🧱 Firewall

Purpose

To prevent unauthorised access to a machine or network.

How?

It monitors all traffic which passes through it and can permit or deny it based on programmed rules.

Types

Hardware and software

Where are they located and what do they protect?

A physical firewall is a physical device which is located at (usually) the internet connection of the network. It protects the entire network from outside intrusion.
A software firewall is a program which runs on an individual device and just protects that device from outside intrusion.

Parameters

The parameters that can filter traffic are:
- Source or destination IP address.
- Protocol used such as HTTP
- Port number used such as 80
- Specific words or phrases
- Domain names
- Program or application

This is not an exhaustive list and are only examples.