Re: Mapping plan
IPv6 is set to use just a fraction of its pool of addresses until some time in the very distant future.
Global routable addresses issued by the IANA start with prefix 2000:
Only one eighth of the total address space is currently allocated for use on the Internet, 2000::/3, in order to provide efficient route aggregation, thereby reducing the size of the Internet routing tables; the rest of the IPv6 address space is reserved for future use or for special purposes. The address space is assigned to the RIRs in large blocks of /23 up to /12.
other addresses are also reserved for IPv4 mapping and translating
This does depend of course on the mechanism they use for mapping but 25% is a stupidly wild number, maybe they meant 25% of the 2000::/3 prefix?
So yes, address space reduced by 25% is complete and utter bollux as they could use a new prefix like 4226::/3 if they wanted and retained the already huge space in 2000::/3 for pure IPv6 use and still avoid address wastage.
there is a lot of misunderstanding, slight of hand and deception going on around IPv6 and all its doing is making people hold onto IPv4 longer. Its time we ditched IPv6 and made a start on IPv8 (odd numbers are experimental apparently) taking advantage of the positives we have learnt in IPv4 and removing the negatives from IPv6.
It's worthwhile noting that IPv6 looks to be designed as a marriage of MAC addressing & IP addressing in 1 protocol. In its original incarnation, it would not have been too hard to get cheap switches to do routing by reading the first 64 bits of the destination address for routing and the last 64 bits for switching, paving the way for the Ethernet frame and IP packet to be collapsed into 1 framing process thereby saving some bits on the wire and making things a bit quicker.
The way we use IPv4 has evolved hugely since 1994 and IPv6 has not kept up which is another reason why IPv6 adoption is so low, its doesn't have any mature tools to go with out and it's like going back to 1994 again in terms of features and how we can use them.