Definition
Packet filtering is a method for controlling network traffic by analyzing data packets transmitted between devices. It acts as a firewall that inspects each packet that passes through a network and decides to allow or block it based on predefined rules.
Usually, it is configured using software placed between two networks. The software inspects packet headers to determine their source and destination addresses, port numbers, and protocol type. Based on this information, the software decides whether to allow or block the traffic.
Why is Packet Filtering Useful?
- Enhanced security: Packet filtering blocks data packets that don’t meet a certain criterion, which can help to prevent unauthorized access.
- Traffic control: It can optimize network performance by blocking unnecessary or harmful packets.
- Cost-effective: It’s a cost-effective security solution since it can be configured using dedicated hardware devices or software on existing network devices.
- Easy to implement: Packet filtering is easy to configure and does not require sophisticated rules to determine which packets should be allowed to pass or blocked.
How Packet Filtering Works
Data transmitted into a network is divided into packets for efficient transmission. Packet filters assess data packets to determine whether or not they should enter the network. Data packets are divided into two:
- Headers: These wrap the packet and contain key information, including the source, identity, and destination of the packet.
- Payloads: Includes the actual data being transmitted. While a packet filter cannot analyze the payload, it relies on the information on the packet exterior.
Packet filtering inspects the following information on the packet header to decide whether packets should be blocked or allowed to pass:
- The IP address of the packets.
- The packets’ header flags.
- The origin and destination address of incoming and outgoing packets.
- Data transfer protocols.
- The NIC interface through which the data packet is transmitted.
The packet filter compares this information with rules and access control lists for approval or denial of entry into the network.
Key Features of Packet Filters
- They don’t perform deep packet inspection.
- They use external packet data such as origin ports, sources, IP addresses, and transfer protocols.
- Act on single data packets.
- Perform based on rule sets to data entering networks.
- They inspect packets on their own.
What is Packet Filtering Used for?
Packet filtering acts as firewalls that protect devices, applications and data from malicious attacks. Unlike advanced firewalls, packet filtering operates at a basic level, which explains its fast-processing speeds.
Packet filtering uses IP allow lists, which enables you to screen incoming traffic by adding authenticated user IP addresses to access control lists (ACLs). The process ensures that only authorized access sensitive data.
Types of Packet Filtering Firewall
Static Packet filtering firewalls
They operate with fixed rules set by the network administrator, making them simple and ideal for small setups. The set rules remain unchanged until modified by the admin. However, they can be configured to manage ports and access. One drawback of static packet filtering firewalls is that they require manual updates and configurations. They also lack automation which limits their scalability.
Dynamic Packet filtering firewalls
These types of packet-filtering firewalls adapt based on pre-set parameters. They allow users to adjust the parameters to their liking. Unlike static packet filtering firewalls, these types support automation, which minimizes administrative workload.
However, they lack machine learning capabilities and advanced security features present in next-generation firewalls. Like static filters, they can be stateless or stateful.
Stateless Packet Filtering Firewalls
These types of filtering firewalls analyze packets individually based on set rules without necessarily storing information regarding packet states. Stateless packet filters rely on limited information such as IP addresses and ports from access control lists (ACLs).
Stateful Packet Filters
Unlike stateless filters, stateful packet filers are more advanced. They evaluate the state of packets before allowing entry into the network. Also, they track network traffic, and store data in state tables for TCP and UDP protocols. While they offer robust security, these filters may be vulnerable to certain attacks like DDoS.
Limitations of Packet Filtering Firewalls
- Poor security: They rely on basic criteria such as IP addresses and ports and lack context about devices and applications. Malicious code can infiltrate the network through spoofing since packet-filtering firewalls can’t inspect external network data. Stateless filters also heighten risks as each request is processed independently, leaving gaps for attacks.
- Primitive data logging: Packet filtering firewalls log minimal information about network traffic, posing a risk of compliance issues. Minimal logging activities reduce the amount of valuable data IT experts collect on access requests, limiting experts’ ability to detect and address suspicious activity.
- Lack of flexibility: Packet filters offer minimal flexibility in managing network access. They also lack insights into user location, type of device, and device usage, limiting experts’ knowledge of how users connect to network assets.
- Not suitable for larger organizations: Packet filters rely on manual configuration and updates, which increases workload and potential errors.
- Overreliance: Packet filtering systems lack payload inspection and historical logging, undermining the Zero Trust Network Access principle. They rely on potentially outdated rule lists, leaving them vulnerable to spoofing attacks.
Benefits of Packet Filtering Firewalls
- Efficiency: Packet filtering firewalls offer fast processing speeds, quickly accepting or rejecting packets based on their attributes. Compared to other types of filtering firewalls, they experience minimal delay, making them highly efficient.
- Transparency: Packet filters operate discreetly, rarely interfering with user activities. They are also user-friendly since you don’t need to configure them manually for specific clients or servers.
- Affordability: Many routers have built-in packet filtering, providing cost-effective security options. Their widespread use makes them one of the most affordable security solutions available.
- Accessibility: Packet filtering is easy to implement and requires minimal expertise. A single screening router can protect your entire network, and you only notice firewall activity when a packet is rejected.