OK, this was weird. I was working in my local address book, not even accessing anything online, when all of a sudden, my hardline connection died. I switched over to wireless and it works fine. I checked the router logs and found a succession of entries like 'Dropped packet from xxxxto xxxxx (IP protocol 17) as unable to create new session. The router did not reboot, nor did I lose my modem connection. At the time this happened, only one of my computers was on, so activity from another device was not possible.
I respect that dropped packets can happen, but I never lost my hardline connection only because of it, with any of my previous routers. Fortunately, the machine I was using this time was my laptop, and so therefore it had a wifi to use. My desktops do not.
Reconnected to hardline, and it works again, like nothing happened. All of my connections have reserved leases, so it's not like one of them had to be renewed.
Never mind, I checked the modem logs, and it had automagically rebooted, for no explainable reason. Funny thing was, I could not use the hardline connect for a couple of minutes, but the wireless picked up first. Strange.