Internet Engineering Task Force
     INTERNET-DRAFT                                  Dimitry Haskin
     Expires January 1998                            Ed Allen
     <draft-ietf-ipngwg-ipv6-over-ppp-02.txt>        Bay Networks, Inc.
                                                     July 1997
     
     
                             IP Version 6 over PPP
     
     
     Status of this Memo
     
     This document  is  an  Internet-Draft.   Internet-Drafts  are  working
     documents  of  the  Internet Engineering Task Force (IETF), its areas,
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     munnari.oz.au  (Pacific  Rim),  ds.internic.net  (US  East  Coast), or
     ftp.isi.edu (US West Coast).
     
     
     Abstract
     
     The Point-to-Point Protocol (PPP) [1] provides a  standard  method  of
     encapsulating  Network  Layer protocol information over point-to-point
     links.  PPP also defines an  extensible  Link  Control  Protocol,  and
     proposes a family of Network Control Protocols (NCPs) for establishing
     and configuring different network-layer protocols.
     
     This document defines the method for transmission of IP Version 6  [2]
     packets  over  PPP links as well as the Network Control Protocol (NCP)
     for establishing and configuring the IPv6 over PPP. It also  specifies
     the method of forming IPv6 link-local addresses on PPP links.
     
     
     
     
     
     
     
     
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     Table of Contents
     
     
        1.     Introduction ..........................................    3
             1.1.  Specification of Requirements ......................   3
        2.     Sending IPv6 Datagrams ................................    4
        3.     A PPP Network Control Protocol for IPv6 ...............    4
        4.     IPV6CP Configuration Options ..........................    5
             4.1.  Interface-Token ...................................    5
             4.2.  IPv6-Compression-Protocol..........................   11
        5.     Stateless Autoconfiguration and Link-Local Addresses ..   12
        6.     IPV6CP Recommended Options .............................  13
        Security Considerations .......................................  13
        References ....................................................  13
        Acknowledgments ...............................................  14
        Authors' Addresses ............................................  14
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     1.  Introduction
     
     PPP has three main components:
     
     1.   A method for encapsulating datagrams over serial links.
     
     2.   A Link Control Protocol (LCP) for establishing, configuring,  and
          testing the data-link connection.
     
     3.   A family of Network Control Protocols (NCPs) for establishing and
          configuring different network-layer protocols.
     
     In order to establish communications over a point-to-point link,  each
     end  of the PPP link must first send LCP packets to configure and test
     the data link.  After the  link  has  been  established  and  optional
     facilities  have  been  negotiated as needed by the LCP, PPP must send
     NCP  packets  to  choose  and  configure  one  or  more  network-layer
     protocols.   Once  each of the chosen network-layer protocols has been
     configured,  datagrams from each network-layer protocol  can  be  sent
     over the link.
     
     In this document, the NCP for establishing and  configuring  the  IPv6
     over PPP is referred as the IPv6 Control Protocol (IPV6CP).
     
     The link will remain configured for communications until explicit  LCP
     or  NCP  packets  close  the  link down,  or until some external event
     occurs (power failure at the other end, carrier drop, etc.).
     
     
     1.1.  Specification of Requirements
     
     In this document, several words are used to signify  the  requirements
     of the specification.  These words are often capitalized.
     
     
     MUST       This word, or the adjective "required", means that the
                definition is an absolute requirement of the specification.
     
     MUST NOT   This phrase means that the definition is an absolute
                prohibition of the specification.
     
     SHOULD     This word, or the adjective "recommended", means that there
                may exist  valid  reasons  in particular circumstances to
                ignore this item, but the full implications must be
                understood and  carefully weighed before choosing
                a different course.
     
     
     
     
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     MAY        This word, or the adjective "optional", means that this
                item  is one  of  an allowed set of alternatives.  An
                implementation which does not include this option MUST be
                prepared  to  inter-operate with another implementation
                which does include the option.
     
     
     2.  Sending IPv6 Datagrams
     
     Before any IPv6 packets  may  be  communicated,  PPP  MUST  reach  the
     Network-Layer Protocol phase, and the IPv6 Control Protocol MUST reach
     the Opened state.
     
     Exactly one IPv6 packet is encapsulated in the  Information  field  of
     PPP Data Link Layer frames where the Protocol field indicates type hex
     0057 (Internet Protocol Version 6).
     
     The maximum length of an IPv6 packet transmitted over a  PPP  link  is
     the  same as the maximum length of the Information field of a PPP data
     link layer frame.  PPP links supporting IPv6 MUST allow at  least  576
     octets in the information field of a data link layer frame.
     
     
     3.  A PPP Network Control Protocol for IPv6
     
     The IPv6 Control Protocol (IPV6CP)  is  responsible  for  configuring,
     enabling,  and disabling the IPv6 protocol modules on both ends of the
     point-to-point link.  IPV6CP uses the same packet  exchange  mechanism
     as  the  Link  Control  Protocol  (LCP).   IPV6CP  packets  may not be
     exchanged until PPP has  reached  the  Network-Layer  Protocol  phase.
     IPV6CP  packets  received  before  this  phase  is  reached  should be
     silently discarded.
     
     The IPv6 Control Protocol is exactly the  same  as  the  Link  Control
     Protocol [1] with the following exceptions:
     
       Data Link Layer Protocol Field
     
            Exactly one IPV6CP packet is encapsulated  in  the  Information
            field  of  PPP  Data Link Layer frames where the Protocol field
            indicates type hex 8057 (IPv6 Control Protocol).
     
     
     
     
     
     
     
     
     
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       Code field
     
            Only  Codes  1  through  7  (Configure-Request,  Configure-Ack,
            Configure-Nak,  Configure-Reject, Terminate-Request, Terminate-
            Ack and Code-Reject) are used.  Other Codes should  be  treated
            as unrecognized and should result in Code-Rejects.
     
       Timeouts
     
            IPV6CP packets may not be exchanged until PPP has  reached  the
            Network-Layer  Protocol  phase.   An  implementation  should be
            prepared  to  wait  for   Authentication   and   Link   Quality
            Determination  to  finish  before  timing  out  waiting  for  a
            Configure-Ack or other  response.   It  is  suggested  that  an
            implementation  give  up  only  after  user  intervention  or a
            configurable amount of time.
     
       Configuration Option Types
     
            IPV6CP has a distinct set of Configuration Options,  which  are
            defined below.
     
     
     4.  IPV6CP Configuration Options
     
     IPV6CP Configuration  Options  allow  negotiation  of  desirable  IPv6
     parameters.   IPV6CP uses the same Configuration Option format defined
     for LCP [1], with a separate  set  of  Options.   If  a  Configuration
     Option  is  not  included  in a Configure-Request packet,  the default
     value for that Configuration Option is assumed.
     
     Up-to-date values of the IPV6CP Option Type field are specified in the
     most  recent  "Assigned Numbers" RFC [4].  Current values are assigned
     as follows:
     
         1       Interface-Token
         2       IPv6-Compression-Protocol
     
     
     4.1.  Interface-Token
     
     Description
     
       This Configuration Option provides a way to negotiate a  unique  64-
       bit interface token to be used for the address autoconfiguration [3]
     
     
     
     
     
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       at the local end of the link (see section 5).  The  interface  token
       MUST  be  unique  within  the PPP link; i.e.  upon completion of the
       negotiation different Interface-Token values are to be selected  for
       the  ends  of  the PPP link.  The interface token MAY also be unique
       over a broader scope.
     
       Before this Configuration Option  is  requested,  an  implementation
       chooses  its  tentative  Interface-Token.  The non-zero value of the
       tentative Interface-Token SHOULD be chosen such that  the  value  is
       both  unique to the link and, if possible, consistently reproducible
       across  initializations  of  the   IPV6CP   finite   state   machine
       (administrative  Close  and reOpen, reboots, etc). The rationale for
       preferring a consistently reproducible unique token to a  completely
       random  token is to provide stability to global scope addresses that
       can be formed from the interface token.
     
       Assuming that interface token bits are numbered from 0 to  63  where
       the  most  significant  bit is the bit number 0, the bit number 6 is
       the "u" bit (universal/local bit in  IEEE  EUI-64  [5]  terminology)
       which  indicates  whether  or  not the interface token is based on a
       globally unique IEEE identifier (EUI-48 or EUI-64 [5]) (see the case
       1  below). It is set to one (1) if a globally unique IEEE identifier
       is used to derive the interface token, and it is  set  to  zero  (0)
       otherwise.
     
       The following are methods for choosing the tentative Interface Token
       in the preference order:
     
     
       1) If an IEEE global identifier  (EUI-48  or  EUI-64)  is  available
          anywhere  on  the  node,  it  should  be  used  to  construct the
          tentative Interface-Token due to its uniqueness properties.
     
          The only transformation from an EUI-64 identifier  is  to  invert
          the  "u"  bit  (universal/local  bit in IEEE EUI-64 terminology).
          For example, for a globally unique EUI-64 identifier of the form:
     
     most-significant                                    least-significant
     bit                                                               bit
     |0              1|1              3|3              4|4              6|
     |0              5|6              1|2              7|8              3|
     +----------------+----------------+----------------+----------------+
     |cccccc0gcccccccc|cccccccceeeeeeee|eeeeeeeeeeeeeeee|eeeeeeeeeeeeeeee|
     +----------------+----------------+----------------+----------------+
     
     
     
     
     
     
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          where "c" are the bits of the assigned  company_id,  "0"  is  the
          value of the universal/local bit to indicate global scope, "g" is
          group/individual bit, and "e"  are  the  bits  of  the  extension
          identifier, the IPv6 interface token would be of the form:
     
     most-significant                                    least-significant
     bit                                                               bit
     |0              1|1              3|3              4|4              6|
     |0              5|6              1|2              7|8              3|
     +----------------+----------------+----------------+----------------+
     |cccccc1gcccccccc|cccccccceeeeeeee|eeeeeeeeeeeeeeee|eeeeeeeeeeeeeeee|
     +----------------+----------------+----------------+----------------+
     
          The only change is inverting the  value  of  the  universal/local
          bit.
     
          In the case of a EUI-48 identifier, it is first converted to  the
          EUI-64  format by inserting two bytes, with hexadecimal values of
          0xFF and 0xFE, in the middle of  the  48  bit  MAC  (between  the
          company_id   and  extension-identifier  portions  of  the  EUI-48
          value).  For  example,  for  a  globally  unique  48  bit  EUI-48
          identifier of the form:
     
     most-significant                   least-significant
     bit                                              bit
     |0              1|1              3|3              4|
     |0              5|6              1|2              7|
     +----------------+----------------+----------------+
     |cccccc0gcccccccc|cccccccceeeeeeee|eeeeeeeeeeeeeeee|
     +----------------+----------------+----------------+
     
          where "c" are the bits of the assigned  company_id,  "0"  is  the
          value of the universal/local bit to indicate global scope, "g" is
          group/individual bit, and "e"  are  the  bits  of  the  extension
          identifier, the IPv6 interface token would be of the form:
     
     most-significant                                    least-significant
     bit                                                               bit
     |0              1|1              3|3              4|4              6|
     |0              5|6              1|2              7|8              3|
     +----------------+----------------+----------------+----------------+
     |cccccc1gcccccccc|cccccccc11111111|11111110eeeeeeee|eeeeeeeeeeeeeeee|
     +----------------+----------------+----------------+----------------+
     
     
     
     
     
     
     
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       2) If an IEEE global identifier is not available a different  source
          of  uniqueness  should  be used.  Suggested sources of uniqueness
          include link-layer addresses, machine serial numbers, et cetera.
     
          In this case the "u" bit of the interface token MUST  be  set  to
          zero (0).
     
     
       3) If a good source of uniqueness cannot be found, it is recommended
          that  a  random number be generated.  In this case the "u" bit of
          the interface token MUST be set to zero (0).
     
       Good sources [1] of uniqueness or randomness are  required  for  the
       Interface-Token  negotiation to succeed.  If neither a unique number
       or a random number can be generated it is recommended  that  a  zero
       value  be used for the Interface-Token transmitted in the Configure-
       Request.  In this case the PPP peer may  provide  a  valid  non-zero
       Interface-Token in its response as described below.  Note that if at
       least one of the PPP peers is able  to  generate  separate  non-zero
       numbers for itself and its peer, the token negotiation will succeed.
     
       When  a  Configure-Request  is  received  with  the  Interface-Token
       Configuration  Option and the receiving peer implements this option,
       the received Interface-Token is compared with the Interface-Token of
       the  last  Configure-Request  sent  to  the  peer.  Depending on the
       result of the comparison an implementation MUST respond  in  one  of
       the following ways:
     
       If  the  two  Interface-Tokens  are  different  but   the   received
       Interface-Token  is  zero,  a  Configure-Nak is sent with a non-zero
       Interface-Token value suggested for use by the remote peer.  Such  a
       suggested  Interface-Token  MUST  be  different  from the Interface-
       Token of  the  last  Configure-Request  sent  to  the  peer.  It  is
       recommended  that  the  value suggested be consistently reproducible
       across  initializations  of  the   IPV6CP   finite   state   machine
       (administrative   Close   and   reOpen,   reboots,   etc).  The  "u"
       universal/local) bit of the suggested token MUST be set to zero  (0)
       regardless  of  its  source unless the globally unique EUI-48/EUI-64
       derived token is provided for the exclusive use by the remote peer.
     
       If  the  two  Interface-Tokens  are  different  and   the   received
       Interface-Token   is   not   zero,   the   Interface-Token  MUST  be
       acknowledged, i.e.  a  Configure-Ack  is  sent  with  the  requested
       Interface-Token,  meaning  that  the responding peer agrees with the
       Interface-Token requested.
     
     
     
     
     
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       If  the  two  Interface-Tokens  are  equal  and  are  not  zero,   a
       Configure-Nak   MUST   be   sent  specifying  a  different  non-zero
       Interface-Token value suggested for use by the remote  peer.  It  is
       recommended  that  the  value suggested be consistently reproducible
       across  initializations  of  the   IPV6CP   finite   state   machine
       (administrative   Close   and   reOpen,   reboots,   etc).  The  "u"
       universal/local) bit of the suggested token MUST be set to zero  (0)
       regardless  of  its  source unless the globally unique EUI-48/EUI-64
       derived token is provided for the exclusive use by the remote peer.
     
       If the two Interface-Tokens  are  equal  to  zero,   the  Interface-
       Tokens   negotiation   MUST   be   terminated  by  transmitting  the
       Configure-Reject with the Interface-Token value set to zero. In this
       case a unique Interface-Token can not be negotiated.
     
       If  a  Configure-Request  is  received  with   the   Interface-Token
       Configuration  Option and the receiving peer does not implement this
       option, Configure-Rej is sent.
     
       A new Configure-Request SHOULD NOT be sent to the peer until  normal
       processing would cause it to be sent (that is, until a Configure-Nak
       is received or the Restart timer runs out).
     
       A new Configure-Request MUST NOT contain the Interface-Token  option
       if a valid Interface-Token Configure-Reject is received.
     
       Reception  of  a  Configure-Nak  with  a  suggested  Interface-Token
       different  from  that  of  the  last  Configure-Nak sent to the peer
       indicates a unique Interface-Token.  In this case a  new  Configure-
       Request  MUST  be  sent  with  the token value suggested in the last
       Configure-Nak from the peer.  But if the received Interface-Token is
       equal  to  the one sent in the last Configure- Nak, a new Interface-
       Token MUST be chosen.  In this case, a new Configure-Request  SHOULD
       be  sent  with  the  new  tentative  Interface-Token.  This sequence
       (transmit  Configure-Request,  receive  Configure-Request,  transmit
       Configure-Nak,  receive  Configure-Nak) might occur a few times, but
       it is extremely unlikely to  occur  repeatedly.   More  likely,  the
       Interface-Tokens   chosen   at  either  end  will  quickly  diverge,
       terminating the sequence.
     
       If negotiation of the Interface-Token is required, and the peer  did
       not  provide  the option in its Configure-Request, the option SHOULD
       be  appended  to  a  Configure-Nak.   The  tentative  value  of  the
       Interface-Token  given  must  be acceptable as the remote Interface-
       Token; i.e. it should be different from the token value selected for
     
     
     
     
     
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       the  local end of the PPP link.  The next Configure-Request from the
       peer may include this option.  If the  next  Configure-Request  does
       not include this option the peer MUST NOT send another Configure-Nak
       with  this  option  included.  It  should  assume  that  the  peer's
       implementation does not support this option.
     
       By default,  an  implementation  SHOULD  attempt  to  negotiate  the
       Interface-Token for its end of the PPP connection.
     
     A summary of the Interface-Token Configuration Option format is  shown
     below.  The fields are transmitted from left to right.
     
     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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |    Length     |    Interface-Token (MS Bytes)
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          Interface-Token (cont)
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          Interface-Token (LS Bytes) |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     
       Type
     
         1
     
       Length
     
         10
     
       Interface-Token
     
         The 64-bit Interface-Token which is very likely to  be  unique  on
         the link or zero if a good source of uniqueness can not be found.
     
       Default Token Value
     
         If no valid interface token can  be  successfully  negotiated,  no
         default  Interface-Token  value  should be assumed. The procedures
         for recovering from such a case are unspecified. One  approach  is
         to manually configure the interface token of the interface.
     
     
     
     
     
     
     
     
     
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     4.2.  IPv6-Compression-Protocol
     
     Description
     
       This Configuration Option provides a way to negotiate the use  of  a
       specific  IPv6  packet  compression protocol.  The IPv6-Compression-
       Protocol Configuration Option is used to  indicate  the  ability  to
       receive  compressed  packets.   Each end of the link must separately
       request this option if bi-directional compression  is  desired.   By
       default, compression is not enabled.
     
       IPv6 compression negotiated with this option  is  specific  to  IPv6
       datagrams  and is not to be confused with compression resulting from
       negotiations  via  Compression   Control   Protocol   (CCP),   which
       potentially effect all datagrams.
     
     A summary of the IPv6-Compression-Protocol Configuration Option format
     is shown below.  The fields are transmitted from left to right.
     
     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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |    Length     |   IPv6-Compression-Protocol   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Data ...
     +-+-+-+-+
     
       Type
     
         2
     
       Length
     
         >= 4
     
       IPv6-Compression-Protocol
     
         The IPv6-Compression-Protocol field is two  octets  and  indicates
         the  compression  protocol  desired.   Values  for  this field are
         always the same as the PPP Data Link Layer Protocol  field  values
         for that same compression protocol.
     
         Up-to-date  values  of  the  IPv6-Compression-Protocol  field  are
         specified in the most recent "Assigned Numbers" RFC [4].
     
     
     
     
     
     
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         Current values are assigned as follows:
     
           Value (in hex)          Protocol
     
           004f                    IPv6 Header Compression
     
       Data
     
         The Data field is zero or more octets and contains additional data
         as determined by the particular compression protocol.
     
       Default
     
         No IPv6 compression protocol enabled.
     
     
     
     5.  Stateless Autoconfiguration and Link-Local Addresses
     
     The interface token, which is used as the Interface ID of IPv6 unicast
     addresses  [6]  of a PPP interface, SHOULD be negotiated in the IPV6CP
     phase of the PPP connection setup  (see  section  4.1).  If  no  valid
     interface  token  has  been  successfully  negotiated,  procedures for
     recovering from such a case  are  unspecified.   One  approach  is  to
     manually configure the interface token of the interface.
     
     As long as the interface token is negotiated in the  IPV6CP  phase  of
     the  PPP  connection  setup,   it  is  redundant  to perform duplicate
     address detection as a part of the  IPv6  Stateless  Autoconfiguration
     protocol [3].  Therefore it is recommended that for PPP links with the
     IPV6CP  Interface-Token  option  enabled  the  default  value  of  the
     DupAddrDetectTransmits autoconfiguration variable [3] be zero.
     
     Link-local addresses of PPP interfaces have the following format:
     
     | 10 bits  |        54 bits         |          64 bits            |
     +----------+------------------------+-----------------------------+
     |1111111010|           0            |      Interface Token        |
     +----------+------------------------+-----------------------------+
     
     The most significant 10 bits of the address is the  Link-Local  prefix
     FE80::.   54  zero  bits  pad  out  the address between the Link-Local
     prefix and the Interface Token fields.
     
     
     
     
     
     
     
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     6.  IPV6CP Recommended Options
     
     The following Configurations Options are recommended:
     
       Interface-Token
     
       IPv6-Compression-Protocol
     
     
     7.  Security Considerations
     
     The IPv6 Control Protocol extension  to  PPP  can  be  used  with  all
     defined PPP authentication and encryption mechanisms.
     
     
     8.  References
     
     [1]  Simpson, W., "The Point-to-Point Protocol",  STD  51,  RFC  1661,
          July 1994.
     
     [2]  Deering, S., and R. Hinden, Editors, "Internet Protocol,  Version
          6 (IPv6) Specification", RFC 1883, December 1995.
     
     [3]  Thomson,   S.,   and   T.   Narten,   "IPv6   Stateless   Address
          Autoconfiguration", RFC 1971, August 1996.
     
     [4]  Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 1700,
          October 1994.
     
     [5]  IEEE,  "Guidelines  for   64-bit   Global   Identifier   (EUI-64)
          Registration Authority",
          http://standards.ieee.org/db/oui/tutorials/EUI64.html,
          March 1997.
     
     [6]  Hinden,  R.,  and  S.   Deering,   "IP   Version   6   Addressing
          Architecture", Work in progress
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     9.  Acknowledgements
     
     This document borrows from the Magic-Number LCP option and as such  is
     partially based on previous work done by the PPP working group.
     
     
     
     10.  Authors' Addresses
     
        Dimitry Haskin
        Bay Networks, Inc.
        2 Federal Street
        Billerica, MA 01821
        email: dhaskin@baynetworks.com
     
        Ed Allen
        Bay Networks, Inc.
        2 Federal Street
        Billerica, MA 01821
        email: eallen@baynetworks.com
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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