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Circuit-Level Gateways: Definition, Features & Examples

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A circuit-level gateway is a type of firewall that operates on layer 5 of the Open Systems Interconnection (OSI) model, which is the session layer. It’s the layer responsible for providing the mechanism of initiating, managing, and closing a communication session between end-user application processes.

Continue reading to learn more about the features, pros and cons, and functionality of a circuit-level gateway.

For more information, also see: Why Firewalls are Important for Network Security

How Circuit-Level Gateways Work

Circuit-level gateway firewalls work by providing a layer of security between TCP and UDP throughout the connection by acting as the handshaking agent. They authenticate the handshake by scanning and examining the IP addresses of the packets as the 5th layers, and stand between the incoming web traffic and the sending hosts.

This type of firewall is rarely used individually as a stand-alone solution for network security. They’re best combined with a stateful inspection firewall for securing layers 3 and 4, and an application-level firewall to secure Layer 7.

Circuit-level gateway firewalls are able to maintain a network’s security by constantly validating and authenticating the connection by only allowing safe data packets to pass. In the case of malicious activity detected in an incoming data packer, the firewall terminates the connection and closes the circuit connection between the nodes.

For more information, also see: What is Firewall as a Service?

Features of Circuit-Level Gateways

When implementing a circuit-level gateway firewall, whether individually or in tandem with other network security and firewall solutions, there is a set of features you can expect upon deployment.

Some of circuit-level gateway firewalls’ most notable features include:

TCP Handshake Verification

While circuit-level gateways don’t check incoming data packets for the destination IP address, they check and verify the TCP handshake required for establishing the connection, and whether it adheres to the security and privacy standards set by the network’s admins.

It checks and authenticates the connection through the three-way TCP handshake. The firewall synchronizes both sides in the connection sessions and mitigates unauthorized interception.

Hides the Network’s Information

When communicating with outside hosts, servers, and devices, a circuit-level gateway’s firewall doesn’t reveal the private information of your network to avoid the exploitation of communication information.

After the initial verification of the communicating party, this type of firewall doesn’t intervene with the type and volume of traffic exchanged.

For more information, also see: Artificial Intelligence in Cybersecurity

Stand-Alone Security Functionality

When it comes to securing the communication and movement of data packets in the 5th layer of the OSI model, circuit-level gateways are fully capable of being a stand-alone solution. It can be used to centralize the management and security policy of the entire layer without the need to integrate third-party tools.

SOCKS Protocol Configurations

When used in a network firewall setting, SOCKS servers allow the hosts of the network’s servers to fully access the public internet while providing complete protection from unauthorized actions and web traffic interception attempts.

Depending on the ports and protocols used in the network communication, the gateways can either use SOCKS as the proxy of the connection or as the client.

For more information, also see: Data Security Trends

Advantages of Circuit-Level Gateways

Similarly to the wide variety of other types of firewall solutions, circuit-level gateway firewalls come with a set of benefits and drawbacks.

Following are a handful of the most notable circuit-level gateways firewall advantages:

  • Keeps private your network’s identifiable information
  • Simple and quick to implement
  • Doesn’t exhaust time and computational power by avoiding the monitoring and scanning of individual data packets
  • Lightweight software with a low impact on the network’s performance
  • Cost-efficient in both software and hardware expenses
  • Doesn’t require dedicated proxy servers for each applications
  • Highly flexible for address schemes development

“A circuit-level gateways firewall operates at the OSI model’s session layer, monitoring TCP (Transmission Control Protocol) connections and sessions,” writes Anshuman Singh, senior executive content developer for Naukri Learning.

“Their foremost objective is to guarantee the safety of the established connections. Circuit-level gateways are inexpensive, simple, and have little impact on network performance,” adds Singh.

Disadvantages of Circuit-Level Gateways

Following are a few of the most notable drawbacks and disadvantages of circuit-level gateways firewalls:

  • Unable to detect malicious files in data packets
  • No support for advanced content filtering
  • Cannot monitor the communications of applications
  • Only compatible with TCP connections
  • Unable to protect more than Layer 5 of the OSI model
  • Requires initial configuration of the network protocol stack

For more information, also see: How to Secure a Network: 9 Steps

When to Use a Circuit-Level Gateways Firewall

Picking out the primary or sole tools for securing your network can be tricky, especially with the wide variety of firewall types and generations available commercially. Luckily, the use cases for a circuit-level gateway firewall aren’t numerous.

For one, it’s the perfect option if you’re on a low budget and unable to provide the necessary hardware and bandwidth to account for the weight of more complex firewall solutions. They allow for more control over the connections of your network with minimal effort as it doesn’t need the capabilities or configuration otherwise required for in-depth packet filtering and monitoring.

On their own, circuit-level gateways aren’t considered to be the most effective at securing a network, especially one where devices and users communicate frequently with outside servers. However, compared to more simplistic options, such as a stand-alone deep-packet inspection firewall, circuit-level gateways are an improvement.

Examples of Circuit-Level Gateways Firewall Providers


Forcepoint is an Austin, Texas-based software company that designs, develops, and sells network security and management software. It offers solutions ranging from data protection and cloud access security to advanced NG firewalls, and even cross-domain solutions.

Stonesoft is one of Forcepoint’s Next-Generation Firewall (NGFW) solutions. It provides both stateless and stateful packet filtering alongside circuit-level firewall capabilities with advanced TCP proxy control agents.

It’s an intelligent firewall solution that can be extended all the way to Layer 7, implementing built-in SSL VPN and IPsec capabilities.

Forcepoint’s NGFW has accumulated high user ratings over the years on various third-party review sites. For example, it has a 3.8 out of 5 rating on PeerSpot and 4.4 out of 5 on G2.

In 2020, Forcepoint was recognized for 4 years in a row by Gartner as a Visionary in Network Firewalls.

Juniper Networks

An enterprise leader, Juniper Networks is a Sunnyvale, California-based developer of computer networking products. It provides its clients with all the necessary software and hardware to build, maintain, and manage a network, from routers and switches to network security and management software.

The Juniper Networks SSR120 is a network appliance that’s software-driven with various NGFW capabilities. It’s a branch of Juniper’s SSR (Session Smart Router) portfolio and supports network security and management capabilities from Layer 2 all through to Layer 5.

Similarly, it includes various additional features such as traffic encryption, built-in VPN support, advanced traffic filtering, and DoS/DDoS protection. 

Juniper’s solution is trusted by its users, as demonstrated by the positive reviews on various third-party reviews sites, such as PeerSpot with a 4 out of 5 rating, and Gartner with a 5 out of 5 rating.

On a related topic, also see: Top Cybersecurity Software

Featured Partners: Firewall Software

Bottom Line: Circuit-Level Gateways

Unlike packet inspection firewalls, circuit-level gateways don’t filter and monitor the contents of exchanged data packets with outside sources. Instead, they confirm the security and authenticity of the connection, and verify that it doesn’t pose a threat to the network through its IP and address and other superficial parameters.

It’s not fully safe to use as circuit level gateway as a stand-alone solution for protecting a network with a wide variety of components, but it remains one of the most affordable and non-resource-intensive network security solutions. There are multiple firewall solutions that include, or consist of, circuit-level gateway capabilities. They are offered by household names in the computing networking cybersecurity and management software industry, such as Juniper Networks and Forcepoint.

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