alt Hacker News> You don't actually own the IPv4-mapped-V6 address, as in packets don't get routed to you, they go to a relay that was notoriously flaky.
6to4 is exactly ownership:
> For any 32-bit global IPv4 address that is assigned to a host, a 48-bit 6to4 IPv6 prefix can be constructed for use by that host (and if applicable the network behind it) by appending the IPv4 address to 2002::/16.
> For example, the global IPv4 address 192.0.2.4 has the corresponding 6to4 prefix 2002:c000:0204::/48. This gives a prefix length of 48 bits, which leaves room for a 16-bit subnet field and 64 bit host addresses within the subnets.
* https://en.wikipedia.org/wiki/6to4
The relaying is a necessity:
OLD DUAL NEW
----------------------
OLD | 32 | 32 | XX |
|------|------|------|
DUAL | 32 | 64 | 64 |
|------|------|------|
NEW | XX | 64 | 64 |
----------------------
There's no way around it: a non-IPng-having node will have to go through a translation box of some kind.
Replies
If I have 1.2.3.4 in ipv4 world, I want 1.2.3.4 in ipv6 world instead of a random new address. I want another ipv6 host to be able to send dst=1.2.3.4 and have it go directly to my ipv6 host. 6to4 isn't comparable to that, it's for translation to/from v4 like you said.
> There's no way around it: a non-IPng-having node will have to go through a translation box of some kind.
Yes. Note that it doesn't need to be someone else's relay; anyone with IPv4 connectivity could easily route 2002::/16 into IPv4-land (without having to announce it in BGP for others to use). You could even announce 2002:aabb:ccdd::/48 as a more-specific in BGP if you wanted, although this was more exotic.