Here's the post I put about the same issue on the SmallNetBuilder forum recently (which is also the home of the forum for the excellent Merlin Asus router firmware).http://www.snbforums.com/threads/monito ... ost-287073
It looks like it's a common problem for several makes of devices as they share a common chipset with issues.
As it's me I decided to over complicate things and put the ping in an app (which I first started looking at in Jan 2015).
Originally I was just trying to confirm that when the link to my router was down, that the connection to my NAS (on a switch this end of the link) stayed up. I also wanted to log this as part of the issue could be interference/spikes on the wiring due to some dodgy bit of kit - maybe I could spot a pattern.
Anyway, I never really got round to finishing it properly but if you want it I could get it sorted.