When my cable modem is connected only to power and cable, the "Activity" light flickers irregularly several times per second, indefinitely. This seems odd, since (I presume) no activity has been requested.
Is this normal? If so, what is this activity? If not, is there a good way to learn about the activity? The cable modem is a Linksys BEFCMU10 ver 3. I've learned (thanks to Usenet, no thanks to any documentation) that it serves HTTP requests at 192.169.100.1, but I haven't found any summary of message traffic, packet types, sources, destinations, or the like.
The best way I can think of to address this question is to snoop the ethernet at the cable-modem's port, but that seems like overkill and would be slightly disruptive. Still, I'll do it if nobody has a better suggestion.