It is simply a different way of acquiring IP addresses automatically, with guaranteed randomness if desired, and with the provision for regularly changing addresses.

They don't get them. Asia has been doing 10/8 for mobile use practically from the beginning of mobile internet access there and Europe has done it for perhaps 10 years now. US is drowning in addresses, so you probably get a real IP address there, but that is not the case almost everywhere else.

However, 17 is Apple... They could handily buy HP these days.

Renumbering is a royal pain, and Ford probably uses 10/8 already. A /8 is too small to comfortably handle a global organisation these days. For most Fortune 500's, an extra /8 for private use would be absolutely great.

You can do address shortening in IPv4 too if you want... The rules are confusing, and much equipment gets them wrong.

Ha! Obviously said by someone who has never tried it.

Yes, definitely. It is generally much easier with IPv6, because you are likely working with either /64 or point-to-point. You are very rarely dealing with splitting stuff on non-nibble boundaries. For the most part you can just forget about the lower 64 bits unless they were manually assigned (and they are likely below 0x100 in that case, so easy as well). That leaves the upper 64 bits, where you can usually ignore the upper 32 (more likely 48) as well, they will almost always be the same for all addresses in an organization. Now you're down to handling just 32 (or even 16) bits, which is dead easy.

The additional space means room for giving sensible addresses to different parts of an organisation. Just hand them 16 subnets if they need 2, that way they won't come back and ask for more.

Don't expect multicast to happen. No one has demonstrated a way to make multicast scale to the Internet. It only works in controlled networks.

You can, and if they are in the same subnet it will even work. If they are NOT in the same network, it works until it doesn't. There are important cases where it works flawlessly, like if every other machine in the same subnet ALSO has an address in both subnets. Good luck enforcing them.

And yes, I'll likely get a hundred replies with "multiple addresses in different subnets work for fine me". Good for you. Don't touch anything, and if you do, don't complain when it breaks.

In IPv6 it actually works, as long as all routers are aware of it or all hosts with multiple addresses do policy routing to hit the right router. Those are workable conditions, you can build a good network like that.

If they can administer your router, it is trivial to discover your MAC address whether you use IPv4 or IPv6 and whether you pick static or automatic assignments. The MAC address is kept in the ARP table for IPv4 and in the neighbor table for IPv6.

Anyway, every modern OS supports privacy extensions to autoconf, so just enable that (they will likely be enabled already). It's a bitch to write firewall rules when the IP address changes daily though.