VPN Gateway Public IP Prerequisite — Site-to-Site VPN Deployment
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
Gateway deployment validation output:
GatewaySubnet: Present
Gateway type: VPN
VPN type: Route-based
Validation error: A public IP address resource must be specified for the gateway.
Current gateway configuration: No public IP attached.
Based on the exhibit, a site-to-site VPN gateway deployment fails. What prerequisite should the administrator provide so the gateway can be created successfully?
Exhibit
Gateway deployment validation output:
GatewaySubnet: Present
Gateway type: VPN
VPN type: Route-based
Validation error: A public IP address resource must be specified for the gateway.
Current gateway configuration: No public IP attached.
A
A public IP address resource that will be associated with the VPN gateway.
Azure VPN gateways need a public-facing IP resource so the gateway can accept encrypted tunnels from the on-premises device. The exhibit shows the gateway subnet is already present, but no public IP was attached. Creating and associating the public IP resource satisfies the deployment prerequisite.
B
A NAT gateway on the GatewaySubnet to translate tunnel traffic.
Why wrong: A NAT gateway is not a prerequisite for VPN gateway deployment. It does not replace the required public IP resource for the VPN gateway itself.
C
A private endpoint in the GatewaySubnet for tunnel termination.
Why wrong: Private endpoints are for accessing supported PaaS services privately. They are not used to terminate site-to-site VPN tunnels.
D
A network security group that allows inbound TCP 443 to the subnet.
Why wrong: VPN gateway deployment depends on a gateway public IP, not on opening TCP 443 to the subnet. NSGs are not the missing resource in the validation error shown.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A public IP address resource that will be associated with the VPN gateway.
A site-to-site VPNgateway in Azure requires a public IP address resource to be associated with it for the tunnel to be established. The VPN gateway uses this public IP as the endpoint for on-premises VPN devices to connect to over the internet. Without a public IP, the gateway cannot be provisioned because it has no routable external address for IPsec/IKE negotiation.
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.
✓
A public IP address resource that will be associated with the VPN gateway.
Why this is correct
Azure VPN gateways need a public-facing IP resource so the gateway can accept encrypted tunnels from the on-premises device. The exhibit shows the gateway subnet is already present, but no public IP was attached. Creating and associating the public IP resource satisfies the deployment prerequisite.
Related concept
Read the scenario before looking for a memorised answer.
✗
A NAT gateway on the GatewaySubnet to translate tunnel traffic.
Why it's wrong here
A NATgateway is not a prerequisite for VPN gateway deployment. It does not replace the required public IP resource for the VPN gateway itself.
When this WOULD be correct
In a scenario where on-premises network uses overlapping IP addresses with Azure VNet, a NATgateway on the GatewaySubnet could be used to translate traffic to avoid conflicts, but this is not a prerequisite for basic VPN gateway creation.
✗
A private endpoint in the GatewaySubnet for tunnel termination.
Why it's wrong here
Private endpoints are for accessing supported PaaS services privately. They are not used to terminate site-to-site VPN tunnels.
When this WOULD be correct
If the question were about securely accessing an Azure SQL Database from on-premises without exposing it to the internet, a private endpoint in a virtual network (not necessarily GatewaySubnet) would be the correct prerequisite to create.
✗
A network security group that allows inbound TCP 443 to the subnet.
Why it's wrong here
VPNgateway deployment depends on a gateway public IP, not on opening TCP 443 to the subnet. NSGs are not the missing resource in the validation error shown.
When this WOULD be correct
This option would be correct if the question asked: 'After deploying a VPNgateway, users cannot connect. What is missing?' or 'What must be configured to allow management traffic from Azure to the VPN gateway?' — where inbound TCP 443 is required for Azure gateway management.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The AZ-104 exam frequently reuses these exact scenarios with slightly different constraints.
✓A public IP address resource that will be associated with the VPN gateway.Correct answer▾
Why this is correct
Azure VPN gateways need a public-facing IP resource so the gateway can accept encrypted tunnels from the on-premises device. The exhibit shows the gateway subnet is already present, but no public IP was attached. Creating and associating the public IP resource satisfies the deployment prerequisite.
✗A NAT gateway on the GatewaySubnet to translate tunnel traffic.Wrong answer — click to see why▾
Why this is wrong here
A NAT gateway is not required for a site-to-site VPN gateway deployment. VPN gateways use public IP addresses for tunnel endpoints, and traffic translation is handled by the VPN gateway itself, not a separate NAT gateway.
★ When this WOULD be the correct answer
In a scenario where on-premises network uses overlapping IP addresses with Azure VNet, a NAT gateway on the GatewaySubnet could be used to translate traffic to avoid conflicts, but this is not a prerequisite for basic VPN gateway creation.
Why candidates choose this
Candidates may confuse NAT gateway with the need for public IP translation or think that outbound traffic from the GatewaySubnet requires NAT, but VPN gateways handle their own public IP addressing.
✗A private endpoint in the GatewaySubnet for tunnel termination.Wrong answer — click to see why▾
Why this is wrong here
A private endpoint is used for private connectivity to Azure PaaS services over a private IP, not for terminating site-to-site VPN tunnels. VPN gateways require a public IP and do not use private endpoints in the GatewaySubnet.
★ When this WOULD be the correct answer
If the question were about securely accessing an Azure SQL Database from on-premises without exposing it to the internet, a private endpoint in a virtual network (not necessarily GatewaySubnet) would be the correct prerequisite to create.
Why candidates choose this
Candidates may confuse private endpoints with VPN endpoints, thinking that a private IP termination is needed for security, but VPN gateways inherently use public IPs for tunnel establishment.
✗A network security group that allows inbound TCP 443 to the subnet.Wrong answer — click to see why▾
Why this is wrong here
A network security group (NSG) on the GatewaySubnet is not a prerequisite for VPN gateway creation; NSGs are optional and can be applied after deployment. The failure is due to missing a public IP resource, not NSG rules.
★ When this WOULD be the correct answer
This option would be correct if the question asked: 'After deploying a VPN gateway, users cannot connect. What is missing?' or 'What must be configured to allow management traffic from Azure to the VPN gateway?' — where inbound TCP 443 is required for Azure gateway management.
Why candidates choose this
Candidates may think NSGs are mandatory for security or that inbound 443 is needed for VPN tunnel establishment, confusing management traffic with tunnel traffic.
Analysis generated from the official AZ-104blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the prerequisite for a VPNgateway with that of an Azure Firewall or NAT gateway, mistakenly thinking a NAT gateway or NSG is required, when in fact only a public IP is mandatory for the VPN gateway to function.
Trap categories for this question
Command / output trap
VPN gateway deployment depends on a gateway public IP, not on opening TCP 443 to the subnet. NSGs are not the missing resource in the validation error shown.
Detailed technical explanation
How to think about this question
Under the hood, the VPNgateway uses the public IP address to establish an IPsec tunnel with the on-premises device, encapsulating traffic in ESP (Encapsulating Security Payload) packets. The public IP must be a Standard SKU public IP resource in the same region, and it is assigned to the gateway's front-end configuration. A common real-world scenario is forgetting to create the public IP before the gateway, leading to a deployment error that can be resolved by provisioning the public IP first.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
Quick reference
VPN Protocol Comparison
Protocol
Port
Encryption
Authentication
Use Case
IKEv2 / IPsec
UDP 500 / 4500
AES-256
Certificates / PSK
Site-to-site & remote access
SSL / TLS VPN
TCP 443
TLS 1.3
Certificates / MFA
Clientless remote access
L2TP / IPsec
UDP 1701
AES (IPsec)
PSK / Certificates
Legacy remote access
WireGuard
UDP 51820
ChaCha20
Public keys
Modern high-performance VPN
PPTP
TCP 1723
MPPE (weak)
MS-CHAPv2
Legacy — avoid in production
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
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: A public IP address resource that will be associated with the VPN gateway. — A site-to-site VPN gateway in Azure requires a public IP address resource to be associated with it for the tunnel to be established. The VPN gateway uses this public IP as the endpoint for on-premises VPN devices to connect to over the internet. Without a public IP, the gateway cannot be provisioned because it has no routable external address for IPsec/IKE negotiation.
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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Variation 1. Based on the exhibit, the VPN gateway deployment fails during validation. What resource is missing?
easy
✓ A.A public IP address resource associated with the VPN gateway.
B.A network security group attached to GatewaySubnet.
C.A route table with a default route to the on-premises network.
D.A private endpoint for the on-premises VPN device.
Why A: A VPN gateway requires a dedicated public IP address resource to establish the IPsec tunnel with the on-premises VPN device. During validation, Azure checks that a public IP address is associated with the gateway; if missing, the deployment fails because the gateway cannot route traffic over the internet or terminate the VPN connection.
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Question Discussion
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