Hello! For about two years now, I've been maintaining a network booting guide for Sun SPARC systems. What does this have to do with NeXT, you may ask? Well, in addition to SunOS and Solaris, I have added a section on network booting NeXTSTEP (tested with NeXTSTEP 3.3 and OPENSTEP 4.2) to the guide (Section III for those interested), and wanted to share my work here! I have gotten a number of good suggestions on how to streamline the process so that a NeXT or Linux system may not be required to extract the files from the CD/ISO file, so I'll be updating that as I get the opportunity to do so. Everything on this guide offers the ability to do a single-host boot, meaning the same server can provide RARP, TFTP, bootparams, and NFS.
Here is the guide! (https://github.com/europa64/SPARCNetBootGuide)
This is seriously useful, thanks for the effort!