The Function of Firewalls
- Packet Inspection: Firewalls analyze packet headers to determine the source and destination IP addresses, port numbers, and protocols (e.g., TCP, UDP).
- Content Filtering: Modern firewalls, known as next-generation firewalls (NGFWs), can inspect the content of packets, providing protection against application-level threats.
- Firewalls operate at different layers of the OSI model.
- Traditional firewalls focus on the network and transport layers, while next-generation firewalls extend their capabilities to the application layer.
Whitelists and Blacklists
- Whitelists: Allow only approved entities (e.g., IP addresses, domain names) to access the network.
- Blacklists: Block known malicious or unwanted entities from accessing the network.
- Use whitelists for critical systems where only specific, trusted sources should have access.
- Blacklists are more suitable for general environments where known threats need to be blocked.
Firewall Rules
- Rule-Based Filtering: Firewalls are configured with a set of rules that specify which types of traffic are allowed or blocked.
- Attributes: Rules are based on source and destination IP addresses, port numbers, and protocols.
- Priority and Sequence: Rules are processed in order, and the first matching rule determines the action (allow or block).
A firewall rule might allow traffic from a specific IP address on port 80 (HTTP) while blocking all other incoming traffic.
Strengths of Firewalls
- Access Control: Firewalls restrict unauthorized access by filtering traffic based on predefined rules.
- Traffic Monitoring and Logging: They provide detailed logs and real-time alerts on suspicious activities.
- Versatility and Scalability: Modern firewalls offer features like VPN support, intrusion prevention systems (IPS), and deep packet inspection (DPI).
- Application-Level Security: Next-generation firewalls can inspect data packets at the application layer, protecting against application-level attacks.
