What is a Firewall?
Firewalls protect networks by filtering incoming and outgoing data, determining whether that data is safe or poses a threat. They are installed inline across network connections and examine every data packet (a group of bits that make up a connection) to determine what should be done with it. A firewall can decide to allow, deny, or drop a packet based on a set of preconfigured rules. The person implementing the firewall, also called a firewall administrator, has a clear idea of what should happen with the traffic and can translate that into a series of technical statements (a ruleset) that tells the hardware or software what to do with the data packets.
In the late 1980s and early 1990s, AT&T Bell Labs researchers, including Presotto, Sharma, and Nigam, developed the circuit-level gateway, a firewall that vetted ongoing connections without having to check each individual data packet. This paved the way for later, more advanced firewall systems.
Modern firewalls can be categorized as either network-based or host-based systems. Network-based firewalls are positioned between two or more networks and can be either a hardware appliance, a software program running on general purpose hardware, or a virtual appliance running on a hypervisor. Host-based firewalls monitor and control the network traffic on a per device basis.
To ensure that your firewall solutions deliver the best performance, implement a consistent update and patch management process. Minimize the number of logging and audit functions that are enabled to reduce the strain on your network, and consider deploying separate firewalls for VPNs to ease bandwidth demands.