RFC 1671 (rfc1671) - Page 2 of 8

IPng White Paper on Transition and Other Considerations

RFC 1671          IPng White Paper on Transition, etc.       August 1994


   presumably under pressure from their Internet service providers.
   Furthermore, once the IPng decision is taken, the next decade (or
   more) of activity in the Internet and in all private networks using
   the Internet suite will be strongly affected by the process of IPng
   deployment. User sites will look at the decision whether to change
   from IPv4 in the same way as they have looked in the past at changes
   of programming language or operating system. It may not be a foregone
   conclusion that what they change to is IPng.  Their main concern will
   be to minimise the cost of the change and the risk of lost
   production.

   This concern immediately defines strong constraints on the model for
   transition and deployment of IPng. Some of these constraints are
   listed below, with a short explanation of each one.

   Terminology: an "IPv4 host" is a host that runs exactly what it runs
   today, with no maintenance releases and no configuration changes. An
   "IPng host" is a host that has a new version of IP, and has been
   reconfigured.  Similarly for routers.

   A) Interworking at every stage and every layer.

   This is the major constraint. Vendors of computer systems, routers,
   and applications software will certainly not coordinate their product
   release dates. Users will go on running their old equipment and
   software.  Therefore, any combination of IPv4 and IPng hosts and
   routers must be able to interwork (i.e., participate in UDP and TCP
   sessions). An IPv4 packet must be  able to find its way from any IPv4
   host, to any other IPv4 or IPng host, or vice versa, through a
   mixture of IPv4 and IPng routers, with no (zero, null) modifications
   to the IPv4 hosts. IPv4 routers must need no modifications to
   interwork with IPng routers.  Additionally, an application package
   which is "aware" of IPv4 but still "unaware" of IPng must be able to
   run on a computer system which is running IPv4, but communicating
   with an IPng host.  For example an old PC in Europe should be able to
   access a NIC server in the USA, even if the NIC server is running
   IPng and the transatlantic routing mechanisms are only partly
   converted.  Or a Class C network in one department of a company
   should retain full access to corporate servers which are running
   IPng, even though nothing whatever has been changed inside the Class
   C network.

   (This does NOT require an IPv4-only application to run on an IPng
   host; thus we accept that some hosts cannot be upgraded until all
   their applications are IPng-compatible. In other words we accept that
   the API may change to some extent. However, even this relaxation is
   debatable and some vendors may want to strictly preserve the IPv4 API
   on an IPng host.)



Carpenter