Intrusion and file policies work together as the last line of defense before traffic is allowed to its destination:
- Intrusion policies govern the system's intrusion prevention capabilities.
- File policies govern the system's file control and AMP for Firepower capabilities.
All other traffic handling occurs before network traffic is examined for intrusions, prohibited files, and malware. By associating an intrusion or file policy with an access control rule, you are telling the system that before it passes traffic that matches the access control rule's conditions, you first want to inspect the traffic with an intrusion policy, a file policy, or both.
You can configure intrusion and file policies on rules that allow traffic only. Inspection is not performed on rules set to trust or block traffic. In addition, if the default action for the access control policy is allow, you can configure an intrusion policy but not a file policy.
For any single connection handled by an access control rule, file inspection occurs before intrusion inspection. That is, the system does not inspect files blocked by a file policy for intrusions. Within file inspection, simple blocking by type takes precedence over malware inspection and blocking. Until a file is detected and blocked in a session, packets from the session may be subject to intrusion inspection.
Note: By default, the system disables intrusion and file inspection of encrypted payloads. This helps reduce false positives and improve performance when an encrypted connection matches an access control rule that has intrusion and file inspection configured. Inspection works with unencrypted traffic only.