The answer is that the firewall policy for the traffic from 10.0.0.0/24 has a route override setting enabled, which bypasses the policy-based routing rule. This happens because, on a FortiGate, policy-based routing is evaluated before the routing table lookup, but if the matching firewall policy explicitly overrides the route—often via the "set route-ttl" or a static route tied to the policy—the PBR decision is discarded. On the Fortinet NSE 4 Network Security Professional NSE4 exam, this question tests your understanding of the interaction between PBR and firewall policies, a common trap where candidates assume PBR alone controls the path. The key insight is that a firewall policy with its destination interface set to "auto" or a specific port can silently override PBR, especially when the policy's routing action is not set to "use policy-based routing." Remember the mnemonic: "PBR picks the path, but the policy can pull the plug."
NSE4 Firewall Policies and NAT Practice Question
This NSE4 practice question tests your understanding of firewall policies and nat. 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 with multiple WAN interfaces uses policy-based routing (PBR) to route traffic from subnet 10.0.0.0/24 through port1 and 10.0.1.0/24 through port2. However, traffic from 10.0.0.0/24 is still using port2. The PBR rule appears correctly configured. 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 policy for that traffic has a route override setting that bypasses PBR
PBR rules are evaluated before routing table lookups. But if a firewall policy is matching the traffic before PBR (depending on configuration), the policy's route may override PBR. Also, PBR requires that the policy does not have a route override. Another common issue is that the policy's destination interface is set to auto or the wrong interface, causing the route table decision to take precedence. However, the most common mistake is that the policy created for that traffic has its 'policy-based routing' option disabled or is using a different routing method.
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 source subnet in the PBR rule is incorrectly specified as 10.0.1.0/24
Why it's wrong here
The admin confirmed it's correct.
✓
The firewall policy for that traffic has a route override setting that bypasses PBR
Why this is correct
If the policy has an explicit route override (like setting the outgoing interface), it will bypass PBR. Disabling route override allows PBR to work.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The PBR rule has a higher priority number than other rules
Why it's wrong here
Priority numbers determine order; lower number is higher priority.
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.
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.
Firewall Policies and NAT — This question tests Firewall Policies and NAT — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The firewall policy for that traffic has a route override setting that bypasses PBR — PBR rules are evaluated before routing table lookups. But if a firewall policy is matching the traffic before PBR (depending on configuration), the policy's route may override PBR. Also, PBR requires that the policy does not have a route override. Another common issue is that the policy's destination interface is set to auto or the wrong interface, causing the route table decision to take precedence. However, the most common mistake is that the policy created for that traffic has its 'policy-based routing' option disabled or is using a different routing method.
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". 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A FortiGate with multiple WAN interfaces uses policy-based routing (PBR) to route traffic from a specific subnet out of a particular interface. The admin also has a firewall policy allowing that subnet to the internet. However, the traffic is not being routed as expected. What could be the issue?
hard
A.The firewall policy is placed above the PBR rule
B.The PBR rule does not have a matching protocol or service defined
✓ C.The PBR rule uses an incorrect source or destination address
D.The FortiGate is in transparent mode
Why C: Policy-based routing is evaluated after the routing table lookup but before firewall policy matching. If the PBR rule is incorrectly configured (e.g., wrong source/destination), traffic may take a different path. Another common issue is that PBR might conflict with the default route. The question asks for the most likely issue — often it's that the PBR rule is not matching the traffic.
Variation 2. What is the purpose of policy-based routing (PBR) in FortiGate?
easy
A.To load balance traffic across multiple WAN links
B.To filter traffic based on application signatures
✓ C.To route traffic based on source address, destination, or other attributes instead of the routing table
D.To authenticate users before allowing traffic
Why C: Policy-based routing (PBR) in FortiGate allows you to override the default routing table lookup by forwarding traffic based on criteria such as source IP address, destination IP address, protocol, or even application. This is configured under the 'policy route' feature and is evaluated before the routing table, enabling granular control over traffic paths that static or dynamic routes cannot provide.
Last reviewed: Jun 21, 2026
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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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