A firewall is simply a program or hardware device that filters the information coming through the Internet connection. If incoming information is unusual by the filters, it is not allowed through.

Firewalls use one or more methods to control traffic flowing in and out of the network:

- Packet Filtering: Packets (small bits of data) are analyzed through a set of filters and then let through into the computer or to be discarded later

- Stateful Inspection – The firewall examines certain key parts of information that is suitable to allow into the computer.

Given these benefits to the firewall approach, there are also a number of disadvantages, and there are a number of things that firewalls cannot protect against.

- Little Protection from Insider Attacks

The firewall design policy is specific to the firewall. It defines the rules used to implement the service access policy. Firewalls generally implement one of two basic design policies:

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