I just noticed that Draytek had sent me a late xmas present, in the form of the 3.8.9.7 firmware , so I thought I'd pop it on the router.

I've had odd, unexpected, un-related 'settings changes' during firmware upgrades in the past, but this time, I claim "Apply Strict Bind to Subnet" was enabled for LAN 1, in the "Bind IP to MAC" section...

I can't prove it happened as a result of the upgrade, but this setting definitely wasn't present in the last configuration backup I did on 3.8.9.6 (I reloaded it, to check).

The result of this change, was even more peculiar - and a sod to find.The symptoms I was getting, was that none of my Hyper-V virtual machines could access the Vigor 2860 properly (even though their hosts could). Said machines are all fixed IP addresses, and have never had any sort of DHCP entry. With this change present, they would be able to access the Vigor for about 5 minutes and then claim it had dropped off the network for a similar amount of time. Since two of these machines are my internal DNS servers, the result was utter chaos!

Diagnosis was not made easier, by the fact that Hyper-V malfunctions of this type are not unknown - but from completely different causes. I only found it, when my other-half's laptop failed to get an IP address, when connecting by Wi-fi (Well sometimes, it got one, but then didn't work )

Never a dull moment!