Description: Last event provoked by the primary interface. Various events can occur provoking changes in the state of the system: (0) Unknown: no event has been produced yet, or the event is unknown. (1) Primary Up: one of the primary interfaces associated to a secondary interface has announced the recovery of the link. (2) Primary Down: one of the primary interfaces associated to this secondary interface has announced link failure. secundario ha anunciado una cada del enlace. (3) First Stabilization Time expired: the timer for the first establishment period of time has lapsed. The First Stabilization Time is length of time the primary interface must be down before activating the secondary (to carry out backup). (4) Stabilization Time expired: the timer for the establishment period of time has lapsed. The Stabilization Time is the minimum length of time the primary interface must be active for before the secondary deactivates (returns from backup to initial situation).