weird network outage

["Steven M. Bellovin" <smb%cs.columbia.edu@localhost>]

I just had a network outage in my house that I can't explain; I'm 
posting here because it may be NetBSD-related.

My house gateway is a Soektris 4801, Hellgate, running -current from
two months ago.  Its serial console is connected to another -current
machine, Bigboy.  All three of the Ethernets on the Soekris are bridged 
together; one is connected to the cable modem.

I decided to upgrade Bigboy to today's version.  When 
I rebooted it, though, I could no longer get out to the net from any 
other machine.  I suspected that perhaps disappearance of any signal on 
the console line had halted the Soekris, so I rebooted it.  But it was 
hung trying to talk over the network to the cable modem.  I'm not sure 
how long that would have lasted (and given the hour, I wasn't inclined 
to wait too long, but by the time I'd seen this it had been a 
reasonable number of minutes.  Power-cycling the cable modem brought 
everything back.

I don't think it was coincidence that rebooting Bigboy made things 
wedge.  I have a plausible explanation for how that reboot could have 
wedged Hellgate, via something that looked like a "break" on a serial 
console.  I have no explanation whatsoever for how that could have 
confused a cable modem.  Any theories?

                --Steven M. Bellovin, http://www.cs.columbia.edu/~smb