How A Firewall Works: The What And The How

Screened Subnet: The Payoff of Preventing Network Attacks

How A Firewall Works: The What And The How

A firewall is a form of security that businesses use to protect their networks. It does this by blocking all unauthorized access and only allowing authenticated connections. A firewall can either be hardware-based or software-based, but they all work in the same way. This blog post will explore how firewalls work and what you need to know about them.

How Does a Firewall Protect Your Data?

A firewall can monitor all incoming and outgoing network traffic and detect any unauthorized access attempts or security breaches. Once detected, firewalls can either send an alert through the logs reviewed by IT staff for potential countermeasures or shut down that communication link entirely until further notice.

Firewalls are also used in wireless routers, virtual private networks (VPNs), and web servers to protect the network from being used without authorization. It is an essential part of business security protocols that are often required by law or regulation. 


Spam is a type of electronic junk mail used to distribute unsolicited content and usually contains advertising. It also protects against viruses, malware, and spyware. It can be hazardous if they access or damage data on your computer. Spyware software that tracks the user’s activity and then sends information back to its creator – can be used for identity theft or other malicious purposes like stealing personal information like credit card numbers, login credentials, etc.

What is a Firewall?

A firewall is a software or hardware-based system that controls the incoming and outgoing network traffic. To get a better understanding of whether a firewall is a software or hardware, read our article.[Is A Firewall Hardware Or Software article here]

It may also be considered a control system that prevents unauthorized access in local area networks (LAN). This makes it easier for companies to maintain compliance with industry standards and legal regulations.

The purpose of this process is to prevent unauthorized access into an organization’s private networks by malicious users, bots, programs, etc. They are commonly used in businesses to protect their digital assets, including company data, financial records, web servers, and email servers.

Hardware-based firewalls are typically appliances that provide firewall services for multiple devices simultaneously. In contrast, software firewalls are applications installed on a computer system that performs these functions by filtering all of its traffic through one particular interface (frequently, but not consistently, the network adapter).

Types of Firewall

There are main types of firewalls,

Packet Filtering Firewall

This basic firewall works by checking each data packet as it passes through the router and allowing or disallowing traffic based on its source address. According to the source or destination port, it can also be filtered.

Proxy Service Firewall

It works by routing all traffic through a proxy server. This is done to access the Internet or another network. The user connects with the proxy server first, and then that server connects on behalf of the client to one more server that that client requests.

Stateful Packet Filtering Firewall

This type of firewall is more complex and more innovative than a packet filtering device. They keep track of all communications going through it for both directions – what came in and went out – maintaining an awareness of each stream which helps protect the network against potential attacks. It maintains an awareness of each stream which helps protect against potential attacks.

Application Layer Gateway (ALG)

This is usually the most secure firewall. It only allows authorized connections to pass through it while blocking all others. Still, it can be challenging to configure and maintain, making them impractical for many companies who cannot afford the time or expertise needed.

Circuit-Level Gateway

This type of firewall creates an individually unique session for every connection passing through it, allowing users to access only those services they need to use while blocking other types (like email). 

This way, if one service becomes compromised, the rest will remain unaffected. The downside of circuit-level gateways is their inability to selectively monitor packets within a communication flow without disrupting it entirely.

What Firewalls Block and Allow

Firewalls work by blocking all unauthorized access while allowing only authenticated connections. This means it will block any connection not sent from a pre-authorized location (such as your computer) or to an authorized destination (the website you are trying to view). 

A firewall makes this using rules, which act as filters on the network traffic passing through them. Each rule has two parts: its “ingressfilter (preventing unauthorized entry) and its egress filter (making sure no data is leaking out of the organization’s networks). 

These rules can be configured manually or automatically according to certain conditions such as time of day, user identity, etc. The following example shows how these types of rules work,

When a computer tries to connect to the Internet, it sends out packets of information filtered by all routers between itself and its destination (in this case, an outside website). If one router is configured with firewall rules blocking certain types of traffic, those packets will be blocked before they reach their intended location. 

A similar process takes place when you try to visit a website on your local network. The web page’s data travels through the firewall, which filters the content based upon predefined rules for authorized users only to have access. In contrast, unauthorized users don’t get in at all or can’t view any sensitive content if allowed inside. Firewalls protect many different things, including:

Inbound Attacks 

Attacks that come from the outside world into your network. These can be anything from a hacker breaking into a computer on your internal network to someone trying to use a malicious program like a virus or worm.

Outbound Attacks 

These are attempts by unauthorized use within the organization’s networks to access data and resources outside of the organization.

Attackers can attempt to use many different types of attacks to get into your system. Still, Firewalls are designed to protect you against all these things by blocking unauthorized communications and access attempts that could be harmful or dangerous.


There are many different types of attacks that can be launched against businesses and other organizations. Firewalls protect you by blocking all unauthorized communications before they reach your internal resources, which means unwanted users will not be able to access or use them for their purposes. They can protect the entire network, including digital assets.

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