Booting over the network must be done on the primary network interface of IA-based systems.
Identifying the primary network interface is a matter of trial and error, but the first or last network device listed on the Boot Solaris menu is likely to be the primary interface.
As soon as you have determined the primary interface, it remains the primary interface every time you boot unless you make a change to the hardware configuration. If you change the hardware configuration, the primary interface may or may not change, depending on the type of changes made.
If you boot from a non-primary network interface, the booting system hangs and a boot server is not contacted. This problem can also occur if the system is not registered as a client of the boot server.