What method allows management access to the FortiGate CLI without any network connectivity?

The method that allows management access to the FortiGate CLI without any network connectivity is the serial console. Using a serial console connection, an administrator can directly connect to the FortiGate device through a physical serial port using a console cable. This connection does not require any network interfaces to be operational, making it ideal for situations where network access may be unavailable, such as initial setup, recovery situations, or troubleshooting.

In contrast, SSH access, web GUI, and Telnet all depend on the presence of network connectivity. SSH and Telnet are protocols used for remote access over the network, while the web GUI requires a functioning HTTP/HTTPS connection. Therefore, in scenarios where the network is down or misconfigured, the serial console remains a reliable choice for accessing the device's CLI directly.