What is a Layer 7 firewall?

The OSI model

The OSI (Open Systems Interconnection) model is a conceptual framework describing how data moves from one device to another over a network. It's divided into seven layers of protocols that communicate with each other to enable reliable data transmission. Each layer has a specific function and provides a foundation for the layer above it while relying on the layer below it.

1. Physical Layer

The lowest layer of the OSI model and is responsible for transmitting raw data bits over a communication channel. It deals with the hardware aspects of communication like cables, connectors, and network interfaces.

2. Data Link Layer

Responsible for reliable point-to-point communication between two devices on the same physical network. It performs tasks such as error detection and correction, flow and access control.

3. Network Layer

Maps out logical addressing and routing of data packets between two devices on the same physical network. It provides services like packet switching, routing, and congestion control.

4. Transport Layer

Handles end-to-end communication between two devices. It ensures that data is transmitted without errors, in the correct order, and with the appropriate flow control. Generally speaking, it segments data from the sender's device and reassembles it when it reaches its destination.

5. Session Layer

Establishes, manages and terminates between applications on different devices. It provides services like session synchronization, checkpointing, and recovery.

6. Presentation Layer

Responsible for the presentation of data to the application layer. It performs tasks such as data encryption, compression and formatting.

7. Application Layer

Provides services to user applications like email, web browsing, and file transfer. It establishes a common interface for user applications to access the network services provided by the lower layers of the OSI model.

By breaking down the data communication process into these seven layers, the OSI model helps to understand different processes occurring at different data transfer and exchange stages.

How does Layer 7 work?

Layer 7 (or the application layer) is the highest layer in the OSI model of network communication. It's responsible for providing network services to application processes running on a host like web browsers, email clients and file-sharing programs. Most user-facing protocols and applications like HTTP, FTP and SMTP operate on layer 7.

These protocols define the format and content of the data being exchanged. Typically they operate over Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) connections established at lower layers of the OSI model. They work by supporting specific application-level functions. For instance, HTTP protocol retrieves web pages and other resources from web servers.

In addition, Layer 7 also provides support for security and encryption with protocols such as Secure Sockets Layer (SSL) and Transport Layer Security (TLS). They enable secure communication by encrypting data and verifying the identity of the communicating parties.

Benefits of Layer 7 firewalls

Layer 7 firewalls filter networks based on specific data packets' contents, including the device's application data. It allows more granular control over the network than traditional firewalls operating and lower OSI model levels.

For this reason Layer 7 firewall provides the following benefits:

Port management capabilities 

Filtering is performed by examining the data flow to detect the application service and sort traffic based on specific port numbers. One of the most common examples is blocking specific ports to deny all communication relying on them.

Specific filtering options 

The traffic can be filtered based on specific application-layer data, allowing for advanced traffic filtering rules. This is particularly useful for organizations requiring more precise network traffic control.

Security against DDoS 

Layer 7 firewalls can alert against Distributed Denial of Service (DDoS) attacks by analyzing traffic patterns and identifying malicious traffic. Additionally, the huge amount of data exchanged on the application layer provides security analysts with much raw data to work on when planning improvements.

Layer 7 and other OSI firewalls

Firewalls can be implemented at different OSI model layers, with each layer providing different levels of security and functionality.

A Layer 7 firewall operates at the application layer of the OSI. It can analyze and filter traffic based on specific applications or protocols rather than just looking at the source and destination IP addresses and ports. They also provide content filtering, user authentication, and intrusion prevention capabilities.

Meanwhile, firewalls that operate at lower layers of the OSI model are known as packet filtering firewalls. They analyze network traffic based on the source and destination IP addresses, ports, and protocols blocking or allowing traffic based on predetermined rules. While they're faster and less complex, they offer less granular control and security.

For example, a firewall operating at the network layer is stateful. It records all connections passing through them and uses that information to make informed decisions about which traffic to allow or block. While they provide better protection against attacks like SYN floods and IP spoofing, they're also more resource-intensive than packet-filtering firewalls.

In short, while all types of firewalls are important for network security, Layer 7 firewalls offer the most advanced protection and functionality. Lower-layer firewalls are faster and less complex but offer less granular controls. Stateful firewalls strike a balance between the two, offering better protection than packet filtering firewalls while still being more efficient than Layer 7 firewalls.

Conclusion

Layer 7 firewalls are one of the most advanced cybersecurity tools helping to defend against various cyber threats. It greatly expands its functionalities on the topmost level of the OSI model layer. For this reason, Layer 7 firewalls provide granular control over network traffic and can filter it based on specific application-layer data.

As such, Layer 7 firewalls provide considerable benefits to organizations like port management capabilities, specific filtering options, and security against DDoS attacks. When compared to other types of firewalls operating at lower OSI model layers, we can conclude that in terms of functionality, Layer 7 firewalls provide the most comprehensive security functionality.