Odd that it uses RARP to get an IP but then uses DHCP for NFS configuration. (Or is it the baked in firmware using RARP and then the modern NetBSD kernel using DHCP? That would make more sense)

Also:

> You need to rename the file with a specific format: the IP address of the JavaStation, but in 8 capitalized hex digits, followed a dot, and then the architecture (in this case “SUN4M”). So, in this example the IP address (as defined in rarpd above) is 192.168.128.45, which in hex is C0A8802D.

This is of course the correct way to do it, but if you're lazy you can just tail the tftpd logs and see what filename it tries to download, rename the file on the server, and reboot again to pick it up. (I did this when netbooting raspberry pis)