The description is here. It listens to ROM monitor download requests and serves for it. The proprietary protocol uses a special Ethernet type and works within a local wire. If the servicing machine has multiple network interfaces in action, this option can be used to specify which network interface to use. Given no provision, isiboot searchs the downloading files in the current directory when started.
Greater number provides more detailed trace.
The protocol uses server's hostname to start the downloading dialogue. Use -s option when necessary. Then type 'g' ROM monitor command to start downloading. Litting front panel LED tells activity. Here is the instruction for manual installation.