IPv6ユニキャストアドレス割り当て体系（勧告）

   We anticipate that the current exponential growth of the Internet
   will continue or accelerate for the foreseeable future. In addition,
   we anticipate a rapid internationalization of the Internet. The
   ability of routing to scale is dependent upon the use of data
   abstraction based on hierarchical IPv6 addresses.  It is therefore
   essential to choose a hierarchical structure for IPv6 addresses with
   great care.

   Great attention must be paid to the definition of addressing
   structures to balance the conflicting goals of:

     - Route optimality

     - Routing algorithm efficiency

     - Ease and administrative efficiency of address registration

     - Considerations for what addresses are assigned by what addressing
        authority

   It is in the best interests of the internetworking community that the
   cost of operations be kept to a minimum where possible. In the case
   of IPv6 address allocation, this again means that routing data
   abstraction must be encouraged.

   In order for data abstraction to be possible, the assignment of IPv6
   addresses must be accomplished in a manner which is consistent with
   the actual physical topology of the Internet. For example, in those
   cases where organizational and administrative boundaries are not
   related to actual network topology, address assignment based on such
   organization boundaries is not recommended.

   The intra-domain routing protocols allow for information abstraction
   to be maintained within a domain.  For zero-homed and single-homed
   routing domains (which are expected to remain zero-homed or single-
   homed), we recommend that the IPv6 addresses assigned within a single
   routing domain use a single address prefix assigned to that domain.
   Specifically, this allows the set of all IPv6 addresses reachable
   within a single domain to be fully described via a single prefix.

   We anticipate that the total number of routing domains existing on a
   worldwide Internet to be great enough that additional levels of
   hierarchical data abstraction beyond the routing domain level will be
   necessary.

   In most cases, network topology will have a close relationship with
   national boundaries. For example, the degree of network connectivity
   will often be greater within a single country than between countries.
   It is therefore appropriate to make specific recommendations based on
   national boundaries, with the understanding that there may be
   specific situations where these general recommendations need to be
   modified.

   Further, from experience with IPv4, we feel that continental
   aggregation is beneficial and should be supported where possible as a
   means of limiting the unwarranted spread of routing exceptions.