FTP Site Properties - Directory Security Property Sheet
The Directory Security property sheet sets access by specific IP address to block individuals or groups from gaining access to your server.
IP Address and Domain Name Restrictions
You can control access to each Internet service by specifying the IP address, subnet mask, or domain name of the computer or computers to be granted or denied access.
If you choose to grant access to all users by default, you can then specify the computers to be denied access. For example, if you discover that a particular user on the Internet is trying to download restricted files from your FTP server, you can prevent the computer at that IP address from connecting to your site. Conversely, if you choose to deny access to all users by default, you can then specify which computers are allowed access.
You can configure Security properties at the FTP Site and virtual directory level.