The Netra X1 chassis never had an optical drive.
The chassis doesn't have room for one.
http://sunsolve.sun.com/handbook_pub/Systems/Netra_X1/Netra_X1.html
(Nor are there any expansion slots or external SCSI ports)
Therefore I'll make an assumption that you've opened up the system
and are attempting to get around the need to install by jumpstart,
which is the default design of that platform.
You forgot to tell us that information.
You could be having two possible issues here.
If I recall correctly, a temporary lash-up of dangling an optical drive
from a partially disassembled Netra will work
if you jumper it as slave on the secondary IDE channel.
The OBP device alias of cdrom will expect that IDE pathing.
See InfoDoc 21216 for default device paths in various common Sun systems.
If that doesn't fix the issue, then you simply have an unreadable CD disk.
Burn a new copy.
I vote for the bad media.