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RFC 2472 - IP Version 6 over PPP


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Network Working Group                                         D. Haskin
Request for Comments: 2472                                     E. Allen
Obsoletes: 2023                                      Bay Networks, Inc.
Category: Standards Track                                 December 1998

                         IP Version 6 over PPP

Status 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 (1998).  All Rights Reserved.

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.

Table of Contents

   1.     Introduction ..........................................    2
        1.1.  Specification of Requirements .....................    2
   2.     Sending IPv6 Datagrams ................................    2
   3.     A PPP Network Control Protocol for IPv6 ...............    3
   4.     IPV6CP Configuration Options ..........................    4
        4.1.  Interface-Identifier ..............................    4
        4.2.  IPv6-Compression-Protocol..........................    9
   5.     Stateless Autoconfiguration and Link-Local Addresses ..   10
   6      Security Considerations ...............................   11
   7      Acknowledgments .......................................   11
   8      Changes from RFC-2023 .................................   11
   9      References ............................................   12
   10     Authors' Addresses ....................................   13

   11     Full Copyright Statement ..............................   14

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.

   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 in [7].

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 the
   information field at least as large as the minimum link MTU size
   required for IPv6 [2].

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.

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-Identifier
       2       IPv6-Compression-Protocol

   The only IPV6CP options defined in this document are Interface-
   Identifier and IPv6-Compression-Protocol.  Any other IPV6CP
   configuration options that can be defined over time are to be defined
   in separate documents.

4.1.  Interface-Identifier

   Description

     This Configuration Option provides a way to negotiate a unique 64-
     bit interface identifier to be used for the address
     autoconfiguration [3] at the local end of the link (see section 5).
     A Configure-Request MUST contain exactly one instance of the
     Interface-Identifier option [1].  The interface identifier MUST be
     unique within the PPP link; i.e.  upon completion of the
     negotiation different Interface-Identifier values are to be
     selected for the ends of the PPP link.  The interface identifier
     MAY also be unique over a broader scope.

     Before this Configuration Option is requested, an implementation
     chooses its tentative Interface-Identifier. The non-zero value of
     the tentative Interface-Identifier 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
     interface identifier to a completely random interface identifier is
     to provide stability to global scope addresses that can be formed
     from the interface identifier.

     Assuming that interface identifier bits are numbered from 0 to 63
     in canonical bit order 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 identifier 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 identifier, and it is set to zero (0) otherwise.

     The following are methods for choosing the tentative Interface
     Identifier 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-Identifier due to its uniqueness
        properties.  When extracting an IEEE global identifier from
        another device on the node, care should be taken to that the
        extracted identifier is presented in canonical ordering [8].

        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|
   +----------------+----------------+----------------+----------------+

        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 identifier 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 identifier 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|
   +----------------+----------------+----------------+----------------+

     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 identifier 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 identifier MUST be set to zero (0).

     Good sources [1] of uniqueness or randomness are required for the
     Interface-Identifier 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-Identifier transmitted in the
     Configure-Request.  In this case the PPP peer may provide a valid
     non-zero Interface-Identifier 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 identifier
     negotiation will succeed.

     When a Configure-Request is received with the Interface-Identifier
     Configuration Option and the receiving peer implements this option,
     the received Interface-Identifier is compared with the Interface-
     Identifier 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-Identifiers are different but the received
     Interface-Identifier is zero, a Configure-Nak is sent with a non-
     zero Interface-Identifier value suggested for use by the remote
     peer.  Such a suggested Interface-Identifier MUST be different from
     the Interface-Identifier 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 identifier MUST be set to
     zero (0) regardless of its source unless the globally unique EUI-
     48/EUI-64 derived identifier is provided for the exclusive use by
     the remote peer.

     If the two Interface-Identifiers are different and the received
     Interface-Identifier is not zero, the Interface-Identifier MUST be
     acknowledged, i.e.  a Configure-Ack is sent with the requested
     Interface-Identifier, meaning that the responding peer agrees with
     the Interface-Identifier requested.

     If the two Interface-Identifiers are equal and are not zero, a
     Configure-Nak MUST be sent specifying a different non-zero
     Interface-Identifier 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 identifier MUST be set to
     zero (0) regardless of its source unless the globally unique EUI-
     48/EUI-64 derived identifier is provided for the exclusive use by
     the remote peer.

     If the two Interface-Identifiers are equal to zero, the Interface-
     Identifiers negotiation MUST be terminated by transmitting the
     Configure-Reject with the Interface-Identifier value set to zero.
     In this case a unique Interface-Identifier can not be negotiated.

     If a Configure-Request is received with the Interface-Identifier
     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-Identifier
     option if a valid Interface-Identifier Configure-Reject is
     received.

     Reception of a Configure-Nak with a suggested Interface-Identifier
     different from that of the last Configure-Nak sent to the peer
     indicates a unique Interface-Identifier.  In this case a new
     Configure-Request MUST be sent with the identifier value suggested
     in the last Configure-Nak from the peer.  But if the received
     Interface-Identifier is equal to the one sent in the last
     Configure-Nak, a new Interface-Identifier MUST be chosen.  In this
     case, a new Configure-Request SHOULD be sent with the new tentative
     Interface-Identifier.  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-
     Identifiers chosen at either end will quickly diverge, terminating
     the sequence.

     If negotiation of the Interface-Identifier 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-Identifier given must be acceptable as the remote
     Interface-Identifier; i.e.  it should be different from the
     identifier 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-Identifier for its end of the PPP connection.

   A summary of the Interface-Identifier 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-Identifier (MS Bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        Interface-Identifier (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Interface-Identifier (LS Bytes) |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Type

       1

     Length

       10

     Interface-Identifier

       The 64-bit Interface-Identifier which is very likely to be unique on
       the link or zero if a good source of uniqueness can not be found.

     Default

       If no valid interface identifier can be successfully negotiated, no
       default Interface-Identifier value should be assumed. The procedures
       for recovering from such a case are unspecified.  One approach is to
       manually configure the interface identifier 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

     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.

       No IPv6-Compression-Protocol field values are currently assigned.
       Specific assignments will be made in documents that define
       specific compression algorithms.

     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 Identifier 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 Identifier
   has been successfully negotiated, procedures for recovering from such
   a case are unspecified.  One approach is to manually configure the
   Interface Identifier of the interface.

   As long as the Interface Identifier 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-Identifier 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 Identifier     |
   +----------+------------------------+-----------------------------+

   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 Identifier fields.

6.  Security Considerations

   The IPv6 Control Protocol extension to PPP can be used with all
   defined PPP authentication and encryption mechanisms.

7.  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.

8.  Changes from RFC-2023

   The following changes were made from RFC-2023 "IP Version 6 over
   PPP":

   - Changed to use "Interface Identifier" instead of the "Interface
     Token" term according to the terminology adopted in [6].

   - Increased the size of Interface Identifier to 64 bits according to
     the newly adopted IPv6 addressing architecture [6].

   - Added methods for selection of an interface identifier that is
     consistently reproducible across initializations of the IPV6CP
     finite state machine.

   - Added the interface identifier selection methods for generating
     globally unique interface identifier from an unique an IEEE global
     identifier when it is available anywhere on the node.

   - Changed to send a Configure-Nak instead a Configure-Ack in response
     to receiving a Configure-Request with a zero Interface-Identifier
     value.

   - Replaced the value assignment of the IPv6-Compression-Protocol
     field of the IPv6-Compression-Protocol Configuration option with
     the text stating that no IPv6-Compression-Protocol field values are
     currently assigned and that specific assignments will be made in
     documents that define specific compression algorithms.

   - Added new and updated references.

   - Minor text clarifications and improvements.

9.  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 2460, December 1998.

   [3]  Thomson, S., and T. Narten, "IPv6 Stateless Address
        Autoconfiguration", RFC 2462, December 1998.

   [4]  Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC
        1700, October 1994.  See also: http://www.iana.org/numbers.html

   [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", RFC 2373, July 1998.

   [7]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels," BCP 14, RFC 2119, March 1997.

   [8]  Narten T., and C. Burton, "A Caution On The Canonical Ordering
        Of Link-Layer Addresses", RFC 2469, December 1998.

10.  Authors' Addresses

   Dimitry Haskin
   Bay Networks, Inc.
   600 Technology Park
   Billerica, MA 01821

   EMail: dhaskin@baynetworks.com

   Ed Allen
   Bay Networks, Inc.
   600 Technology Park
   Billerica, MA 01821

   EMail: eallen@baynetworks.com

11.  Full Copyright Statement

   Copyright (C) The Internet Society (1998).  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.

 

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