What Is a Firewall?
A firewall is a system that filters and authorizes network traffic based on predetermined rules. Firewalls can be hardware or software, and they are used in many businesses and homes. Depending on the type of firewall, it can look like a standard rack-mount networking box with ports and LEDs or it may have a user interface for settings and traffic data.
Firewalls protect networks by creating a border between an internal trusted network and external untrusted networks such as the Internet. This is done by inspecting incoming and outgoing network traffic for malicious data. Firewalls can then filter out the unwanted or threatening data and allow only legitimate traffic through, while blocking potentially harmful traffic.
Network security professionals must regularly review and update firewall rules. This process helps prevent excessive complexity that can negatively impact firewall performance or create openings for attacks. The process also includes evaluating rules to ensure they conform with regulatory frameworks such as PCI-DSS and HIPAA.
In addition to basic packet filtering, modern firewalls can incorporate content and application layer analysis. For example, a firewall that detects malware trying to spread across a network can block traffic between the affected machines to stop the spread of infection. This is known as dynamic packet inspection (DPI). Firewalls can also use this technology to prevent employees from visiting websites that are considered inappropriate for a business. This is known as web filtering or content filtering. However, it is important to consider the impact of this type of technology on employee privacy and freedom of expression.