RFC 1888 (rfc1888) - Page 3 of 16

OSI NSAPs and IPv6

Alternative Format: Original Text Document


RFC 1888                   OSI NSAPs and IPv6                August 1996


   Three warnings must be carefully considered in every case:

   1. The ES-IS/IS-IS model employs a routing hierarchy down to the Area
   level, but not all end systems in an Area need to be in the same
   physical subnet (on the same "wire" or "link"). IS routers on
   different links within a given Area exchange information about the
   end systems they can each reach directly.  In contrast, the IPv6
   routing model extends down to the subnet level and all hosts in the
   same subnet are assumed to be on the same link. In mapping a CLNP
   addressing plan into IPv6 format, without changing the physical
   topology, it may be necessary to add an extra level of hierarchy to
   cope with this mismatch. In other words, the Area number cannot
   blindly be mapped as a subnet number, unless the physical network
   topology corresponds to this mapping.

   2. It is highly desirable that subnet addresses can be aggregated for
   wide area routing purposes, to minimise the size of routing tables.
   Thus network implementors should ensure that the address prefix used
   for all their subnets is the same, regardless of whether a particular
   subnet is using a pure IPv6 addressing scheme or one derived from a
   CLNP scheme as above.

   3. Some hosts have more than one physical network interface.  In the
   ES-IS model, an end system may have more than one NSAP address, each
   of which identifies the host as a whole.  Such an end system with
   more than one physical interface may be referenced by any one of the
   NSAPs, and reached via any one of the physical connections.  In the
   IPv6 model, a host may have multiple IPv6 addresses per interface,
   but each of its physical interfaces must have its own unique
   addresses. This restriction must be applied when mapping an NSAP
   addressing plan into an IPv6 addressing plan for such hosts.

   This document does not address the issues associated with migrating
   the routing protocols used with CLNP (ES-IS or IS-IS) and transition
   of their network infrastructure.
















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