What is IPS?

IPS is the active counterpart to IDS: rather than watching a copy of traffic on a TAP or SPAN port, it sits inline between segments so every packet passes through its inspection engine before continuing to its destination. That position is what lets it drop malicious traffic in real time, but it also means the engine has to be fast enough that inspection does not add unacceptable latency to normal traffic, a hard constraint that shapes how vendors design detection logic.

Modern IPS combines several detection layers. Signature databases, updated continuously by the vendor's threat intel feed, match known exploit patterns such as a specific buffer overflow payload or a known webshell upload string. Protocol anomaly detection flags traffic that technically conforms to a protocol's syntax but violates its expected behavior, malformed HTTP headers or unusual DNS query patterns. Rate-based detection mitigates denial-of-service attempts by capping connection rates per source. Some platforms add reputation-based blocking, dropping traffic to or from IPs and domains flagged by threat intelligence regardless of payload content.

Next-generation firewalls now fold IPS in as a built-in engine rather than requiring a separate inline appliance, which is why standalone IPS boxes are less common than they were a decade ago. The IPS logic itself, though, still runs as a distinct rule set inside the NGFW and in cloud-native equivalents like AWS Network Firewall or Azure Firewall Premium.

The central operational risk with IPS is false positives that block legitimate traffic. Because the action is automatic and immediate, a poorly tuned signature can take down a business-critical application the moment it matches. For that reason, security teams typically stage new signatures in detection-only mode, validate them against real traffic for a period, and only promote a signature to blocking mode once they are confident it is not catching benign patterns.