As the subject line sais, I wish to make sure that the problem resides with our ISP or modem, and not with the router itself. I pulled a log from the router:

after that, it just continued its usual NTP updates on an hourly basis.

Am I right, in that its either the modem (seperate box) or something further upstream causing these issues, or does this point to a problem with our router?[/quote]

The fact that it's saying the WAN link is down implies the physical Ethernet link is going down because the modem is doing something (like rebooting itself or whatnot), but you can't be certain that the message your router is generating isn't misleading without knowing exactly the conditions under which it may generate those messages.

A datum that would lend support to the theory: physically unplug the cable between your modem and router- does it generate the same "Ethernet link down" message?