Firewall Ultimate Guide: An Introduction


Network firewall security or firewall for short refers to a network security system. It tracks and manages incoming and outgoing traffic in a network infrastructure. With a set of security protocols and firewall settings, a firewall serves as a fence. It's a boundary between a trusted internal network from untrusted external channels.

Why You Should Get A Firewall?

The areas of 5G, artificial intelligence (AI), and Internet of things (IoT) continue to grow. But cybercriminals are also using these technologies to enhance their security breach approaches. They aim at your personal data and hard-earned money.

The full rollout of 5G in 2020 skyrockets the adoption of more IoT devices in homes and offices. More devices get linked to networks and the Internet. Unfortunately, cybercriminals can exploit any of these to penetrate internal networks. Also, new zero-day exploits can work with AI-enabled systems. This allows cybercriminals to strike in spots where entities are not prepared to defend.

These trends call for the necessity of having a more sophisticated firewall. A firewall that can respond and block today’s wave of threats. Through this ultimate guide, we’ll help you choose the right firewall solution that you should install for your home and organization.

Firewall: A Brief History

The etymology of the word firewall refers to a physical wall that isolates a fire. The wall works to prevent the spreading of fire among nearby structures. The term is also used in a structure that separates the engine room of a vehicle from the passenger area.

The growth of computers and the Internet in the 1980s led to the use of firewalls in network technology. The earliest forms of hardware firewall were the routers employed in that era. Separating networks from one another, they prevented the spread of problems among them. These firewall hardware routers served as first cybersecurity solutions.

1st Generation Firewalls

In 1988, the first paper on firewall technology surfaced. Digital Equipment Corporation (DEC) engineers developed packet filter firewalls. Bill Cheswick and Steve Bellovin of AT&T Bell Labs focused on packet filter research. They came up with a working solution for the company.

2nd Generation Firewalls

AT&T Bell Labs employees Dave Presotto, Janardan Sharma, and Kshitij Nigam worked on the next wave of firewalls from 1989 to 1990. Called as circuit-level gateways, these firewall hardware solutions still do their predecessors' functions. They can remember the communications between endpoints as well.

But this type of firewall can be vulnerable to denial-of-service (DoS) attacks. Cybercriminals do this by bombarding the firewall with false connections. Doing so overwhelms the firewall's connection state memory.

3rd Generation Firewalls

In 1993, Wei Xu, Peter Churchyard, and Marcus Ranum came up with a software or application firewall. They called it Firewall Toolkit (FWTK). This served as the foundation of Trusted Information Systems' Gauntlet firewall.

Application layer filters can recognize applications and protocols. These include Domain Name System (DNS), File Transfer Protocol (FTP), and Hypertext Transfer Protocol (HTTP). This type of firewall uses this feature to detect any rogue app or service that tries to go past the firewall.

Next Generation Firewalls

Next generation firewall (NGFW) surfaced in 2012. This type of firewall performs a deeper or wider inspection at the application layer. Current firewalls feature intrusion prevention systems (IPS), web application firewall (WAF), and user identity management integration.

Thirty years of firewall technology’s development resulted in the many types and brands that you can choose from.

Types of Firewalls

Firewalls fall into either of these two categories: network-based firewall or host-based firewall. Network-based firewalls sift traffic between two or more networks on network hardware. Meanwhile, host-based firewalls run on host computers and handle network traffic on them.

Packet Filters

Packet filters or network layer firewalls are the first reported kind of firewalls. These firewalls inspect the packets transferred among computers. Packet filters operate at the low level of the TCP/IP stack. They can reject and notify the sender when the packet does not match the admin's firewall rules. Packets are filtered by source and destination network addresses, port numbers, and protocol. Network layer firewalls fall into two sub-categories: stateful and stateless. Most packet filters are classified as an open source firewall.

Stateful Firewalls vs Stateless Firewalls

Stateful firewalls track the operating state and properties of network connections. They can recognize network packets and let those that match a known active connection pass.

Meanwhile, stateless firewalls protect networks based on static information. They filter packets based on the individual packets alone. Compared to stateful firewalls, stateless firewalls are less rigorous. They cannot observe the general pattern of incoming packets. Patterns are essential when blocking larger attacks beyond the individual packet level.

Application Layers

This type of firewall runs on the TCP/IP stack’s application level. It intercepts all packets coming in and going out among applications. Application firewalls attach to socket calls. Thus, they are also known as socket filters. They regulate the link between the application layer and the lower layers of the OSI (Open Systems Interconnection) model.

Application firewalls perform like packet filters. But their filtering works on a per-process basis instead of a per-port basis. This per-process approach has limited efficacy. They cannot filter every potential connection that may happen with other processes. This approach cannot defend against a process modification like a memory corruption exploit. Considering these vulnerabilities, application firewalls, new generation application firewalls emerged. These rely on mandatory access control (MAC) or sandboxing to protect vulnerable services.

Proxy Servers

Proxy servers work as a firewall by addressing input packets while blocking other packets. Proxy servers serve as a gateway from one network to another. They do it for a specific network application and function as a proxy on behalf of a user in the network.

Proxy servers make tampering with an internal network from an external one harder. An internal anomaly does not mean a security breach that external elements can use. Still, cybercriminals may try to pass packets to an internal network by IP spoofing.

NAT Functionality

Firewalls’ network address translation (NAT) functionality works to hide computers' true addresses. NAT function resolves the limited IPv4 routable addresses available for individuals or organizations. This reduces the cost of getting public addresses for each computer in a company. NAT functionality’s ability to hide addresses protects devices against network vulnerabilities.

Hardware Firewalls vs Software Firewalls

Hardware firewalls are like routers but with more features. Today, many routers integrate a hardware firewall. Still, they lack the features of true hardware firewalls. Hardware firewalls are placed in between the modem and the router. They act as a barrier between the internal network and the Internet, filtering the packets.


100% network traffic control
Almost impossible to hack or disable
Effective in blocking websites
Effective in restricting access to non-PC devices
Easy to install
No impact on network performance


Cannot restrict access based on user
Easy to bypass on mobile devices
Incapable of filtering based on content
Installation can be physically challenging
More limited in terms of features

Hardware Firewall Vendors

Barracuda Firewall
Cisco ASA Firewall
Cisco Meraki Firewall
Checkpoint Firewall
Cujo Firewall
F5 Firewall
Fortinet Firewall
Fortigate Firewall
Juniper Firewall
Mikrotik Firewall
Netgear Firewall
Palo Alto Firewall
Raspberry Pi Firewall
RATtrap Firewall
Sonicwall Firewall
Sophos Firewall
Ubiquiti Firewall
Watchguard Firewall
Zyxel Firewall

Software firewalls are applications that you install on your device. Operating systems come with built-in software firewalls. There is a Linux firewall, Mac firewall, Windows firewall, and Ubuntu firewall. The latest version of Windows OS comes with Windows 10 firewall. While Android doesn't have a native firewall, many Android firewall options are available for download. Third-party software firewalls can also be installed on other OSes as well.

Equipped with more advanced features, software firewalls provide greater granularity of control. They can filter all traffic, including encrypted ones like HTTPS. These firewalls analyze data based on content including keywords.


Greater granularity of control
Can block based on content
Provides more in-depth reports
Provides real-time notifications
Better cybersecurity protection for kids


Per-device installation
Compatibility issues
Can slow down your system
Subscription-based and more costly

Software Firewall Vendors

Avast Firewall
AVG Firewall
AVS Firewall
AWS Firewall
Azure Firewall
Bitdefender Firewall
Comodo Firewall
Debian Firewall
Endian Firewall
Firewalld CentOS Firewall
McAfee Firewall
NoRoot Firewall
Sucuri Firewall
Zonealarm Firewall
Things To Look For When Buying A Firewall

Whether you are buying a hardware firewall or a software firewall as a home owner or a network administrator of a company’s IT department, there are points that you should consider before making a decision and shelling out cash.

1Gb Throughput

With NGFWs, one Gigabit is as claimed. You get one Gigabit of throughput with all of the applications and services active.

Device Monitoring

Your NGFW must be capable of finding a device by user name and not just by an IP address. This allows you to identify how many devices each of network users are accessing the infrastructure.
Protection & Threat Prevention

NGFWs can track and control all of the applications and information on your network. They can limit traffic and risks to your network by only allowing approved applications to be used. You can even scan these applications to ensure there are no potential threats.

Remote User Coverage

NGFWs should be able to monitor and control traffic coming in and going out among remote users who are connected to your infrastructure.
Streamlined Security Infrastructure
NGFWs should have the necessary security infrastructure components like built-in anti-virus protection, spam filtering, deep packet inspection, and application filtering.
Visibility & Control

With the right firewall installed, you can apply rules to network users. You can permit and prohibit them from accessing certain applications. NGFWs can even limit access to specific functions of an application.

The last but not least, price is always a factor when it comes to choosing the right firewall. It's important that you think about not only how much something costs but how it will fit into your budget.