path: root/rfc/rfc5072.txt

Network Working Group                                     S. Varada, Ed.
Request for Comments: 5072                                    Transwitch
Obsoletes: 2472                                               D. Haskins
Category: Standards Track                                       E. Allen
                                                          September 2007


                         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.

Abstract

   The Point-to-Point Protocol (PPP) 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 sending IPv6 packets over PPP
   links, the NCP for establishing and configuring the IPv6 over PPP,
   and the method for forming IPv6 link-local addresses on PPP links.

   It also specifies the conditions for performing Duplicate Address
   Detection on IPv6 global unicast addresses configured for PPP links
   either through stateful or stateless address autoconfiguration.

   This document obsoletes RFC 2472.

















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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 .........................3
   4. IPV6CP Configuration Options ....................................4
      4.1. Interface Identifier .......................................4
   5. Stateless Autoconfiguration and Link-Local Addresses ............9
   6. Security Considerations ........................................11
   7. IANA Considerations ............................................11
   8. Acknowledgments ................................................11
   9. References .....................................................12
      9.1. Normative References ......................................12
      9.2. Informative references ....................................12
   Appendix A:  Global Scope Addresses................................14
   Appendix B:  Changes from RFC-2472.................................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 to 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.).

   This document obsoletes the earlier specification from RFC 2472 [7].
   Changes from RFC 2472 are listed in Appendix B.



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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 [6].

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 to be 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 LCP.  IPV6CP packets may not be exchanged until PPP has
   reached the network-layer protocol phase.  IPV6CP packets that are
   received before this phase is reached should be silently discarded.

   The IPv6 Control Protocol is exactly the same as the LCP [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.

4.  IPV6CP Configuration Options

   IPV6CP Configuration Options allow negotiation of desirable IPv6
   parameters.  IPV6CP uses the same Configuration Option format defined
   for LCP [1] but 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 online database of "Assigned Numbers" maintained at IANA [9].
   The current value assignment is as follows:

      1 Interface-Identifier

   The only IPV6CP option defined in this document is the interface
   identifier.  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



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   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 unique to the link and, preferably, 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 (see Appendix A) 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 [4] terminology), which indicates whether or not the interface
   identifier is based on a globally unique IEEE identifier (EUI-48 or
   EUI-64 [4])(see 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 that the extracted identifier is
      presented in canonical ordering [14].

      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
      the 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 hexa-decimal 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
      the 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.



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      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 nor 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,
   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



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   (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
   identifier's negotiation MUST be terminated by transmitting the
   Configure-Reject with the interface-identifier value set to zero.  In
   this case, a unique interface identifier cannot be negotiated.

   If a Configure-Request is received with the Interface-Identifier
   Configuration Option and the receiving peer does not implement this
   option, Configure-Reject 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 [1]).

   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.





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   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
         cannot 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.

5.  Stateless Autoconfiguration and Link-Local Addresses

   The interface identifier of IPv6 unicast addresses [5] 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.





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   The negotiated interface identifier is used by the local end of the
   PPP link to autoconfigure an IPv6 link-local unicast address for the
   PPP interface.  However, it SHOULD NOT be assumed that the same
   interface identifier is used in configuring global unicast addresses
   for the PPP interface using IPv6 stateless address autoconfiguration
   [3].  The PPP peer MAY generate one or more interface identifiers,
   for instance, using a method described in [8], to autoconfigure one
   or more global unicast addresses.

   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 (DAD) as a part of the IPv6 Stateless Address
   Autoconfiguration protocol [3] on the IPv6 link-local address
   generated by the PPP peer.  It may also be redundant to perform DAD
   on any global unicast addresses configured (using an interface
   identifier that is either negotiated during IPV6CP or generated, for
   instance, as per [8]) for the interface as part of the IPv6 Stateless
   Address Autoconfiguration protocol [3] provided that the following
   two conditions are met:

      1) The prefixes advertised through the Router Advertisement
         messages by the access router terminating the PPP link are
         exclusive to the PPP link.

      2) The access router terminating the PPP link does not
         autoconfigure any IPv6 global unicast addresses from the
         prefixes that it advertises.

   Therefore, it is RECOMMENDED that for PPP links with the IPV6CP
   interface-identifier option enabled and satisfying the aforementioned
   two conditions, the default value of the DupAddrDetectTransmits
   autoconfiguration variable [3] is set to zero by the system
   management.  3GPP2 networks are an example of a technology that uses
   PPP to enable a host to obtain an IPv6 global unicast address and
   satisfies the aforementioned two conditions [10].  3GPP networks are
   another example ([11] [13]).

   Link-local addresses

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

   | 10 bits  |        54 bits         |          64 bits            |
   +----------+------------------------+-----------------------------+
   |1111111010|           0            |    Interface-Identifier     |
   +----------+------------------------+-----------------------------+






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   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

   Lack of link security, such as authentication, trigger the security
   concerns raised in [3] when the stateless address autoconfiguration
   method is employed for the generation of global unicast IPv6
   addresses out of interface identifiers that are either negotiated
   through the IPV6CP or generated, for instance, using a method
   described in [8].  Thus, the mechanisms that are appropriate for
   ensuring PPP link security are addressed below, together with the
   reference to a generic threat model.

   The mechanisms that are appropriate for ensuring PPP link Security
   are: 1) Access Control Lists that apply filters on traffic received
   over the link for enforcing admission policy, 2) an Authentication
   protocol that facilitates negotiations between peers [15] to select
   an authentication method (e.g., MD5 [16]) for validation of the peer,
   and 3) an Encryption protocol that facilitates negotiations between
   peers to select encryption algorithms (or crypto-suites) to ensure
   data confidentiality [17].

   There are certain threats associated with peer interactions on a PPP
   link even with one or more of the above security measures in place.
   For instance, using the MD5 authentication method [16] exposes one to
   replay attack, where an attacker could intercept and replay a
   station's identity and password hash to get access to a network.  The
   user of this specification is advised to refer to [15], which
   presents a generic threat model, for an understanding of the threats
   posed to the security of a link.  The reference [15] also gives a
   framework to specify requirements for the selection of an
   authentication method for a given application.

7.  IANA Considerations

   The IANA has assigned value 1 for the Type field of the IPv6 datagram
   interface-identifier option specified in this document.  The current
   assignment is up-to-date at [9].

8.  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.

   The editor is grateful for the input provided by members of the IPv6
   community in the spirit of updating RFC 2472.  Thanks, in particular,



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   go to Pete Barany and Karim El Malki for their technical
   contributions.  Also, thanks to Alex Conta for a thorough review,
   Stephen Kent for helping with security aspects, and Spencer Dawkins
   and Pekka Savola for the nits.  Finally, the author is grateful to
   Jari Arkko for his initiation to bring closure to this specification.

9.  References

9.1.  Normative References

   [1]   Simpson, W., Ed., "The Point-to-Point Protocol (PPP)", STD 51,
         RFC 1661, July 1994.

   [2]   Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
         Specification", RFC 2460, December 1998.

   [3]   Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address
         Autoconfiguration", RFC 4862, September 2007.

   [4]   IEEE, "Guidelines For 64-bit Global Identifier (EUI-64)",
         http://standards.ieee.org/regauth/oui/tutorials/EUI64.html

   [5]   Hinden, R. and S. Deering, "IP Version 6 Addressing
         Architecture", RFC 4291, February 2006.

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

   [7]   Haskin, D. and E. Allen, "IP Version 6 over PPP", RFC 2472,
         December 1998.

   [8]   Narten T., Draves, R., and S. Krishnan, "Privacy Extensions for
         Stateless Address Autoconfiguration in IPv6", RFC 4941,
         September 2007.

9.2.  Informative references

   [9]   IANA, "Assigned Numbers," http://www.iana.org/numbers.html

   [10]  3GPP2 X.S0011-002-C v1.0, "cdma2000 Wireless IP Network
         Standard: Simple IP and Mobile IP Access Services," September
         2003.

   [11]  3GPP TS 29.061 V6.4.0, "Interworking between the Public Land
         Mobile Network (PLMN) Supporting packet based services and
         Packet Data Networks (PDN) (Release 6)," April 2005.





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   [12]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, C.,
         and M. Carney, "Dynamic Host Configuration Protocol for IPv6
         (DHCPv6)", RFC 3315, July 2003.

   [13]  3GPP TS 23.060 v6.8.0, "General Packet Radio Service (GPRS);
         Service description; Stage 2 (Release 6)," March 2005.

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

   [15]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
         Levkowetz, Ed., "Extensible Authentication Protocol (EAP)", RFC
         3748, June 2004.

   [16]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April
         1992.

   [17]  Meyer, G., "The PPP Encryption Control Protocol (ECP)", RFC
         1968, June 1996.
































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Appendix A:  Global Scope Addresses

   A node on the PPP link creates global unicast addresses either
   through stateless or stateful address autoconfiguration mechanisms.
   In the stateless address autoconfiguration [3], the node relies on
   sub-net prefixes advertised by the router via the Router
   Advertisement messages to obtain global unicast addresses from an
   interface identifier.  In the stateful address autoconfiguration, the
   host relies on a Stateful Server, like DHCPv6 [12], to obtain global
   unicast addresses.

Appendix B:  Changes from RFC 2472

   The following changes were made from RFC 2472 "IPv6 over PPP":

   -  Minor updates to Sections 3 and 4

   -  Updated the text in Section 4.1 to include the reference to
      Appendix A and minor text clarifications.

   -  Removed Section 4.2 on IPv6-Compression-Protocol based on IESG
      recommendation, and created a new standards-track document to
      cover negotiation of the IPv6 datagram compression protocol using
      IPV6CP.

   -  Updated the text in Section 5 to: (a) allow the use of one or more
      interface identifiers generated by a peer, in addition to the use
      of interface identifier negotiated between peers of the link, in
      the creation of global unicast addresses for the local PPP
      interface, and (b) identify cases against the DAD of created non-
      link-local addresses.

   -  Added new and updated references.

   -  Added Appendix A
















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Authors' Addresses

   Dimitry Haskin
   Ed Allen

   Srihari Varada (Editor)
   TranSwitch Corporation
   3 Enterprise Dr.
   Shelton, CT 06484. US.

   Phone: +1 203 929 8810
   EMail: varada@ieee.org







































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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
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Varada, et al.              Standards Track                    [Page 16]