Proxy Firewall: Network Security Explained

Key takeaways

• A proxy firewall serves as a gateway that monitors and filters network traffic to protect against security threats.

• A proxy firewall operates within the application layer of the OSI model, using its own separate IP address to restrict direct communication between networks.

• The advantages of using a proxy firewall include preventing network intrusions, safeguarding servers, and assisting with security investigations by providing logs of user activity, while the disadvantages may include compatibility issues and delays during periods of heavy traffic.

A proxy is an intermediary that monitors network traffic and helps prevent intrusions; you might use one instead of a traditional firewall because it can inspect the contents of data packets to reduce risk. Read on to discover what a proxy firewall is, its key functions, and how it differs from a traditional firewall.

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What is a proxy firewall?

A proxy firewall, which operates at the application layer of the open systems interconnection (OSI) model, forbids direct connection between a user’s computer and internet sites. The OSI model is a universally accepted conceptual standard for computer networking.

By acting as a gateway, a proxy firewall monitors and blocks network traffic to safeguard against threats. Other names for a proxy firewall include application firewall, gateway firewall, and proxy server.

A few notable functions of a proxy firewall are:

• Limits computer network resources to authorized users.

• Inspects application-layer traffic for potential threats.

• Logs, caches, filters, and regulates requests from devices.

Did you know? Proxy firewalls add to your browsing experience. By storing cached web pages and traffic data from frequently visited websites, a proxy firewall alleviates your network's bandwidth burden. It enables faster loading times for frequently accessed pages.

How do proxy firewalls work?

A proxy firewall works by using its own separate internet protocol (IP) address to bar direct communication between internal and external networks. That separate IP address is where the “proxy” in proxy firewalls comes from.

As per the National Institute of Standards and Technology (NIST), an agency of the United States Department of Commerce, an application-proxy gateway “can make decisions to permit or deny traffic based on information in the application protocol headers or payloads [1].”

At its core, a proxy firewall complements transmission control protocol/internet protocol (TCP/IP), an extensive protocol suite that defines how data transmits over networks, including the internet.

If you are using a proxy firewall and want to access an external site, it typically requires the following steps:

1. A user requests access to the internet through a specific internet protocol such as hypertext transfer protocol (HTTP).

2. The user’s IP address sends a synchronize (SYN) message packet to the server’s IP address, starting an internet session.

3. If the firewall guidelines allow it, the proxy firewall sends a synchronize-acknowledge (SYN-ACK) message packet in response to the request from the requested server's IP address.

4. Upon receiving the SYN-ACK packet, the user’s computer dispatches an ACK packet to the server's IP address, allowing the proxy and the user's computer to connect.

5. As it establishes a TCP connection, the proxy firewall sends the external server a SYN packet from its IP address, prompting the external server to respond with a SYN-ACK packet. The proxy then sends an ACK packet to establish a valid TCP connection between itself, the user's computer, and the external server.

6. Finally, it monitors any request made through the client-to-proxy connection and proxy-to-server connection to ensure compliance with corporate policy. This process repeats until someone (it can be the client or the server) ends the connection.

Who can use a proxy firewall?

Anyone who wants to protect their network resources from unauthorized access and keep their network secure and free of intruders and malicious traffic can use a proxy firewall.

In enterprise environments, proxy firewalls provide a layer of security for internal networks. Proxy firewalls can also help limit access to select websites. An instance of this could be a proxy firewall in schools and universities that prevents students from accessing social media websites like Instagram while still allowing access to educational websites.

Pros and cons of proxy firewall network security

A proxy firewall has several merits, including providing security and preventing network intrusions. However, it also has some limitations that may affect its overall performance. The following sections offer an overview of both.

Advantages

In addition to websites, a proxy firewall can also help safeguard servers. Some of the key security capabilities of this firewall include:

• Performs meticulous inspection of data packets flowing into or out of a network

• Helps trace and investigate security incidents through logging

• Maintains access logs to generate comprehensive reports on user activities

Disadvantages

A proxy firewall establishes a new connection for each outgoing and incoming data packet, which can quickly increase processing load. Other factors to consider before investing in a proxy firewall include the following:

• May not be compatible with all network protocols

• Latency or delayed response during heavy network traffic

• Installation and configuration can be tedious

Proxy firewall vs. traditional firewall

Proxy firewalls operate at the application layer(Layer 7 of the OSI model), while traditional firewalls are part of the network and transport layers (Layer 3 and Layer 4 of the OSI model).

Traditional firewalls, such as packet filtering firewalls and circuit-level gateways, lack the capability to inspect the content of data packets, making them susceptible to malicious data originating from trusted source IPs.

On the contrary, a proxy firewall investigates the content and context of data packets by its very nature, making it more secure than traditional firewalls.

Read more: Understanding the Application Layer of the OSI Model

Proxy firewall examples

Proxy firewalls are widely available and sold by numerous vendors. The following sections offer insight into two popular options: AWS WAF and Barracuda WAF.

Amazon Web Services Web Application Firewall (AWS WAF)

AWS WAF targets common issues, including structured query language (SQL) injection, cross-site scripting (XSS), and bots that can cause downtime. A unique feature of AWS WAF is its account takeover prevention (ATP). This managed rule group scans an application’s login page for credential stuffing and brute-force login attempts, among other suspicious activities.

Barracuda Web Application Firewall

Barracuda WAF offers security against automated and targeted online attacks. It provides protection from OWASP Top 10, zero-day threats, and application-layer denial of service (DoS) attacks, among others. Its machine learning model helps detect “almost-human bot attacks,” while multi-factor authentication thwarts account takeover attempts by bad actors.

Choosing the right firewall: How to make a choice?

When choosing a firewall, be sure to assess factors such as the sensitivity of your data and compatibility with your existing tools and security policies.

• Risk assessment: You have two options: a traditional firewall and a next-generation firewall. If your data is sensitive or you deal with finance regularly, a next-generation firewall, such as a proxy server, is a good choice.

• Compatibility: Some firewalls may not be compatible with select internet protocols or corporate security tools, which can limit their effectiveness in protecting against certain types of attacks. This issue is why it always helps to check for documentation concerning a firewall.

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