[ppml] PIv6 for legacy holders (/w RSA + efficient use)

[Randy Bush]

> With IPv4, NAT allows one to isolate most of the internal network by
> using non-routable addresses.  So, switching ISPs means renumbering the
> external nodes and revising some firewall rules.
> 
> With IPv6, without NAT, switching vendors with PA space means
> renumbering both the external and the internal network.

so now we know yet another reason nats will be prevalent in the pure
ipv6 world of our grandchildren

randy