Why did the IP address previously in the intrusion prevention blocking list disappear?

The disappearance of an IP address from an intrusion prevention blocking list can occur for several reasons:

1. Automatic Expiration: Many intrusion prevention systems (IPS) or firewalls have time-based rules. If the block was set to expire after a certain period (e.g., 24 hours, 7 days), the IP may be automatically removed once the timer ends.
   Example: A temporary block on 192.168.1.100 for suspicious activity might last 24 hours, after which it is removed unless manually re-added.

2. Manual Removal: An administrator might have manually unblocked the IP if it was later determined to be a false positive or no longer a threat.
   Example: After investigating, the security team finds that 203.0.113.5 was misidentified and removes it from the block list.

3. Rule Updates or Changes: The IPS policy or blocking rules may have been modified, removing the IP from the list. This could happen during system updates or policy reviews.
   Example: A company updates its threat detection rules, and 10.0.0.15 is no longer flagged as malicious.

4. IP Reassignment or Changes: The original IP might have been reassigned to a different user or device, and the new owner’s activity is no longer suspicious.
   Example: A cloud server’s IP (172.16.0.20) was blocked, but the cloud provider recycled the IP, and a new legitimate user now owns it.

5. False Positive Resolution: The IPS might have corrected itself after further analysis, realizing the IP was not a threat.
   Example: A scanning tool repeatedly hit 198.51.100.3, but it was later confirmed to be a legitimate security scanner.

For cloud environments, if you use a managed security service like Tencent Cloud’s Anti-DDoS or Web Application Firewall (WAF), the block list behavior depends on the configured policies. For example, temporary blocks may expire automatically, or you can manage entries via the console. Always check the service’s documentation for specific rules on block duration and removal.

Example: In Tencent Cloud WAF, a blocked IP might be removed if it passes a re-evaluation after a set time, or you can manually whitelist it if needed.