Why ipsengine Consumes High CPU on FortiGate
A FortiGate is experiencing high CPU usage. The administrator runs 'diagnose sys top' and sees that the process 'ipsengine' is using the most CPU. What is the most likely cause?
Quick Answer
The answer is a large volume of traffic being inspected by IPS, often due to a DoS attack. The ipsengine process is responsible for Intrusion Prevention System deep packet inspection, and when it consumes high CPU on a FortiGate, it indicates that the device is overwhelmed by the computational load of matching traffic against IPS signatures. This is a core concept tested on the Fortinet NSE 7 Advanced Security NSE7 exam, where you must distinguish between normal IPS processing and an abnormal spike caused by a surge in traffic, such as a DoS attack. A common trap is to blame a misconfigured firewall policy or a hardware failure, but the key is that ipsengine specifically handles signature-based inspection, not routing or NAT. Remember the memory tip: "IPS eats CPU when traffic is deep and steep"—if the CPU is high and ipsengine is the culprit, look for a flood of traffic requiring deep inspection.
⚠ Common exam trap
Watch out — candidates often confuse ipsengine with avengine or assume high CPU is always due to a memory leak, but the specific process name directly points to IPS inspection overload.
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
✓
A large volume of traffic is being inspected by IPS, possibly due to a DoS attack.
The ipsengine process handles Intrusion Prevention System (IPS) inspection. High CPU usage by ipsengine typically indicates that the FortiGate is processing a large volume of traffic through IPS signatures, which is computationally intensive. This is often triggered by a DoS attack or a sudden surge in traffic that requires deep packet inspection, overwhelming the CPU.
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 is experiencing a memory leak.
Why it's wrong here
Memory leaks cause high memory usage, not necessarily high CPU by ipsengine.
- ✓
A large volume of traffic is being inspected by IPS, possibly due to a DoS attack.
Why this is correct
IPS engine uses CPU for deep packet inspection; high volume or many signatures increases load.
- ✗
The antivirus engine is scanning large files.
Why it's wrong here
Antivirus uses a separate process, not ipsengine.
- ✗
There is a routing loop causing packet bouncing.
Why it's wrong here
Routing loops affect forwarding plane, not ipsengine.
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Same concept, more angles
1 more way this is tested on NSE7
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 network administrator runs 'diagnose sys top' and sees that the 'ipsengine' process is consistently using 99% CPU. What is the BEST immediate action to reduce CPU load?
easy- A.Reboot the FortiGate
- B.Increase the session limit
- ✓ C.Disable IPS inspection on policies that don't require it
- D.Change IPS engine to flow-based mode
Why C: The 'ipsengine' process consuming 99% CPU indicates that IPS inspection is being applied to traffic that may not require it, causing excessive processing overhead. Disabling IPS on policies that do not need it (Option C) directly reduces the workload on the IPS engine without affecting other security functions or requiring a reboot. This is the most immediate and targeted action to alleviate CPU pressure.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This NSE7 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 NSE7 exam.