In computing, a firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. A firewall typically establishes a barrier between a trusted network and an untrusted network, such as the Internet.

Firewalls are categorized as a network-based or a host-based system. Network-based firewalls are positioned between two or more networks, typically between the local area network (LAN) and wide area network (WAN). They are either a software appliance running on general-purpose hardware, a hardware appliance running on special-purpose hardware, or a virtual appliance running on a virtual host controlled by a hypervisor. Firewall appliances may also offer non firewall functionality, such as DHCP or VPN services. Host-based firewalls are deployed directly on the host itself to control network traffic or other computing resources.This can be a daemon or service as a part of the operating system or an agent application for protection.

Setting up a firewall is a complex and error-prone task. A network may face security issues due to configuration errors.^[30]

Firewall policy configuration is based on specific network type (e.g., public or private), and can be set up using firewall rules that either block or allow access to prevent potential attacks from hackers or malware.

Resource: Wikipedia