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Chances are if you’ve used the internet for anything more than cat pictures in your lifetime you’ve probably heard the term firewall before. A firewall is basically a protective barrier set up on a network to prevent anything unwanted from being received by the network’s devices. A firewall is often placed in between the machine intended to be protected and it’s connection to the internet, or router.
Firewalls have several methods for deciding which traffic to allow through and which traffic to drop (disallow). When firewalls drop packets, it is often without sending a message to the sender that they were not received.
Packet Filtering is done by analyzing individual packets based on a set of filters. The filters can consist of things such as particular header information (such as a particular source web address) or body information (such as containing certain data). Packets that make it through the filter are allowed through the firewall, whilst the rest are dropped..
Stateful Inspection is a newer method that does not have to analyze individual packets in their entirety but instead only looks at a few key parts of the packet, and compares those parts with a database of what trusted data would look like. If the certain characteristics match, the packets are allowed through — otherwise, they are dropped.
Firewalls are an essential security measure these days — often all networks you will find have at least one. Firewalls prevent just anyone from connecting to your network or server and having more or less free access to anything they can get their hands on.