A Permanent License is a license that never expires. Once a permanent license is installed on a router, it is good for that particular feature set for the life of the router even across IOS versions. For example, once a UC, Security or Data license is installed on a router, the subsequent features for that license will be activated even if the router is upgraded to a new IOS release. A permanent license is the most common license type used when a feature set is purchased for a device.