Google, IPv6, and ... IPv4 multicast space?

[nick hatch]

I have been using Google services over IPv6 (SixXS tunnel) for a few days,
and noticed something odd.

Within Gmail, you can view the IP addresses which have recently logged into
your account for security purposes. When using gmail over IPv6, my IP
address shows up as being in IPv4 multicast space -- 239.93.229.239 .

I'm having a hard time wrapping my head around what they'd be using
multicast for. Perhaps its an internal hack to shim v6 addresses into a
management system which still expects IPv4 addresses?

Any idea what Google is doing?

-Nick
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