IDS vs. IPS: What Are the Differences, and Do You Need Both?

Defining IDS and IPS systems

Intrusion detection systems (IDS) and intrusion prevention systems (IPS) are cybersecurity tools that can alert security teams to possible intrusions in company systems. Intrusion prevention and detection is sometimes referred to as two parts of a single system (IDPS). However, historically, many organizations have deployed one or the other or consider IDS vs. IPS separate but mutually reinforcing functions.

IDS and IPS can operate on hosts (HIDS and HIPS, respectively) or the network (NIDS and NIPS). The earliest IDS applications date back to the 1990s; IPS functionality emerged as organizations looked for automated methods to block malicious activity instead of simply alerting their security teams to its existence.

Processes, applications, and tools that deliver IDS and IPS functionality are common in many organizations. Each tool type has incorporated more automation and machine learning over time. However, many organizations gain detection and prevention capabilities from other technologies in their security stack and may consider replacing legacy IPS and IDS to reduce tool sprawl and modernize their security posture.

Other combinations of security solutions can deliver the detection and response capabilities of IDS, IPS, or IDPS. Some platforms, such as Network Detection and Response (NDR) and Endpoint Detection and Response (EDR), can provide robust IDS or IPS capabilities or enrich these systems with contextualized data, threat analytics, and deeper visibility into networks and endpoints.

IDS-IPS-graphic

What is an intrusion detection system (IDS)?

An IDS is a passive monitor of the network. It sits out of band (not directly in the network path) and relies on a TAP or SPAN port to copy network traffic in real time. Monitored traffic is analyzed against a database of attack signature sets; when it identifies potential traffic that matches a signature, the IDS system fires an alert or generates log data that prompts the SOC to investigate further.

Signature-based detections can be augmented by anomaly-based detections, which are the product of ML-assisted models that analyze traffic against models of normal network traffic to surface unusual activity patterns.

Modern IDS often combine these detection methods to better defend against novel attack patterns that signature-only detection systems would miss. Being out of band, IDS does not interfere with normal traffic and operations. IDS can operate on traditional networks, cloud deployments, and hybrid environments.

What is an intrusion prevention system (IPS)?

An IPS is an inline tool that combines the detection functionality of IDS with blocking capabilities. It is often placed before or after a firewall in the network path. Like an IDS, an IPS works off a set of signatures and ML models. It inspects network traffic and, like the firewall, can block or reject traffic it finds consistent with known attack patterns or deems potentially harmful based on pre-set rules.

Poorly calibrated, an IPS could block legitimate traffic and disrupt critical business processes. It can also introduce latency if it analyzes traffic at high volume or complexity. Because of this, many IPS systems are set to operate in a detection-only mode, effectively turning the tool into an IDS with unused IPS capability. Increasingly, IPS functionality has been built into next-generation firewalls (NGFW) or unified threat management solutions rather than standalone.

Why IDS and IPS are important

Intrusion detection systems (IDS) and intrusion prevention systems (IPS) improve network security and reduce the risk of successful intrusions by identifying and, in some cases, mitigating network-based attacks. IPS’s control function can automatically block certain traffic and reduce demands on the SOC workflow. Well-tuned IDS, and to an extent IPS, can alert the SOC to suspicious traffic flows that may require further investigation or threat hunting.

Both technologies have expanded to cover hosts and networks in cloud environments. Cloud versions must be scalable and able to observe traffic and hosts. In some cases, a legacy IDS or IPS may not have sufficient cloud capabilities and will need to work in conjunction with security tools built for cloud deployments.

IDS and IPS enable advanced threat detection and can also help SOCs undertake incident response that can thwart attackers before they accomplish their strategic objectives. IDS and IPS deployments can help organizations comply with industry regulations or third-party due diligence. IDS can also aid digital forensic investigations, alert SOCs to behaviors that do not comply with internal policies, or uncover evidence of shadow IT that could leave the organization vulnerable to cyber attacks.

IDS vs. IPS: similarities and differences

Feature	IDS	IPS
Signature-based detections	Yes	Yes
Anomaly-based detections	Limited	Limited
Position in network	Out of band	Inline
Real-time traffic monitoring	Yes	Yes
Blocking traffic	No	Yes
Can impact network operations (e.g., latency, unwanted blocks)	No	Yes
Can generate alerts	Yes	Yes

The primary difference between IDS and IPS comes down to their essential function. An IDS is a monitoring process or tool that can identify known malicious traffic patterns or suspicious activity, but it typically does not perform any preventative or remedial steps.

When fully functional, an IPS is a control process or tool that actively allows or restricts traffic. Depending on the organization's needs, traffic permissions may be relaxed or tightened; in some cases, an IPS may operate effectively as a passive IDS.

While IDS and IPS both exist as standalone solutions, increasingly IPS functionality has folded into advanced security solutions such as next-generation firewalls (NGFW) and unified threat management (UTM) platforms. In practical terms, many organizations derive IDS and IPS functionality from a variety of tools in their security stack.

While they have distinct functions, IDS and IPS are not “either/or” solutions. Dual IDPS solutions are simply one proof point that a layered, in-depth defense approach of deploying strong prevention and monitoring is the most effective strategy in a threat landscape where novel attacks and human error are constants.

Limitations and challenges of legacy IDS and IPS

Challenges	Details
False positives	Without regular tuning, IDS/IPS can generate a high number of false positives and contribute to alert fatigue.
Novel attacks/ false negatives	Signature-based detection systems will not pick up attack patterns that do not correlate to the signature database.
Visibility	IDS/IPS do not provide complete visibility into network traffic or address gaps in on-premises, cloud and hybrid network environments.
End-of-life / lack of support	Many IDS/IPS tools are nearing the end of service or do not integrate well with more advanced security solutions.

Augmenting detection and prevention with NDR

Network Detection and Response (NDR) is a prime example of a security platform that encompasses IDS functionality while delivering enhanced capabilities for capturing and analyzing packets from the wire. Similarly to how many NGFW incorporate IPS functionality, NDR platforms deliver and expand on IDS’s detection and alerting ability.

At its core, an IDS operates by matching patterns. It analyzes and compares traffic against a database of known attack signatures or ML-generated models of normal network behavior. When matches to signatures of malicious activity or anomalies occur, it fires alerts to notify the security team. Analysts can leverage IDS alerts when analyzing traffic patterns or threat hunting, and they can write new IDS detections when they discover new threats. In complex environments, however, SOCs need greater visibility and detail about their network traffic than many legacy IDS systems can provide.

A broad and scalable NDR platform can make monitoring and analysis of even the most complex environments possible. Its benefits to the SOC include:

Richer alert context that reduces false positives.

NDR’s monitoring can generate deeper insights into data transfer volume, connecting hosts, ports in use and timestamps than IDS alerts typically provide; best-in-class solutions will also summarize the metadata into comprehensive analysis. The enriched alert context gives security teams greater confidence when they prioritize alerts and determine remediation steps.

Enrichment of encrypted traffic.

Most on-premises and cloud network traffic (including malicious traffic) is encrypted, and decryption is often expensive or impractical. NDR’s analytics can help SOCs understand characteristics of encrypted traffic, including timestamps, packet sizes, flow direction, and even behaviors within the encrypted applications.

Tool integration.

Best-in-class NDR integrates with a wide variety of security solutions and helps SOCs build a comprehensive view of their networks. Its IDS monitoring and alerting capabilities can work in concert with other tools, like packet capture and storage, to improve the organization's overall security posture.

Corelight’s Open NDR Platform delivers IDS and more

Corelight’s Open NDR Platform incorporates open-source Suricata IDS. Enriched network telemetry delivered via the Zeek® analysis platform, combined with Suricata detections, forms the foundation of Corelight’s network evidence. Zeek® aids investigators by generating a unique connection ID (UID) that links all relevant logs generated by individual connections. The combination of alerting, enriched logging, and evidence supports the SOC in streamlining workflows, reducing false positives, and improving detection and threat hunting abilities.

Corelight expands detection and analysis through:

Multi-dimensional detections from signature, behavioral, and anomaly-based to machine-learning
based models.

Targeted collections for network traffic including the Encrypted Traffic Collection, which provides analysts data and detections for monitoring VPN, SSH, RDP, and other connection services as well as the C2 collection for detection of command and control activity.

Integration with IPS, SIEM and other detection solutions. Corelight’s platform is vendor-neutral, and designed to integrate with other tools in the security stack, including endpoint detection and response (EDR), SIEM, and extended detection and response (XDR). Corelight can also supplement NGFW with security-based network analysis that may detect malicious traffic that bypasses the firewall or passes through undetected.

Scalable to cloud environments. Corelight’s functionality extends to cloud and hybrid deployments and covers network traffic and connections that cloud-based security tools can often miss.

Complete triage through a single screen. The Open NDR Platform consolidates telemetry from virtual private clouds, firewalls, north-south and east-west (internal) traffic and all IP addresses within or connected to the network.