Debug Configuration deals with both the verbosity of messages and if Telnet is available.
The drop-down shows seven verbosity levels:
LOG_LEVEL_SILENTNo logging output is displayed
LOG_LEVEL_FATALShows only fatal events
LOG_LEVEL_ERRORShows errors and fatal events
LOG_LEVEL_WARNINGShows errors and warnings
LOG_LEVEL_NOTICEShows errors, warnings, and notices
LOG_LEVEL_TRACEShows errors, warnings, notices, and traces
LOG_LEVEL_VERBOSEShows all log output
Higher logging levels are helpful for debugging tasks. There is no performance impact from the various levels. Serial logging is enabled by default, and you may connect with a micro USB data cable to your computer. The baud rate is 115200, and the connected controller is easily powered through this cable.
Telnet is a valuable tool when debugging or monitoring is required, and the system is in a place where connecting a serial cable is impractical. You may connect to the controller via port 23; no authentication is required. Because this can present a security risk in some environments, this is disabled by default.
Never open your controller, either the web UI or Telnet, to the Internet.