Question 170 of 1,000

Firewall Policies and NAT →mediumMultiple SelectObjective-mapped

Quick Answer

The answer is that the PBR rule is disabled, the gateway is unreachable, or the rule is applied to the wrong incoming interface. Policy-based routing on a FortiGate overrides the routing table only when the rule is enabled, the specified next-hop gateway on wan2 is reachable via a valid ARP entry, and the rule is bound to the correct incoming interface where the traffic from subnet 172.16.1.0/24 enters the FortiGate. If any of these three conditions fail, the FortiGate falls back to the default route via wan1. On the Fortinet NSE 4 Network Security Professional exam, this question tests your understanding that PBR is a policy-based override, not a static route, and that its priority (lower number wins) must also be higher than other matching routes. A common trap is assuming a PBR rule works automatically once created, but it requires explicit enablement and a reachable gateway. Memory tip: think of PBR as a three-legged stool—Enabled, Reachable, and Correct Interface—if any leg is missing, the stool collapses to the default route.

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.

An administrator is configuring policy-based routing (PBR) on a FortiGate to route traffic from a specific subnet (172.16.1.0/24) through a different internet connection (wan2) instead of the default route via wan1. The administrator has created a PBR rule matching source 172.16.1.0/24 and set the gateway to the next-hop IP on wan2. The traffic is still using wan1. Which THREE of the following could be causing the issue? (Choose three.)

Question 1mediummulti select

Review the full subnetting walkthrough →

A
The PBR rule's gateway is not reachable from the FortiGate
If the next-hop is unreachable, the rule is not used and traffic falls back to the routing table.
B
The PBR rule's priority is set too high (e.g., 100) and a static route with lower priority is used instead
Why wrong: PBR is evaluated before the routing table; priority among PBR rules matters, but static routes do not override PBR.
C
The PBR rule is applied to the wrong incoming interface
PBR rules are applied per incoming interface. If the traffic arrives on a different interface than the one specified, the rule won't match.
D
The PBR rule is disabled
A disabled rule is not evaluated.
E
The PBR rule's destination is set to 'all' but the traffic's destination is not covered
Why wrong: If destination is 'all', it matches any destination. This would not cause the issue.

Full breakdown with real-world context →

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

✓

The PBR rule's gateway is not reachable from the FortiGate

PBR requires the rule to be enabled, the gateway to be reachable, and the rule's priority to be higher (lower number) than other routes. Also, the PBR must be applied to the correct incoming interface. If the interface is wrong, or the gateway is unreachable, or the rule is disabled, PBR will not work.

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 PBR rule's gateway is not reachable from the FortiGate
Why this is correct
If the next-hop is unreachable, the rule is not used and traffic falls back to the routing table.
Related concept
CIDR notation defines the prefix length.
✗
The PBR rule's priority is set too high (e.g., 100) and a static route with lower priority is used instead
Why it's wrong here
PBR is evaluated before the routing table; priority among PBR rules matters, but static routes do not override PBR.
✓
The PBR rule is applied to the wrong incoming interface
Why this is correct
PBR rules are applied per incoming interface. If the traffic arrives on a different interface than the one specified, the rule won't match.
Related concept
CIDR notation defines the prefix length.
✓
The PBR rule is disabled
Why this is correct
A disabled rule is not evaluated.
Related concept
CIDR notation defines the prefix length.
✗
The PBR rule's destination is set to 'all' but the traffic's destination is not covered
Why it's wrong here
If destination is 'all', it matches any destination. This would not cause the issue.

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.

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FAQ

Questions learners often ask

What does this NSE4 question test?

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's gateway is not reachable from the FortiGate — PBR requires the rule to be enabled, the gateway to be reachable, and the rule's priority to be higher (lower number) than other routes. Also, the PBR must be applied to the correct incoming interface. If the interface is wrong, or the gateway is unreachable, or the rule is disabled, PBR will not work.

What should I do if I get this NSE4 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

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