DHC Working Group                                                 R. Yan
Internet Draft                                                  Y. Jiang
Expiration Date: June 2006                                        L. Gui
                                                   Alcatel Shanghai Bell
                                                                 X. Duan
                                                            China Mobile

                     Domain Suffix Option for DHCPv6

                          September 26, 2005

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Copyright Notice

   Copyright (C) The Internet Society (2005).


   This document specifies a new DHCPv6 (DHCP for IPv6) option which is
   passed from a DHCPv6 server to a DHCPv6 client to specify the
   domain suffix name used to perform domain name update.

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1.  Introduction

   This document describes a new option for DHCPv6 [RFC3315] that
   provides a mechanism for the transfer of a domain suffix name.
   Using this option, an IPv6 device, which works as a DHCPv6 client,
   can configure the domain suffix name automatically.

   For example, a service provider could use this option to transfer a
   domain suffix name to a Customer Premise Equipment (CPE) device
   acting as a router between the subscriber's internal network and the
   service provider's core network.

   The configured domain suffix name is intended to be used by the IPv6
   device to perform DNS update for the hosts inside its local network.
   The DNS update can be realized by several methods, e.g. the DHCPv6
   Client FQDN Option [FQDNv6] provides a mechanism to exchange client's
   FQDN information during a stateful DHCPv6 session, and [RADNS]
   defines a DNS update mechanism for IPv6 stateless configuration.

1.1  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   This document should be read in conjunction with the DHCPv6
   specification, [RFC3315]. Definitions for terms and acronyms used in
   this document are defined in [RFC3315] and [RFC3633].

2.  Domain Suffix Option

   The domain suffix option is used to carry a domain suffix to the
   DHCPv6 client, which will be used to construct and update the domain
   name for the hosts in local network.

   The format of the domain suffix option is:

     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
    |             Type            |            Length               |
    |                                                               |
    ~                          Domain suffix                        ~
    |                                                               |

   Type:         16-bits identifier of the type of option (TBD).

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   Length:       Length of the "domain suffix" field in octets.

   Domain suffix:  The specification of a domain suffix.

   The domain suffix in the 'domain suffix' MUST include only one item,
   and MUST be encoded as specified in section "Representation and use
   of domain names" of [RFC3315].

2.1  Usage

   In stateful DHCPv6 [RFC3315], the DHCPv6 server MAY place a domain
   suffix option in the options field of IA_PD option [RFC3363] in an
   outgoing DHCPv6 message.  The DHCPv6 server MUST NOT place a domain
   suffix option in any other portion of a stateful DHCPv6 message.

   In stateless DHCPv6 [RFC3736], the DHCPv6 server MAY place a domain
   suffix option in the main option buffer of any DHCPv6 message sent to
   a client.

   A DHCPv6 server may provide different values for the domain suffix
   option to different clients.  This is useful to avoid domain name
   conflict in large-scale network. The mechanism for choosing which
   suffix to assign to which client is a matter of implementation and
   administrative policy, and is therefore not specified in this

3.  Example

     +------+       +  CPE  +-+
     | Node +--+    +-------+ |
     +------+  |              |
               |    +-------+ |
     +------+  |    +  CPE  +-+
     | Node +--+    +-------+ |                        +----------+
     +------+  |              :                        |          |
               :    +-------+ |  +------------------+  | ISP Core |
               +----+  CPE  +-+--|Aggregation device|--|          |
     +------+  |    +-------+    +------------------+  |  Network |
     | Node +--+                                       |          |
     +------+                                          +----------+

    \____________  __________/ \_________________  ________________/
                 \/                              \/
          Subscriber network                ISP network

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   The above figure shows a typical usage of the domain suffix option.
   In this model, ISP has the ISP level domain name suffix (e.g.
   example.com). CPE in subscriber network may include a DNS server
   for name resolution for local hosts.

   The CPE in the subscriber network, which acts as a requesting
   router, initiates a DHCPv6 session with the ISP's aggregation device,
   acting as a delegation route.  During the DHCP session, an IPv6
   prefix, along with the corresponding domain suffix name (i.e.
   example.com) will be transferred to the CPE.

   The domain suffix name can then be used to construct the domain name
   for the hosts in subscriber network, using mechanisms defined in
   [FQDNv6] or [RADNS].

   To avoid frequent domain name conflicts, aggregation device might
   allocate different domain suffix name for the CPEs. An example way
   can be selection based on an external authority such as a RADIUS
   server, in which a unique domain suffix name prefix, called
   "home name", is negotiated between user and ISP when subscribing.
   For example, "user1.example.com" and "user2.example.com".

4.  Security Considerations

   Security considerations in DHCP are described in section 23,
   "Security Considerations" of [RFC3315].

   A rogue DHCP server can issue bogus domain suffix to a client. This
   may cause wrong domain name update.

   A malicious client may be able to mount a denial of service attack
   by repeated DHCP requests for domain suffix, thus exhausts the DHCP
   server's resource.

   Currently, it is difficult for DHCP servers to develop much
   confidence in the identities of its clients, given the absence of
   entity authentication from the DHCP protocol itself. To guard against
   attack, DHCP Authentication as described in section 21 of [RFC3315]
   can be used.

5.  IANA Considerations

   IANA is requested to assign a DHCPv6 option code for the Domain
   Suffix Option.

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6.  Acknowledgements

   The authors thank Ralph Droms, Ted Lemon, Bernie Volz, Tatuya Jinmei,
   Joe Quanaim and Stefaan De Cnodder for valuable discussions and

7.  References

7.1 Normative References

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

   [RFC3315]  Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B.
              and R. Droms (ed.), "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, May 2003.

   [RFC3363]  O. Troan, R. Droms, "IPv6 prefix option for DHCPv6",
              RFC 3363, December 2003.

7.2 Informative References

   [FQDNv6]   B. Volz, "The DHCPv6 Client FQDN Option", draft-ietf-dhc-
              dhcpv6-fqdn-00.txt, September, 2004.

   [RFC3736]  R. Droms, "Stateless Dynamic Host Configuration Protocol
              (DHCP) Service for IPv6", RFC 3736, April 2004.

   [RADNS]    R. Yan, "DNS update in IPv6 stateless configuration",
              draft-yan-ipv6-ra-dns-01.txt, June 2005.

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Authors' Addresses

   Renxiang Yan
   Yinglan Jiang
   Luoning Gui
   Research & Innovation Center
   Alcatel Shanghai Bell Co., Ltd.
   388#, NingQiao Road, Pudong Jinqiao,
   Shanghai 201206 P.R. China
   Phone: +86 (21) 5854-1240, ext. 7169

   Email: renxiang.yan@alcatel-sbell.com.cn

   Xiaodong Duan
   Research & Development Center
   China Mobile Communications Corporation
   53A, Xibianmennei Ave., Xuanwu District,
   Beijing, 100053 P.R. China
   Phone: +86 (10) 6600-6688, ext. 3062

   Email: duanxiaodong@chinamobile.com

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