- A
The policy's source interface is not the incoming interface
Why wrong: Incorrect interface matching would cause 'no matching policy', but the debug shows 'send to x.x.x.x via intf port1', indicating the routing decision is made before policy lookup. This suggests a routing issue, not a policy interface mismatch.
- B
The firewall policy is disabled
Why wrong: A disabled policy would still be listed but not matched; however, the debug would show 'policy disabled' rather than 'no matching policy'.
- C
The VPN tunnel is down
Why wrong: If the tunnel is down, the debug would not show 'send to x.x.x.x via intf port1' because the routing table would not have an entry for the tunnel.
- D
A static route is missing or incorrect, causing the traffic to exit the wrong interface
The traffic should be routed into the VPN tunnel (e.g., interface ssl.root or vpn-interface). Instead, it is routed out port1 (the internet interface). This is a routing problem. The policy lookup then fails because there is no policy on port1 for that destination (or the policy on port1 has different source/destination).
Quick Answer
The answer is a missing or incorrect static route. When the debug flow output shows “no matching policy” despite a seemingly valid firewall policy, it indicates the traffic is being evaluated on the wrong interface—in this case, exiting via port1 instead of the VPN tunnel interface. The debug trace reveals the traffic is routed out the physical WAN, so the policy lookup fails because no policy exists on port1 for that destination. On the Fortinet NSE 4 exam, this scenario tests your understanding that policy matching is interface-specific: a policy from the VPN tunnel to the destination subnet cannot match if routing sends the traffic out a different interface. The common trap is to assume the policy itself is misconfigured, but the root cause is almost always a routing deficiency—either the static route for the remote subnet is missing or points to the wrong next-hop. Remember the mnemonic: “Route first, policy second—if the path is wrong, the policy is gone.”
NSE4 High Availability and Diagnostics Practice Question
This NSE4 practice question tests your understanding of high availability and diagnostics. 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.
A FortiGate admin is troubleshooting intermittent VPN disconnections. The admin enables debug flow with 'diagnose debug flow filter daddr 10.0.0.1' and 'diagnose debug flow trace start 10'. The output shows 'msg: send to x.x.x.x via intf port1' but then immediately 'msg: no matching policy'. However, the firewall policy list shows a policy that should match. 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.
Clue:
"immediately / without restart"Why it matters: Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
A static route is missing or incorrect, causing the traffic to exit the wrong interface
The 'no matching policy' message indicates that the traffic did not match any policy. Since the debug shows the traffic is going out via port1, but the policy might be configured on a different interface (e.g., the VPN interface). In a VPN scenario, traffic destined for the remote subnet must match a policy from the VPN tunnel interface to the destination. If the traffic is being routed out port1 (the physical WAN) instead of through the VPN tunnel, the policy check fails. This is often due to missing or incorrect routing. Alternatively, the policy might be correctly configured but the traffic is being processed on the wrong VDOM, but the routing issue is more common.
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.
- ✗
The policy's source interface is not the incoming interface
Why it's wrong here
Incorrect interface matching would cause 'no matching policy', but the debug shows 'send to x.x.x.x via intf port1', indicating the routing decision is made before policy lookup. This suggests a routing issue, not a policy interface mismatch.
- ✗
The firewall policy is disabled
Why it's wrong here
A disabled policy would still be listed but not matched; however, the debug would show 'policy disabled' rather than 'no matching policy'.
- ✗
The VPN tunnel is down
Why it's wrong here
If the tunnel is down, the debug would not show 'send to x.x.x.x via intf port1' because the routing table would not have an entry for the tunnel.
- ✓
A static route is missing or incorrect, causing the traffic to exit the wrong interface
Why this is correct
The traffic should be routed into the VPN tunnel (e.g., interface ssl.root or vpn-interface). Instead, it is routed out port1 (the internet interface). This is a routing problem. The policy lookup then fails because there is no policy on port1 for that destination (or the policy on port1 has different source/destination).
Clue confirmation
The clue words "most likely", "immediately / without restart" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
Common exam traps
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.
Trap categories for this question
Command / output trap
Incorrect interface matching would cause 'no matching policy', but the debug shows 'send to x.x.x.x via intf port1', indicating the routing decision is made before policy lookup. This suggests a routing issue, not a policy interface mismatch.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related NSE4 subnetting questions on CIDR, address ranges, and subnet selection.
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High Availability and Diagnostics — study guide chapter
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FAQ
Questions learners often ask
What does this NSE4 question test?
High Availability and Diagnostics — This question tests High Availability and Diagnostics — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: A static route is missing or incorrect, causing the traffic to exit the wrong interface — The 'no matching policy' message indicates that the traffic did not match any policy. Since the debug shows the traffic is going out via port1, but the policy might be configured on a different interface (e.g., the VPN interface). In a VPN scenario, traffic destined for the remote subnet must match a policy from the VPN tunnel interface to the destination. If the traffic is being routed out port1 (the physical WAN) instead of through the VPN tunnel, the policy check fails. This is often due to missing or incorrect routing. Alternatively, the policy might be correctly configured but the traffic is being processed on the wrong VDOM, but the routing issue is more common.
What should I do if I get this NSE4 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 NSE4 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "immediately / without restart". 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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Last reviewed: Jun 21, 2026
This NSE4 practice question is part of Courseiva's free Fortinet certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the NSE4 exam.
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