What is a Packet Filtering Firewall?

Having functional network security can improve the performance of your systems, protect valuable data, and keep processes running smoothly. One important function of packet filtering firewalls is to control and monitor network data to ensure its authenticity and compliance. When deciding whether to employ this technique, it’s helpful to understand what the different options are along with the pros and cons. In this article, we define what packet filtering firewalls are, list their common types, explain some advantages of the feature, and outline several disadvantages that can help you learn everything you need to know about them.

What is a Packet Filtering Firewall?

A packet-filtering firewall is a type of firewall that filters network traffic to block any packets that carry malicious code or files.

To understand this, here’s some background: Data packets are the primary unit used for transferring data between networks in telecommunications. In addition to content, packets carry sender and receiver information from IP addresses to ports and communication protocols.

In packet filtering, data passes through a network interface or layer that stands between the sender and the network’s internal components. This layer determines whether the packet is blocked or allowed to pass, depending on its content and superficial contact information.

When this process is used in network firewalls, the result is a packet-filtering firewall. Similar to standard firewall solutions, packet-filtering firewalls sit at the outer perimeter of the network and monitor the flow of outgoing and incoming web and network traffic. Each data packet is scanned and checked against a set of security policies and configurations, allowing the software to determine whether to allow or block the communication.

How does it work?

Packet filtering firewalls inspect individual packets of data as they enter or exit a network. These firewalls use a predetermined set of rules, often called access control lists (ACLs), to make decisions about whether to allow or block these packets. Rules are typically based on criteria such as:

• Source and Destination IP Addresses: Determining the origin and destination of the packet.
• Port Numbers: Identifying the specific service or application the packet is intended for.
• Protocols: Analyzing the protocol being used (e.g., TCP, UDP).

Each packet is evaluated based on these criteria. If it matches the established rules, it’s permitted to pass through the firewall; otherwise, it’s blocked. However, this evaluation occurs on a packet-by-packet basis without considering the context of the overall communication.

Types of Packet Filtering Firewalls

Dynamic 

It is adaptive and can modify rules based on network traffic conditions. They allow for a more flexible approach to network security. Dynamic packet filtering firewalls can be useful for handling transfer protocols that allocate ports dynamically. Dynamic packet filtering firewalls are beneficial because they can open and close ports as needed, which enhances security without sacrificing the functionality of applications like FTP.

Static 

It is characterized by its fixed configuration. Administrators manually set rules that remain unchanged unless updated by human intervention. This type of firewall is practical for smaller networks with consistent traffic patterns, where the administrative overhead of frequent rule changes is not viable. Static firewalls are straightforward and dependable, providing a basic level of security that can be sufficient for less complex network environments.

Stateless 

It evaluates each packet in isolation without considering previous or future packets. They rely on predetermined rules to manage network access, offering a fast and lightweight solution. However, the lack of contextual understanding can make stateless firewalls less secure, as they cannot detect patterns in malicious traffic that could indicate a sophisticated attack.

Stateful 

It maintains a record of active connections and makes decisions based on the state of network traffic. This means they can identify and allow packets that are part of an established connection, which increases security by preventing unauthorized access that a stateless system might not detect. Stateful firewalls provide a higher level of security.

Packet Filtering Firewall Pros

Packet filtering firewalls are popular for many reasons. Most notably, they are a cost-efficient defensive tool that is straightforward to use and effective for warding off a high percentage of undesirable traffic. Other pros include:

• Speed and Effectiveness – It works rapidly to make quick decisions based on the rules set up by administrators and, usually, not much more. Unlike more comprehensive network security tools, packet filtering firewalls don’t conduct internal traffic inspections or store state information. More advanced firewall technology utilizes methods that are slower but more thorough.
• Transparency – Packet filtering firewalls function autonomously. This means users aren’t informed about packet transmissions unless something is rejected.
• Value – It is a good value. Without a massive investment, unprotected networks see marked security improvements when packet filtering firewalls are introduced. Also, many devices and websites have packet filtering capabilities built in.
• Ease of Use – Packet filtering firewalls are straightforward to set up and monitor since users only need to review packet transfers that are rejected. Users don’t need extensive training to operate packet filtering firewalls.

Drawbacks of Packet Filtering Firewalls

There are several potential drawbacks of packet filtering to be aware of, including:

• Reduced security – One potential drawback is their reduced security. Because they’re so accessible and commonly used, hackers have exploited rules and invaded systems. Stateless packet filtering firewalls can be vulnerable because they test each packet on its own, creating more opportunities for hacks. Hackers can use fake IP addresses in packets to intrude into networks because most packet filters don’t provide safety from address spoofing. However, stateful options remove some of these risks. And, in some applications, security isn’t a top priority or concern.
• Inflexibility – Another potential drawback is their inflexibility. The technique uses IP address authentications and port numbers rather than contextual clues to identify and restrict packets. Many programs don’t remember previously filtered packets or past invasions, meaning they don’t learn and improve. When users manually configure rules, taking extra care to create guidelines that produce desired functionality can remove any issues this may cause.
• Inconsistent applicability – In wide-scale applications, the predictable and standardized requirements of packet filters can be a benefit. For more specific applications requiring heightened security or functionality, consider exploring more advanced options. Packet filtering firewalls aren’t the best option for all networks. Implementing firewalls with desirable filters can be time-consuming, as can configuring ACLs. Be sure to research your exact specifications and needs when deciding on a security option that works best for you.

Conclusion

Ensuring tight network security is vital. Choosing the right firewall can make a critical difference when defending against data breaches and malware infection.

Packet filters are one option when putting in place firewall systems. A packet filtering firewall inspects packet data and applies security rules. This allows filters to deny access to malicious traffic. However, packet filtering has limitations. It cannot look inside packets. And it rarely includes stateful monitoring.

These limitations make packet filters less popular than in the past. A packet filtering firewall may still be useful when speed is essential and security is not a priority. However other firewalls will often be preferable when designing robust cyber security environments.