Cisco IOU Licensing
Cisco IOS on UNIX is protected by a software licensing mechanism which limits the ability of a third-party who obtained the software to use it.
The licensing mechanism used information from the specific host that was licensed. Thus, if you copied or moved the software to another host the license would be invalid and the software unusable.
In a video created to demonstrate how software licensing mechanisms work, I describe the process that Cisco IOS on UNIX (IOU) uses to verify a particular license key is a valid one. Intended merely as an educational exercise, the video demonstrates using the IDA Pro Disassembler to trace the execution of the program and determine how the licensing verification works.
This video was created while I was an instructor at a post-secondary educational institution and is intended for educational purposes only. The video demonstrates only one way of bypassing licensing protections common to many software programs and this particular method is an inefficient, trivial method of doing so (using NOPs would be a much better way, for example). Besides, several key generators (such as iougen) are available that make this process completely unnecessary.