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rfc:rfc1888

Network Working Group J. Bound Request for Comments: 1888 Digital Equipment Corporation Category: Experimental B. Carpenter

                                                                  CERN
                                                         D. Harrington
                                         Digital Equipment Corporation
                                                        J. Houldsworth
                                                   ICL Network Systems
                                                              A. Lloyd
                                                Datacraft Technologies
                                                           August 1996
                         OSI NSAPs and IPv6

Status of this Memo

 This memo defines an Experimental Protocol for the Internet
 community.  This memo does not specify an Internet standard of any
 kind.  Discussion and suggestions for improvement are requested.
 Distribution of this memo is unlimited.

Abstract

 This document recommends that network implementors who have planned
 or deployed an OSI NSAP addressing plan, and who wish to deploy or
 transition to IPv6, should redesign a native IPv6 addressing plan to
 meet their needs.  However, it also defines a set of mechanisms for
 the support of OSI NSAP addressing in an IPv6 network.  These
 mechanisms are the ones that MUST be used if such support is
 required.  This document also defines a mapping of IPv6 addresses
 within the OSI address format, should this be required.

Table of Contents

    1. General recommendation on NSAP addressing plans..............2
    2. Summary of defined mechanisms................................4
    3. Restricted NSAPA in a 16-byte IPv6 address for ICD and DCC...4
    3.1 Routing restricted NSAPAs...................................5
    4. Truncated NSAPA used as an IPv6 address......................6
    4.1 Routing truncated NSAPAs....................................8
    5. Carriage of full NSAPAs in IPv6 destination option...........9
    6. IPv6 addresses inside an NSAPA..............................10
    7. Security Considerations.....................................11
    Acknowledgements...............................................11
    References.....................................................12
    Annex A: Summary of NSAP Allocations...........................13
    Annex B: Additional Rationale..................................14
    Authors' Addresses.............................................16

Bound, et. al. Experimental [Page 1] RFC 1888 OSI NSAPs and IPv6 August 1996

1. General recommendation on NSAP addressing plans

 This recommendation is addressed to network implementors who have
 already planned or deployed an OSI NSAP addressing plan for the usage
 of OSI CLNP [IS8473] according to the OSI network layer addressing
 plan [IS8348] using ES-IS and IS-IS routing [IS9542, IS10589].  It
 recommends how they should adapt their addressing plan for use with
 IPv6 [RFC1883].
 The majority of known CLNP addressing plans use either the Digital
 Country Code (DCC) or the International Code Designator (ICD) formats
 defined in [IS8348]. A particular example of this is the US
 Government OSI Profile Version 2 (GOSIP) addressing plan [RFC1629].
 The basic NSAP addressing scheme and current implementations are
 summarised in Annex A.
 [IS8348] specifies a maximum NSAPA (NSAP address) size of 20 bytes
 and some network implementors have designed address allocation
 schemes which make use of this 20 byte address space.
 Other NSAP addressing plans have been specified by the ITU-T for
 public data services, such as X.25 and ISDN, and these can also have
 addresses up to 20 bytes in length.
 The general recommendation is that implementors SHOULD design native
 IPv6 addressing plans according to [RFC1884], but doing so as a
 natural re-mapping of their CLNP addressing plans. While it is
 impossible to give a general recipe for this, CLNP addresses in DCC
 or ICD format can normally be split into two parts: the high order
 part relating to the network service provider and the low order part
 relating to the user network topology and host computers.
 For example, in some applications of US GOSIP the high order part is
 the AFI, ICD, DFI, AA and RD fields, together occupying 9 bytes. The
 low order part is the Area and ID fields, together occupying 8 bytes.
 (The selector byte and the two reserved bytes are not part of the
 addressing plan.) Thus, in such a case, the high-order part could be
 replaced by the provider part of an IPv6 provider-based addressing
 plan.  An 8-byte prefix is recommended for this case and [RFC1884]
 MUST be followed in planning such a replacement. The low order part
 would then be mapped directly in the low-order half of the IPv6
 address space, and user site address plans are unchanged.  A 6-byte
 ID field, exactly as used in US GOSIP and other CLNP addressing
 plans, will be acceptable as the token for IPv6 autoconfiguration
 [RFC1971].
 Analogous rules would be applied for other CLNP addressing plans
 similar to US GOSIP, which is used only as a well known example.

Bound, et. al. Experimental [Page 2] 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 [Page 3] RFC 1888 OSI NSAPs and IPv6 August 1996

2. Summary of defined mechanisms

 This document defines four distinct mechanisms.  All of these are
 ELECTIVE mechanisms, i.e. they are not mandatory parts of an IPv6
 implementation, but if such mechanisms are needed they MUST be
 implemented as defined in this document.
    1. Restricted NSAPA mapping into 16-byte IPv6 address
    2. Truncated NSAPA for routing, full NSAPA in IPv6 option
    3. Normal IPv6 address, full NSAPA in IPv6 option
    4. IPv6 address carried as OSI address
 To clarify the relationship between the first three mechanisms, note
 that:
    If the first byte of an IPv6 address is hexadecimal 0x02 (binary
    00000010), then the remaining 15 bytes SHALL contain a restricted
    NSAPA mapped as in Chapter 3 below. The term "restricted" is used
    to indicate that this format is currently restricted to a subset
    of the ICD and DCC formats.
    If the first byte of an IPv6 address is hexadecimal 0x03 (binary
    00000011), then the remaining 15 bytes SHALL contain a truncated
    NSAPA as described in Chapter 4 below. EITHER a destination option
    containing the complete NSAPA of any format, as described in
    Chapter 5 below, OR an encapsulated CLNP packet, SHALL be present.
    With any other format of IPv6 address, a destination option
    containing a complete NSAPA, as defined in Chapter 5 below, MAY be
    present.

3. Restricted NSAPA in a 16-byte IPv6 address for ICD and DCC

 Some organizations may decide for various reasons not to follow the
 above general recommendation to redesign their addressing plan.  They
 may wish to use their existing OSI NSAP addressing plan unchanged for
 IPv6. It should be noted that such a decision has serious
 implications for routing, since it means that routing between such
 organizations and the rest of the Internet is unlikely to be
 optimised. An organization using both native IPv6 addresses and NSAP
 addresses for IPv6 would be likely to have inefficient internal
 routing.  Nevertheless, to cover this eventuality, the present
 document defines a way to map a subset of the NSAP address space into
 the IPv6 address space. The mapping is algorithmic and reversible
 within this subset of the NSAP address space.

Bound, et. al. Experimental [Page 4] RFC 1888 OSI NSAPs and IPv6 August 1996

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

0-3 |0 0 0 0 0 0 1 0| AFcode| IDI (last 3 digits) |Prefix(octet 0)|

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4-7 | Prefix (octets 1 through 4) |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

8-11 | Area (octets 0 and 1) | ID (octets 0 and 1) |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

12-15| ID (octets 2 through 5) |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The AFcode nibble is overloaded, and encoded as follows
     0000-1001      Implied AFI value is 47 (ICD)
     (0-9 decimal)  AFcode is first BCD digit of the ICD
                    IDI is last three BCD digits of the ICD
     1010           Implied AFI value is 39 (DCC)
     (hex. A)       IDI is the three BCD digits of the DCC
     1011-1111      Reserved, not to be used.
     (hex. B-F)
 The NSEL octet is not included. It is of no use for TCP and UDP
 traffic.  In any case where it is needed, the mechanism described in
 the next chapter should be used.
 The longest CLNP routing prefixes known to be in active use today are
 5 octets (subdivided into AA and RD fields in US GOSIP version 2).
 Thus the semantics of existing 20-octet NSAPAs can be fully mapped.
 DECnet/OSI (Registered Trade Mark) address semantics are also fully
 mapped.
 It is expected that hosts using restricted NSAPAs could be configured
 using IPv6 auto-configuration [RFC1971], and that they could use
 normal IPv6 neighbour discovery mechanisms [RFC1970].
 Restricted NSAPAs, assuming that they can be fully routed using IPv6
 routing protocols, may be used in IPv6 routing headers.

3.1 Routing restricted NSAPAs

 As mentioned in Chapter 1, there is a mismatch between the OSI or
 GOSIP routing model and the IPv6 routing model. Restricted NSAPAs can
 be routed hierarchically down to the Area level but must be flat-
 routed within an Area. Normal IPv6 addresses can be routed

Bound, et. al. Experimental [Page 5] RFC 1888 OSI NSAPs and IPv6 August 1996

 hierarchically down to physical subnet (link) level and only have to
 be flat-routed on the physical subnet.
 Thus, packets whose destination address is a restricted NSAPA can be
 routed using any normal IPv6 routing protocol only as far as the
 Area. If the Area contains more than one physical subnet reached by
 more than one router, no IPv6 routing protocol can route the packet
 to the correct final router.  There is no solution to this problem
 within the existing IPv6 mechanisms.  Presumably a flooding
 algorithm, or a suitably adapted implementation of ES-IS, could solve
 this problem.
 In the absence of such a routing protocol, either the Area number
 must be hierarchically structured to correspond to physical subnets,
 or each Area must be limited to one physical subnet.
 It is necessary in an IPv6 network that routes may be aggregated to
 minimise the size of routing tables. If a subscriber is using both
 normal IPv6 addresses [RFC1884] and restricted NSAPAs, these two
 types of address will certainly not aggregate with each other, since
 they differ from the second most significant bit onwards. This means
 that there may be a significant operational penalty for using both
 types of address with currently known routing technology.

4. Truncated NSAPA used as an IPv6 address

 An NSAP address contains routing information (e.g. Routing Domain and
 area/subnet identifiers) in the form of the Area Address (as defined
 in [IS10589]). The format and length of this routing information are
 typically compatible with a 16 byte IPv6 address, and may be
 represented as such using the following format:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

0-3 |0 0 0 0 0 0 1 1| High order octets of full NSAP address |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4-7 | NSAP address continued |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

8-11 | NSAP address continued |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

12-15| NSAP address truncated … zero pads if necessary |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 If appropriate, when used as a destination IPv6 address, the
 truncated NSAPA may be interpreted as an IPv6 anycast address.  An
 anycast address may be used to identify either an IPv6 node, or
 potentially even an OSI End System or Intermediate System.  For

Bound, et. al. Experimental [Page 6] RFC 1888 OSI NSAPs and IPv6 August 1996

 example, it might be configured to identify the endpoints of a CLNP
 tunnel, or it might identify a particular OSI capable system in a
 particular subnet.
 If a truncated NSAPA is used as a source address, it must be
 interpreted as a unicast address and must therefore be uniquely
 assigned within the IPv6 address space.
 If a truncated NSAPA is used as either the source or destination IPv6
 address (or both), EITHER an NSAPA destination option OR an
 encapsulated CLNP packet MUST be present. It is the responsibility of
 the destination system to take the appropriate action for each IPv6
 packet received (e.g. forward, decapsulate, discard) and, if
 necessary, return to the originating host an appropriate ICMP error
 message.
 If the truncated NSAPA is used to identify a router, and an NSAPA
 destination option is present, then it is the responsibility of that
 router to forward the complete IPv6 packet to the appropriate host
 based upon the Destination NSAP field in the NSAPA option.  This
 forwarding process may be based upon static routing information (i.e.
 a manual mapping of NSAPs to IPv6 unicast addresses), or it may be
 gathered in an automated fashion analogous to the ES-IS mechanism,
 perhaps using extensions to the Neighbor Discovery protocol
 [RFC1970].  The details of such a mechanism are beyond the scope of
 this document.
 This document does not restrict the formats of NSAP address that may
 be used in truncated NSAPAs, but it is apparent that binary ICD or
 DCC formats will be much easier to accomodate in an IPv6 routing
 infrastructure than the other formats defined in [IS8348].
 It is not expected that IPv6 autoconfiguration [RFC1971] and
 discovery [RFC1970] will work unchanged for truncated NSAPAs.
 Truncated NSAPAs are not meaningful within IPv6 routing headers, and
 there is no way to include full NSAPAs in routing headers.
 If a packet whose source address is a truncated NSAPA causes an ICMP
 message to be returned for whatever reason, this ICMP message may be
 discarded rather than being returned to the true source of the
 packet.

Bound, et. al. Experimental [Page 7] RFC 1888 OSI NSAPs and IPv6 August 1996

4.1 Routing truncated NSAPAs

 This is a grey area. If the truncated NSAPA retains a hierarchical
 structure, it can be routed like a restricted NSAPA, subject to the
 same problem concerning the mismatch between Areas and subnets.  If
 possible, in the case of a GOSIP-like NSAPA, it should be truncated
 immediately after the Area number. In this case the routing
 considerations will be similar to those for restricted NSAPAs, except
 that final delivery of the packet will depend on the last IPv6 router
 being able to interpret the NSAPA destination option (or an
 encapsulated CLNP packet).
 In the general case, nothing can be said since the NSAPA could have
 almost any format and might have very little hierarchical content
 after truncation. There may be many cases in which truncated NSAPAs
 cannot be routed across large regions of the IPv6 network.
 The situation for route aggregation is similar to that described in
 Section 3.1 as long as the truncated NSAPAs have ICD or DCC format.
 However, if arbitrary NSAPAs are used nothing can be predicted about
 route aggregation and we must assume that it will be poor.

Bound, et. al. Experimental [Page 8] RFC 1888 OSI NSAPs and IPv6 August 1996

5. Carriage of full NSAPAs in IPv6 destination option

 In the case of a truncated NSAPA used as an IPv6 address other than
 for a CLNP tunnel, the full NSAPA must be carried in a destination
 option. Any format defined in [IS8348] is allowed.
 The NSAPA destination option is illustrated below. It has no
 alignment requirement.
 The option type code is 11-0-00011 = 195 decimal.
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |1 1 0 0 0 0 1 1|  Opt Data Len |Source NSAP Len| Dest. NSAP Len|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                                                               |
     +                         Source NSAP                           +
     |                                                               |
     +                                                               +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                                                               |
     +                       Destination NSAP                        +
     |                                                               |
     +                                                               +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The length fields are each one octet long and are expressed in
 octets.  The destination node should check the consistency of the
 length fields (Option Data Length = Source NSAP Length + Dest. NSAP
 Length +2).  In case of inconsistency the destination node shall
 discard the packet and send an ICMP Parameter Problem, Code 2,
 message to the packet's source address, pointing to the Option Data
 Length field.
 The boundary between the source NSAP and the destination NSAP is
 simply aligned on an octet boundary. With standard 20 octet NSAPs the
 total option length is 44 bytes and the Option Data Length is 42.

Bound, et. al. Experimental [Page 9] RFC 1888 OSI NSAPs and IPv6 August 1996

 The NSAP encodings follow [IS8348] exactly.
 If this option is used, both end systems concerned SHOULD use NSAP
 addresses. In the exceptional case that only one of the end systems
 uses NSAP addresses, the NSAP Length field of the other SHALL be set
 to zero in the NSAP destination option.
 This destination option is used in two cases. Firstly, an IPv6 source
 node using normal IPv6 addresses (unicast address or anycast address)
 MAY supply an NSAP destination option header for interpretation by
 the IPv6 destination node. Secondly, an IPv6 node MAY use a truncated
 NSAP address in place of a normal IPv6 address.
 IPv6 nodes are not required to implement this option, except for
 nodes using truncated NSAPAs other than for CLNP tunnels.

6. IPv6 addresses inside an NSAPA

 If it is required, for whatever reason, to embed an IPv6 address
 inside a 20-octet NSAP address, then the following format MUST be
 used.
 A specific possible use of this embedding is to express an IP address
 within the ATM Forum address format.  Another  possible use would be
 to allow CLNP packets that encapsulate IPv6 packets to be routed in a
 CLNP network using the IPv6 address architecture. Several leading
 bytes of the IPv6 address could be used as a CLNP routing prefix.
 The first three octets are an IDP in binary format, using the AFI
 code in the process of being allocated to the IANA. The AFI value
 provisionally allocated is 35, but this requires a formal
 modification to [IS8348].  The encoding format is as for AFI value 47
 [IS8348]. The third octet of the IDP is known as the ICP (Internet
 Code Point) and its value must be zero. All other values are reserved
 for allocation by the IANA.
 Thus an AFI value of 35 with an ICP value of zero means that "this
 NSAPA embeds a 16 byte IPv6 address".
 The last octet is a selector.  To maintain compatibility with both
 NSAP format and IPv6 addressing, this octet must be present, but it
 has no significance for IPv6. Its default value is zero.

Bound, et. al. Experimental [Page 10] RFC 1888 OSI NSAPs and IPv6 August 1996

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

0-3 | AFI = 35 | ICP = 0000 | IPv6 (byte 0)|

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4-7 | IPv6 (bytes 1-4) |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

8-11 | IPv6 (bytes 5-8) |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

12-15| IPv6 (bytes 9-12) |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

16-19| IPv6 (bytes 13-15) |0 0 0 0 0 0 0 0|

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Theoretically this format would allow recursive address embedding.
 However, this is considered dangerous since it might lead to routing
 table anomalies or to loops (compare [RFC1326]).  Thus embedded IPv6
 address MUST NOT have the prefixes 0x02 or 0x03, and an NSAPA with
 the IANA AFI code MUST NOT be embedded in an IPv6 header.
 An NSAPA with the IANA AFI code and ICP set to zero is converted to
 an IPv6 address by stripping off the first three and the twentieth
 octets. All other formats of NSAPA are handled according to the
 previous Chapters of this document.

7. Security Considerations

 Security issues are not specifically addressed in this document, but
 it is compatible with the IPv6 security mechanisms [RFC1825].

Acknowledgements

 The authors are pleased to acknowledge the suggestions and comments
 of Ross Callon, Richard Collella, Steve Deering, Dirk Fieldhouse,
 Joel Halpern, Denise Heagerty, Cyndi Jung, Yakov Rekhter, and members
 of the former TUBA and current IPNG working groups of the IETF. The
 support of Scott Bradner and Allison Mankin of the IESG was
 essential.
 Herb Bertine, Alan Chambers, Dave Marlow, and Jack Wheeler were all
 active in arranging the AFI allocation by ISO/IEC JTC1/SC6.

Bound, et. al. Experimental [Page 11] RFC 1888 OSI NSAPs and IPv6 August 1996

References

 [IS8473] Data communications protocol for providing the
 connectionless-mode network service, ISO/IEC 8473, 1988.
 [IS8348] Annex A, Network Layer Addressing, and Annex B, Rationale
 for the material in Annex A, of ISO/IEC 8348, 1993 (identical to
 CCITT Recommendation X.213, 1992).
 [IS10589] Intermediate system to intermediate system intra-domain-
 routeing routine information exchange protocol for use in
 conjunction with the protocol for providing the connectionless-mode
 Network Service (ISO 8473), ISO 10589, 1992.
 [IS9542] End system to Intermediate system routeing exchange
 protocol for use in conjunction with the Protocol for providing the
 connectionless-mode network service (ISO 8473), ISO 9542, 1988.
 [RFC1629] Colella, R., Callon, R., Gardner, E., and Y. Rekhter,
 "Guidelines for OSI NSAP Allocation in the Internet", RFC 1629, May
 1994.
 [RFC1326] Tsuchiya, P., "Mutual Encapsulation Considered
 Dangerous", RFC 1326, May 1992.
 [RFC1883] Deering, S., and R. Hinden, "Internet Protocol, Version 6
 (IPv6) Specification", RFC 1883, December 1995.
 [RFC1884] Hinden, R., and S. Deering, "IP Version 6 Addressing
 Architecture", RFC 1884, December 1995.
 [RFC1971] Thompson, S., and T. Narten, "IPv6 Stateless Address
 Autoconfiguration", RFC1971, August 1996.
 [RFC1970] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
 Discovery for IP Version 6 (IPv6)", RFC1970, August 1996.
 [RFC1825] Atkinson, R., "Security Architecture for the Internet
 Protocol", RFC 1825, August 1995.

Bound, et. al. Experimental [Page 12] RFC 1888 OSI NSAPs and IPv6 August 1996

Annex A: Summary of NSAP Allocations

  1. —-IDP——
  2. —————————————————-

| AFI | IDI | DOMAIN SPECIFIC PART |

  1. —————————————————-
  2. ——————-20 bytes max———————
 The Initial Domain Part (IDP) is split into Authority and Format
 Identifier (AFI) followed by the Initial Domain Identifier (IDI).
 This combination is followed by the Domain Specific Part and
 allocation within that part is domain specific.
 The following is a summary of current allocations:
 ISO DCC Scheme
 AFI = decimal 38 or binary 39 = ISO Data Country Code Scheme.  IDI =
 3 decimal or binary digits specifying the country.  ISO allocate the
 country codes.  The DSP is administered by the standards authority
 for each country.  In the UK, the British Standards Institution have
 delegated administration to the Federation of Electronics Industries
 - FEI
 The UK DSP is split into a single digit UK Format Indicator (UKFI)
 which indicates large, medium or small organisation rather like IP
 addressing and a UK Domain Identifier (UKDI).  Using binary coded
 decimal examples only (there are binary equivalents):
 UKFI = 0 is reserved UKFI = 1, UKDI = nnn, UK Domain Specific Part =
 31 digits.  UKFI = 2, UKDI = nnnnn, UKDSP = 29 digits max.  UKFI = 3,
 UKDI = nnnnnnnn, UKDSP = 26 digits max.
 UKFI = 4 to 9 reserved
 The UK Government have been allocated a UKDI in the UKFI = 1 (large
 organisation) format and have specified the breakdown of the
 Government Domain Specific Part with sub domain addresses followed by
 a station ID (which could be a MAC address) and a selector (which
 could be a TSAP selection).
 ITU-T X.121
 AFI = decimal 36 or 52, binary 37 or 53 indicates that the IDI is a
 14 digit max X.121 International Numbering Plan address (prefix, 3
 digit Data Country Code, dial up data network number).  The full
 X.121 address indicates who controls the formatting of the DSP.

Bound, et. al. Experimental [Page 13] RFC 1888 OSI NSAPs and IPv6 August 1996

 ITU-T F.69
 AFI = 40,54 or binary 41,55 indicates that the IDI is a telex number
 up to 8 digits long.
 ITU-T E.163
 AFI = 42,56 or binary 43,57 indicates that the IDI is a normal
 telephone number up to 12 digits long.
 ITU-T E.164
 AFI = 44,58 or binary 45,59 indicates that the IDI is an ISDN number
 up to 15 digits long.
 ISO 6523-ICD
 AFI = 46 or binary 47 indicates that the IDI is an International Code
 Designator allocated according to ISO 6523.  You have to be a global
 organisation to get one of these.  The Organisation to which the ISO
 6523 designator is issued specifies the DSP allocation.

Annex B: Additional Rationale

 This annex is intended to give additional rationale, motivation and
 justification for the support of NSAPAs in an IPv6 network.
 There are several models for OSI-IPv6 convergence, of which address
 mapping is only one. The other models can be identified as
  1. Dual stack coexistence, in which a CLNP network and an IPv6
     network exist side by side indefinitely using multiprotocol
     routers.
  2. CLNP tunnels over IPv6.
  3. OSI transport over IPv6.
  4. OSI transport over UDP.
  5. OSI transport over TCP (compare RFC 1006)
 The present model is more fundamental, as it attempts to unify and
 reconcile the OSI and IPv6 addressing and routing schemes, and
 replace CLNP by IPv6 at the network level. The rationale for this
 choice is to preserve investment in NSAPA allocation schemes, and to
 open the door for peer-to-peer routing models between IPv6 and bearer
 services (such as ATM) using NSAPA addressing. It should be noted

Bound, et. al. Experimental [Page 14] RFC 1888 OSI NSAPs and IPv6 August 1996

 that such peer-to-peer models are contentious at the time of writing,
 but in any case a consistent address mapping is preferable to
 multiple mappings.
 In addition to their use to retain an existing addressing plan,
 certain other uses of restricted NSAPAs could be envisaged.  They
 could be used as an intermediate addressing plan for a network making
 a transition from CLNP to IPv6. They could be used in a header
 translation scheme for dynamic translation between IPv6 and CLNP.
 They could be used to allow CLNP and IPv6 traffic to share the same
 routing architecture within an organization ("Ships in the Day").
 It should be noted that the use of full NSAPA addresses in end
 systems impacts many things. The most obvious are the API and DNS. If
 applications are to work normally, everything that has to be modified
 to cope with IPv6 addresses has to be further modified for full
 NSAPAs.  The mechanisms defined in the present document are only a
 small part of the whole.
 A destination option was chosen to carry full NSAPAs, in preference
 to a dedicated extension header.  In the case of an extension header,
 all IPv6 nodes would have needed to understand its syntax merely in
 order to ignore it. In contrast, intermediate nodes can ignore the
 destination option without any knowledge of its syntax. Thus only
 nodes interested in NSAPAs need to know anything about them.
 Thus we end up with two classes of IPv6 nodes:
 1. Nodes knowing only about 16 byte addresses (including restricted
 NSAPAs, which behave largely like any other IPv6 addresses).
 2. Nodes also knowing about 20 byte NSAPAs, either as an extension of
 the IPv6 address space or as the CLNP address space. In either case,
 regions of the network containing such nodes are connected to each
 other by unicast or anycast tunnels through the 16 byte address
 space. Routing, system configuration, and neighbour discovery in the
 NSAPA regions are outside the scope of the normal IPv6 mechanisms.

Bound, et. al. Experimental [Page 15] RFC 1888 OSI NSAPs and IPv6 August 1996

Authors' Addresses

 Jim Bound
 Member Technical Staff                    Phone: (603) 881-0400
 Network Operating Systems                 Fax:   (603) 881-0120
 Digital Equipment Corporation             Email: bound@zk3.dec.com
 110 Spitbrook Road, ZKO3-3/U14
 Nashua, NH 03062
 Brian E. Carpenter
 Group Leader, Communications Systems      Phone:  +41 22 767-4967
 Computing and Networks Division           Fax:    +41 22 767-7155
 CERN                                      Telex:  419000 cer ch
 European Laboratory for Particle Physics  Email: brian@dxcoms.cern.ch
 1211 Geneva 23, Switzerland
 Dan Harrington                            Phone: (508) 486-7643
 Digital Equipment Corp.
 550 King Street (LKG2-2/Q9)               Email: dan@netrix.lkg.dec.com
 Littleton, MA  01460
 Jack Houldsworth            Phone- ICL: +44 438 786112
 ICL Network Systems               Home: +44 438 352997
 Cavendish Road              Fax:        +44 438 786150
 Stevenage                   Email: j.houldsworth@ste0906.wins.icl.co.uk
 Herts
 UK SG1 4BQ
 Alan Lloyd                  Phone:  +61 3 727 9222
 Datacraft Technologies      Fax:    +61 3 727 1557
 252 Maroondah Highway       Email:  alan.lloyd@datacraft.com.au
 Mooroolbark 3138
 Victoria       Australia
 X.400- G=alan;S=lloyd;O=dcthq;P=datacraft;A=telememo;C=au

Bound, et. al. Experimental [Page 16]

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