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Versions: 00 01                                                         
Network Working Group                                       B. Carpenter
INTERNET-DRAFT                                                      CERN
Expires: December 22nd, 1995
                                                                 D. Katz
                                                     cisco Systems, Inc.

                                                               S. Thomas
                                                             AT&T Tridom

                                                              K. Sklower
                                               University of California,
                                                                Berkeley


                 Mechanisms for OSI CLNP and TP over IPv6
                      draft-carpenter-ipv6-osi-01.txt

Status of This Memo

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet- Drafts as reference
   material or to cite them other than as ``work in progress.''

   To learn the current status of any Internet-Draft, please check the
   ``1id-abstracts.txt'' listing contained in the Internet- Drafts
   Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net
   (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific
   Rim).

   Distribution of this memo is unlimited.

Abstract

   This document defines a set of mechanisms for the support of OSI
   CLNP, and Transport Protocols over an IPv6 network.  These mechanisms
   are the ones that MUST be used if such support is required.

Acknowledgements

   All direct contributors of text are listed below as authors.  The
   writers are also pleased to acknowledge the suggestions and comments
   of Richard Collella, Dirk Fieldhouse, Denise Heagerty, Cyndi Jung,



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   Yakov Rekhter, and many other members of the former TUBA and new IPv6
   working groups of the IETF. The support of Scott Bradner and Allison
   Mankin of the IESG was essential.

Conventions

   The following language conventions are used in the items of
   specification in this document:

   o    MUST, SHALL or MANDATORY -- the item is an absolute requirement
        of the specification.

   o    SHOULD or RECOMMENDED -- the item should generally be followed
        for all but exceptional circumstances.

   o    MAY or OPTIONAL -- the item is truly optional and may be
        followed or ignored according to the needs of the implementor.

Table of Contents

   Status of this memo ............................................    1
   Acknowledgements ...............................................    1
   Conventions ....................................................    2
   Table of Contents...............................................    2
   1. Summary of defined mechanisms ...............................    2
   2. CLNP encapsulated in IPv6 ...................................    4
   3. ISO Transport Protocols over IPv6 ...........................    5
   3.1. Protocol Classes ..........................................    5
   3.2. Maximum TPDU Size .........................................    5
   3.2.1. Path MTU Discovery and Fragmentation ....................    6
   3.2.2. No Path MTU Discovery or Fragmentation ..................    6
   3.3. PDU Lifetime ..............................................    6
   3.4. Related work ..............................................    6
   4. Security condiderations .....................................    6
   5. References ..................................................    7
   6. Authors' Addresses ..........................................    9
   7. Expiration Date of this Draft ...............................    9

1.  Summary of defined mechanisms

   This document defines two mechanisms for carrying OSI traffic over an
   IPv6 network:

        1. CLNP encapsulated in IPv6
        2. Transport Protocol carried over IPv6

   These are ELECTIVE mechanisms, i.e. they are not mandatory parts of
   an IPv6 implementation, but if such mechanisms are needed they MUST



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   be implemented as defined in this document.

   Note in addition that an Internet Standard STD-35 "ISO Transport
   Service on top of the TCP" exists already [RFC1006].  There is a also
   a Proposed Standard for "OSI Connectionless Transport Service over
   UDP" [RFC1240]. Both of these documents may need revision for IPv6.
   All of these mechanism may co-exist.












































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2.  CLNP encapsulated in IPv6

   If it is required to tunnel CLNP [IS8473] through an IPv6 network,
   then the upper layer header SHALL be a CLNP PDU, and the final IPv6
   Next Header field SHALL have the value 80 decimal (as defined for
   ISO-IP in [assigned]).

   Mechanisms for the creation of CLNP tunnels and their management are
   outside the scope of this document.

   Note that the tunnelling of CLNP over the Internet is discussed in
   detail in [RFC1070], but that document has no standards status and
   makes different assumptions about address mapping.  In contrast to
   [RFC1070], CLNP tunnels through an IPv6 network are simply a virtual
   point-to-point encapsulation technology, using statically configured
   tunnel endpoints.  There is no support for simulating a multipoint
   subnetwork, nor for dynamic mapping between NSAP addresses and IP
   addresses.  Instead, IP addresses are simply viewed as Subnetwork
   Point of Attachment (SNPA) addresses that must be statically
   configured to create the tunnel.

   Once a tunnel is established, data is transmitted using CLNP
   [IS8473].  The ES-IS [IS9542], IS-IS [IS10589], and IDRP [IS10747]
   protocols may be used to dynamically establish neighbor adjacencies
   and routing.  Any NSAP addresses may be assigned to the systems at
   either end of the tunnel.  There is no need to constrain the NSAP
   address format as documented in [RFC1070], since there is no need to
   perform dynamic address mapping. The "EON" header of [RFC1070] is not
   present.

   No attempt is required to implement feedback of error indications
   from ICMP in the IP subnetwork into CLNP error PDUs.  The tunnel is
   ignorant of problems in the IP subnetwork, and depends upon
   mechanisms in the OSI routing protocols to detect connectivity
   failures.

   If a CLNP tunnel has an anycast destination, i.e. the packets are
   decapsulated by any one of a set of decapsulators, and if an IPv6
   packet needs to be fragmented to get through the tunnel, the
   fragments may not be sent via same path. If this happens the original
   CLNP packet can never be decapsulated, since its fragments have
   arrived at different decapsulators. To avoid this problem, CLNP PDUs
   must be segmented as defined in [IS8473] if their size would create
   IPv6 packets exceeding the IPv6 path MTU.  Reassembly will take place
   at the final destination according to [IS8473].






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3.  ISO Transport Protocols over IPv6

   If it is required to carry ISO Transport Protocols [ISO8072, ISO8073]
   over an IPv6 network, then the IPv6 transport header SHALL be a TP
   PDU, and the final IPv6 Next Header field SHALL have the value 29
   decimal (as defined for ISO-TP in [assigned]).

      +---------------+------------------------
      |  IPv6 header  | TP PDU
      |               |
      | Next Header = |
      |       ISO-TP  |
      +---------------+------------------------


      +---------------+----------------+------------------------
      |  IPv6 header  | Routing header | TP PDU
      |               |                |
      | Next Header = | Next Header =  |
      |       Routing |       ISO-TP   |
      +---------------+----------------+------------------------

3.1.  Protocol Classes

   The ISO connection-oriented transport protocol [ISO8073] supports
   five different classes of service. Only one such class, class 4
   (TP4), is suitable for use on a connectionless network service such
   as provided by IPv6. Transport classes 0 through 3 should not carried
   over an IPv6 network in this manner.

   Note that the connectionless transport protocol [ISO8072] has no such
   restriction. Its PDUs should be carried exactly as described above.
   There is no conflict inherent in using the same IPv6 Next Header
   value for both connection-oriented and connectionless protocols.  ISO
   transport implementations can distinguish the two protocols by their
   different PDU types.

3.2.  Maximum TPDU Size

   When negotiating a maximum TPDU size, TP4 implementations may
   consider the services available from the network layer. Unlike IPv4
   or CLNP, IPv6 only permits fragmentation by the originating system.
   TP4 may use its knowledge of the capabilities of the local system to
   maximize the efficiency of data transfer.







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3.2.1.  Path MTU Discovery and Fragmentation

   If the TP4 implementation can accept Path MTU Discovery [RFC1191]
   information, and if the TP4 implementation can efficiently invoke the
   IPv6 fragmentation function, then the TP4 may propose the largest
   TPDU size and/or preferred maximum TPDU size that the implementation
   can support.

   If, during the life of the connection, IPv6 reports PMTU information
   to the TP4 implementation, TP4 should adjust its local TPDU size
   accordingly. Note that the original TPDU (the one which solicited the
   PMTU) cannot be repacketized; TP4 must instead rely on IPv6
   fragmentation for that PDU's retransmission.

3.2.2.  No Path MTU Discovery or Fragmentation

   If the TP4 implementation cannot accept Path MTU Discovery
   information from IPv6, or if it cannot efficiently invoke the IPv6
   fragmentation function, then TP4 may propose a TPDU size of 512
   octets and a preferred maximum TPDU size of 512 octets. These sizes
   will ensure that TPDUs are no larger than the IPv6 minimum MTU of 576
   bytes [IPv6].

3.3.  PDU Lifetime

   Unlike IPv4 and CLNP, IPv6 nodes are not required to enforce PDU
   lifetimes.  Any transport protocol that relies on the network
   protocol to limit packet lifetime ought to be upgraded to provide its
   own mechanisms for detecting and discarding obsolete packets.

3.4.  Related work

   The carriage of OSI Connectionless Transport Services over UDP is
   described in [RFC1240], which is currently a Proposed Standard.  The
   present proposal is independent of that one.

4.  Security condiderations

   Security issues are not specifically addressed in this document, but
   it is compatible with the IPv6 security mechanisms [security].  Note,
   however, that when CLNP is tunnelled through IPv6 the IPv6 security
   mechanisms can at best protect the tunnel, but not the end-to-end
   CLNP service.








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5.  References

   [ISO8072] International Organisation for Standardization, "Transport
       Service Definition", International Standard 8072, 1987.

   [ISO8073] International Organisation for Standardization, "Protocol
       for providing the connection-mode transport service",
       International Standard 8073 (2nd ed.), 1992.

   [RFC1191] Mogul, J., and S. Deering, "Path MTU Discovery", DECWRL and
       Stanford University, November 1990.

   [IS8473] International Organisation for Standardization, "Data
       communications protocol for providing the connectionless-mode
       network service", International Standard 8473, 1988.

   [IS9542] International Organisation for Standardization, "ISO, "End
       system to Intermediate system routeing exchange protocol for use
       in conjunction with the Protocol for providing the
       connectionless-mode network service (ISO 8473)," International
       Standard 9542, 1988.

   [IS10589] International Organisation for Standardization,
       "Intermediate system to Intermediate system routeing information
       exchange protocol for use in conjunction with the Protocol for
       providing the Connectionless-mode Network Service (ISO 8473),"
       International Standard 10589, 1992.

   [IS10747] International Organisation for Standardization,
       "Intermediate system to Intermediate system interdomain routeing
       information exchange protocol for use in conjunction with the
       Protocol for providing the Connectionless-mode Network Service
       (ISO 8473)," International Standard 10747, 1993.

   [IPv6] The IPv6 base documents, especially S. Deering, R. Hinden,
       Internet Protocol, Version 6 (IPv6) Specification, work in
       progress, draft-hinden-ipng-ipv6-spec-01.txt, March 1995.

   [RFC1006] Rose, M., and D. Cass, "ISO Transport Service on top of the
       TCP", STD-35, RFC 1006, Northrop Research and Technology Center,
       May 1987.

   [RFC1070] Hagens, R., Hall, N., and M. Rose, "Use of the Internet as
       a Subnetwork for Experimentation with the OSI Network Layer", RFC
       1070, University of Wisconsin, February 1989.

   [RFC1240] Shue, C.,  Haggerty, W., and K. Dobbins, "OSI
       Connectionless Transport Services on top of UDP", RFC 1240, Open



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       Software Foundation, June 1991

   [assigned] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2,
       RFC 1700, USC/Information Sciences Institute, October 1994.

   [security] IPv6 security spec, especially, R. Atkinson, "Security
       Architecture for the Internet Protocol", work in progress, draft-
       ietf-ipsec-arch-02.txt, May 1995.











































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6.  Authors' Addresses

   Brian E. Carpenter
   Group Leader, Communications Systems
   Computing and Networks Division
   European Laboratory for Particle Physics (CERN)
   1211 Geneva 23, Switzerland

   Phone:  +41 22 767-4967
   Fax:    +41 22 767-7155
   Email: brian@dxcoms.cern.ch


   Dave Katz
   cisco Systems, Inc.
   1525 O'Brien Dr.
   Menlo Park, CA 94025

   Phone:  (415) 688-8284
   EMail:  dkatz@cisco.com


   Stephen Thomas
   Associate Principal Engineer
   AT&T Tridom
   840 Franklin Court
   Marietta, GA 30067  USA

   Phone: (404) 514-3522
   Fax:   (404) 514-3491
   Email: stephen.thomas@tridom.com


   Keith Sklower
   Computer Science Department
   384 Soda Hall, Mail Stop 1776
   University of California
   Berkeley, CA 94720-1776

   Phone:  (510) 642-9587
   EMail:  sklower@CS.Berkeley.EDU

7.  Expiration Date of this Draft

   December 22nd, 1995






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