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Network Working Group                                       G. ArmitageRequest for Comments: 2492                          Lucent TechnologiesCategory: Standards Track                                   P. Schulter                                               BrightTiger Technologies                                                                M. Jork                                                 Digital Equipment GmbH                                                           January 1999IPv6 over ATM NetworksStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (1999).  All Rights Reserved.Abstract   This document is a companion to the ION working group's architecture   document, "IPv6 over Non Broadcast Multiple Access (NBMA) networks".   It provides specific details on how to apply the IPv6 over NBMA   architecture to ATM networks. This architecture allows conventional   host-side operation of the IPv6 Neighbor Discovery protocol, while   also supporting the establishment of 'shortcut' ATM forwarding paths   (when using SVCs).  Operation over administratively configured Point   to Point PVCs is also supported.1. Introduction.   This document is an ATM-specific companion document to the ION   working group's, "IPv6 over Non Broadcast Multiple Access (NBMA)   networks" specification [1].  Terminology and architectural   descriptions will not be repeated here.   The use of ATM to provide point to point PVC service, or flexible   point to point and point to multipoint SVC service, is covered by   this document.   A minimally conforming IPv6/ATM driver SHALL support the PVC mode of   operation. An IPv6/ATM driver that supports the full SVC mode SHALL   also support PVC mode of operation.G. Armitage, et. al.        Standards Track                     [Page 1]

RFC 2492                 IPv6 over ATM Networks             January 19992. Specification Terminology   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this   document are to be interpreted as described inRFC 2119 [16].3. PVC Environments   When the ATM network is used in PVC mode, each PVC will connect   exactly two nodes and the use of Neighbor Discovery and other IPv6   features is limited.  IPv6/ATM interfaces have only one neighbor on   each Link. The MARS and NHRP protocols are NOT necessary, since   multicast and broadcast operations collapse down to an ATM level   unicast operation. Dynamically discovered shortcuts are not   supported.   The actual details of encapsulations, MTU, and link token generation   are provided in the following sections.   This use of PVC links does not mandate, nor does it prohibit the use   of extensions to the Neighbor Discovery protocol which may be   developed for either general use of for use in PVC connections (for   example, Inverse Neighbor Discovery).   Since ATM PVC links do not use link-layer addresses, the link-layer   address options SHOULD not be included in any ND message [11].  If a   link-layer address option is present in an ND message, then the   option SHOULD be ignored.   A minimally conforming IPv6/ATM driver SHALL support the PVC mode of   operation.  PVC only implementations are not required to support any   SVC mode of operation.3.1 Default Packet Encapsulation   Following the model inRFC 1483 [2], AAL5 SHALL be the default   Adaptation Layer service, and (LLC/SNAP) encapsulation SHALL be   default encapsulation used by unicast and multicast packets across   pt-pt PVC links. As defined in [1], the default IPv6 packet   encapsulation SHALL be:         [0xAA-AA-03][0x00-00-00][0x86-DD][IPv6 packet]             (LLC)       (OUI)     (PID)G. Armitage, et. al.        Standards Track                     [Page 2]

RFC 2492                 IPv6 over ATM Networks             January 19993.2 Optional null encapsulation   IPv6/ATM drivers MAY also support null encapsulation as a   configurable option. When null encapsulation is enabled, the IPv6   packet is passed directly to the AAL5 layer. Both ends of the PVC   MUST be configured to use null encapsulation. The PVC will not be   available for use by protocols other than IPv6.3.3 PPP encapsulation   The concatentation of IPv6 over PPP with PPP over AAL5 PVCs is not   covered by this specification.3.4 MTU For PVC Environments   The default IP MTU size for PVC links is 9180 bytes as specified in   [7].  Other IP MTU values MAY be used.3.5 Interface Token Formats in PVC Environments   When the ATM network is used in PVC mode interface tokens SHALL be   generated using one of the methods described insection 5. Interface   tokens need only be unique between the two nodes on the PVC link.4 SVC environments4.1 SVC Specific Code Points4.1.1 ATM Adaptation Layer encapsulation for SVC environments   Following the model inRFC 1483 [2], AAL5 SHALL be the default   Adaptation Layer service, and (LLC/SNAP) encapsulation SHALL be the   default encapsulation used by unicast and multicast packets across   SVC links.4.1.2 Unicast Packet Encapsulation   As defined in [1], the default IPv6 unicast packet encapsulation   SHALL be:         [0xAA-AA-03][0x00-00-00][0x86-DD][IPv6 packet]             (LLC)       (OUI)     (PID)G. Armitage, et. al.        Standards Track                     [Page 3]

RFC 2492                 IPv6 over ATM Networks             January 19994.1.3 Multicast packet encapsulation   As defined in [1], the default IPv6 multicast packet encapsulation   SHALL be:         [0xAA-AA-03][0x00-00-5E][0x00-01][pkt$cmi][0x86DD][IPv6         packet]             (LLC)       (OUI)     (PID)    (mars encaps)         The IPv6/ATM driver's Cluster Member ID SHALL be copied into         the 2 octet pkt$cmi field prior to transmission.4.1.4 Optional null encapsulation   IPv6/ATM drivers MAY also support null encapsulation as a   configurable option. Null encapsulation SHALL only be used for   passing IPv6 packets from one IPv6/ATM driver to another. Null   encapsulation SHALL NOT be used on the pt-pt SVC between the IPv6/ATM   driver and its local MARS.   If null encapsulation is enabled, the IPv6 packet is passed directly   to the AAL5 layer. Both ends of the SVC MUST agree to use null   encapsulation during the call SETUP phase.  The SVC will not be   available for use by protocols other than IPv6.   If null encapsulation is enabled on data SVCs between routers,   inter-router NHRP traffic SHALL utilize a separate, parallel SVC.   Use of null encapsulation is not encouraged when IPv6/ATM is used   with MARS/NHRP/ND as described in [1].4.1.5 MARS control messages   The encapsulation of MARS control messages (between MARS and MARS   Clients) remains the same as shown inRFC 2022 [3]:      [0xAA-AA-03][0x00-00-5E][0x00-03][MARS control message]         (LLC)       (OUI)     (PID)   The key control field values are:      The mar$afn field remains 0x0F (ATM addresses)      The mar$pro field SHALL be 0x86DD (IPv6)      The mar$op.version field remains 0x00 (MARS)G. Armitage, et. al.        Standards Track                     [Page 4]

RFC 2492                 IPv6 over ATM Networks             January 1999   The mar$spln and mar$tpln fields (where relevant) are either 0 (for   null or non-existent information) or 16 (for the full IPv6 protocol   address)   The way in which ATM addresses are stored remains the same as shown   inRFC 2022 [3]4.1.6 NHRP control messages   The encapsulation of NHRP control messages remains the same as shown   inRFC 2332 [4]:      [0xAA-AA-03][0x00-00-5E][0x00-03][NHRP control message]         (LLC)       (OUI)     (PID)   The key control field values are:      The ar$afn field remains 0x0F (ATM addresses)      The ar$pro field SHALL be 0x86DD (IPv6)      The ar$op.version field remains 0x01 (NHRP)   The ar$spln and ar$tpln fields (where relevant) are either 0 (for   null or non-existent information) or 16 (for the full IPv6 protocol   address)   The way in which ATM addresses are stored remains the same as shown   inRFC 2022 [3]4.1.7 Neigbor Discovery control messages   Section 5.2 of [1] describes the ND Link-layer address option.  For   IPv6/ATM drivers, the subfields SHALL be encoded in the following   manner:      [NTL] defines the type and length of the ATM number immediately      following the [STL] field. The format is as follows:            7 6 5 4 3 2 1 0            +-+-+-+-+-+-+-+-+            |0|x|  length   |            +-+-+-+-+-+-+-+-+G. Armitage, et. al.        Standards Track                     [Page 5]

RFC 2492                 IPv6 over ATM Networks             January 1999      The most significant bit is reserved and MUST be set to zero.  The      second most significant bit (x) is a flag indicating whether the      ATM number is in:          ATM Forum AESA format (x = 0).          Native E.164 format (x = 1).      The bottom 6 bits represent an unsigned integer value indicating      the length of the associated ATM address field in octets.   The [STL] format is the same as the [NTL] field. Defines the length   of the subaddress field, if it exists. If it does not exist this   entire octet field MUST be zero. If the subaddress exists it will be   in AESA format, so flag x SHALL be zero.   [NBMA Number] is a variable length field containing the ATM address   of the Link layer target. It is always present.   [NBMA Subaddress] is a variable length field containing the ATM   subaddress of the Link layer target. It may or may not be present.   When it is not, the option ends after the [NBMA Number] (or any   additional padding for 8 byte alignment).   The octet ordering of the [NBMA Number] and [NBMA Subaddress] fields   SHALL be the same as that used in MARS and NHRP control messages.4.2 UNI 3.0/3.1 signaling issues (SVC mode).   When an IPv6 node places a call to another IPv6 node, it SHOULD   follow the procedures in [6] and [7] for signalling UNI 3.0/3.1 SVCs   [9] and negotiating MTU.  The default IP MTU size on a LL is 9180   bytes as specified in [7].   Note that while the procedures in [7] still apply to IPv6 over ATM,   IPv6 Path MTU Discovery [8] is used by nodes and routers rather than   IPv4 MTU discovery. Additionally, while IPv6 nodes are not required   to implement Path MTU Discovery, IPv6/ATM nodes SHOULD implement it.   Also, since IPv6 nodes will negotiate an appropriate MTU for each VC,   Path MTU should never be triggered since neither node should ever   receive a Packet Too Big message to trigger Path MTU Discovery.  When   nodes are communicating via one or more routers Path MTU Discovery   will be used just as it is for legacy networks.5 Interface Tokens   For both PVC and SVC modes of operation, one of the following methods   SHALL be used to generate Interface Tokens as required by section 5.1   of [1].G. Armitage, et. al.        Standards Track                     [Page 6]

RFC 2492                 IPv6 over ATM Networks             January 19995.1 Interface Tokens Based on ESI values   When the underlying ATM interface is identified by an ATM End System   Address (AESA, formerly known as an NSAPA), the interface token MAY   be formed from the ESI and SEL values in the AESA as follows:          [0x00][ESI][SEL]   [0x00] is a one octet field which is always set to 0.          Note that the bit corresponding to the EUI-64 Global/Local bit          [5] is always reset indicating that this address is not a          globally unique IPv6 interface token.   [ESI] is a six octet field.          This field always contains the six octet ESI value for the          AESA used to address the specific instance of the IPv6/ATM          interface.   [SEL] is a one octet field.          This field always contains the SEL value from the AESA used to          address the specific instance of the IPv6/ATM interface.5.2 Interface Tokens Based on 48 Bit MAC Values   Where the underlying ATM NIC driver has access to a set of one or   more 48 bit MAC values unique to the ATM NIC (e.g. MAC addresses   configured into the NIC's ROM), the IPv6/ATM interface MAY use one of   these values to create a unique interface token as described in [10].5.3 Interface Tokens Based on EUI-64 Values   Where the underlying ATM NIC driver has access to a set of one or   more 64 bit EUI-64 values unique to the ATM NIC (e.g. EUI-64   addresses configured into the NIC's ROM), the IPv6/ATM interface   SHOULD use one of these values to create a unique interface token.   after inverting the Global/Local identifier bit [10].  (Any   relationship between these values and the ESI(s) registered with the   local ATM switch by the ATM driver are outside the scope of this   document.)   When EUI-64 values are used for IPv6 interface tokens the only   modification allowed to the octet string read from the NIC is   inversion of the Global/Local identifier bit.G. Armitage, et. al.        Standards Track                     [Page 7]

RFC 2492                 IPv6 over ATM Networks             January 19995.4 Interface Tokens Based on Native E.164 Addresses   When an interface uses Native E.164 addresses then the E.164 values   MAY be used to generate an interface token as follows:          [D14][D13D12][D11D10][D9D8][D9D6][D5D4][D3D2][D1D0]   [D14] A single octet containing the semi-octet representing the most   significant E.164 digit shifted left four bits to the most   significant four bits of the octet.  The lower four bits MUST be set   to 0.  Note that the EUI-64 Global/Local indicator is set to 0   indicating that this is not a globally unique IPv6 interface token.   [D13D12] A single octet containing the semi-octet representing the   second most significant E.164 digit [D13] shifted left four places to   the most significant bits of the octet, and the third most   significant semi-octet in the four least significant bits of the   octet.   [D11D10] - [D1D0] Octets each containing two E.164 digits, one in the   most significant four bits, and one in the least significant four   bits as indicated.5.5 Nodes Without Unique Identifiers   If no MAC, EUI-64, AESA, or E.164 value is available for generating   an interface token, then the interface token SHALL be generated as   described inAppendix A of [10].5.6 Multiple Logical Links on a Single Interface   A logical ATM interface might be associated with a different SEL   field of a common AESA prefix, or a set of entirely separate ESIs   might have been registered with the local ATM switch to create a   range of unique AESAs.   The minimum information required to uniquely identify each logical   ATM interface is (within the context of the local switch port) their   ESI+SEL combination.   For the vhost case described in section 5.1.2 of [1], vhost SHALL   select a different interface token from the range of 64 bit values   available to the ATM NIC (as described in 4.1). Each vhost SHALL   implement IPv6/ATM interfaces in such a way that no two or more   vhosts end up advertising the same interface token onto the same LL.   (Conformance with this requirement may be achieved by choosing   different SEL values, ESI values, or both.)G. Armitage, et. al.        Standards Track                     [Page 8]

RFC 2492                 IPv6 over ATM Networks             January 19996. Conclusion and Open Issues.   This document is an ATM-specific companion document to the ION   working group's, "IPv6 over Non Broadcast Multiple Access (NBMA)   networks" specification [1]. It specifies codepoints for the   administratively configured PVC, and dynamically established SVC,   modes of operation.   There are no major open issues. Comments to the ION mailing list are   solicited (ion@nexen.com).7. Security Considerations   While this proposal does not introduce any new security mechanisms   all current IPv6 security mechanisms will work without modification   for ATM.  This includes both authentication and encryption for both   Neighbor Discovery protocols as well as the exchange of IPv6 data   packets.Acknowledgments   The original IPv6/ATM work by G. Armitage occurred while employed at   Bellcore. Elements ofsection 4 were borrowed from Matt Crawford's   memo on IPv6 over Ethernet.   The authors would like to thank Kazuhiko Yamamoto, Kenjiro Cho,   Yoshinobu Inoue, Hiroshi Esaki, Yoshifumi Atarashi, and Atsushi   Hagiwara for their contributions based on actual PVC implementations.G. Armitage, et. al.        Standards Track                     [Page 9]

RFC 2492                 IPv6 over ATM Networks             January 1999Authors' Addresses   Grenville Armitage   Bell Laboratories, Lucent Technologies   101 Crawfords Corner Road   Holmdel, NJ 07733   USA   EMail: gja@lucent.com   Peter Schulter   BrightTiger Technologies   125 Nagog Park   Acton, MA 01720   EMail: paschulter@acm.org   Markus Jork   European Applied Research Center   Digital Equipment GmbH   CEC Karlsruhe   Vincenz-Priessnitz-Str. 1   D-76131 Karlsruhe   Germany   EMail: jork@kar.dec.comG. Armitage, et. al.        Standards Track                    [Page 10]

RFC 2492                 IPv6 over ATM Networks             January 1999References   [1] Armitage, G., Schulter, P., Jork, M. and G. Harter, "IPv6 over       Non-Broadcast Multiple Access (NBMA) networks",RFC 2491, January       1999.   [2] Heinanen, J., "Multiprotocol Encapsulation over ATM Adaption       Layer 5",RFC 1483, July 1993.   [3] Armitage, G., "Support for Multicast over UNI 3.1 based ATM       Networks",RFC 2022, November 1996.   [4] Luciani, J., Katz, D., Piscitello, D., Cole, B. and N. Doraswamy,       "NBMA Next Hop Resolution Protocol (NHRP)",RFC 2332, April 1998.   [5] "64-Bit Global Identifier Format Tutorial",http://standards.ieee.org/db/oui/tutorials/EUI64.html.   [6] Perez, M., Liaw, F., Mankin, A., Hoffman, E., Grossman, D. and A.       Malis, "ATM Signalling Support for IP over ATM",RFC 1755,       February 1995.   [7] Atkinson, R., "Default IP MTU for use over ATM AAL5",RFC 1626,       May 1994.   [8] McCann, J., Deering, S. and J. Mogul, "Path MTU Discovery for IP       version 6",RFC 1981, August 1996.   [9] ATM Forum, "ATM User Network Interface (UNI) Specification       Version 3.1", ISBN 0-13-393828-X, Prentice Hall, Englewood       Cliffs, NJ, June 1995.   [10] Hinden, B. and S. Deering, "IP Version 6 Addressing        Architecture",RFC 2373, July 1998.   [11] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for        IP Version 6 (IPv6)",RFC 2461, December 1998.G. Armitage, et. al.        Standards Track                    [Page 11]

RFC 2492                 IPv6 over ATM Networks             January 1999Full Copyright Statement   Copyright (C) The Internet Society (1999).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.G. Armitage, et. al.        Standards Track                    [Page 12]