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Internet Engineering Task Force (IETF)                        D. HankinsRequest for Comments: 6334                                        GoogleCategory: Standards Track                                   T. MrugalskiISSN: 2070-1721                          Gdansk University of Technology                                                             August 2011Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Optionfor Dual-Stack LiteAbstract   This document specifies a DHCPv6 option that 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 is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6334.Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Hankins & Mrugalski          Standards Track                    [Page 1]

RFC 6334                  DS-Lite DHCPv6 Option              August 2011Table of Contents1. Introduction ....................................................22. Requirements Language ...........................................23. The AFTR-Name DHCPv6 Option .....................................24. DHCPv6 Server Behavior ..........................................45. DHCPv6 Client Behavior ..........................................46. Security Considerations .........................................57. IANA Considerations .............................................68. Acknowledgements ................................................69. Normative References ............................................61.  Introduction   Dual-Stack Lite [RFC6333] is a solution to offer both IPv4 and IPv6   connectivity to customers that 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.2.  Requirements Language   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inRFC 2119 [RFC2119].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 to which the client MAY connect.Hankins & Mrugalski          Standards Track                    [Page 2]

RFC 6334                  DS-Lite DHCPv6 Option              August 2011   The AFTR-Name option SHOULD NOT appear in any DHCPv6 messages other   than the following: 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: 64       |          option-len           |     +-------------------------------+-------------------------------+     |                                                               |     |                  tunnel-endpoint-name (FQDN)                  |     |                                                               |     +---------------------------------------------------------------+         OPTION_AFTR_NAME: 64               option-len: Length of the tunnel-endpoint-name field in                           octets.     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 toSection 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 "aftr.example.com.".      +------+------+------+------+------+------+------+------+------+      | 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.Hankins & Mrugalski          Standards Track                    [Page 3]

RFC 6334                  DS-Lite DHCPv6 Option              August 2011   The option is validated by confirming that all of the following   conditions are met:   1.  the option-len is greater than 3;   2.  the option-len is less than or equal to the remaining number of       octets in the DHCPv6 packet;   3.  the individual label lengths do not exceed the option length;   4.  the tunnel-endpoint-name is of valid format as described in       DHCPv6Section 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 as exceptions   by the client, so an operator using software that does not perform   these validations should be careful not to configure multiple domain   names.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 an 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   [RFC6333]) and conforms to this specification MUST include   OPTION_AFTR_NAME on its OPTION_ORO.   Because it requires a DNS name for address resolution, the client MAY   also wish to include the OPTION_DNS_SERVERS [RFC3646] option on its   OPTION_ORO.   If the client receives the AFTR-Name option, it MUST verify the   option contents as described inSection 3.Hankins & Mrugalski          Standards Track                    [Page 4]

RFC 6334                  DS-Lite DHCPv6 Option              August 2011   Note that in different environments, the B4 element and DHCPv6 client   may be integrated, joined, or separated by a third piece 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.   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 the 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, seeAppendix A.3 ("High Availability") of   [RFC6333].   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 an AFTR-Name and DS-Lite tunnel configuration to a given   interface in a multiple-interface device are out of scope of this   document.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 for trusting the access   level represented by the DS-Lite softwire connection, and DS-Lite   should therefore not bypass any security mechanisms such as IP   firewalls.Hankins & Mrugalski          Standards Track                    [Page 5]

RFC 6334                  DS-Lite DHCPv6 Option              August 2011   [RFC3315] discusses DHCPv6-related security issues.   [RFC6333] discusses DS-Lite-related security issues.7.  IANA Considerations   IANA has allocated a single DHCPv6 option code, 64, referencing this   document, delineating OPTION_AFTR_NAME.8.  Acknowledgements   The 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.  The authors acknowledge significant support for this   work, provided by Internet Systems Consortium, Inc.   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   [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., Ed., 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., Ed., "DNS Configuration options for Dynamic              Host Configuration Protocol for IPv6 (DHCPv6)",RFC 3646,              December 2003.   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-              Stack Lite Broadband Deployments Following IPv4              Exhaustion",RFC 6333, August 2011.Hankins & Mrugalski          Standards Track                    [Page 6]

RFC 6334                  DS-Lite DHCPv6 Option              August 2011Authors' Addresses   David W. Hankins   Google, Inc.   1600 Amphitheatre Parkway   Mountain View, CA  94043   USA   EMail: dhankins@google.com   Tomasz Mrugalski   Gdansk University of Technology   ul. Storczykowa 22B/12   Gdansk  80-177   Poland   Phone: +48 698 088 272   EMail: tomasz.mrugalski@eti.pg.gda.plHankins & Mrugalski          Standards Track                    [Page 7]