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Security · Cisco / Network Engineer Difference between IPS, IDS, and a firewall?
Firewall — policy-based traffic filtering by IP/port/protocol. Stateless (legacy) or stateful (modern). Default-deny rule set. IDS (Intrusion Detection System) — passive monitoring. Detects malicious patterns and alerts. Doesn't block traffic by itself. Sits on a SPAN/mirror port. IPS (Intrusion Prevention System) — inline detection + automatic blocking of malicious traffic. Sits in-line in traffic path. Modern next-gen firewalls (NGFW like Palo Alto, Fortinet, Cisco Firepower) combine all three.
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