Types of Firewalls
A firewall is software or hardware that protects a computer against malicious attacks. These include viruses and spyware that can collect data, disrupt system functions or even render a computer unusable. Firewalls work by monitoring data traffic to detect and stop threats at the network perimeter, in between networks or on individual devices.
Most operating systems include a built-in firewall feature and can be augmented by downloaded software from an established computer store or software vendor. These personal firewalls are installed on the host computer and control incoming and outgoing data specific to that device. They operate based on predefined rules that examine the information contained within each data packet, such as headers and query strings. This allows the user to control what applications are allowed to access the system’s network services.
Another type of firewall is a circuit-level gateway, which works between trusted networks to control communication. This type of firewall analyzes the information contained in each data packet at a session level (OSI model’s session layer) and keeps track of vetted connections. This can help prevent unauthorized access and malware by not allowing new sessions unless they are verified as legitimate.
Other types of firewalls are more advanced and may use stateful inspection technologies or TCP handshake verification to offer more serious protection against malicious activities. These systems can also keep a contextual database of vetted connections and draw on historical traffic data to determine how much scrutiny each new packet warrants. These systems can be expensive and slow down performance compared to other solutions, but they offer the most comprehensive security available.