Firewall

01What is a Firewall?

Firewall works like a "security gate":

• Examines incoming and outgoing traffic
• Allows or blocks based on rules
• Prevents unauthorized access

Internet → [Firewall] → Internal Network
             ↓
         Rules:
         ✓ Port 80 (HTTP) - Allow
         ✓ Port 443 (HTTPS) - Allow
         ✗ Port 23 (Telnet) - Block

02Firewall Types

1. Packet Filtering Firewall

• Simplest type
• Looks at IP address and port number
• Fast but basic

2. Stateful Firewall

• Tracks connection state
• Makes smarter decisions
• "Is this packet part of an existing connection?"

3. Application Layer Firewall

• Application-level control
• Analyzes HTTP, FTP content
• Most detailed control

4. Next-Generation Firewall (NGFW)

• Combines all features
• IPS, antivirus, SSL inspection
• Modern enterprise solution

03Firewall Rules

Example Rule Table:

Rule Logic:

• Rules are checked in order
• First matching rule is applied
• Default: "Deny All"

04Software vs Hardware Firewall

05DMZ (Demilitarized Zone)

Safe zone for servers open to the outside:

Internet → [Firewall] → DMZ → [Firewall] → Internal Network
                         ↓
                    Web Server
                    Mail Server

• Servers in DMZ are accessible from internet
• But they can't access internal network
• If attacked, internal network is protected

06Summary

• Firewall = Network security gate
• Filters incoming/outgoing traffic
• Rules applied in order
• DMZ isolates external servers