In computing, a firewall is a network security system that monitors and controls the incoming and outgoing network traffic based on predetermined security rules.

Network security consists of the policies and practices adopted to prevent and monitor unauthorized access, misuse, modification, or denial of a computer network and network-accessible resources.

Computing is any goal-oriented activity requiring, benefiting from, or creating a mathematical sequence of steps known as an algorithm — e.g. through computers.

Network traffic or data traffic is the amount of data moving across a network at a given point of time.

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A firewall typically establishes a barrier between a trusted, secure internal network and another outside network, such as the Internet, that is assumed not to be secure or trusted.

The Internet is the global system of interconnected computer networks that use the Internet protocol suite to link billions of devices worldwide.

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Firewalls are often categorized as either network firewalls or host-based firewalls.


Network firewalls filter traffic between two or more networks; they are either software appliances running on general purpose hardware, or hardware-based firewall computer appliances.

A software appliance is a software application combined with just enough operating system to run optimally on industry-standard hardware or in a virtual machine.


Host-based firewalls provide a layer of software on one host that controls network traffic in and out of that single machine.


Firewall appliances may also offer other functionality to the internal network they protect, such as acting as a DHCP or VPN server for that network.

A virtual private network extends a private network across a public network, and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network.

The Dynamic Host Configuration Protocol is a standardized network protocol used on Internet Protocol networks.

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