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.
Bound, et. al. Experimental