This preserves the negotiated lifetime in seconds of a now-expired control tunnel, per its description, the historical companion to the live cisgIpsSgTunLifeTime. It tells an admin reviewing history exactly what rekey interval had actually been in effect for a since-closed connection, useful for correlating a tunnel's negotiated lifetime against how long it actually stayed active to see whether it expired naturally or was cut short. A tunnel with a negotiated lifetime of 86400 seconds but an active time of only 600 seconds clearly terminated well before its scheduled rekey, pointing to some other failure as the real cause.