Firewall Configuration

Overview

Firewalls enforce traffic rules at network boundaries and host level, allowing only approved communication paths.

Rule Design Principles

• Default deny posture
• Explicit allow for required ports and sources
• Minimal broad CIDR ranges
• Version-controlled rule changes

flowchart LR
    A[Incoming Traffic] --> B{Rule Match?}
    B -->|Allowed| C[Forward]
    B -->|Denied| D[Drop and Log]

Practical Example

# Allow HTTPS
ufw allow 443/tcp
# Deny everything else by default
ufw default deny incoming

Production Example

Cloud environments frequently combine security groups, network ACLs, and host firewalls for layered defense.

Common Pitfalls

• Overly permissive temporary rules never removed
• No logging for denied traffic
• Manual rule drift across environments

Key Takeaways

• Default deny plus explicit allow improves security.
• Logging supports troubleshooting and audit requirements.
• Rule automation reduces configuration drift.