linux from kernel.org and ipv6

Hello All,

If there is a better place to know, pls. let me know; in that case,
apologies in advance.

I'm under the impression, Linux has USAGI distribution in the kernel.
I'm reading IPv6 in Practice by Benedikt. He mentioned that Linux
would unify IPv6 by chosing KAME distribution for Linux. It was around
2006 timescale. Can any one tell me which distribution of IPv6 current
kernel has? Are there any variations across various kernels - Debian,
RedHat, etc. - that warrants me to be aware of different
distributions? Or they'all happily inter-operate?

Thanks
Venkat