The answer is an inter-VDOM policy on the inter-VDOM link interface. This is correct because traffic moving between different VDOMs on a FortiGate cannot be handled by a standard firewall policy, which only governs traffic within a single VDOM. Instead, an inter-VDOM link—either a physical cable connecting two ports assigned to different VDOMs or a logical inter-VDOM link created in the system interface—must be established, and a dedicated inter-VDOM policy is then applied to that link to permit or deny the cross-VDOM traffic. On the Fortinet NSE 4 Network Security Professional exam, this concept tests your understanding of VDOM segmentation and the unique policy requirements for inter-VDOM routing, often appearing as a trap where candidates mistakenly select a regular intra-VDOM policy. A common memory tip is to think of the inter-VDOM link as a bridge between two separate firewalls: just as you would need a policy on each firewall’s connecting interface, here you need one policy on the link itself. Remember: “Inter-VDOM traffic needs an inter-VDOM link and an inter-VDOM policy.”
NSE4 Firewall Policies and NAT Practice Question
This NSE4 practice question tests your understanding of firewall policies and nat. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 has multiple VDOMs. The administrator needs to allow traffic from VDOM A (port1) to VDOM B (port2). What type of firewall policy is required?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An inter-VDOM policy on the inter-VDOM link interface
An inter-VDOM link policy (or simply a policy between VDOMs) must be configured, often using a physical or logical inter-VDOM link. Option D correctly identifies the need for an inter-VDOM policy.
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.
✓
An inter-VDOM policy on the inter-VDOM link interface
Why this is correct
Inter-VDOM link policies allow traffic between VDOMs.
Related concept
Static NAT maps one inside address to one outside address.
✗
A policy using a virtual wire pair
Why it's wrong here
Virtual wire pairs are for transparent mode, not inter-VDOM.
✗
A regular intra-VDOM policy on VDOM A with destination interface port2
Why it's wrong here
Interfaces belong to different VDOMs; you need an inter-VDOM link.
✗
A policy on each VDOM with the same source/destination
Why it's wrong here
Traffic cannot flow directly between VDOMs without an inter-VDOM link.
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.
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
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 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 NSE4 NAT questions on configuration and troubleshooting.
Firewall Policies and NAT — This question tests Firewall Policies and NAT — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: An inter-VDOM policy on the inter-VDOM link interface — An inter-VDOM link policy (or simply a policy between VDOMs) must be configured, often using a physical or logical inter-VDOM link. Option D correctly identifies the need for an inter-VDOM policy.
What should I do if I get this NSE4 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 NSE4 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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