IPv6ユニキャストアドレス割り当て体系（プライベートリンク）

   The discussion up to this point concentrates on the relationship
   between IPv6 addresses and routing between various routing domains
   over transit routing domains, where each transit routing domain
   interconnects a large number of routing domains and offers a more-
   or-less public service.

   However, there may also exist a number of links which interconnect
   two routing domains in such a way, that usage of these links may be
   limited to carrying traffic only between the two routing domains.
   We'll refer to such links as "private".

   For example, let's suppose that the XYZ corporation does a lot of
   business with MBII. In this case, XYZ and MBII may contract with a
   carrier to provide a private link between the two corporations, where
   this link may only be used for packets whose source is within one of
   the two corporations, and whose destination is within the other of
   the two corporations. Finally, suppose that the point-to-point link
   is connected between a single router (router X) within XYZ
   corporation and a single router (router M) within MBII. It is
   therefore necessary to configure router X to know which addresses can
   be reached over this link (specifically, all addresses reachable in
   MBII). Similarly, it is necessary to configure router M to know which
   addresses can be reached over this link (specifically, all addresses
   reachable in XYZ Corporation).

   The important observation to be made here is that the additional
   connectivity due to such private links may be ignored for the purpose
   of IPv6 address allocation, and do not pose a problem for routing on
   a larger scale. This is because the routing information associated
   with such connectivity is not propagated throughout the internet, and
   therefore does not need to be collapsed into a TRD's prefix.

   In our example, let's suppose that the XYZ corporation has a single
   connection to a regional, and has therefore uses the IPv6 address
   space from the space given to that regional.  Similarly, let's
   suppose that MBII, as an international corporation with connections
   to six different providers, has chosen the second solution from
   Section 4.4, and therefore has obtained six different address
   allocations. In this case, all addresses reachable in the XYZ
   Corporation can be described by a single address prefix (implying
   that router M only needs to be configured with a single address
   prefix to represent the addresses reachable over this link). All
   addresses reachable in MBII can be described by six address prefixes
   (implying that router X needs to be configured with six address
   prefixes to represent the addresses reachable over the link).

   In some cases, such private links may be permitted to forward traffic
   for a small number of other routing domains, such as closely
   affiliated organizations. This will increase the configuration
   requirements slightly. However, provided that the number of
   organizations using the link is relatively small, then this still
   does not represent a significant problem.

   Note that the relationship between routing and IPv6 addressing
   described in other sections of this paper is concerned with problems
   in scaling caused by large, essentially public transit routing
   domains which interconnect a large number of routing domains.
   However, for the purpose of IPv6 address allocation, private links
   which interconnect only a small number of private routing domains do
   not pose a problem, and may be ignored. For example, this implies
   that a single leaf routing domain which has a single connection to a
   `public' provider (e.g., the Alternet), plus a number of private
   links to other leaf routing domains, can be treated as if it were
   single-homed to the provider for the purpose of IPv6 address
   allocation.  We expect that this is also another way of dealing with
   multi-homed domains.