Gateway Anti-Virus service does not work for DPI-SSH because TCP streams for Anti-Spyware are not supported. If the option is checked, the system takes no action.

Deep Packet Inspection (DPI) technology allows a packet filtering-firewall to classify passing traffic based on signatures of the Layer 3 and Layer 4 contents of the packet. DPI also provides information that describes the contents of the packet’s payload (the Layer 7 application data). DPI is an existing SonicOS feature that examines the data and the header of a packet as it passes through the SonicWall firewall, searching for protocol non-compliance, viruses, spam, intrusions, or defined criteria to decide whether the packet might pass or if it needs to be routed to a different destination for action or other tracking.

SSH (Secure Shell) is a cryptographic network protocol for secure data communication, remote command-line login, remote command execution, and other secure network services between two networked computers. SSH connects, by way of a secure channel over an insecure network—a server and a client running SSH server and SSH client programs, respectively. The protocol distinguishes between two different versions, referred to as SSH-1 and SSH-2. SonicWall only supports SSH-2; SSH-1 sessions are not intercepted and inspected.

SSH clients with different version numbers cannot be used at the same time.

To effectively inspect an encrypted message, such as SSH, the payload must be decrypted first. DPI-SSH works as a man-in-the-middle (MITM) or a packet proxy. Any preset end-to-end communication is broken, and preshared keys cannot be used.

DPI-SSH divides the one SSH tunnel into two tunnels as it decrypts the packets coming from both tunnels and performs the inspection. If the packet passes the DPI check, DPI-SSH sends the re-encrypted packet to the tunnels. If the packet fails the check, it is routed to another destination, based on the policies, or submitted for collecting statistical information, and DPI-SSH resets the connection.


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