Following
Jelv's experience of getting IPv6 up-and-running but seemingly some apps still preferring the use of IPv4 instead of IPv6 (the opposite of accepted general convention) it would appear that one potential cause of this is Microsoft's bespoke implementation of
RFC 3484 - Default Address Selection for IPv6.
In particular, according to
this MSDN blog post:
| Quote |
Windows 8 tests IPv6 connectivity when you connect to a new network that advertises IPv6 routabilty, and it will only use IPv6 if IPv6 connectivity is actually functioning. This approach is a modification of our implementation of RFC 3484. Instead of sorting addresses as a result of policy, we use the actual state of the network as input to our algorithm. On a misconfigured network, this approach improves the experience not only for browsers but also for apps that connect to dual-stack destinations using standard Windows APIs.
Windows 8 performs the network connectivity test when you first connect to a new network; it caches this information and repeats the test every 30 days. The actual test for connectivity is a simple HTTP GET to an IPv6-only server that is hosted by Microsoft. (For standards buffs, this is implemented between rules 5 and 6 of destination address sorting in our implementation of RFC 3484.) |
Yes, it is referring to Windows 8 however many 'features' of Windows 8 are often released as updates to Windows 7 too and from digging around this looks to be one of them.
This is, in my view, a pretty poor thing for MS to do. The intent is understandable - afterall broken IPv6 stacks can cause mayhem - however their fix is using a sledgehammer to crack a nut. There are many ways in which the approach can fail and thus lead to a 'de-preferencing' of IPv6 even when it is actually available and working. Sure, Internet connectivity should continue but it doesn't help matters when you are trying to deploy and test IPv6 like we are here!
I haven't found whether or not there is a way to perform a retest (why does it wait 30 days?!
30 days!!) and it should be stressed that this won't always be the cause of IPv6 seemingly working but not being used.
If anyone sees similar, or knows/finds further information, I'd be interested to hear about it.
