the root can come from the file server -- answer il to root from ... -- but the file server itself doesn't
boot terminals using bootp/tftpd.  that's done by a cpu server running ip/dhcpd and ip/tftpd.
see the commented-out lines in /rc/bin/cpurc.
furthermore the terminals need to be set for booting in /lib/ndb (eg, /lib/ndb/local),
for instance

ip=200.1.1.46 ether=00a0cc3cd489 sys=vivido
	dom=vivido.vitanuova.com
	bootf=/386/9pc
	proto=il

the ether= and bootf= are needed for booting; proto=il is needed to cause the
terminal once booted to use il for other services (such as cpu).
if ip/dhcpd is running on a cpu server, you can look at /sys/log/ipboot
to track its actions.

for the above entry to work, the /lib/ndb/local also should have fs= and auth=
entries at the subnet or network level.  (you can include them per terminal, but
that's normally done only if they need to be different from the default configuration.)