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

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 6334.
Authors David Hankins , Tomek Mrugalski
Last updated 2015-10-14 (Latest revision 2011-03-07)
Replaces draft-dhankins-softwire-tunnel-option
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Additional resources Mailing list discussion
Stream WG state WG Document
Document shepherd (None)
IESG IESG state Became RFC 6334 (Proposed Standard)
Action Holders
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD Ralph Droms
IESG note
Send notices to (None)
Softwire                                                      D. Hankins
Internet-Draft                                                    Google
Intended status: Standards Track                            T. Mrugalski
Expires: September 8, 2011               Gdansk University of Technology
                                                           March 7, 2011

 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 Basic Bridging Broadband (B4) element to discover
   the IPv6 address of its corresponding Address Family Transition
   Router (AFTR).

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 8, 2011.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as

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   described in the Simplified BSD License.

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 . . . . . . . . . . . . . . . . . . . . . . 7
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   9.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8

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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 service, and if it did would not know the
   remote endpoint of the tunnel to establish a 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 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 MAY connect to.

   The AFTR-Name option SHOULD NOT appear in any other than 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:

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        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 in

       tunnel-endpoint-name: A fully qualified domain name of the AFTR
                             tunnel 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
   (Figure 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 all of the following
   conditions are met:

   1.  the option-len is greater than 3;

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   2.  the option data can be contained by the option length (that the
       option length does not run off the end of the packet);

   3.  the individual label lengths do not exceed the option length;

   4.  the tunnel-endpoint-name is of valid format as described in
       DHCPv6 Section 8 [RFC3315];

   5.  there are no compression tags;

   6.  there is at least one label of nonzero length.

4.  DHCPv6 Server Behavior

   A DHCPv6 server SHOULD NOT send more than one AFTR-Name option.  It
   SHOULD NOT permit the configuration of multiple names within one
   AFTR-Name option.  Both of these conditions are handled exceptionally
   by the client, so an operator using software that does not perform
   these validations should be careful not to configure multiple domain

   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 AFTR-Name option if the client has not
   explicitly enumerated it on its 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, the client MAY
   also wish to include the OPTION_DNS_SERVERS [RFC3646] option on its

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

   Note that in different environments, the B4 element and DHCPv6 client
   may be integrated, joined, or separated by a third pieces of
   software.  For the purpose of this specification, we refer to the "B4
   system" when specifying implementation steps that may be processed at
   any stage of integration between the DHCPv6 client software and the
   B4 element it is configuring.

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   If the B4 system receives more than one AFTR-Name option, it MUST 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 B4 system MUST use only
   the first FQDN listed in configuration.

   The B4 system performs standard DNS resolution using the provided
   FQDN to resolve a AAAA Resource Record, as defined in [RFC3596] and
   STD 13 [RFC1034] [RFC1035].

   If any DNS response contains more than one IPv6 address, the B4
   system picks only one IPv6 address and uses it as a remote tunnel
   endpoint for the interface being configured in the current message
   exchange.  The B4 system MUST NOT establish more than one DS-Lite
   tunnel at the same time per interface.  For a redundancy and high
   availability discussion, see Section 12.3 "High availability" of

   Note that a B4 system 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 B4 system
   should approach this specification on an interface-by-interface
   basis.  For example, if the B4 system is attached to multiple
   networks that provide the AFTR Name option, then the B4 system MUST
   configure a tunnel for each interface separately as each DS-Lite
   tunnel provides IPv4 connectivity for each distinct interface.  Means
   to bind a AFTR Name and DS-Lite tunnel configuration to a given
   interface in a multiple interfaces device are out of scope of this

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.

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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, Roberta Maglione and
   Shawn Routhier 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.

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Authors' Addresses

   David W. Hankins
   Google, Inc.
   1600 Amphitheatre Parkway
   Mountain View, CA  94043


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

   Phone: +48 698 088 272

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