Turning on passive mode when using ftp_put

Hi there,

I am using ftp_put to upload a zip from one server to the other. It was working fine until this wkend. I sorted the problem by using ftp_pasv (turning on passive mode). I really dont understand why suddenly i need to use the passive mode as it was fine before.

Could somebody help me understand why i should using passive mode. is it a security risk too?

Also does anybody know any resource about the best way to use in order to upload/download files from one server to another.

Thanks a lot for any help.

Regards,

Jerome Chevreau