A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. A firewall establishes a barrier between a trusted internal network and an untrusted external network, such as the Internet. Firewalls can be hardware or software-based and are used to prevent unauthorized access to or from a private network. They can help protect against attacks that exploit vulnerabilities in the network infrastructure.
A firewall works by monitoring incoming and outgoing network traffic and comparing it against a set of predefined security rules. These rules determine whether the traffic is allowed or blocked. For example, a firewall rule might allow all traffic from a specific IP address or block all traffic to a specific port. Firewalls can also use more advanced techniques such as stateful inspection, where the firewall tracks the state of network connections and makes decisions based on the context of the traffic. By filtering network traffic based on these rules, firewalls can help prevent unauthorized access to or from a private network.
Firewall rules can vary depending on the specific needs of an organization or individual. Some common firewall rules include allowing or blocking traffic based on the source or destination IP address, port number, or protocol. For example, a firewall rule might allow all traffic from a specific IP address range or block all traffic to a specific port. Other common firewall rules include allowing or blocking traffic based on the application or service being used, such as allowing web browsing traffic but blocking file sharing traffic. Firewall rules can also be used to restrict access to specific websites or online services.