What Is a Firewall?
Firewalls are network security devices that maintain a secure gateway between devices inside the network perimeter and those outside it. They’re commonly deployed in hardware or software form, or a combination of both, and can be positioned at the network edge, or on each host device.
A firewall’s ruleset defines which data is allowed to enter and leave a network based on parameters such as source and destination IP addresses, port numbers and communication protocols. The rules are nested together into Access Control Lists (ACL) that evaluate traffic in order, and once a packet matches a rule, the firewall takes action—such as allowing or denying the traffic.
When a new application is added to a business network, a firewall allows the security team to apply specific security policies to that particular application. This helps ensure critical applications have the resources they need to function properly and that non-essential applications don’t use up bandwidth that could be better spent on other important tasks.
In addition to traditional firewall capabilities, many next-generation firewalls (NGFW) include advanced functionality such as identity awareness, sandboxing and threat intelligence feeds. This creates a well-rounded mechanism for protection against sophisticated malware attacks and prevents the spread of new risks in real time.
Some firewalls have been used unethically for censorship and control purposes, such as the Great Firewall of China, which restricts access to certain websites and content deemed sensitive politically or socially, and monitors online activity to keep tabs on users. Other firewalls can also be used to track employee activities, raising concerns about privacy and personal freedom.