Key Takeaways
- Defense in depth—multiple security layers.
- Segment networks to limit lateral movement.
- Firewalls are essential but not sufficient alone.
- Monitor traffic for anomalies and threats.
- Encrypt traffic where possible.
- Regular audits identify misconfigurations.
Table of Contents
1. Network Security Fundamentals
Network security encompasses the policies, practices, and technologies used to protect network infrastructure from unauthorized access, misuse, and attack. It operates at multiple layers of the OSI model and requires a defense-in-depth approach.
Key goals include: confidentiality (preventing unauthorized disclosure), integrity (preventing unauthorized modification), and availability (ensuring authorized access when needed).
2. Security Architecture
2.1 Typical Enterprise Architecture
# Network security zones:
┌───────────────────────────────────────┐
│ INTERNET │
└───────────────┬───────────────────────┘
│
┌───────┴───────┐
│ Edge Firewall │
└───────┬───────┘
│
┌───────┴───────┐
│ DMZ │ (Web servers, email, DNS)
└───────┬───────┘
│
┌───────┴───────┐
│ Internal FW │
└───────┬───────┘
│
┌───────────┼───────────┐
│ │ │
┌───┴───┐ ┌─────┴─────┐ ┌───┴────┐
│ Users │ │ Servers │ │Database│
└───────┘ └───────────┘ └────────┘3. Firewalls & ACLs
3.1 Firewall Types
| Type | Layer | Capabilities |
|---|---|---|
| Packet Filter | 3-4 | IP, port, protocol filtering |
| Stateful | 3-4 | Connection tracking |
| Application (NGFW) | 7 | Deep packet inspection, app awareness |
| WAF | 7 | HTTP/HTTPS specific protection |
3.2 Firewall Rules Best Practices
- Default deny—only allow what's needed
- Most specific rules first
- Document purpose of each rule
- Regular rule review and cleanup
- Log denied connections for monitoring
4. IDS/IPS Systems
4.1 IDS vs IPS
| Feature | IDS | IPS |
|---|---|---|
| Mode | Passive (monitoring) | Inline (blocking) |
| Action | Alerts only | Alerts and blocks |
| Risk | No service impact | False positives can block legit traffic |
4.2 Detection Methods
- Signature-based: Known attack patterns
- Anomaly-based: Deviations from baseline
- Behavioral: Protocol violations, suspicious behavior
Tuning Required
Out-of-the-box IDS/IPS generates excessive false positives. Invest time in tuning rules to your environment. Untuned systems lead to alert fatigue and missed real threats.
5. Network Segmentation
Segmentation limits attack spread by dividing networks into zones with controlled access between them.
- VLANs: Logical network separation
- Subnets: IP-based segmentation
- Firewalls: Control inter-segment traffic
- Microsegmentation: Per-workload policies (Zero Trust)
6. Security Monitoring
# Essential network monitoring:
- NetFlow/IPFIX: Traffic metadata
- Full packet capture: Deep analysis
- SIEM integration: Correlation and alerting
- DNS logging: Detect C2, data exfiltration
- SNMP monitoring: Device health7. Wireless Security
- Use WPA3 or WPA2-Enterprise (802.1X)
- Separate guest WiFi from corporate
- Implement wireless IDS
- Disable WPS
- Regular rogue AP scanning
Regular Assessments
Network security isn't set-and-forget. Regular vulnerability scans, penetration tests, and configuration audits identify issues before attackers do. Schedule assessments quarterly at minimum.
8. Frequently Asked Questions
Conclusion
Network security requires defense in depth—multiple layers working together. Segment networks, implement proper firewall rules, deploy IDS/IPS, and monitor continuously. Regular assessments ensure controls remain effective. No single technology provides complete protection; a layered approach is essential.
Continue Learning:
Firewall Guide
Zero Trust