Enter the name of the file that is used for debug logging of the DPI engine.

The file used for debug logging of the DPI (Deep Packet Inspection) engine is named "dpi.log." This file specifically captures the debug-level messages from the DPI engine, which can be crucial for troubleshooting and understanding how the DPI processes traffic. By analyzing the contents of this log, administrators can gain insights regarding DPI behavior, including how packets are inspected and any potential issues that may arise during traffic handling.

In the context of the other files mentioned, "ips.log" is associated with logging events related to the Intrusion Prevention System, “debug.log” is a general log file that might contain a wide range of debugging information across different functionalities within the firewall, and "proxy.log" specifically pertains to logging events related to the proxy services of the firewall. Each of these files serves a different purpose, making the identification of "dpi.log" as the correct answer significant to understanding the functionality of the DPI engine specifically.