Definition
Application Layer Gateway
Application Layer Gateways (ALGs) are security gateway operating in application layer. They are often called “security proxies” since they interrupt the direct data flow between source and destination.
In fact, they are stateful inspection firewalls.
Comparison
Benefits
- Inspection of data during the interruption
- Filtering data during the interruption
Drawbacks
- Protocol-specific → not every protocol is supported by an ALG
- Proxy only knows the transferred data
- Across-protocol analyses can’t take place while proxying