When an LDK-enabled RIP is run it looks for a key that it can use. If the RIP has been run before, it will look in SW\Config for the file previous.key. This file contains the license number that the RIP used the last time it was run. The RIP will then see if that license is available and, if so, will use it again. The RIP can also made to use a specific license with the -k or -kp command line parameters (see https://documentation.hybridhelix.com/hqnc/using-the-clrip-application for details).
The SW\Config folder can also contain one or more other .key files that are named xxxxx.key where xxxxx is a RIP license number. These files are also generated by the RIP when it is run and are linked to the license that appears in their name and was used to run the RIP. They can be deleted if issues arise with licensing or RIP features not working.