Intrusion Detection System
✅ What is an Intrusion Detection System (IDS)?
An Intrusion Detection System (IDS) is a security tool or software that monitors network or system activities to detect malicious activities, unauthorized access, or policy violations.
➡️ Purpose:
To identify potential security breaches (like hackers, malware, or abnormal behavior).
Alert administrators so they can take appropriate action (e.g., block traffic, investigate).
🔑 Key Functions of IDS:
Monitor Traffic
Continuously checks network or system activities
Detect Threats
Identifies potential attacks or suspicious behavior
Alert Administrators
Sends notifications about possible security incidents
Log Events
Keeps records for auditing and future analysis
Analyze Traffic Patterns
Detects abnormal or malicious patterns
📊 Types of IDS:
Network-based IDS (NIDS)
Monitors entire network traffic for suspicious activities
Detecting DDoS, port scanning, malware in traffic
Host-based IDS (HIDS)
Monitors specific computers/servers (system logs, file changes)
Detecting unauthorized file access or malware
Signature-based IDS
Detects threats using a database of known attack patterns (signatures)
Detects known malware, exploits
Anomaly-based IDS
Detects abnormal behavior compared to usual patterns (uses AI/ML sometimes)
Detects zero-day attacks or unknown threats
Hybrid IDS
Combines signature and anomaly detection
More accurate, reduces false positives
🛡️ Examples of Famous IDS Solutions:
Snort
Network-based (NIDS)
Open-source, widely used for network traffic analysis
Suricata
Network-based (NIDS)
Fast, supports high-speed networks, multi-threaded
OSSEC
Host-based (HIDS)
Open-source, monitors file integrity, logs
Bro/Zeek
Network-based (NIDS)
Focus on analyzing complex traffic behaviors
Security Onion
NIDS + HIDS + SIEM
Comprehensive, open-source threat hunting platform
Cisco Secure IDS
Commercial NIDS
Enterprise-grade with advanced features
⚙️ How IDS Works:
Monitor: IDS listens to all incoming and outgoing traffic (NIDS) or watches system activities (HIDS).
Analyze: It inspects the data using rules, patterns, or behavior models.
Detect: It identifies any suspicious or malicious activity.
Alert: Sends real-time alerts to administrators (via email, dashboards, etc.).
Log: Records the incident for analysis and compliance.
🚨 Example of Attacks IDS Can Detect:
Malware infection
Worm trying to spread inside a network
Brute force attack
Repeated login attempts to guess passwords
DDoS attack
Overwhelming a server with traffic
Port scanning
Attacker scanning for open ports to exploit
SQL injection
Malicious database query via vulnerable web form
🧠 Simple Analogy:
Think of an IDS like a security camera with motion detection:
It watches everything.
If someone tries to break in, it alerts the security team.
It records events for review.
But it doesn't stop the attacker — it only detects and alerts.
(Note: Unlike a Firewall, IDS does not block traffic — it only monitors and alerts.)
🔥 IDS vs Firewall — Quick Comparison:
Primary role
Block/allow network traffic
Detect suspicious activities
Action
Prevent unauthorized access
Alerts on suspicious behavior
Type
Active defense
Passive detection
Example use case
Block access to certain IPs or ports
Detect malware spreading inside network
✅ Summary:
Purpose
Detect attacks and suspicious behavior
Types
NIDS, HIDS, Signature-based, Anomaly-based
Examples
Snort, OSSEC, Suricata, Zeek
Action taken
Monitor, Detect, Alert, Log
Difference from firewall
IDS detects and alerts, firewalls block/allow traffic
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