The answer is that the switch ports are not configured for LACP or static aggregation. This is the most likely cause because a FortiGate aggregate interface requires both the FortiGate member ports and the corresponding switch ports to use the same aggregation protocol—either LACP active/passive or static aggregation—to form a single logical link. When the switch ports remain in their default individual mode, they treat the FortiGate member ports as separate connections, creating a protocol mismatch that keeps the aggregate interface down even though each port shows as up. On the Fortinet NSE 4 Network Security Professional exam, this scenario tests your understanding of Layer 2 interface bundling and the necessity of matching aggregation settings end-to-end; a common trap is assuming that simply connecting cables and enabling the aggregate interface is sufficient. Remember the memory tip: “Both sides must bundle—if the switch doesn’t bundle, the bundle stays down.”
NSE4 System and Network Administration Practice Question
This NSE4 practice question tests your understanding of system and network administration. 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.
An administrator configures an aggregate interface (port1 and port2) on a FortiGate. After connecting the switch ports, the aggregate interface shows 'down'. The individual member ports are up. 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.
Why wrong: FortiGate can aggregate ports of different speeds, but the bundle will operate at the speed of the slowest port; this would not cause the interface to be down.
B
The switch ports are not configured for LACP or static aggregation
The switch must have the corresponding ports in an aggregate group with matching LACP settings; otherwise, the FortiGate will not see the aggregation and the interface stays down.
C
The aggregate interface IP address is in the same subnet as the management interface
Why wrong: IP address conflicts would cause routing issues but not prevent the interface from coming up.
D
The FortiGate needs a reboot after creating an aggregate interface
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The switch ports are not configured for LACP or static aggregation
The aggregate interface remains down because the switch ports are not configured for LACP or static aggregation. For a FortiGate aggregate interface to come up, both the FortiGate member ports and the corresponding switch ports must be configured with the same aggregation protocol (LACP active/passive or static). Without this, the switch treats the ports as individual links, causing a mismatch that keeps the aggregate interface down.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 member ports are set to different speeds
Why it's wrong here
FortiGate can aggregate ports of different speeds, but the bundle will operate at the speed of the slowest port; this would not cause the interface to be down.
✓
The switch ports are not configured for LACP or static aggregation
Why this is correct
The switch must have the corresponding ports in an aggregate group with matching LACP settings; otherwise, the FortiGate will not see the aggregation and the interface stays down.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The aggregate interface IP address is in the same subnet as the management interface
Why it's wrong here
IP address conflicts would cause routing issues but not prevent the interface from coming up.
✗
The FortiGate needs a reboot after creating an aggregate interface
Why it's wrong here
Reboot is not required.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume the aggregate interface will come up automatically if the member ports are physically up, overlooking the requirement for matching aggregation configuration on the switch side.
Detailed technical explanation
How to think about this question
FortiGate aggregate interfaces use IEEE 802.3ad LACP or static aggregation to bundle multiple physical ports into a single logical link. The switch must be configured with the same aggregation mode (e.g., LACP active/passive or static trunk) on the corresponding ports; otherwise, the switch will not send LACP frames or will not accept the aggregated MAC address, causing the FortiGate to detect a protocol mismatch and keep the aggregate interface administratively down. In a real-world scenario, forgetting to configure the switch side is a common oversight during initial deployment.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
System and Network Administration — This question tests System and Network Administration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The switch ports are not configured for LACP or static aggregation — The aggregate interface remains down because the switch ports are not configured for LACP or static aggregation. For a FortiGate aggregate interface to come up, both the FortiGate member ports and the corresponding switch ports must be configured with the same aggregation protocol (LACP active/passive or static). Without this, the switch treats the ports as individual links, causing a mismatch that keeps the aggregate interface down.
What should I do if I get this NSE4 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
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