firewall is your network’s gatekeeper / controlling exactly which data flows in and out. By defining rules, an administrator can allow or block traffic based on criteria such as:

• Source: Is the packet coming from an approved IP or network?

• Destination: Is it headed to a permitted host or subnet?

• Port: Does it target an authorized service port (e.g., 80 for HTTP)?

• Protocol: Is it using TCP, UDP, ICMP, or another protocol your policy allows?

  

Why Firewalls Matter

• Traffic Control: Decide which connections are allowed or blocked.
• Perimeter Defense: Protect internal networks from external threats.
• Policy Enforcement: Ensure only approved services and users can communicate.
• Threat Containment: Limit the spread of malware or attacks by isolating segments.

Primary Functions

1. Packet Filtering
   • Inspects individual packets’ headers (IP address, port, protocol).
   • Fast and lightweight, but stateless (treats each packet independently).
2. Stateful Inspection
   • Tracks the state of active connections (TCP handshakes, sequence numbers).
   • Makes decisions based on the context of the entire session.
3. Application‑Layer Filtering (Proxying)
   • Interprets application protocols (HTTP, FTP) to block malicious payloads.
   • Acts as a “middleman” that terminates and re‑initiates connections.
4. Next‑Generation Features (in NGFWs)
   • Deep packet inspection (DPI), intrusion prevention (IPS), user identity awareness, SSL/TLS decryption.

Firewall Types