IPS Sensor Target Default Not Blocking Attacks in Flow-Based Inspection
An administrator sees the following CLI output when checking an IPS sensor: 'config ips sensor edit test config entries edit 1 set severity medium set action block set target default end'. However, attacks with severity medium are still passing. The IPS sensor is applied to a policy with flow-based inspection. What is the likely issue?
Quick Answer
The answer is that the IPS sensor rule has 'target' set to 'default', which may not match the traffic direction in flow-based inspection. In flow-based inspection, the 'target' parameter determines whether the rule applies to client-to-server traffic, server-to-client traffic, or both; setting it to 'default' often means the rule inherits the protocol decoder's default target, which might be 'server' or 'client' only, causing medium severity attacks to pass if the traffic flows in the opposite direction. On the Fortinet NSE 4 exam, this tests your understanding of how IPS sensors interact with flow-based inspection versus proxy-based inspection, and it’s a common trap to assume 'default' always blocks both directions. Remember the memory tip: "Default is not always both—check the flow direction to avoid the block's growth."
⚠ Common exam trap
It's easy for candidates to assume 'default' means the rule applies to all traffic, but in FortiGate IPS, 'default' typically refers to a specific direction (client-to-server), and failing to set the correct target for bidirectional attack patterns is a common oversight.
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 IPS sensor rule has 'target' set to 'default' which may not apply to the traffic direction
The 'set target default' command in the IPS sensor configuration means the rule is applied to traffic that matches the default target, which is typically the 'client-to-server' direction. If the attack traffic is flowing in the opposite direction (server-to-client), the rule will not trigger. This is a common misconfiguration when using flow-based inspection, where the target direction must match the actual traffic flow for the action to be enforced.
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 IPS sensor is not enabled in the policy
Why it's wrong here
The admin confirms it is applied.
- ✓
The IPS sensor rule has 'target' set to 'default' which may not apply to the traffic direction
Why this is correct
For flow-based inspection, target must be 'client' or 'server' to match direction. 'default' may not work as expected.
- ✗
The FortiGate needs a FortiSandbox for IPS to work
Why it's wrong here
IPS does not require FortiSandbox.
- ✗
The severity level is set too high
Why it's wrong here
Medium is appropriate for medium severity attacks.
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Same concept, more angles
1 more way this is tested on NSE4
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 FortiGate is configured with an IPS profile to protect a web server. The administrator notices that some attacks are not being detected. The IPS signature database is up to date. What should the administrator check first?
medium- A.Increase the severity level of the IPS sensor.
- ✓ B.Ensure the IPS profile is applied to the firewall policy that handles traffic to the web server.
- C.Disable flow-based inspection and enable proxy-based inspection.
- D.Change the IPS signature action from 'default' to 'block'.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This NSE4 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 NSE4 exam.