Softwires                                                     D. Hankins
Internet-Draft                                                       ISC
Intended status: Standards Track                            T. Mrugalski
Expires: September 3, December 26, 2010               Gdansk University of Technology
                                                           March 2,
                                                           June 24, 2010

Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Options for Dual-
                               Stack Lite
              draft-ietf-softwire-ds-lite-tunnel-option-02
              draft-ietf-softwire-ds-lite-tunnel-option-03

Abstract

   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.

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
   Task Force (IETF), its areas, and its working groups. (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts.
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on September 3, December 26, 2010.

Copyright Notice

   Copyright (c) 2010 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
   (http://trustee.ietf.org/license-info) 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
   described in the Simplified BSD License.

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

1.  Requirements Language

   In this document, the

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

2.  Introduction

   Dual-Stack Lite [I-D.softwire-ds-lite-03] [I-D.softwire-ds-lite-04] 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 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 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.

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

   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 is of 16 octets in length or greater.  The client MUST ignore
   any 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 interpreted.

   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-03] [I-D.softwire-ds-lite-04] 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-03]. [I-D.softwire-ds-lite-04].

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.

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

   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.  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-03]. [I-D.softwire-ds-lite-04].

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,
   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 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.

   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-03])
   [I-D.softwire-ds-lite-04]) 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 establish a softwire tunnel to the 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 options, it MUST proceed with resolving the
   OPTION_DS_LITE_NAME.

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-03]

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

   [I-D.softwire-ds-lite-03]

   [I-D.softwire-ds-lite-04]
              Durand, A., Ed., "Dual-stack lite broadband deployments
              post IPv4 exhaustion",
              draft-ietf-softwire-dual-stack-lite-03
              draft-ietf-softwire-dual-stack-lite-04 (work in progress),
              February
              March 2010.

   [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
   US

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

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

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