The tinc daemon can send a lot of messages to the syslog. The higher the debug level, the more messages it will log. Each level inherits all messages of the previous level:
This will log a message indicating tinc has started along with a version number. It will also log any serious error.
This will log all connections that are made with other tinc daemons.
This will log status and error messages from scripts and other tinc daemons.
This will log all requests that are exchanged with other tinc daemons. These include authentication, key exchange and connection list updates.
This will log a copy of everything received on the meta socket.
This will log all network traffic over the virtual private network.