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Dynamic Host Configuration Working                            D. Hankins
Group                                                                ISC
Internet-Draft                                              T. Mrugalski
Intended status: Standards Track         Gdansk University of Technology
Expires: May 16, 2010                                  November 12, 2009


Dynamic Host Configuration Protocol (DHCPv6) Option for Dual-Stack Lite
                draft-dhankins-softwire-tunnel-option-05

Abstract

   This document describes how Dual-Stack Lite configuration (the
   Softwire Concentrator (SC)'s address) can be obtained by a Softwire
   Initiator (SI) via DHCPv6.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on May 16, 2010.

Copyright Notice

   Copyright (c) 2009 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
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   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
   described in the BSD License.


Table of Contents

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

































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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
   to extend IPv4 access to an IPv6-only addressed host.  One of its key
   components is an IPv4-over-IPv6 tunnel, commonly referred to as a
   Softwire, but a host 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.

   These are two separate pieces of information; 1) Should the client
   shut down its dual-stack IPv4 side, and use the softwire exclusively
   for IPv4 access? 2) At what IPv6 address should the client establish
   a softwire connection?

   These two questions can be answered with one DHCPv6 [RFC3315] option.

   DISCUSSION: It can be argued that if you inform a client it should
   perform Dual-Stack Lite, but fail to deliver an IPv6 tunnel endpoint,
   then its IPv4 access is certainly broken.  If you give the client an
   IPv6 tunnel endpoint but fail to inform it that it must use Dual-
   Stack Lite for IPv4 access, then again its access is likely broken,
   or is operating in a degraded mode of service (if an operator offers
   a Dual-Stack Lite method of access, there either isn't any native
   IPv4 access, or the Dual-Stack Lite method works better than native
   access - if a network had better native IPv4 access than Dual-Stack
   Lite access, there would be no reason to extend the service).  So the
   presence of a tunnel address also indicates the operator's intent for
   the client to use the Softwire.


3.  The Dual-Stack Lite DHCPv6 Option

   The Dual-Stack Lite DHCPv6 Option is simply a fully qualified domain
   name that specifies the remote tunnel endpoint, expected to be
   located at the AFTR (DS-Lite Address Family Transition Router
   element).

   The Dual-Stack Lite Option Format is presented in Figure 1.






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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_DS_LITE (TBD)      |           option-len         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                 tunnel-endpoint-domain-name                   |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          DS Lite option format.

                                 Figure 1

   option-code:  OPTION_DS_LITE (TBD)

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

   tunnel-endpoint-domain-name:  Fully Qualified Domain Name of the
      remote tunnel endpoint, located at the AFTR.

   The DS Lite 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 option MUST NOT appear more than once in a message.

   tunnel-endpoint-domain-name field MUST be encoded as specified in
   Section 8 "Representation and Use of Domain Names" of the [RFC3315].


4.  DHCPv6 Server behavior

   If configured with a value, DHCPv6 servers will include the DS Lite
   option if it appears 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.

   DHCPv6 servers will not send the DS Lite option if it has not been
   requested by the client.

   The provided domain name must be a resolvable fully qualified domain
   name.

   It is RECOMMENDED that server will be configured to also 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



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   to resolve domain name provided in DS Lite option.


5.  DHCPv6 Client behavior

   A client that supports B4 functionality of the DS Lite (defined in
   [draft-ietf-softwire-dual-stack-lite-02]) MUST include OPTION_DS_LITE
   on its OPTION_ORO.

   When requesting OPTION_DS_LITE option, the client also SHOULD request
   OPTION_DNS_SERVERS defined in [RFC3646] to be able to resolve the
   received domain name.

   If the client receives a DS Lite Option, it MUST verify that the
   option length is less than or equal to 256 octets (the maximum length
   of a single FQDN allowed by DNS), and that the tunnel endpoint domain
   name is a properly encoded single FQDN, as specified in Section 8
   "Representation and Use of Domain Names" of the [RFC3315].  If the
   option is not of valid length or content (for example, if it contains
   compression tags), it MUST be ignored (and the client SHOULD continue
   in attempts to acquire native IPv4 access).

   Once the client receives and verifies validity of the DS Lite option,
   it should resolve the received domain name using standard DNS
   resolution as defined in [RFC3596].  If the DNS response contains
   more than one IPv6 address, the client picks the first IPv6 address
   in the response 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 the [draft-ietf-softwire-dual-stack-lite-02].

   The client SHOULD terminate or withdraw any native DHCPv4 [RFC2131]
   configuration on the same interface.  If DHCPv4 configuration has
   concluded, the client SHOULD perform a DHCPRELEASE as it tears down
   its IPv4 configuration.

   DISCUSSION: The author's best understanding of the current
   epistemology on IPv6 multihoming is that the client will have IPv6
   addresses on multiple different IPv6 prefixes.  If a host is
   multihomed, then, it is strange enough to wonder how DHCPv6
   configuration will work as most DHCPv6 clients will attach to only
   one DHCPv6 server.  It is even stranger to wonder how the client
   would react if all of its multiple homes wished to provide IPv4
   access via DS Lite.  Would a client establish more than one tunnel?







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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.

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


7.  IANA Considerations

   IANA is requested to allocate one DHCPv6 Option code, referencing
   this document.


8.  Normative References

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

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, 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.







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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,
   Poland

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































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