What are two ways that an SRX Series device identifies content?

SRX Series devices provide content security features that rely on advanced identification mechanisms. File identification is not based merely on file extensions (which can be easily spoofed), but instead on deep inspection techniques :

AppID (Application Identification): AppID is part of the AppSecure suite, allowing the device to classify applications and content regardless of port or protocol. This enables the SRX to detect applications and their related content for enforcement.

Protocol-based file type identification: The SRX can recognize and identify file types embedded within HTTP, FTP, and e-mail (SMTP, IMAP, POP3) protocols . This provides accurate content inspection and filtering, independent of file naming conventions.

Why not the others?

File extensions (Option A) are not reliable for content security, so SRX does not use them.

ALGs (Option D) are used for protocol handling, such as SIP or FTP control channels, not for content identification.