What is a  firewall ?

We explain what a firewall is, what it is for and how this system works. In addition, the types that exist and the Windows firewall.

1. What is a  firewall ?

In computer science , and more specifically in telecommunications, it is understood by  firewall  (in English) or firewall to a system or device capable of allowing, limiting, encrypting or decoding communications traffic between a computer (or a local network) and the rest of the Internet, preventing unauthorized users or systems from accessing.

A firewall may well be physical or digital, that is, an apparatus or a piece of software , and in both cases it is only a first step of defense in the world of computer networks , indispensable but not sufficient to guarantee security against to cyber attacks and third party intrusion.

This type of technology borrows from the mechanism for fire prevention that is usually applied in green areas or in vulnerable buildings, and which consists of a wall or a wasteland area, free of any flammable content, which limits the indefinite expansion of the Fire in case of fire.

The precursors of the firewall  emerged during the 1980s , when the Internet was still a recent field of knowledge and had not yet been considered the possible margin of damage through  hacking  or cyber terrorism.

Since the first massive cyber attacks by viruses and digital worms at the beginning of the following decade, digital protection has been getting better and better , at the rate at which new pieces of harmful software, known as  malware, appear.

2. What is a firewall for?

A firewall simply serves to interrupt unauthorized or suspicious connections between a computer or computer system, and the Internet. In this way the remote communication between malicious users ( hackers ) and the local system is cut , or between pieces of malware installed furtively on the system and the outside of the system, thus preventing it from operating as a spearhead in the cyber invasion.

It is, therefore, a guard who prevents the entry or exit of unauthorized or suspicious communications , based on discernment criteria that are updated from time to time.

3. How does a firewall work?

Firewalls distinguish between permitted and dangerous or suspicious connections, based on different procedures, such as:

• Firewall policies . Using the IP numbers and other identification systems, the firewall suspends any communication request that does not come from the internal network or from the system itself, disguising behind the internal IP the set of internal resources, so that no one can monitor them from outside.
• Content filtering . Through a system of exclusion rules in which the user can have the last word, the firewall distinguishes between problematic, suspicious or insecure content, and those that remain at the user’s discretion. Thus, access to Web pages or entire servers can be blocked as a precaution.
• Services  antimalware . Many firewalls have built-in virus and malware definitions provided by various defensive programs, so as to also help to have the expansion of these pernicious programs.
• Services  DPI . This is called the Deep  Package Inspection (IPP or DPI  ) procedure, which adds a second layer of security to the system, reviewing the deep content of the information packets received. 

4. Firewall Types

There are the following types of firewall:

• Gateway application level . Applies only for specific applications considered risky, such as FTP servers or free exchange of information between users (P2P). It is usually very effective, but imposes a reduction in system resources.
• Gateway level circuit . Monitor the establishment of TCP or UDP connections through security sessions.
• Network layer firewall . It operates based on the inspection of IP addresses and the exchange of IP packets, using alternate data such as the MAC address.
• Application layer firewall . It already operates based on applications, controlling its way of reaching the Internet, for example, through Proxys.
• Personal firewall . Firewalls chosen by the user and installed in the system to meet the individual system use requirements.

5. Windows firewall

The famous Microsoft operating system , called Windows, includes a firewall software among its automatic defense options. This option was included in the System Security Center from its XP Service Pack 2 version , seeking to offer greater control and defense of system stability for its users.

This firewall is updated along with the other Windows applications to be up-to-date on cyber threats, and is automatically activated unless there is some other antivirus or firewall software that has the connection management privileges, in which case the firewall of Windows will remain disabled.