What Is Firewall Software?
A firewall is software that guards your devices against unauthorized internet traffic. It does this by acting as a barrier between your devices and the rest of the internet. Any traffic going through a software firewall will be stopped and inspected before it is allowed to reach your devices. This inspection process helps to ensure that only traffic that matches your rules goes through and that any dangerous or unwanted traffic is blocked.
Key benefits of firewall software:
Before we go into the various types of firewalls, we need to explain what Open Systems Interconnection (OSI) layers are and what they have to do with firewalls in the first place.
The OSI system describes how data packets travel over a network from one computer to another. It is made up of seven layers, with each representing a different part of the process.
1. Physical Layer - This layer handles the physical connection between devices. This includes the cables and other hardware used to connect devices and is responsible for raw data transmission.
2. Data Link Layer - This layer handles the movement of data between adjacent network nodes. The data link layer provides functional and procedural methods for sending data between network entities. It can also find problems in the physical layer and fix them if possible.
3. Network Layer - This layer handles the movement of data between different networks. It is responsible for separating data into network packets, reassembling them at the receiving end, and finding the best routing path to the desired destination.
4. Transport Layer - This layer handles data movement between different computers. It ensures that data is delivered correctly and in the same order it was sent in. The majority of firewall solutions operate on the third and fourth OSI layers.
5. Session Layer - This layer handles the establishment and maintenance of communication sessions between computers. It is responsible for setting up, managing, and closing communication sessions.
6. Presentation Layer - This layer handles the conversion of data into a format that can be displayed or used by applications. It defines the encoding, encryption, and compression methods that should be used by two devices for communication to go smoothly.
7. Application Layer - This layer handles the communication between applications and the network. Its job is to ensure that data is formatted correctly and sent to the correct application. Web browsers and other applications use this layer to display information to end users.
Types of Firewalls
Now that we know the basics of firewalls and the OSI model let’s take a look at the different types of firewall software available. Based on their structure, we can observe three basic types of firewalls:
- Hardware firewall
- Software firewall
- Cloud-based firewall
Because we're focused on home network firewalls in this article, we'll skip hardware and cloud-based solutions because they are primarily used as business firewalls.
Nonetheless, each of these types can be further categorized by the way how they filter data:
- Stateless packet-filtering firewall
- Circuit-level gateways firewall
- Stateful packet-filtering firewall
Stateless Packet-Filtering Firewall
A stateless packet-filtering firewall treats each packet individually and does not track any information about the connection that the packet is part of. It makes decisions about whether to allow or deny traffic based on criteria such as source and destination IP address, port number, and protocol type.
Because it does not track the connection state, a stateless packet-filtering firewall cannot make decisions based on whether a packet is part of an established connection or not. It operates on OSI layer 3 (network layer).
Circuit-Level Gateways Firewall
A circuit-level gateway firewall does not allow any traffic through until a connection has been properly established. Once it is, the firewall allows all traffic from that connection without examining the contents of the individual packets. A circuit-level gateway can be implemented as a software program or hardware device. It operates on OSI layer 4 (transport layer).
As previously said, most firewalls operate on OSI levels 3 and 4 and hence fall into these two groups. However, in today's environment, they are unable to protect us from all dangers. Therefore, for complete network firewall security, we must look for firewalls that operate on several OSI layers, like the next three types.
Stateful Packet-Filtering Firewall
A stateful packet-filtering firewall tracks the state of every connection passing through it and makes decisions about whether to allow or deny traffic based on criteria such as source and destination IP address, port number, and protocol type. Stateful packet-filtering firewalls can also make decisions based on whether a packet is part of an established connection or not.
They are typically implemented as hardware devices but can also be implemented as software programs. Unlike the previous two firewalls, they can operate across several OSI layers starting from 4 and going up all the way to layer 7.
A proxy firewall routes all outgoing and incoming traffic via a machine that holds it. It effectively functions like a gateway for all traffic. It intercepts all traffic and then decides whether to allow or deny it. Because everything is done on a separate hardware device, it falls into the hardware firewall category. Just like Stateful packet filtering, it operates on OSI multiple layers.
A next-gen firewall, also known as 3rd generation firewall, is a type of firewall that uses multiple methods to filter traffic. It typically uses a stateful packet-filtering engine but can also use other methods, such as application-level filtering, deep packet inspection, and intrusion detection and prevention.
Just like the last two, it works on multiple OSI layers and provides advanced malware protection.
Because we are going to look into the best home network firewall solution, we’ll have to exclude proxy firewalls because they are a hardware solution too complicated for regular users to set up and too expensive to be used in the first place. They are an excellent solution for companies but a bit overkill for home network security.
Again, since we are looking for home solutions, we’ll primarily focus on software and companies that offer firewalls in combination with anti-malware tools to provide complete protection for our machines.