The answer is that the firewall’s Outbound SNAT is disabled for the spoke VNet ranges. When you configure Azure Firewall DNAT rules to forward traffic, the firewall changes the destination IP and port for inbound packets, but for the return traffic to flow back through the firewall symmetrically, the firewall must also perform Source Network Address Translation (SNAT) on the source IP. If SNAT is disabled, the destination VM sees the original private source IP and sends its reply directly to that IP, bypassing the firewall entirely—this creates asymmetric routing and breaks the DNAT session. On the Microsoft Azure Security Engineer Associate AZ-500 exam, this scenario tests your understanding of how Azure Firewall handles stateful packet inspection and the critical role of SNAT in DNAT flows. A common trap is assuming that allowing the traffic in firewall rules is sufficient, but without SNAT, return packets take a different path. Remember the memory tip: “DNAT changes the destination, but SNAT keeps the return path straight.”
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 have a hub-spoke network with Azure Firewall in the hub. Spoke VNet1 contains a VM that needs to communicate with a VM in Spoke VNet2. Both spoke VNets are peered to the hub. You configure Azure Firewall DNAT rules to forward traffic to specific VMs, but the communication fails. You verify that the firewall rules allow the traffic and that the VMs can reach each other's private IPs if the firewall is bypassed. What is the most likely 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 firewall's Outbound SNAT is disabled for the spoke VNet ranges.
When using DNAT, the firewall changes the destination IP and port. For return traffic, the firewall must perform SNAT (source NAT) to ensure the return traffic goes back through the firewall. If SNAT is not enabled (or disabled), the return traffic may go directly from the destination VM to the source VM's private IP, bypassing the firewall and causing asymmetric routing.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The spoke VNets have overlapping IP address spaces.
Why it's wrong here
Overlapping IPs would cause routing issues, but the scenario states they can communicate if firewall is bypassed.
✗
The firewall's Threat Intelligence mode is blocking the traffic.
Why it's wrong here
Threat intelligence would block based on malicious IPs, not cause asymmetric routing.
✓
The firewall's Outbound SNAT is disabled for the spoke VNet ranges.
Why this is correct
Without SNAT, the source IP remains the original VM IP; return traffic may not go through the firewall, breaking flow.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
Azure Firewall does not support DNAT between spoke VNets.
Why it's wrong here
Azure Firewall supports DNAT for any traffic, including inter-spoke.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Trap categories for this question
Scenario analysis trap
Overlapping IPs would cause routing issues, but the scenario states they can communicate if firewall is bypassed.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related AZ-500 NAT questions on configuration and troubleshooting.
Secure networking — This question tests Secure networking — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The firewall's Outbound SNAT is disabled for the spoke VNet ranges. — When using DNAT, the firewall changes the destination IP and port. For return traffic, the firewall must perform SNAT (source NAT) to ensure the return traffic goes back through the firewall. If SNAT is not enabled (or disabled), the return traffic may go directly from the destination VM to the source VM's private IP, bypassing the firewall and causing asymmetric routing.
What should I do if I get this AZ-500 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related AZ-500 NAT questions on configuration and troubleshooting.
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?
Static NAT maps one inside address to one outside address.
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