First It'l ask for a password. Then after the password is entered, an Ip check is engaged, and if the client matches authorized IP addresses, then they are allowed to enter and use the FTP service. Otherwise, an email is dispatched to me, Glassy, (and his mom?), Informing them of this attempted intrusion, and what action to take (ignore, quarentine [which blocks that ip from even going to the page], or allow, which whitelists their ip.)
2 errors in this.
1) IP's say nothing about a persons identity. They change daily, unless it's a static.
2) FTP has nothing to do with PHP, or any script. Unless you mean a PHP File Manager, at which point, good luck.