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:

Function	Description
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:

Type	Description	Example Use Case
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:

IDS Name	Type	Notes
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:

1. Monitor: IDS listens to all incoming and outgoing traffic (NIDS) or watches system activities (HIDS).

2. Analyze: It inspects the data using rules, patterns, or behavior models.

3. Detect: It identifies any suspicious or malicious activity.

4. Alert: Sends real-time alerts to administrators (via email, dashboards, etc.).

5. Log: Records the incident for analysis and compliance.

---

🚨 Example of Attacks IDS Can Detect:

Attack Type	Example
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:

Feature	Firewall	IDS
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:

Aspect	IDS
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