Good news for service providers that faced with issue of necessarily NAT from client network to client network, from client network to provider network and etc. They faced situations where networks from RFC 1918 is not enough.
The new RFC 6598 wants to help them and defines new “private” network 100.64.0.0/10, that can be used only in service provider network. You must maintain it as old (RFC 1918) networks – it could not be declared from your AS in the world, not resolved from public DNS, you have to filter it on the border from world.
Please, fix your prefix list now 🙂
I want to note, that this RFC was born as predictable, but such a sad evidence of unavailability to handle of IPv6 in the all world now.