The input that is suitable for debugging HTTPS inspection issues isfw debug tls on TDERROR_ALL_ALL=5. This input will enable the TLS debug mode and set the debug level to 5, which is the highest level of verbosity. Thefw debugcommand is used to control the debug features of the firewall modules, such as TLS, CPTLS, HTTP, etc. Thetlsoption will enable the debug mode for the TLS module, which is responsible for handling the HTTPS inspection feature. TheTDERROR_ALL_ALLenvironment variable will set the debug level to 5, which will generate the most detailed and comprehensive debug output.The debug output will be written to the$FWDIR/log/tls.elgfile, which can be collected and analyzed with the TLSView tool1to see the details of the HTTPS inspection process, such as certificate validation, SSL/TLS negotiation, encryption/decryption, etc. The other options are incorrect because:

fw ctl debug -m fw + conn drop cptlswill enable the kernel debug mode for the firewall module, with the flagsconn,drop, andcptls. The kernel debug mode will generate thekdebug.txtfile in the$FWDIR/logdirectory, which contains information about the firewall traffic processing in the kernel.The kernel debug mode is useful for troubleshooting issues related to policy, NAT, routing, and inspection, but not for issues related to HTTPS inspection, which is handled by the TLS module in the user space2.

vpn debug cptls onwill enable the IKE debug mode for the CPTLS module, which is a component of the VPN module. The IKE debug mode will generate theike.elgandikev2.xmllfiles in the$FWDIR/logdirectory, which contain information about the IKE negotiation, authentication, and key exchange between the VPN peers.The CPTLS module is responsible for handling the SSL/TLS encryption/decryption for the VPN traffic, but not for the HTTPS inspection traffic3.

fw diag debug tls enableis not a valid command and will not enable the TLS debug mode. Thefw diagcommand is used to control the diagnostic features of the firewall, such as packet capture, core dump, etc. Thedebugoption is not a valid option for thefw diagcommand, and thetlsoption is not a valid option for thedebugoption.Reference:

How to use the TLSView tool

How to debug the Firewall kernel (fw) module

How to debug VPN issues on Quantum Spark (SMB) Appliances

[fw diag - Check Point CLI Reference Card]