    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.

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    Varada, et al.              Standards Track                    [Page 16]