Softwire                                                      D. Hankins
Internet-Draft                                                    Google
Intended status: Standards Track                            T. Mrugalski
Expires: June 2, 13, 2011                   Gdansk University of Technology
                                                       November 29,
                                                       December 10, 2010

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


   This document specifies a DHCPv6 option which is meant to be used by
   a Dual-Stack Lite client (Basic Basic Bridging BroadBand element, B4) Broadband (B4) element to discover
   the IPv6 address of its corresponding Address Family Transition
   Router (AFTR) address. (AFTR).

Status of this Memo

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   This Internet-Draft will expire on June 2, 13, 2011.

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Table of Contents

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

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] 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.  A DS-Lite "Basic Bridging
   BroadBand" (B4) device will not know if the network it is attached to
   offers Dual-Stack Lite support, service, and if it did would not know the
   remote end endpoint of the tunnel to establish a connection. softwire.

   To inform the B4 of the Address Family Transition Router's (AFTR)
   location, a DNS [RFC1035] hostname 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, a single
   DHCPv6 [RFC3315] option is used, expressing the AFTR's Fully
   Qualified Domain Name (FQDN) to the B4 element.

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

3.  The AFTR-Name DHCPv6 Option

   The AFTR-Name option consists of option-code and option-len fields
   (as all DHCPv6 options have), and a variable length tunnel-endpoint-
   name field containing a fully qualified domain name that refers to
   the AFTR which the client is asked to MAY connect to.

   The OPTION_AFTR_NAME AFTR-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 OPTION_AFTR_NAME option received inside in any other
   option MUST be ignored.

   The OPTION_AFTR_NAME option MUST NOT appear more than once in a
   message.  Clients that receive more than one OPTION_AFTR_NAME options
   MUST discard all instances of that option, acting as if none were
   sent. the following
   DHCPv6 messages: Solicit, Advertise, Request, Renew, Rebind,
   Information-Request and Reply.

   The format of the AFTR-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_AFTR_NAME: (TBD)    |          option-len           |
       |                                                               |
       |                  tunnel-endpoint-name (FQDN)                  |
       |                                                               |

           OPTION_AFTR_NAME: (TBD)

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

       tunnel-endpoint-name: A fully qualified domain name identifying of the AFTR
                             tunnel endpoint, located at the DS-Lite
                             AFTR. endpoint.

                 Figure 1: AFTR-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 63 octets), followed by
   the label contents.  This repeats until all labels in the FQDN are
   exhausted, including a terminating zero-length label.  Any updates to
   Section 8 of DHCPv6 [RFC3315] also apply to encoding of this field.
   An example format for this option is shown in Figure 2, which conveys
   the FQDN "".

        | 0x04 |   a  |   f  |   t  |   r  | 0x07 |   e  |   x  |   a  |
        |   m  |   p  |   l  |   e  | 0x03 |   c  |   o  |   m  | 0x00 |

                  Figure 2: Example tunnel-endpoint-name.

   Note that in the specific case of the example tunnel-endpoint-name, tunnel-endpoint-name
   (Figure 2) 2), the length of the tunnel-endpoint-name is 18 octets, and
   so an option-len field value of 18 would be used.

   The option is validated by confirming that the option-len 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), that
   individual label lengths do not exceed the option length, 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.

4.  DHCPv6 Server Behavior

   A DHCPv6 server MUST NOT send more than one OPTION_AFTR_NAME AFTR-Name option.

   A DHCPv6 server MUST  It
   SHOULD NOT send the OPTION_AFTR_NAME option as a
   suboption in other options; it MUST appear only in permit the root scope configuration of
   any DHCPv6 messages made in response to clients (Reply, Advertise, et
   al). multiple names within one
   AFTR-Name option.

   RFC 3315 Section 17.2.2 [RFC3315] describes how a DHCPv6 client and
   server negotiate configuration values using the Option Request Option
   (OPTION_ORO).  As a convenience to the reader, we mention here that a
   server will not reply with a value for the OPTION_AFTR_NAME AFTR-Name option if the client has not
   explicitly enumerated it on its OPTION_ORO. Option Request Option.

5.  DHCPv6 Client Behavior

   A client that supports the B4 functionality of DS-Lite (defined in
   [I-D.softwire-ds-lite]) and conforms to this specification MUST
   include OPTION_AFTR_NAME on its OPTION_ORO.

   Because it requires DNS name to address resolution, a the client MAY
   also wish to include the OPTION_DNS_SERVERS [RFC3646] option on its

   If the client receives the OPTION_AFTR_NAME AFTR-Name option, it MUST verify the
   option contents as described in Section 3.

   If the client receives more than one OPTION_AFTR_NAME AFTR-Name option, it MUST
   discard all instances use
   only the first instance of that option.

   If the AFTR-Name option contains more than one FQDN, as distinguished
   by the presence of multiple root labels, the client MUST use only the
   first FQDN listed in configuration.

   The client performs standard DNS resolution using the provided FQDN
   to resolve a AAAA record, Resource Record, as defined in [RFC3596] and STD 13
   [RFC1034] [RFC1035].

   If any DNS response contains more than one IPv6 address, the client
   picks only one IPv6 address and uses it as a remote tunnel endpoint. endpoint
   for the interface being configured in the current message exchange.
   The client MUST NOT establish more than one DS-Lite tunnel at the
   same time. time per interface.  For a redundancy and high availability
   discussion, see Section 7.2 "High availability" of

   Note that a client may have multiple network interfaces, and these
   interfaces may be configured differently; some may be connected to
   networks that call for DS-Lite, and some may be connected to networks
   that are using normal dual stack or other means.  The client should
   consider the above on an interface-by-interface basis.  For example,
   if the client is attached to multiple networks that provide the AFTR
   Name option, then the client MUST configure a tunnel for each
   interface separately as each DS-Lite tunnel provides IPv4
   connectivity for each distinct interface.

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 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.

7.  IANA Considerations

   IANA is requested to allocate single DHCPv6 option code referencing
   this document, delineating OPTION_AFTR_NAME.

8.  Acknowledgements

   Authors would like to thank Alain Durand, Rob Austein, Dave Thaler,
   Paul Selkirk, Ralph Droms, Mohamed Boucadair and Maglione Roberta Maglione for
   their valuable feedback and suggestions.

   This work has been partially supported by the Polish Ministry of
   Science and Higher Education under the European Regional Development
   Fund, Grant No.  POIG.01.01.02-00-045/09-00 (Future Internet
   Engineering Project).

9.  Normative References

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

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [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
   Google, Inc.
   1600 Amphitheatre Parkway
   Mountain View, CA  94043


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

   Phone: +48 698 088 272