Is an IPS just an IDS that blocks?

Essentially yes. An IPS performs the same detection an IDS does, but because it sits inline it can drop or reset malicious traffic instead of only alerting on it.

Can one device be both an IDS and an IPS?

Yes. Many next-generation firewalls and security appliances include both, and you can run a given signature in detect (alert only) or prevent (block) mode.

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IDS vs IPS

IDS and IPS both inspect network traffic for malicious activity, but only one of them can stop it. The difference comes down to where the device sits and whether it can take action.

Last updated June 2026

IDS vs IPS side by side
Aspect	IDS	IPS
Full name	Intrusion Detection System	Intrusion Prevention System
Placement	Out of band, watches a copy of traffic (SPAN or TAP)	Inline, traffic passes through it
Action	Detects and alerts only	Detects and actively blocks or drops
Response	Passive: logs and notifies	Active: drops packets, resets connections
If it fails	No effect on traffic flow	Can interrupt the traffic path
Main risk	May not stop an attack in time	A false positive can block legitimate traffic

The bottom line

An IDS watches and warns; an IPS sits in the traffic path and can stop an attack as it happens. On the exam, "inline and blocks" means IPS, while "out of band and alerts only" means IDS.

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FAQ

Is an IPS just an IDS that blocks?
Essentially yes. An IPS performs the same detection an IDS does, but because it sits inline it can drop or reset malicious traffic instead of only alerting on it.
Can one device be both an IDS and an IPS?
Yes. Many next-generation firewalls and security appliances include both, and you can run a given signature in detect (alert only) or prevent (block) mode.

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Written to the CompTIA Security+ SY0-701 objectives. CompTIA and Security+ are trademarks of CompTIA, used here for identification only.