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Versions: 00 01 02 03 RFC 2023

Internet Engineering Task Force
INTERNET-DRAFT                                           Dimitry Haskin
Expires November 1996                                          Ed Allen
<draft-ietf-ipngwg-pppext-ipv6cp-03.txt>             Bay Networks, Inc.

                                                               May 1996


                     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
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     To learn the current status of any Internet-Draft, please check
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     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 ..........................................    2
        1.1.  Specification of Requirements ......................   3

   2.     Sending IPv6 Datagrams ................................    3

   3.     A PPP Network Control Protocol for IPv6 ...............    4

   4.     IPV6CP Configuration Options ..........................    5
        4.1.  Interface-Token ...................................    8
        4.2.  IPv6-Compression-Protocol

   5.     Stateless Autoconfiguration and Link-Local Addresses ..    9

   A.     IPV6CP Recommended Options .............................  10

   Security Considerations .......................................  10

   References ....................................................  10

   Acknowledgments ...............................................  10

   Authors' Addresses ............................................  11



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



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   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.

   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).



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   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).

   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.



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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 [5].  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
      32-bit interface token to be used for the address
      autoconfiguration [3] 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.

      Before this Configuration Option is requested, an implementation
      must choose its tentative Interface-Token.  It is recommended that
      a non-zero value be chosen in the most random manner possible in
      order to guarantee with very high probability that an
      implementation will arrive at a unique token value.  A good way to
      choose a unique random number is to start with a unique seed.
      Suggested sources of uniqueness include machine serial numbers,
      other network hardware addresses, system clocks, etc. Note that it
      may not be sufficient to use a link-layer address alone as the
      seed, since it will not always be unique.  Thus it is suggested
      that the seed should be calculated from a variety of sources that
      are likely to be different even on identical systems and as many
      sources as possible be used simultaneously.  Good sources of
      uniqueness or randomness are required for the Interface-Token
      negotiation to succeed.  If a good source of randomness cannot be
      found,  it is recommended that a zero value be used for the
      Interface-Token transmitted in the Configure-Request.  In this case



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      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 a unique random number, 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-Ack 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.

        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.

        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.

        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



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      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 about 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. should be different from the token value
      selected for 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         Interface-Token (cont)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      1

   Length

      6



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   Interface-Token

      The 32-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.


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


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   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 [5].

      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 for forming IPv6 addresses 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.




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   Link-local addresses of PPP interfaces have the following format:

   | 10 bits  |              86 bits               |     32 bits     |
   +----------+--------------+---------------------+-----------------+
   |1111111010|              0                     | Interface Token |
   +----------+--------------+---------------------+-----------------+

   The most significant 10 bits of the address is the Link-Local prefix
   FE80::.  86 zero bits pad out the address between the Link-Local
   prefix and the Interface Token fields.

A.  IPV6CP Recommended Options

   The following Configurations Options are recommended:

      Interface-Token

      IPv6-Compression-Protocol



Security Considerations

   Security issues are not discussed in this memo.



References

   [1]  W. Simpson, "The Point-to-Point Protocol", RFC 1661, July 1994.

   [2]  S. Deering, R. Hinden, Editors, "Internet Protocol, Version 6
        (IPv6) Specification", RFC 1883, December 1995.

   [2]  R. Hinden, S. Deering, "IP Version 6 Addressing Architecture",
        RFC 1884, December 1995.

   [3]  S. Thomson, T. Narten, "IPv6 Stateless Address
        Autoconfiguration", Work in progress

   [4]  T. Narten, E. Nordmark, W. A. Simpson, "Neighbor Discovery for
        IP Version 6 (IPv6)",  Work in progress

   [5]  J. Reynolds, J. Postel, "Assigned Numbers", RFC 1700,
        October 1994.



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Acknowledgments

   This document borrows from the Magic-Number LCP option and as such is
   partially based on previous work done by the PPP working group.



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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