Tried to upload a network diagram in SVG format, that upload not accepted.
Not sure if this is a security decision, or simply overlooked, but the SVG graphic is distinctly clearer, and scales up faultlessly.
Re-exported the diagram in PNG format, that uploaded OK so completed my post.
Surprisingly the PNG file is substantially smaller than the exported SVG file, while the original Dia version of the same file is less than 10% of the PNG.
JPG format is very much poorer, so I avoided that.