@lessndro said:
fortunately i found also this page https://www.designwright.com.au/articles/update-a-fog-server-ip-address because it explain how to modify the default.ipxe file (maybe someone should update the wiki!) and finally i can get in the FOG menù at every boot.
Glad someone found my boredom useful and thank you for referencing my site rather than copying and pasting the info.