The correct first step is to change one VNet to a non-overlapping address space before creating the peering. Azure VNet peering requires that the address spaces of the peered virtual networks do not overlap, because overlapping ranges create routing conflicts where Azure cannot determine which VNet should receive traffic destined for the same IP block. This question tests your understanding of the fundamental peering prerequisite on the AZ-104 exam, often appearing as a scenario where two development VNets share a common CIDR range like 10.0.0.0/24. A common trap is to assume you can use Network Address Translation (NAT) or gateway transit to resolve the conflict, but Azure does not support overlapping address spaces in a direct peering relationship. Remember the memory tip: "No overlap, no conflict—peering requires distinct address real estate."
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.
Exhibit
VNet-DevA address space: 10.20.0.0/16
VNet-DevB address space: 10.20.128.0/17
Peering status: Not created
Deployment note: The peering wizard returns an address space overlap error.
Based on the exhibit, two development virtual networks must be peered so the workloads can exchange traffic directly. What should the administrator do first?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
VNet-DevA address space: 10.20.0.0/16
VNet-DevB address space: 10.20.128.0/17
Peering status: Not created
Deployment note: The peering wizard returns an address space overlap error.
A
Create a VPN gateway in each VNet before attempting peering.
Why wrong: A gateway is not required for standard VNet peering, so this would not resolve the overlap error.
B
Change one VNet to a non-overlapping address space before creating the peering.
Azure VNet peering does not allow overlapping address spaces. The first step is to redesign one network so its address range does not intersect the other. After the address conflict is removed, peering can be created normally and traffic can flow directly between the VNets.
C
Add a user-defined route to each subnet so the VNets can ignore the overlap.
Why wrong: Routes control traffic selection after connectivity exists, but they do not remove peering validation failures caused by overlapping IP ranges.
D
Enable service endpoints on both VNets to allow cross-network communication.
Why wrong: Service endpoints are for Azure PaaS services, not for connecting one virtual network to another or fixing overlapping ranges.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Change one VNet to a non-overlapping address space before creating the peering.
Azure Virtual Network peering requires that the address spaces of the peered VNets do not overlap. Overlapping address spaces cause routing conflicts because Azure cannot determine which VNet should receive traffic destined for the overlapping range. Therefore, the administrator must first change one VNet to a non-overlapping address space before creating the peering.
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.
✗
Create a VPN gateway in each VNet before attempting peering.
Why it's wrong here
A gateway is not required for standard VNet peering, so this would not resolve the overlap error.
✓
Change one VNet to a non-overlapping address space before creating the peering.
Why this is correct
Azure VNet peering does not allow overlapping address spaces. The first step is to redesign one network so its address range does not intersect the other. After the address conflict is removed, peering can be created normally and traffic can flow directly between the VNets.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Add a user-defined route to each subnet so the VNets can ignore the overlap.
Why it's wrong here
Routes control traffic selection after connectivity exists, but they do not remove peering validation failures caused by overlapping IP ranges.
✗
Enable service endpoints on both VNets to allow cross-network communication.
Why it's wrong here
Service endpoints are for Azure PaaS services, not for connecting one virtual network to another or fixing overlapping ranges.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume overlapping address spaces can be resolved with routing tweaks (like UDRs) or additional gateways, but Azure explicitly blocks VNet peering when address spaces overlap, requiring a non-overlapping address space as a prerequisite.
Detailed technical explanation
How to think about this question
VNet peering relies on Azure's internal routing table, which uses the VNet's address space as a prefix. When two peered VNets have overlapping CIDR blocks (e.g., both use 10.0.0.0/16), Azure cannot create distinct routes for each VNet, leading to a peering failure with an 'OverlappingAddressSpace' error. In a real-world scenario, you might need to redesign IP addressing using RFC 1918 ranges or use NAT to translate overlapping addresses before peering.
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 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-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: Change one VNet to a non-overlapping address space before creating the peering. — Azure Virtual Network peering requires that the address spaces of the peered VNets do not overlap. Overlapping address spaces cause routing conflicts because Azure cannot determine which VNet should receive traffic destined for the overlapping range. Therefore, the administrator must first change one VNet to a non-overlapping address space before creating the peering.
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.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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