What Is an Application Level Gateway? Guide to Proxy Firewalls

Application-level gateways, also known as proxy firewalls, are a type of network security solution that takes action on behalf of the apps and programs they’re set to monitor in a network. They’re primarily responsible for filtering messages and exchanging data flow at the application layer.

By being permitted to access the traffic, activity, and behavior of a network’s applications, proxy firewalls can maintain the integrity, security, and privacy of the network’s servers, apps, and databases from malicious traffic, malware, and unauthorized access attempts.

Continue reading to learn more about how application-level gateways work, their most beneficial features, their pros and cons, and examples of leading vendors. 

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

How Application-Level Gateways Work

As the name suggests, application-level gateways work by being the only gateway between the network’s internal activities, like users and applications, and the public internet. All traffic that’s incoming or outgoing to the application layer in the network passes through the gateway and gets scanned for any malicious or unauthorized activity.

It’s also called a proxy firewall because it utilizes proxies to set up a private connection that remote users can access the network through, without compromising on speed or security. However, this type of firewall only works on Layer 7 of the Open Systems Intercommunication (OSI) model, which is the layer where the network’s applications, software, and programs operate and access the internet.

This process allows the firewall to avoid direct connections between your network’s applications and outside traffic before it’s completely verified. As a result, this creates an added barrier that makes it harder for intruders and infiltrators to either access your network or even extract information from any exchanged data packets.

With this setup, only one server per network segment has direct access to the public internet. All other devices would have to route their traffic through it, whether it’s outgoing or incoming.

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

Features of Application-Level Gateways

Proxy firewalls are one of the best solutions available on the market for application-based networks. They stand out from all the other types of firewalls that can also protect applications, thanks to a number of features the average proxy firewall comes equipped with, such as:

Bandwidth Usage Reduction

Application-level gateways routinely save cache webpages and traffic of the most visited sites and addresses. This reduces the strain on your network’s bandwidth by not having to load frequently-requested pages multiple times in a row.

This also enables the gateway to improve overall performance. Applications and users looking to access the website can reach it more quickly, without having to go through the rest of the network’s traffic first.

Intruder Protection

By continuously monitoring the inbound network traffic and scanning it thoroughly before it even makes contact with any of the network’s internal elements, proxy firewalls are capable of detecting intruders more effectively.

Sophisticated Filtering

Application-level firewalls often carry many traffic filters used to scan both incoming and outgoing data, searching for malicious intent or suspicious behavior. Additionally, some filters are also capable of monitoring other Layer 7 activity, such as network requests, external logs, and manually saved cached files.

Security Policy Enforcement

Similarly to other types of firewalls, application-level firewalls also centralize and simplify the process of setting up and enforcing security policies on the application layer of the network.

This ensures all regulations and configurations in the network are up to date, and no application is left following outdated—and possibly risky—security policies.

Site Access Control

As the middleman between all of the network’s applications and the public internet, application-level firewalls can also restrict and control which websites can be accessed through its proxy.

You can set this up manually, blocking all communications to a number of determined websites. Alternatively, the process could be automated to block or restrict access to all websites that are flagged on databases of malicious sites or meet a set of conditions, such as a security or privacy policy you don’t deem suitable.

Internet Access Control

Application-level firewalls are capable of mass-preventing specific users and applications from gaining access to the internet as a whole. The restrictions can be exclusive to high-risk users and applications, or simply members deemed in no need of immediate internet access.

For more information, also see: Artificial Intelligence in Cybersecurity

Advantages and Disadvantages of Using Application-Level Gateways

When it comes to understanding the inner workings of application-level gateways, it’s important that you acquire a general knowledge of their advantages and disadvantages as a stand-alone solution.

Advantages of Application-Level Gateways

Application-level gateways are most known for the added level of security it provides by using proxy technology to isolate the application layer in the network from outside connections. It’s also responsible for the verification and authentication of incoming traffic and connection requests.

This allows it to greatly reduce the risks of DDoS (Distributed Denial of Service) attacks and IP spoofing attacks. Additionally, they allow for optimal user anonymity by hiding the network’s IP address from any outside parties, even during verified connections. Any connection request is forwarded through the main IP address of the network’s proxy.

When it comes to individual threats, proxy firewalls are highly effective at identifying and assessing the levels of incoming threats. Most options employ Deep Packet Inspection (DPI) technology alongside the proxy servers to analyze threats and block them promptly.

For individual applications connected to the proxy, all of their commands get screened and analyzed while in data packets before they’re executed or released outside the network. This can all be logged for further examination and auditing efforts later on.

Disadvantages of Application-Level Gateways

Application-level gateways still have a handful of drawbacks and weak points, especially when used as a stand-alone security solution with no added tools or features.

For one, they’re more prone to experiencing bottlenecks as all the network’s incoming and outgoing data is redirected towards a single point of processing. The stricter the monitoring rules on the proxy server, the slower the data flow.

Proxy firewalls also have major compatibility problems, as they can’t support a wide variety of connection types and network protocols. This can greatly limit the pool of servers and agents your application layer is able to connect with, without needing additional tools.

Similarly, not all applications are compatible with proxy servers. By not being proxy-aware, applications can sometimes ignore the presence of the proxy server and attempt to connect to the internet directly.

While some application-level gateways’ drawbacks can be fixed or reduced in effect through proper configuration, that’s not easy to do. Furthermore, any misconfigurations in the setup of the firewall may leave some gaps in your security, such as open ports.

On a related topic, also see: Top Cybersecurity Software

Examples of Application-Level Gateway Providers

There are countless cybersecurity providers on the market that offer proxy firewalls, either exclusively or as a part of a bigger ecosystem of network security solutions.

Following are a couple of the leading application-level gateways providers on the market:

F5 Networks

F5 Networks is a Seattle, Washington-based IT and technology company that provides application security, cloud management, and online fraud prevention solutions among many others. 

The Advanced Web Application Firewall (AWAF) is the core security component of F5’s suite of application delivery and management services. It employs cutting-edge technology to help you consolidate and manage traffic, network firewall, SSL inspection, and application access.

Juniper Networks

Juniper Networks is a Sunnyvale, California-based technology and networking company that develops and sells a number of computer networking software and hardware, from routers and switches to network management software and network security solutions.

The Application Layer Gateway (ALG) is a piece of software that’s capable of managing session protocols and providing application-layer-aware packet processing on network switches on devices running Junos OS.

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

When to Use an Application-Level Gateway?

Application-level gateway solutions are the perfect solution for networks with a high percentage of their traffic originating from Layer 7 in the OSI model. It can help you better control the activity and behavior of your network’s applications and the users that access them, reducing the risks of malicious attacks, DDoS attacks, unauthorized access, and IP spoofing attacks.

It’s important that your application layer is never left to connect to the public internet unguarded and without a firewall or proxy. Whether you’re looking to segment and better specialize your network security strategy or simply need to secure the newly-added application layer to your network, proxy firewalls are the way to go.

Bottom Line: Application-Level Gateways

Application-level gateways behave as an intermediary between a network’s applications and the open internet. Also called proxy firewalls, they help you set up a proxy server between the applications and outside connection, where exchanged traffic is constantly monitored for malicious activity.

It’s the perfect solution for securing applications that regularly connect to the web. However, their capabilities don’t stretch to the remaining layers of the networks and shouldn’t be used alone as a holistic security solution.

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