Airport internet share over ethernet

Hi, It’s the newbie again.

So, setting up a simple network between my Mac and the Iyonix works, in that i can ftp from the Iyonix and see and download the directory contents.
However, what i want to do is use the Airport connection on the Mac to serve the Iyonix box over ethernet. This is proving to be harder than it ever normally is.

Anyone do this? It is usually such a simple thing, click the sharing button on the Mac side and it, well, normally just works.

Oh, i have looked at the guides for setting up the Iyonix and a Mac, but they seem to deal with either setting up the Iyonix with a router or a simple peer to peer.

if anyone wants to share then feel free!
However i have it all sorted through a pair of ethernet over power line adapters.
Now online.
cheers!