I have a l2tp connection to a remote site, after it connects it stays up for about 30 min then it disconnects with
:terminating… -administrator request
:disconnected
Well, the “administrator request” looks pretty obvious to me 
Are you SURE that noone (not you, not another admin, not perhaps a script) is terminating this connection?
If not, you will have to provide more information (software version, config, …).
Best regards,
Christian Meis