The command fw debug tls on TDERRORALLALL=5 is the primary and most comprehensive method for debugging HTTPS Inspection issues on a Check Point Security Gateway. This command enables kernel-level debugging for the 'TLS' module, which is responsible for the SSL/TLS handshake and traffic inspection processes. The flag TDERRORALLALL=5 sets the debug verbosity to the highest level, capturing detailed information about TLS session establishment, certificate validation, and encryption/decryption processes, which is essential for troubleshooting complex inspection problems.

B. fw ctl debug -m fw + conn drop cptls

This command is too specific, focusing only on dropped connections related to a 'cptls' flag. It would not provide the comprehensive handshake and processing data needed for general HTTPS Inspection debugging.

C. vpn debug cptls on

The vpn debug command is used to debug the VPN daemon (vpnd), which handles IPsec and SSL VPNs. HTTPS Inspection is a function of the firewall kernel module, not the VPN daemon.

D. fw diag debug tls enable

The fw diag utility is used for system diagnostics, but fw diag debug is not the standard syntax for enabling real-time kernel debugging for specific modules like TLS.

1. Check Point SecureKnowledge (sk101223): "How to debug HTTPS Inspection".

Section: "Procedure" -> "Step 1 - Collect debugs on Security Gateway".

Content: The article explicitly states, "The main debug for HTTPS Inspection is the kernel debug of the 'TLS' module." It then provides the exact command: fw debug tls on TDERRORALLALL=5. This document is the primary official source for this procedure.

2. Check Point R81 CLI Reference Guide:

Chapter: "Firewall and Kernel Commands" -> "fw" -> "fw debug".

Content: This guide details the syntax and usage of the fw debug command for enabling and disabling kernel debug flags. It confirms that fw debug on is the correct structure for activating kernel debugging for a specific module, validating the syntax used in the correct answer.