Preseeding provides a way to set answers to questions asked during the installation process of a Debian operating system, without having to manually enter the answers while the installation is running. This makes it possible to fully automate most types of installation and even offers some features not available during normal installations.
Adding the preseed file to the installer's initrd.gz
Installation can be fully automated by adding a preseed file to the installer ISO's initrd.gz. The downside of this method is that net installer has to be generated whenever a preseed file is modified.
Autoloading the preseeding file from a webserver via DHCP
If you have control over the DHCP server on your network, this method allows fully automated installations.
Loading the preseeding file from a webserver
Type "auto url=http://webserver/path/preseed.cfg", replacing the URL with the address to your preseed configuration file