Introduction: What is firewall?

Many times we heard the word firewall and we know that it's something  related to our computer's security but we don't really understand what exactly is firewall. In this post, you'll be able to have a clearer idea of what are firewalls and a little about the development of firewalls over time.

Definition of Firewall

Firewalls are security software or hardware that control access to a network. They can be a combination of both software and hardware too. Firewalls protect all systems against external threats.

They are designed to permit or deny network transmissions based on a set of rules called protocols.

This technology emerged in the late 1980s when the Internet technology is still quite a new technology.

Development of firewalls

First Generation

The first generation is known as packet filtering. The packet filters works by inspecting the packets that are transferred between computers and the Internet. The packet match the packet filters' set of rules then the filter will determine whether to drop or reject the packet that is transmitted.

Second Generation

The second generation is known as stateful filters. It is also known as circuit level firewall. This stateful packet filters can work up to four layers. They work by maintaining  records of all connections passing through the firewalls. These filters can also determine if a packet is the start of a new connection, part of an existing connection or an invalid connection. Another special feature is that these filters can store all packets and search for malicious codes when the packets are combined.

Third Generation

The third generation is known as application layer. Third generation firewalls control inputs, outputs and/or access to,from or by an application  or service. These firewalls can detect if an unwanted protocol is sneaking through non-standard protocol or if the protocol is abused in any harmful ways.


References:
Timothy J. O'Leary, Linda I. O'Leary,Computing Essentials 2012,McGraw Hill,2011
en.wikipedia.org/wiki/Application_layer
en.wikipedia.org/wiki/Firewall_(computing)