Dynamic Host Configuration Working                            D. Hankins
Group                                                                ISC
Internet-Draft                                              T. Mrugalski
Intended status: Standards Track         Gdansk University of Technology
Expires: June 24, July 9, 2010                                    January 5, 2010                                 December 21, 2009

Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Options for Dual-Stack Dual-
                               Stack Lite
              draft-ietf-softwire-ds-lite-tunnel-option-00
              draft-ietf-softwire-ds-lite-tunnel-option-01

Abstract

   This document specifies two DHCPv6 Options which are meant to be used
   by Softwire Initiator (SI) to retrieve its attached DS-Lite AFTR
   (Address Family Transition Router).

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Abstract

   This  Code Components extracted from this document describes how Dual-Stack Lite configuration (the
   Softwire Concentrator (SC)'s address) can be obtained by a Softwire
   Initiator (SI) via DHCPv6. must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.

Table of Contents

   1.  Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  DHCPv6 Options  . . . . . . . . . . . . . . . . . . . . . . . . 3
     3.1.  The Dual-Stack Lite Softwire Concentrator Address
           DHCPv6 Option . . . . . . . . . . . . . . . . . . . . . . . . . . 3
     3.2.  The Dual-Stack Lite Softwire Concentrator Name DHCPv6
           Option  . . . 4 . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  DHCPv6 Server behavior Behavior  . . . . . . . . . . . . . . . . . . . . 6
   5.  DHCPv6 Client behavior Behavior  . . . . . . . . . . . . . . . . . . . . 6 7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 8
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7 8
   9.  Normative References  . . . . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8 9

1.  Requirements Language

   In this document, the key words "MAY", "MUST", "MUST NOT",
   "OPTIONAL", "RECOMMENDED", "SHOULD", and "SHOULD NOT", are to be
   interpreted as described in BCP 14, RFC 2119 [RFC2119].

2.  Introduction

   Dual-Stack Lite [draft-ietf-softwire-dual-stack-lite-02] is a method
   solution to extend offer both IPv4 access and IPv6 connectivity to an IPv6-only customers which
   are addressed host. only with an IPv6 prefix (no IPv4 address is assigned
   to the attachment device).  One of its key components is an IPv4-over-IPv6 IPv4-
   over-IPv6 tunnel, commonly referred to as a Softwire, but a Software Initiator DS-Lite
   Basic Bridging BroadBand (B4) will not know if the network it is
   attached to offers Dual-Stack Lite support, and if it did would not
   know the remote end of the tunnel to establish a connection.

   To inform the Softwire Initiator B4 of the Softwire Concentrator's Address Family Transition Router's (AFTR)
   location, either an IPv6 address or Fully Qualified Domain Name
   (FQDN) may be used.  Once this information is conveyed, the presence
   of the configuration indicating the Softwire Concentrator's AFTR's location also informs a
   host to initiate Dual-Stack Lite (DS-Lite) service and become a
   Softwire Initiator.

   To provide the conveyance of the configuration information, two
   DHCPv6 [RFC3315] options Options are used; one in the case where the host
   receives an IPv6 address, and one in the case where the host receives
   an FQDN in order to derive an IPv6 address.

   This document assumes that the SI is provided with appropriate
   instructions for the activation of an IPv4-in-IPv6 scheme which is
   supposed to be supported in both B4 and AFTR.  Consequently, this
   memo does not precise the IPv4-in-IPv6 encapsulation scheme to be
   used by B4.

3.  DHCPv6 Options

   Following sections sub-sections define two new DHCPv6 options, Options, conformant with
   requirements specified in DHCPv6 [RFC3315] Section 22.1.

3.1.  The Dual-Stack Lite Softwire Concentrator Address DHCPv6 Option

   The Dual-Stack Lite Softwire Concentrator Address Option consists of
   option-code and option-len fields (common for all DHCPv6 options), Options),
   and a 128 bit tunnel-endpoint-addr field, containing one IPv6
   address.  The tunnel-endpoint-addr specifies the location of the
   remote tunnel endpoint, expected to be located at an AFTR (DS-Lite
   Address Family Transition Router element).

   The DS Lite DS-Lite Address option DHCPv6 Option MAY appear in the root scope of a
   DHCPv6 packet.  It MUST NOT appear inside any IA_NA, IA_TA, IA_PD,
   IAADDR, or similar.

   The DS Lite DS-Lite Address option DHCPv6 Option MUST NOT appear more than once in a
   message.

   The format of the Dual-Stack Lite Softwire Concentrator Addr DHCPv6
   Option is shown in the following figure:

        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
       +-------------------------------+-------------------------------+
       |   OPTION_DS_LITE_ADDR (TBD)   |         option-len: 16        |
       +-------------------------------+-------------------------------+
       |                                                               |
       |               tunnel-endpoint-addr (IPv6 Address)             |
       |                                                               |
       |                                                               |
       +---------------------------------------------------------------+

                DS Lite IPv6 Address option DHCPv6 Option format.

                                 Figure 1

   Below is provided the description of the enclosed fields:

   option-code:  OPTION_DS_LITE_ADDR (TBD)

   option-len:  Length of the tunnel-endpoint-addr field, which is
      currently defined to be precisely 16 octets.

   tunnel-endpoint-addr:  This field contains a single IPv6 address in
      binary representation of the remote tunnel endpoint, located at
      the DS-Lite AFTR.  It is precisely 16 octets in length.

   The client validates the DS-Lite Address option DHCPv6 Option by confirming
   the option is of 16 octets in length or greater.  The client MUST
   ignore tunnel-endpoint-addr shorter than 16 octets.  In the event the
   option is greater than 16 octets in length, only the first 16 octets
   are
   intrepreted. interpreted.

   Because this option conveys the tunnel-endpoint-addr value, no
   further processing is required of the client.

   The definition of this option is simple and encloses only a single
   IPv6 address.  It is temping to define a flexible option which may
   convey several IPv6 addresses (for robustness and service
   availability reasons), but for the sake of simplicity and consistency
   it is recommended to use a FQDN Option instead of conveying several
   IPv6 addresses.

3.2.  The Dual-Stack Lite Softwire Concentrator Name DHCPv6 Option

   The Dual-Stack Lite Softwire Concentrator Name Option consists of
   option-code and option-len fields (common for all DHCPv6 options), Options),
   and a variable length tunnel-endpoint-name field, containing a Fully
   Qualified Domain Name that refers to the AFTR (DS-Lite Address Family
   Transition Router element) the client is requested
   to establish a connection with.

   The DS Lite DS-Lite Name option MAY appear in the root scope of a DHCPv6
   packet.  It MUST NOT appear inside any IA_NA, IA_TA, IA_PD, IAADDR,
   or similar.

   The DS Lite DS-Lite Name option DHCPv6 Option MUST NOT appear more than once in a
   message.

   The format of the Dual-Stack Lite Softwire Concentrator Name DHCPv6
   Option is shown in th following figure:

        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
       +-------------------------------+-------------------------------+
       |   OPTION_DS_LITE_NAME (TBD)   |           option-len          |
       +-------------------------------+-------------------------------+
       |                   tunnel-endpoint-name (FQDN)                 |
       +---------------------------------------------------------------+

                        DS Lite

                    DS-Lite FQDN option DHCPv6 Option format.

                                 Figure 2

   Below is provided the description of the enclosed fields:

   option-code:  OPTION_DS_LITE_NAME (TBD)

   option-len:  Length in octets of the tunnel-endpoint-name field.

   tunnel-endpoint-name:  This field contains a single Fully Qualified
      Domain Name of the remote tunnel endpoint, located at the DS-Lite
      AFTR.

   The tunnel-endpoint-name field is formatted as required in DHCPv6

   [RFC3315] Section 8 ("Representation and Use of Domain Names").
   Briefly, the format described is using a single octet noting the
   length of one DNS label (limited to at most 64 octets), followed by
   the label.  This repeats until all labels in the FQDN are exhausted.
   The root label (or the end of the FQDN) is denoted as a zero length
   label.  An example FQDN format for this option is shown in Figure 3.

        +------+------+------+------+------+------+------+------+------+
        | 0x07 |   e  |   x  |   a  |   m  |   p  |   l  |   e  | 0x03 |
        +------+------+------+------+------+------+------+------+------+
        |   i  |   s  |   c  | 0x03 |   o  |   r  |   g  | 0x00 |
        +------+------+------+------+------+------+------+------+

                       Example tunnel-endpoint-name.

                                 Figure 3

   Note that in the specific case of the example tunnel-endpoint-name,
   (Figure 3) the length of the option is 17 octets, and so an option-
   len field value of 17 would be used.

   The client (B4) validates the option in this format by first
   confirming that the option length is greater than 3, that the option
   data can be contained by the option length (that the option length
   does not run off the end of the packet), and that the tunnel-endpoint-name tunnel-
   endpoint-name is of valid format as described in DHCPv6 Section 8
   [RFC3315]; there are no compression tags, there is at least one label
   of nonzero length.

   The client (B4) determines a value for the tunnel-endpoint-addr from
   the tunnel-endpoint-name using standard DNS resolution, as defined in
   [RFC3596].  If the DNS response contains more than one IPv6 address,
   the client picks only one IPv6 address and uses it as a remote tunnel
   endpoint.  The client MUST NOT establish more than one DS Lite tunnel
   at the same time.  For a redundancy and high availability discussion,
   see Section 7.2 "High availability" of
   [draft-ietf-softwire-dual-stack-lite-02].

4.  DHCPv6 Server behavior Behavior

   DHCP servers must translate user input from their own specific and
   unique operator's interfaces into configuration state for the client.
   The server MUST provide a way to configure the OPTION_DS_LITE_ADDR,
   and SHOULD allow the operator to enter a Fully Qualified Domain Name,
   upon which the server performs DNS Resolution to assemble its
   OPTION_DS_LITE_ADDR contents.  The server MAY either provide the same
   Fully Qualified Domain Name as OPTION_DS_LITE_NAME contents, or
   simply provide a distinct method of configuring it.

   If configured with values, DHCPv6 servers will include the DS Lite
   Address and/or Name options Options if either or both appear on the client's
   Option Request Option (OPTION_ORO).  RFC 3315 Section 17.2.2
   [RFC3315] describes how a DHCPv6 client and server negotiate
   configuration values using the ORO.

   A DHCPv6 server MAY NOT send either option Option if it has not been
   explicitly requested by the client.

   If the server is configured with an FQDN as the tunnel endpoint
   locator, the configured FDQN value must MUST contain a resolvable Fully
   Qualified Domain Name, having appropriate delegations from the root,
   and having a AAAA record locating the Softwire Concentrator.

   If OPTION_DS_LITE_NAME is being configured, it is RECOMMENDED that the server also MUST be
   configured to provide OPTION_DNS_SERVERS defined in [RFC3646]
   together with the DS Lite option, so that clients will be able to ask
   for DNS servers locations to resolve the domain name provided in the DS Lite
   DS-Lite Name DHCPv6 option.

5.  DHCPv6 Client behavior Behavior

   A client that supports B4 functionality of the DS Lite DS-Lite (defined in
   [draft-ietf-softwire-dual-stack-lite-02]) MUST include
   OPTION_DS_LITE_ADDR on its OPTION_ORO, and MAY include
   OPTION_DS_LITE_NAME at its option and ability.

   If requesting the OPTION_DS_LITE_NAME option, DHCPv6 Option, the client also
   SHOULD request OPTION_DNS_SERVERS defined in [RFC3646] to be able to
   resolve any received domain name.

   If the client receives either DS Lite DS-Lite Option, it MUST verify the
   option contents as described in Section 3.1 and Section 3.2.  The
   client (B4) SHOULD establish a softwire tunnel to the tunnel-endpoint-addr tunnel-
   endpoint-addr IPv6 address it determines from either of these
   options.

   If the client requests and receives both the OPTION_DS_LITE_ADDR and
   the OPTION_DS_LITE_NAME, it MUST proceed with resolving the
   OPTION_DS_LITE_NAME.

6.  Security Considerations

   This document does not present any new security issues, but as with
   all DHCPv6-derived configuration state, it is completely possible
   that the configuration is being delivered by a third party (Man In
   The Middle).  As such, there is no basis to trust that the access the
   DS-Lite softwire Softwire connection represents can be trusted, and it should
   not therefore bypass any security mechanisms such as IP firewalls.

   RFC 3315 [RFC3315] discusses DHCPv6 related DHCPv6-related security issues.

   [draft-ietf-softwire-dual-stack-lite-02] discusses DS Lite related
   security issues.

7.  IANA Considerations

   IANA is requested to allocate two DHCPv6 Option codes referencing
   this document.  One delineating OPTION_DS_LITE_ADDR, and one
   delineating OPTION_DS_LITE_NAME.

8.  Acknowledgements

   Authors would like to thank Alain Durand, Rob Austein and Dave Thaler
   for their valuable feedback and suggestions.

9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3596]  Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
              "DNS Extensions to Support IP Version 6", RFC 3596,
              October 2003.

   [RFC3646]  Droms, R., "DNS Configuration options for Dynamic Host
              Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
              December 2003.

   [draft-ietf-softwire-dual-stack-lite-02]
              Durand, A., Ed., "Dual-stack lite broadband deployments
              post IPv4 exhaustion", October 2009.

Authors' Addresses

   David W. Hankins
   Internet Systems Consortium, Inc.
   950 Charter Street
   Redwood City, CA  94063
   US

   Phone: +1 650 423 1307
   Email: David_Hankins@isc.org

   Tomasz Mrugalski
   Gdansk University of Technology
   Storczykowa 22B/12
   Gdansk,   80-177
   Poland

   Phone: +48 698 088 272
   Email: tomasz.mrugalski@eti.pg.gda.pl