In the olden days of 7-mode it was nice with http, but it was also easy to just drop image on etc$ either via export or cifs share, BUT with cDOT, in my honest opinion, that goes out of the window.
The below is directly from the Netapp Guide.
Copy the software image (for example, 91_q_image.tgz) from the NetApp Support Site to the
directory on the HTTP or FTP server from which the image will be served.
