From the course: Juniper Security Policies Fundamentals
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Introduction to ALG
From the course: Juniper Security Policies Fundamentals
Introduction to ALG
- [Instructor] An application layer gateway, is a software component on Juno's devices that is responsible for managing specific protocols, such as file transfer protocol, or FTP, DNS, real time streaming protocol, etc. To understand application layer gateway, let's use FTP as an example. The client initiates a connection to the FTP server, on port 21. This is a normal TCP connection involving the TCP three-way handshake. This connection is referred to as the control channel. This is used to pass commands to the server. This channel, however, cannot be used to pass data from the server, back to the client. To pass the requested data, the server opens a new connection to the client, with a source port of 20. This is referred to as the data channel. To allow this traffic on a Juno's device, you would need two security policies. One from trust to untrust, for the control channel, and another from untrust to trust for the data channel. FTP is not the only protocol that uses multiple…
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