The dead network out of the box made me wonder if some connection was dirty or something had come unseated. So I dismantled everything, cleaned the case and the insides (based on procedures described in these forums), and re-assembled everything. Still no network. So I don't think it's anything simple like the system module not being seated properly.
Of course before I even considered any of that, I made sure I had a known good network cable (tried several), known good port on the switch (again, tried several), and that the networking was properly configured under IRIX. ifconfig shows a proper (static) IP address for my home network and I can ping myself under IRIX. But there's no traffic to/from the rest of my network and no status lights on my switch (where I would expect two LEDs to indicate a 100Mbps, full-duplex connection). I wondered if the Octane was simply failing to auto-negotiate with my switch, so I tried forcing modes according to the instructions in the ethernet(7) man page. Again, ifconfig showed what looked right, but no switch lights and no connection to the outside world.
So I think I've ruled out all of the following:
- unseated/dirty connectors
- bad cables
- bad switch
- failed auto-negotiation
- software mis-configuration
Can anybody else think of anything I should try? Or is it finally time to accept that the motherboard is faulty?