Why does netbooting work from OF but not 'N' key?

["Eric C. Cooper" <ecc@cmu.edu>]

I can netboot my G4 cube successfully from Open Firmware using
	boot enet:,yaboot
Using ethereal, I see that the G4 gets the DHCPACK and proceeds to
download yaboot from my TFTP server.

But when I boot holding down the 'N' key, it does something different. 
After getting the exact same DHCPACK, it continues to broadcast
DHCPINFORM packets (which the stock dhcpd ignores).  It never contacts
the TFTP server.

Does anyone know what additional config information it's trying to get?
I hacked up dhcpd so that it also ACKed the DHCPINFORMs, but it didn't
seem to make any difference.  Has anyone else figured out how to make
'N'-booting work on a recent-vintage machine?

Eric
ecc@cmu.edu