve it.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this AZ-500 question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related AZ-500 subnetting questions on CIDR, address ranges, and subnet selection.
Secure networking — This question tests Secure networking — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The private DNS zone is not linked to VNet2. — Private DNS zones linked to VNet1 are not automatically resolvable from peered VNets unless the DNS zone is also linked to VNet2 or VNet2 is configured to use a custom DNS server that can resolve the zone. The clients in VNet2 may resolve to the private IP, but the firewall or NSG may block traffic. However, typical issue is DNS resolution not being propagated.
What should I do if I get this AZ-500 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related AZ-500 subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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