A firewall is a form of network security that acts as a barrier between a computer network and the external world. It prevents unauthorized access to the internal network by controlling the incoming and outgoing network traffic based on predetermined security rules. Firewalls are commonly used for internet security, protecting a computer from malicious software, and other types of malicious attacks.
The concept of a firewall is said to have originated in the late 1980s, when the U.S. Defense Advanced Research Projects Agency (DARPA) implemented an internet firewall to protect their internal network. It was designed to prevent external users from gaining access to the internal network. From this point, the idea of a firewall as a form of network security was developed and evolved over time.
A firewall is a network security system that monitors and controls incoming and outgoing network traffic. It is designed to protect a network from malicious attacks by inspecting and filtering the traffic that passes through it. It can be implemented in hardware or software form, or a combination of both.
A firewall is composed of two main components:
Ruleset: The ruleset defines the criteria for determining which traffic is allowed to pass through the firewall. Each rule contains a set of conditions that must be met for the traffic to be allowed or denied.
Filter: The filter is responsible for applying the ruleset to incoming and outgoing network traffic. It examines the data packets that pass through it and either allows or blocks them based on the ruleset.
To illustrate the workings of a firewall, consider the following example. Let's say a company's network is protected by a firewall that has a ruleset that allows only web traffic (HTTP and HTTPS) to pass through it. Any other traffic, such as FTP or SSH, will be blocked.
When a user on the internal network attempts to access a website, the firewall will examine the data packets that are sent and received. If the packets match the criteria specified in the ruleset (i.e. HTTP or HTTPS traffic) then they will be allowed to pass through. If the packets do not match the criteria, they will be blocked.
Firewalls are an effective form of network security, as they provide a barrier between a network and the external world. However, they can also be a source of frustration for users, as they can block legitimate traffic. Additionally, they can be difficult to configure and maintain, and may require ongoing maintenance and updates to remain effective.