The following post will detail how you can build a bootable ESXi installer flash-drive, for use with ESXi hosts that do not have a DVD Drive. Or maybe use it over KVM/iDRAC connections.
a) First you will need to download :
1. RUFUS – https://rufus.ie/
2. ESXi (in this case 6.5) Install ISO –https://my.vmware.com/web/vmware/details?downloadGroup=ESXI650&productId=614&rPId=14060
b) Next you will need to insert the USB Flash Drive and start Rufus.
Select your USB drive that you want to create as a bootable Flash-Drive. If it is not listed , use the List USB Hard Drives button
c) Select your ISO and add a name to the Volume Label Box
d) make sure you select Partition Scheme MBR and Target system BIOS/UEFI, and the File System is set to FAT32
e) on the lower part of the screen, click on the START button
f) select YES when Rufus asks to replace menu.c32
g) confirm when Rufus will ask, in regards to the deletion of all data on the USB drive
h) watch the process until the end, and you will have a ready-to-go installer of ESXi