I have successfully set up a Windows XP machine as an IPv6 router using netsh, that is, it announces prefixes and forwards packets on two interfaces, as verified by pinging.
Now I'd like to forward multicast frames between both subnets; hosts on both sides are properly sending out multicast listener reports, so all it would take would be for the router to process these and start forwarding datagrams.
How can I enable IPv6 multicast routing between two interfaces?
To merely forward IPv6 multicast packets, you need to have Windows Vista/Server 2008 or later. Windows XP does not support this at all. (XP's IPv6 stack was very limited and is not recommended for production use.)
With the proper OS, you would enable IPv6 multicast forwarding with:
or in PowerShell:
At this time, however, no version of Windows is capable of acting as a full IPv6 multicast router:
This information taken from Understanding IPv6, Third Edition, pages 201-202.