Excerpts from internet.computing.netbsd.port-sparc64: 5-Nov-101 420R
fails to boot by Kenny Root@the-b.org 
> Rebooting with command: boot net /netbsd
> Boot device: /pci@1f,4000/network@1,1  File and args: /netbsd
> Timeout waiting for ARP/RARP packet
> 23a00 hostname: netbsdtest
> domainname: xxx.com
> root server: xxx
> root directory: /install/netbsd/NetBSD-1.5.2/sparc64/root
> Illegal Instruction
It looks to me like you booted the solaris netboot loader ("inetboot")
instead of the netbsd one ("ofwboot.net") from the tftp server.

In any event, it's not likely that you will be able to get anything to
work. I tried booting netbsd on an ultra 60 over the weekend (1.5.2, the
20010821 snapshot, and a 1.5Y kernel), and it just doesn't work yet
(though the failure mode of 1.5.2 was different from the others, IIRC).

Ultra 60's and Enterprise 220R's use identical motherboards
Ultra 80's and Enterprise 420R's also use identical motherboards.

While a U80 and a U60 are not identical, they seem to have the same components
(Ultrasparc II CPU, pci architecture) so they should have the same results