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
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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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