So that a user identity can’t be tracked a node may create temporary addresses with interface identifiers based on time and which have relatively short lifetimes (hours to days), after which they are replaced with new addresses.
Temporary addresses may be used as source address for originating connections, while external hosts use a public address.
Network interfaces configured for IPv6 use temporary addresses by default in OS X Lion and later Apple systems as well as in Windows Vista, Windows 2008 Server and later Microsoft systems.