Well despite me telling them to opt me out of any beta-testing* it appears Sky don't listen as they have opted me into the IPv6 trial
Its a rather strange trial as well because it appears to be only active on the LAN side
So I waken up this morning & notice exceptionally slow DNS resolution on my machine (which has been in sleep mode overnight). Takes a while to work it out as the Win2k3 server (yeah yeah I know) in the garage isn't throwing any errors up.
The reason for this is that Sky decided to enable an IPv6 DHCP server on the router
Edit - the LAN IPv6 DHCP server is set to use a pseudo-random link-local block rather than a globally routed IPv6 block which says "NAT" to me. Probably makes my gripe clearer
This little gem strongly implies that Sky don't get the point of IPv6 at all as why in the name of sanity would I need a NAT interface on IPv6 if its done properly?
Anyway this resulted in my machine having two ipv6 link-local addresses (one from the Win2k3 server and one from the router) and the initial lookup was on the wrong address. The lookup obviously fails and after timing out several times it falls back to the other IPv6 link-local address which then immediately falls back to IPv4 as the server knows it has no external IPv6 connectivity.
To cut a long story short, Sky have set the default state for the IPv6 stack to supply DHCP services to the LAN. Now (ignoring the wtf are you using NAT with IPv6? elephant in the room) this would be reasonably logical except of course that my router has IPv4 DHCP services disabled - the logical course of action then would be for the upgrade agent to set IPv6 DHCP disabled as well. These sort of glitches are what beta-tests are for but when you're not even on the damn beta-test then its mildly annoying when it eats your time up.
For information the current firmware on the SR102 is 2.88.1086.R - which, despite the "R", does not necessarily indicate that its release firmware.
In retrospect I suppose I'm lucky that Sky hadn't assigned an external IPv6 address or I wouldn't have noticed that the SR102 was now resolving DNS lookups - which I really don't want.
Hopefully this is helpful to anyone else who runs their own caching DNS resolver.
*its utterly pointless as Sky won't fix anything other than "gamestopper" bugs, and often not even those - SR101 still has the bug I identified 3 years ago which crashes the http proxy daemon (used for the "Block Sites using keyword" options). Gave them step by step instructions & told them why it was happening but they didn't give a damn.