Firewalls and IDS Guide
Table of Contents
Firewalls
Types of Firewalls
| Type |
Description |
Use Cases |
| Packet Filtering |
Basic filtering based on packet headers |
Network perimeter, basic protection |
| Stateful Inspection |
Tracks connection state |
Enterprise networks, advanced filtering |
| Application Layer |
Deep packet inspection |
Web applications, complex protocols |
| Next-Generation |
Advanced features and integration |
Modern enterprise security |
Firewall Rules
# Basic iptables rule structure
iptables -A INPUT -p tcp --dport 80 -j ACCEPT
# Windows Firewall rule
New-NetFirewallRule -DisplayName "Allow HTTP" -Direction Inbound -Protocol TCP -LocalPort 80 -Action Allow
# Common rule components:
- Source/Destination IP
- Port numbers
- Protocol
- Action (Allow/Deny)
- Direction
Intrusion Detection Systems (IDS)
IDS Types
Common Types:
- Network-based IDS (NIDS)
- Host-based IDS (HIDS)
- Protocol-based IDS
- Application Protocol-based IDS
Detection Methods
| Method |
Description |
Advantages |
Disadvantages |
| Signature-based |
Pattern matching |
Low false positives |
Can't detect new threats |
| Anomaly-based |
Behavior analysis |
Can detect new threats |
Higher false positives |
| Heuristic |
Rule-based detection |
Flexible detection |
Complex configuration |
Configuration Guidelines
Firewall Configuration
# Zone-based configuration
zone trusted
default-action permit
interface eth0
zone untrusted
default-action deny
interface eth1
# Policy rules
policy from trusted to untrusted
match protocol tcp
match port 80,443
action permit
IDS Configuration
# Snort rule example
alert tcp any any -> $HOME_NET 80 (msg:"Web Attack"; content:"exploit"; sid:1000001;)
# Suricata configuration
vars:
address-groups:
HOME_NET: "[192.168.0.0/16,10.0.0.0/8]"
EXTERNAL_NET: "!$HOME_NET"
Monitoring and Management
Monitoring Tools
- SIEM (Security Information and Event Management)
- Log analyzers
- Network monitoring tools
- Performance monitors
Alert Management
Alert Priorities:
- Critical: Immediate response required
- High: Response within 1 hour
- Medium: Response within 24 hours
- Low: Review during maintenance
Best Practices
Firewall Best Practices
- Default deny policy
- Regular rule review
- Proper documentation
- Change management
- Regular backups
IDS Best Practices
1. Sensor Placement
- Network chokepoints
- Critical segments
- DMZ monitoring
2. Tuning
- Regular rule updates
- False positive reduction
- Performance optimization
3. Response Planning
- Incident response procedures
- Escalation matrix
- Documentation requirements
Popular Tools
| Tool |
Type |
Key Features |
| pfSense |
Firewall |
Open-source, feature-rich |
| Snort |
IDS/IPS |
Rule-based detection |
| Suricata |
IDS/IPS |
Multi-threaded, high performance |
| OSSEC |
HIDS |
File integrity, log analysis |
Implementation Steps
Deployment Process:
- Network assessment
- Policy development
- Tool selection
- Initial deployment
- Testing and validation
- Tuning and optimization
- Documentation and training
- Ongoing maintenance
Performance Considerations
# Resource requirements
- CPU: Multi-core recommended
- Memory: 8GB minimum
- Storage: Fast disks for logging
- Network: Sufficient bandwidth
# Optimization tips
- Rule optimization
- Log rotation
- Regular maintenance
- Performance monitoring