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 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?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The PBR rule uses an incorrect source or destination address
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.
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 firewall policy is placed above the PBR rule
Why it's wrong here
PBR is evaluated before firewall policies, so policy order doesn't affect routing.
✗
The PBR rule does not have a matching protocol or service defined
Why it's wrong here
PBR can match on source/destination and optionally protocol, but missing protocol usually doesn't cause no match.
✓
The PBR rule uses an incorrect source or destination address
Why this is correct
If the PBR rule does not match the traffic (e.g., wrong subnet), traffic follows the routing table instead.
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 PBR rule uses an incorrect source or destination address — 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.
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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