Before you can boot the system over a network interface, you must complete the installation procedure; see:
Specifically, you must perform the following tasks:
Set up a system console; see "About Setting Up a Console"
Configure the Ethernet port; see "How to Configure the Standard Ethernet Interface"
Attach the Ethernet port to a network; see "How to Attach a Twisted-Pair Ethernet (TPE) Cable" or "How to Attach an MII Ethernet Transceiver"
Power on the system; see "How to Power On the System"
To boot the system over an Ethernet network, it is necessary that there be a bootable image for Sun4u architecture somewhere on the network. For details, see the installation instructions accompanying your Solaris software.