your Ocarina of Time ROM must match this SHA1 hash:
0227d7c0074f2d0ac935631990da8ec5914597b4
there is a download link on archive.org that has the ROM. (PAL GC is the one you want)
download this build of Ship of Harkinian (Ocarina of Time PC Port) - for Windows or GNU/Linux
extract the contents of the zip file, and place your ROM in the same folder. run the soh file.
once you have the game open, press F1 and open the Network tab.
change the remote IP to soh.cult9.xyz. you can leave the port as default.
set your name, tunic color and the room ID (the room ID is important; make sure all players have the same one)
that's it, enjoy :)