You can specify the path to an installation or upgrade script.
ks=http://XXX.XXX.XXX.XXX/kickstart/KS.CFG is the path to the ESXi installation script, where XXX.XXX.XXX.XXX is the IP address of the machine where the script resides. See About Installation and Upgrade Scripts.
To start an installation script from an interactive installation, you enter the ks= option manually. See Enter Boot Options to Run an Installation or Upgrade Script.