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 are troubleshooting connectivity from an on-premises network to an Azure VM. The connection uses a site-to-site VPN. The VM can be pinged from on-premises, but an application running on the VM cannot connect to an on-premises database server. The database server's firewall is configured to allow connections from the Azure VPN gateway public IP. What is the most likely cause of the issue?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The on-premises firewall is allowing the wrong IP address. The Azure VPN gateway's private IP should be allowed.
Option C is correct because traffic from Azure to on-premises uses the VPNgateway's private IP from the gateway subnet, not its public IP. The on-premises firewall should allow the VPN gateway's private IP address range. Option A is wrong because the VPN tunnel is established. Option B is wrong because NSG rules affect traffic within Azure, not outbound to on-premises. Option D is wrong because route tables could affect routing but the database is on-premises.
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.
✗
An NSG on the VM's subnet is blocking outbound traffic.
Why it's wrong here
NSGs do not block traffic to on-premises; they block inbound/outbound within Azure.
✗
The VPN tunnel is not established.
Why it's wrong here
If ping works, the tunnel is up.
✗
The effective routes on the VM are misconfigured.
Why it's wrong here
Ping works, so routing is likely correct.
✓
The on-premises firewall is allowing the wrong IP address. The Azure VPN gateway's private IP should be allowed.
Why this is correct
Azure VPNgateway uses its private IP for traffic to on-premises, not the public IP.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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 on-premises firewall is allowing the wrong IP address. The Azure VPN gateway's private IP should be allowed. — Option C is correct because traffic from Azure to on-premises uses the VPN gateway's private IP from the gateway subnet, not its public IP. The on-premises firewall should allow the VPN gateway's private IP address range. Option A is wrong because the VPN tunnel is established. Option B is wrong because NSG rules affect traffic within Azure, not outbound to on-premises. Option D is wrong because route tables could affect routing but the database is on-premises.
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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