Softwires                                                     D. Hankins
Internet-Draft                                                       ISC
Intended status: Standards Track                            T. Mrugalski
Expires: December 26, 2010 March 19, 2011                  Gdansk University of Technology
                                                           June 24,
                                                      September 15, 2010

Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Options for Dual-
                               Stack Lite


   This document specifies two DHCPv6 options which are meant to be used
   by a Dual-Stack Lite client (Basic Bridging BroadBand element, B4) to
   discover its Address Family Transition Router (AFTR) address.

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Table of Contents

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

1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Introduction

   Dual-Stack Lite [I-D.softwire-ds-lite-04] [I-D.softwire-ds-lite] is a solution to offer both
   IPv4 and IPv6 connectivity to customers which are addressed only with
   an IPv6 prefix (no IPv4 address is assigned to the attachment
   device).  One of its key components is an IPv4-over-IPv6 tunnel,
   commonly referred to as a Softwire, but a 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 B4 of the AFTR's Address Family Transition Router's (AFTR)
   location, either an IPv6 address or address, Fully Qualified Domain Name (FQDN)
   or both may be used.  Once this information is conveyed, the presence
   of the configuration indicating the 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 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.

   The details of how the B4 establishes an IPv4-in-IPv6 tunnel to the
   AFTR are out of scope for this document.

3.  The Dual-Stack Lite Address DHCPv6 Option

   The Dual-Stack Lite Address option consists of option-code and
   option-len fields (common for all DHCPv6 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.

   The DS-Lite Address 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.  Any DS-Lite Address option received inside any other
   option MUST be ignored.

   The DS-Lite Address option MUST NOT appear more than once in a
   message.  Client that receives more than one DS-Lite Address option
   MUST discard all instances of that option.

   The format of the Dual-Stack Lite Address 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)             |
       |                                                               |
       |                                                               |

                option-code: OPTION_DS_LITE_ADDR (TBD)

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

       tunnel-endpoint-addr: A single IPv6 address in binary
                             representation of the remote tunnel
                             endpoint, located at the DS-Lite AFTR.

            Figure 1: DS-Lite IPv6 Address DHCPv6 Option Format

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

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

   This option conveys a single IPv6 address, as the Dual-Stack Lite
   specification [I-D.softwire-ds-lite-04] [I-D.softwire-ds-lite] defines only one Softwire
   connection between a B4 and any AFTR.  Multiple connections or
   endpoints are undefined.  For more information, see Section 7.2 "High
   Availability" of [I-D.softwire-ds-lite-04]. [I-D.softwire-ds-lite].

4.  The Dual-Stack Lite Name DHCPv6 Option

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

   The 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.  Any DS-Lite Name option received inside any other option
   MUST be ignored.

   The DS-Lite Name option MUST NOT appear more than once in a message.
   Client that receives more than one DS-Lite Name option MUST discard
   all instances of that option.

   The format of the Dual-Stack Lite Name 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_NAME (TBD)   |           option-len          |
       |                   tunnel-endpoint-name (FQDN)                 |

                option-code: OPTION_DS_LITE_NAME (TBD)

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

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

                Figure 2: DS-Lite Name DHCPv6 Option Format

   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.  Any possible updates to Section 8 of DHCPv6 [RFC3315] also
   apply to encoding of this FQDN field.  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 |

                  Figure 3: Example tunnel-endpoint-name.

   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 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 [I-D.softwire-ds-lite-04]. [I-D.softwire-ds-lite].

5.  DHCPv6 Server 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,
   As a convenience to the operator, the server MAY 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 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 MUST NOT send either option if it has not been
   explicitly requested by the client.

   A DHCPv6 server MUST NOT send more than one DS-Lite Address option.
   A DHCPv6 server MUST NOT send more than one DS-Lite Name option.

   A DHCPv6 server MUST NOT send DS-Lite Address or DS-Lite Name options
   as suboptions in other options.

   If the server is configured with an FQDN as the tunnel endpoint
   locator, the configured FQDN value 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, the server MUST be
   configured to provide OPTION_DNS_SERVERS defined in [RFC3646]
   together with the DS-Lite Name option, so that clients will be able
   to ask for DNS servers locations to resolve the domain name provided
   in the DS-Lite Name option.

6.  DHCPv6 Client Behavior

   A client that supports B4 functionality of DS-Lite (defined in
   [I-D.softwire-ds-lite]) and conforms to this specification 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, 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 option, it MUST verify the
   option contents as described in Section 3 and Section 4.  The client
   (B4) SHOULD is expected to establish a softwire tunnel to the tunnel-endpoint-addr tunnel-
   endpoint-addr IPv6 address it determines from either of these

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

7.  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 connection represents can be trusted, and it should
   not therefore bypass any security mechanisms such as IP firewalls.

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


   [I-D.softwire-ds-lite] discusses DS-Lite related security issues.

8.  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.

9.  Acknowledgements

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

10.  Normative References


              Durand, A., Ed., "Dual-stack lite broadband deployments
              post IPv4 exhaustion",
              draft-ietf-softwire-dual-stack-lite-04 draft-ietf-softwire-dual-stack-lite
              (work in progress),
              March 2010. progress).

   [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.

Authors' Addresses

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

   Phone: +1 650 423 1307

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

   Phone: +48 698 088 272