What Is an Application-Level Gateway? How ALGs Work

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Application-level gateways (ALGs), also known as application proxies or simply application gateways, are software components that augment a firewall or network address translation (NAT) within a computer network. These tools filter messages at the application layer 7 of the OSI model.

How Application-Level Gateways Work

Application gateways perform various functions on layer 7 of a network infrastructure. They manage specific application protocols such as session initiation protocol (SIP) and file transfer protocol (FTP). They also allow applications to use dynamic ports like TCP and UDP to communicate with known ports used by server applications.

Here’s a step-by-step guide to how ALGs work:

  1. A user makes contact with the ALG. First, a user must contact an application gateway using a TCP or IP application. A common example of this is HTTP.
  2. The ALG asks for the user’s ID. Once the user makes contact with the gateway, it will ask about the remote host they are trying to establish a connection with. The gateway will also request login credentials, such as a username and password.
  3. The ALG verifies the user’s authenticity. The gateway will then authenticate—or deny—the user based on their login credentials.
  4. The ALG delivers the packets. Once the user is authenticated, the gateway will access the remote host on their behalf to deliver the data packets required for the application.

Advantages of Application-Level Gateways

Due to their enhanced security, ALGs are becoming increasingly popular with organizations of all types—especially as the cybersecurity landscape becomes more threatening. Here are some of the advantages offered by ALGs:

1. Better security

Perhaps the biggest advantage of using an ALG is the degree of protection it provides for corporate networks. ALGs deliver one of the highest-level secure network systems for communications, allowing companies to maintain their cybersecurity posture. The tool uses deep packet inspection (DPI) to detect and block potential attacks at every layer of the OSI model.

2. Simple traffic logging

Organizations can gain more insight into who or what is trying to access their server with ALGs’ simplified traffic logging. Traffic server records store information about every transaction on the server, so IT teams can review the granular details of potential access attempts. This fine-grained control can help even the largest organizations identify threats.

3. Content caching support

ALGs also support content caching, which allows for optimal application performance. This is crucial in today’s fast-paced and competitive business environment. Companies cannot afford to have slow load speeds on their webpages, as delays can turn users away in frustration and hamper search performance, ultimately costing the company thousands of dollars in lost revenue.

You can get more help improving website security and performance using a content delivery network (CDN). Here are the best CDN companies in today’s market.

Disadvantages of Application-Level Gateways

Like any cybersecurity tool, ALGs come with some drawbacks, including network performance issues, requiring a protocol for each proxy, and higher costs. Companies must understand these drawbacks to help them determine if using ALGs is right for their business.

1. Impact to network performance

Since ALGs are complex firewalls with more capabilities than traditional firewalls, they can slow down performance on unprepared networks. ALGs examine every data packet at the application level–a much more intensive process than simply examining packet headers. Before implementing an ALG, you’ll want to ensure your network is prepared to handle the additional load.

2. Each protocol needs a proxy

Another disadvantage of application gateways is that each protocol, like SMTP or HTTP, requires its own proxy application to function. Most firewall vendors offer companies generic proxy agents to support these undefined assets, but they typically allow traffic to tunnel through the firewall. This approach ultimately goes against the reasoning for having an ALG in the first place.

3. More expensive

Because ALGs offer more robust and complex security, they’re often more expensive than other types of network security tools. Most vendors charge for application gateways on an hourly basis. For example, Microsoft Azure charges around 7 cents per hour for a basic, medium ALG,. That may not seem like a lot, but it can add up quickly—especially since in most cases, you’ll want the ALG in addition to, rather than instead of, your traditional network firewall.

3 Best Application-Level Gateways

According to Market Watch, the ALG market is expected to grow in the coming years, reaching around $4.4 billion by 2030. Numerous vendors are driving growth in the market, especially since application-layer attacks are becoming increasingly frequent and sophisticated.

Here are three of the best vendors with ALG firewalls to consider using for your business. 

Microsoft Azure: Best overall

The Microsoft Azure Application Gateway is a useful tool to help companies build scalable and available websites, offering features such as HTTP load balancing and delivery control. 

Application Gateway through Azure provides deployment with one or more instances within the same cloud service. The company guarantees a 99.95% uptime for multi-instance deployments, and offers centralized SSL offload, SSL policy, and easy management through various Azure APIs.

Key features

The Azure Application Gateway offers a wide variety of features including:

  • SSL/TLS termination
  • Autoscaling
  • Web application firewall (WAF)
  • Multisite hosting
  • Cookie-based session affinity


  • Comes in three SKUs: Basic, Standard, and Premium
  • Cloud-native
  • Provides unrestricted scalability


  • Can be expensive for some companies
  • Some features are hard to understand
  • Could benefit from more detailed logs


Microsoft is one of the few companies in the space that provides upfront pricing information—which varies based on your company’s needs and location—on their website. You can also reach out to their sales team for a tailored quote, or start with a free trial.

Palo Alto Networks: Best for remote-first organizations

The Palo Alto Networks next-generation firewall (NGFW) also has an ALG feature. The firewall can identify an application’s unique properties and transaction characteristics using App-ID technology. The Palo Alto firewall serving as an ALG for SIP will perform NAT on the payload and open pinholes for media ports.

Companies using Palo Alto firewalls can also easily disable the ALG feature if necessary. Palo Alto Networks is a highly regarded security vendor in the industry, so if your business needs an ALG, consider using one of its firewalls.

Key features

Key features of the Palo Alto Networks ALG solution include:

  • Inline prevention using embedded machine learning (ML) algorithms
  • 5G-Native Security for easy transition to 5G infrastructure
  • Cloud Identity Engine for identity-based security and authentication


  • Compatible with online file-sharing
  • Uses site-to-site VPNs
  • Offers cloud-centered protection


  • Not specifically designed for small offices
  • Complex configurations can be hard to manage
  • No private backbone—builds its points of presence (PoPs) on third-party cloud platforms


Palo Alto doesn’t list pricing on their website, but you can reach out to the vendor to request demos, free trials, personalized tours, and quotes of their network security solutions.

SAP Netweaver: Best for customizability

SAP Netweaver is a highly flexible open application platform that allows businesses to develop, provision, and manage applications across a unified software environment. Although SAP does not directly offer firewalls, they do have two ALGs, SAProuter and SAP Web Dispatcher, that integrate with other firewalls to provide additional levels of fully integrated application security. 

Key features

SAProuter and SAP Web Dispatcher ALG solutions filter SAP network traffic by:

  • Filtering requests on the network based on IP address or protocol
  • Requiring that a password is sent with a request
  • Rejecting any request not using SAP protocols
  • Requiring that secure authentication and data encryption are used at the network layer using Secure Network Communications (SNC)


  • Only need to open a single port on the firewall for SAP protocols
  • SAProuter complements the firewall, providing an additional layer of filtering
  • SAP Web Dispatcher leverages the use of SSL protocol for secure communications at the transport level
  • Extremely sustainable


  • Product integration is potentially complex
  • Could have more streamlined risk analysis/mitigation
  • Full customization can be confusing to understand and implement


SAP’s offerings vary broadly based on business’ needs. To work with the company or get more information, you can fill out a web form, live chat with a representative, or call them directly.

Who Should and Shouldn’t Use Application-Level Gateways?

Any organization looking to increase cybersecurity strength should consider using ALGs. Smaller businesses might not need an ALG, as they often lack the number of users trying to access a network server that a larger corporate network would have—but they can still benefit from its protections. In short, any company vulnerable to cyberattacks should consider using application-level tools such as an ALG.

Application-layer attacks are becoming more common than ever before. According to research from NETSCOUT, an application performance management company, there was a major uptick in botnet direct-path attacks in 2021 and 2022, causing increases in application-layer attacks. 

Bottom Line: Application-Level Gateways Boost Enterprise Network Security

ALGs are becoming important tools for companies, employees, and remote workers. These network security tools can help businesses maintain good cyber hygiene when cyberattacks are increasing in intensity, sophistication, complexity, and frequency.

Companies big and small must leverage all the cybersecurity tools at their disposal. This enables them to protect their data and operate at peak efficiency.

If you’re looking for a more comprehensive security package, here are the best network security companies to trust with your organization’s data.

Devin Partida
Devin Partidahttps://rehack.com/
Devin Partida is a contributing writer for Enterprise Networking Planet who writes about business technology, cybersecurity, and innovation. Her work has been featured on Yahoo! Finance, Entrepreneur, Startups Magazine, and many other industry publications. She is also the Editor-in-Chief of ReHack.

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