What is an SPI Firewall: Benefits, Types, and Use Cases

What is an SPI Firewall?

An SPI firewall, also known as dynamic packet filtering, or a stateful firewall, is a barrier between online data files and your digital security. A stateful packet inspection firewall examines the data packets whenever you try to download a file, open a website, or watch a video and identifies which ones are safe to let through.

There are several types of firewalls and they mostly differ by their method of inspecting data packets. Some inspect only individual data packets instead of understanding the whole overlying context and connection.

How An SPI Firewall Works

1. You visit a website
2. SPI firewall automatically creates a session for this specific event.
3. SPI firewall dynamically applies pre-configured rules based on the context of the session.
4. During the session, the SPI firewall checks all incoming packets and ensures they match the rules.

You visit a website.

Essentially, stateful packet inspection firewalls examine the metadata of each packet, like source and destination address. Then, it maintains a state table to check active connections in the session. This enables the SPI firewall to differentiate between safe and malicious data packets by comparing the current packet with the established rules of the session.

Benefits of Using an SPI Firewall

• Increased security. SPI firewalls constantly track connection states and only allow safe and legitimate traffic through. Unauthorized data packets will be prevented from entering and harming your digital security.
• Protection against common cyber threats. SPI firewalls can be effectively used against IP spoofing by blocking packets that do not match the expected state of a session; against DDoS attacks by identifying data packets coming from a single IP; and against unauthorized access by evaluating the context of connections.
• Performance impact. Since stateful packet inspection firewalls don’t examine every single data packet and can understand the session from overlying context, it doesn’t take a toll on network performance and speed.
• User experience. SPI firewalls don’t require any heavy configuration and integrate smoothly with existing network architectures.

SPI Firewall vs. Other Firewall Types

As mentioned before, there are more than one type of firewalls out there. Let's see how the dynamic packet filtering, or SPI, firewall compares against others.

SPI Firewall vs. Packet Filtering Firewall

Packet filtering firewalls, more commonly known as stateless firewalls, are the most basic types out there. They don’t examine the contents of data packets, which makes them faster, but also less secure.

Stateless firewalls only authenticate packets based on the same set of firewall rules that consider fixed values – source, destination, communication port, or size. Since stateless firewalls only apply the same set of rules for different packets, you need to configure the rules yourself to make it suitable for protection.

For these reasons, stateful firewalls are significantly more effective against digital threats. It tracks the overall context of the data packets and continuously compares this data against the expected behavior which gives it a better chance at spotting irregularities and threats.

SPI Firewall vs. Deep Packet Inspection (DPI) Firewall

A DPI firewall, on the other hand, examines the entire content of each data packet. It checks for signs of malware, malicious code, inappropriate content, which allows this firewall to detect and block advanced threats.

The main downfall of deep packet inspection firewalls is network performance. Since they check everything, it takes time. In turn, this slows down connection speeds significantly.

As a result, DPI firewalls are usually used in environments where security is a lot more important than speed (government agencies, schools, financial institutions).

SPI Firewall vs. Proxy Firewall

A proxy firewall is the cornerstone of internet anonymity. It does not operate like the stateless, SPI, or DPI firewalls. Instead, it acts as a middle man between the user and the internet.

In other words, whatever you search, will not be tracked back to you. The proxy firewall intercepts the established connection between you and the network, forwards the request on your behalf, receives the response, and then gives it back to you.

The external network only interacts with the proxy instead of your IP address or your device, which allows for complete separation between you and the network.

SPI Firewall Use Cases

1. Small businesses. It’s not a secret that small businesses often lack resources for advanced network security setups. It offers protection for critical systems and defends against cyberattacks. Stateful firewalls provide a cost-effective solution that strikes a balance between security and performance.
2. Enterprises. In large organizations, network security is critical due to the sheer volume of sensitive data that could cause a crisis if left unattended. For enterprises, SPI firewalls are a great option because they can handle high network traffic loads while maintaining both security and performance.
3. Home networks. Everyone uses a smart device nowadays, which makes everyone vulnerable to cyberattacks. Companies often integrate SPI firewalls into consumer-grade routers to provide an extra layer of security for people who are not familiar with cybersecurity.
4. Industry-specific. Protecting patient data in the healthcare industry is not just optional, it’s regulated by the law. Same goes for sensitive financial data. Stateful firewalls enable these sectors to protect electronic health records, sensitive patient information, and prevent financial breaches, identity theft, and fraud.

Pros and Cons of SPI Firewalls

There are 3 main advantages that stateful packet inspection firewalls offer:

• Real-time packet filtering. SPI firewalls analyze network traffic in real-time, which makes it a lot harder for attackers to exploit weaknesses.
• Easy setup. They typically don’t require complex configurations and can be easily integrated with existing network architectures.
• Low resource usage. Compared to DPI firewalls, SPI firewalls use less system resources and do not overload network loading times.

One main disadvantage is that a stateful packet inspection firewall may fail to detect deep-layered attacks. They don’t inspect the contents of the data packets, hence they might miss more sophisticated threads that a DPI firewall could catch.