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This is something I’ve been thinking about for several months. In the context of IPv4, multicasting is about broadcasting data to a group of clients that have established a connection to a specific multicast address, and this can be used for broadcasting media such as IPTV and Internet radio. Currently with most the Internet still being IPv4-based, the nodes in a multicast group are invariably routers. When IPv6 is fully deployed, the nodes could be the endpoints themselves, and this is why I reckon IPv6 multicasting could be used as the basis for a group messaging system or a new type of distributed social network. The need for a central server would be removed, and the endpoints would be communicating pretty much directly. At least that’s the assumption I’m building on.

The concept I’m developing was partly inspired from a job I worked several years ago, where there was a demand for highly secure IP-based group communications, and the expensive proprietary stuff being deployed for that had some very serious flaws. IPv6 multicasting has certain features that should make it a much better alternative.
From what I gather, any address with the FF:: prefix, apart from the FF01:: to FF0F:: block and a few reserved addresses, can be used for multicasting, and this is what might provide confidentiality for a group. Anyone who wanted to listen in on the communications would have to sift through roughly 1.3 x 10e36 addresses to find the correct one.
Of course, the major flaw in my argument is the communications would vulnerable to Deep Packet Inspection anyway, but we have IPsec which is supposedly a native feature of IPv6. With each client having a persistent address, and Security Association Databases being able to accommodate any number of endpoints, it should be possible for a closed group to communicate securely over IPsec links. It would also solve the problem of authenticating the group membership. It seems Cisco and Louise McKeag at Techworld have already thought of multicasting/IPsec combinations before I did.