Backup and dyndns

[Absimiliard]

the machine where i want to put the backup has a dynamic IP, so i use a dyndns alias to configure the FTP server hostname for the backup (???.dyndns.org)

and the ip changes, if I make an ftp from a ssh shell on the plesk server ... that works

but the backup still trying to connect to the old IP (check with tcpdump)

is there a dns cache ?