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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 5006

Individual Submission
Internet Draft                                       Jaehoon Paul Jeong
                                                                   ETRI
                                                    Soohong Daniel Park
                                                    SAMSUNG Electronics
                                                            Luc Beloeil
                                                     France Telecom R&D
                                                       Syam Madanapalli
                                                            SAMSUNG ISO
draft-jeong-dnsop-ipv6-dns-discovery-00.txt
Expires: January 2004                                      21 July 2003


             IPv6 DNS Discovery based on Router Advertisement


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 except that the right to
   produce derivative works is not granted [1].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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.

Abstract

   This document specifies the steps a node takes in deciding how to
   autoconfigure DNS information, such as the address of recursive DNS
   server and DNS zone suffix.

Conventions used in this document

   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 in RFC 2119 [2].



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Table of Contents

   1. Terminology...................................................2
   2. Introduction..................................................2
   3. Overview......................................................3
   4. Neighbor Discovery Extension..................................3
      4.1  DNS Server Option........................................3
      4.2  DNS Zone Suffix Option...................................4
   5. Procedure of DNS Discovery....................................5
   6. Autoconfiguration of DNS Information..........................6
      6.1  RDNSS Configuration and Selection........................6
      6.2  DNS Zone Suffix Configuration............................7
   7. Applicability Statements......................................7
   8. Open Issues...................................................8
   9. Security Considerations.......................................8
   10. Copyright....................................................8
   11. Normative References.........................................9
   12. Informative References.......................................9
   13. Authors' Addresses..........................................10


1. Terminology

   This memo uses the terminology described in [3][4].  In addition, a
   new term is defined below:

   Recursive DNS Server (RDNSS)    A Recursive DNS Server is a name
                                   server that offers the recursive
                                   service of DNS name resolution.

2. Introduction

   IPv6 stateless address autoconfiguration provides a way to
   autoconfigure either fixed or mobile nodes with one or more IPv6
   addresses, default routes and some other parameters [3][4].

   For the support of the various services in the Internet, such as web
   service, not only the configuration of IP address for network
   interface, but also that of at least one recursive DNS server for DNS
   name resolution is necessary.

   This document defines the process of DNS discovery based on IPv6
   Router Advertisement (RA) to find out DNS information, such as the
   address of recursive DNS server and DNS zone suffix within the local
   network.




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3. Overview

   An IPv6 host can autoconfigure DNS information via RA message sent
   periodically by router [5]-[7].  Namely, an IPv6 host can
   autoconfigure the IPv6 address of RDNSS for DNS name resolution
   through DNS Server option included in RA message. Also, through DNS
   Zone Suffix option in RA message, the IPv6 host can acquire the DNS
   zone suffix within the local network.

4. Neighbor Discovery Extension

   The DNS discovery mechanism in this document needs two new RA options
   in Neighbor Discovery; (1) DNS Server option and (2) DNS Zone Suffix
   option that will introduce 4.1 and 4.2 sections.

4.1 DNS Server Option

   DNS Server option contains the IPv6 address of the recursive DNS
   server.  When advertising more than one DNS Server option, as many
   DNS Server options as DNS servers are included in an RA message.
   Figure 1 shows the format of DNS Server option.

    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    |  Pref |        Reserved       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Valid Lifetime                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                                                               +
    |                                                               |
    +                   IPv6 Address of DNS Server                  +
    |                                                               |
    +                                                               +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 1. DNS Server Option Format

    Fields:

      Type            8-bit identifier of the option type (TBD: IANA)

                               Option Name               Type

                               DNS Server                (TBD)



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      Length          8-bit unsigned integer.  The length of the
                      option (including the type and length fields)
                      in units of 8 octets.  The value 0 is invalid.
                      Nodes MUST silently discard an ND packet that
                      contains an option with length zero.

      Pref            The preference of a DNS server.  A 4 bit unsigned
                      integer.  A decimal value of 15 indicates the
                      highest preference.  A decimal value of 0
                      indicates that the DNS server can not be used.
                      The field can be used for load balancing of DNS
                      queries with multiple RDNSSes according to local
                      policy.

      Valid Lifetime  32-bit unsigned integer.  The maximum time, in
                      seconds, over which this DNS server is used for
                      name resolution.  Hosts should contact the source
                      of this information, router, before expiry of
                      this time interval.  A value of all one bits
                      (0xffffffff) represents infinity.

      IPv6 Address of DNS Server
                      Recursive DNS Server's address for DNS name
                      resolution.

   "Pref"=0 SHOULD require a "Valid Lifetime"=0 because the
   corresponding DNS server SHOULD not be used any more.

4.2 DNS Zone Suffix Option

   DNS Zone Suffix option contains the suffix of the DNS zone where the
   subnet is placed.  When advertising more than one DNS Zone Suffix
   option, as many DNS Zone Suffix options as DNS zones are included in
   an RA message.  Figure 2 shows the format of DNS Zone Suffix option.

    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    |  Pref |        Reserved       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Valid Lifetime                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    ~                        DNS Zone Suffix                        ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 2. DNS Zone Suffix Option Format


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    Fields:

      Type            8-bit identifier of the option type (TBD: IANA)

                               Option Name               Type

                             DNS Zone Suffix             (TBD)

      Length          8-bit unsigned integer.  The length of the
                      option in units of 8 octets.

      Pref            The preference of a DNS zone suffix.  A 4 bit
                      unsigned integer.  A decimal value of 15
                      indicates the highest preference.  A decimal
                      value of 0 indicates that the DNS zone suffix can
                      not be used.  The field can be used for arranging
                      DNS zone suffix according to local policy.

      Valid Lifetime  32-bit unsigned integer.  The maximum time, in
                      seconds, over which this DNS zone suffix is valid.
                      Hosts should contact the source of this
                      information, router, before expiry of this time
                      interval.  A value of all one bits (0xffffffff)
                      represents infinity.

      DNS Zone Suffix
                      The DNS zone suffix of the domain where the
                      subnet is placed.  This field is comprised of
                      a sequence of labels, where each label consists
                      of a length octet followed by that number of
                      octets.  The suffix terminates with the zero
                      length octet for the null label of the root.
                      This field SHOULD be padded with zeroes to be
                      the multiple of 8 octets.

5. Procedure of DNS Discovery

    IPv6 Host                         Router
         |            global              |
      (a)|(-------------RS-------------->)|
      (b)|<------RA w/ DNS options--------|
      (c)|       Processing of RA         |
      (d)|    Address Autoconfiguration   |
      (e)|(Stateful DNS Autoconfiguration)|
         |                                |

      Figure 3. Procedure of DNS Discovery


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   Figure 3 shows the procedure of DNS Discovery on the basis of IPv6 RA
   message.  The procedure consists of the following steps.

   Step (a) : IPv6 Host sends RS (Router Solicitation) message to get RA
              message.  It is optional.

   Step (b) : For the RS message received from IPv6 Host, Router sends
              RA message, which contains prefix information option for
              the stateless address autoconfiguration and MAY contain
              DNS options for DNS information, namely the address of DNS
              server and DNS zone suffix.  For DNS Zone Suffix option to
              be contained, DNS Server option SHOULD be contained ahead.

   Step (c) : If there are DNS options, IPv6 Host processes the options
              and stores them in its DNS configuration file or database.

   Step (d) : Through stateless or stateful address autoconfiguration, a
              unique global IPv6 address is autoconfigured in the
              network interface of the IPv6 Host.

   Step (e) : Unless DNS information is configured through RA message,
              the IPv6 Host MAY try to get DNS information through
              stateful mechanism, such as DHCPv6.  In order to allow
              stateful protocol used for DNS discovery, O-bit (Other
              stateful configuration flag) within RA message SHOULD be
              set.  When DNS information has been delivered through RA
              message, the DNS discovery by stateful protocol is skipped.

6. Autoconfiguration of DNS Information

   The addresses of DNS servers are announced by DNS options in RA
   message.  These addresses can be used for recursive DNS service
   providing DNS name resolution.  The newly discovered DNS information,
   the RDNSS's address and DNS zone suffix, are stored in the
   configuration file for DNS resolver; i.e., /etc/resolv.conf in UNIX.

6.1 RDNSS Configuration and Selection

   When an IPv6 host perceives multiple RDNSSes through RA message, it
   stores the RDNSS addresses in order into the configuration file which
   the resolver on the host uses for DNS name resolution on the basis of
   the value of "Pref" field in the DNS Server option.  The following
   algorithm is simply based on the rule of selecting an RDNSS in the
   order from the most preferred RDNSS, provided that its preference
   value is not zero.  The processing of the DNS Server option received
   in RA message by an IPv6 host is as follows:



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   The IPv6 host's operation is like below for each DNS Server option:

   Step (a) : Receive and parse all DNS Server options.

   Step (b) : Arrange the addresses of RDNSSes in a descending order,
              starting with the biggest value of "Pref" field of the
              DNS Server option and store them in the configuration file
              used by resolver for DNS name Resolution (DNS
              configuration).

   Step (c) : For each DNS Server option, check the following: If the
              Value of "Pref" or "Valid Lifetime" field is set to zero,
              exclude the corresponding RDNSS entry from the list of
              RDNSSes of DNS configuration in order to let the RDNSS not
              used any more.

   Whenever the resolver on the host performs the name resolution, it
   refers to the address of RDNSS in order from the first RDNSS stored
   in DNS configuration.

   In case that there are several routers advertising DNS information in
   a subnet, "Pref" field is used to arrange the information.

6.2 DNS Zone Suffix Configuration

   DNS zone suffix is delivered as DNS Zone Suffix option via RA message
   from router.  The processing of the DNS Zone Suffix option received
   in RA message by an IPv6 host is as follows:

   Step (a) : Receive and parse all DNS Zone Suffix options.

   Step (b) : Arrange the DNS zone suffix in a descending order,
              starting with the biggest value of "Pref" field of the
              DNS Zone Suffix option and store them in DNS configuration.

   Step (c) : For each DNS Zone Suffix option, check the following: If
              the value of "Pref" or "Valid Lifetime" field is set to
              zero, exclude the corresponding DNS zone suffix from the
              list of DNS zone suffixes of DNS configuration in order to
              let the DNS zone suffix not used any more.

   This DNS zone suffix MAY be used for forming IPv6 host's DNS name.

7. Applicability Statements

   RA-based DNS discovery is efficient in many kinds of wireless
   networks where IPv6 address is autoconfigured by IPv6 stateless
   address autoconfiguration, such as SOHO, home network, HMIPv6 [8],


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   NEMO and MANET connected to the Internet.  Especially, in the
   environments where DHCPv6 is difficult to adapt, RA-based DNS
   discovery is recommended.

8. Open Issues

   There might be some issues regarding RA-based DNS discovery as
   follows:

   o  How to optimize bandwidth on the link?
   o  How to implement RA-based DNS discovery?
   o  What about the use of "Pref" or "Valid Lifetime" field?
   o  How to interact with stateful mechanism?
   o  What about several routers on the same link that could advertise
      distinct parameters? (Multihoming considerations)

9. Security Considerations

   This security is essentially related to Neighbor Discovery protocol
   security [3].

   If someone wants to hijack correct RS message, they could send an RA
   message with incorrect DNS Server options and DNS Zone Suffix options
   to the originated host and they would take incorrect RA message
   through the above mechanism, which is unsafe processing.  As
   described in [3], an IPv6 host can check the validity of NDP messages.
   If the NDP message includes an IP Authentication Header, the message
   can be authenticated.  Security issues regarding the Neighbor
   Discovery protocol are being discussed in IETF SEND (Securing
   Neighbor Discovery) working group [9].

10. Copyright

   The following copyright notice is copied from RFC 2026 [Bradner,
   1996], Section 10.4, and describes the applicable copyright for this
   document.

   Copyright (C) The Internet Society July 12, 2001. All Rights
   Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other


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   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assignees.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

11. Normative References

   [1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
       9, RFC 2026, October 1996.

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

   [3] T. Narten, E. Nordmark and W. Simpson, "Neighbour Discovery for
       IP version 6", RFC 2461, December 1998.

   [4] S. Thomson and T. Narten, "IPv6 Stateless Address
       Autoconfiguration", RFC2462, December 1998.

12. Informative References

   [5] Jaehoon Paul Jeong, Byungyeob Kim, Jungsoo Park and Hyoungjun Kim,
       "IPv6 Router Advertisement based DNS Autoconfiguration", draft-
       jeong-ipv6-ra-dns-autoconf-00.txt, April 2003.

   [6] Luc Beloeil, "IPv6 Router Advertisement DNS resolver Option",
       draft-beloeil-ipv6-dns-resolver-option-01.txt, January 2003.

   [7] Soohong Daniel Park and Syam Madanapalli, "IPv6 Extensions for
       DNS Plug and Play", draft-park-ipv6-extensions-dns-pnp-00.txt,
       April 2003.

   [8] Jaehoon Paul Jeong, Jungsoo Park, Kyeongjin Lee and Hyoungjun Kim,
       "The Autoconfiguration of Recursive DNS Server and the
       Optimization of DNS Name Resolution in Hierarchical Mobile IPv6",
       draft-jeong-hmipv6-dns-optimization-01.txt, June 2003.



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   [9] J. Arkko, J. Kempf, B. Sommerfeld, B. Zill and P. Nikander,
      "SEcure Neighbor Discovery (SEND)", draft-ietf-send-ipsec-01.txt,
      June 2003.

13. Authors' Addresses

   Jaehoon Paul Jeong
   ETRI / PEC
   161 Gajong-Dong, Yusong-Gu
   Daejon 305-350
   Korea

   Phone: +82-42-860-1664
   EMail: paul@etri.re.kr

   Soohong Daniel Park
   Mobile Platform Laboratory,
   SAMSUNG Electronics
   Korea

   Phone: +82-31-200-3728
   EMail: soohong.park@samsung.com

   Luc Beloeil
   France Telecom R&D
   42, rue des coutures
   BP 6243
   14066 CAEN Cedex 4
   France

   Phone: +33-02-3175-9391
   EMail: luc.beloeil@francetelecom.com

   Syam Madanapalli
   Network Systems Division,
   SAMSUNG India Software Operations
   India

   Phone: +91-80-555-0555
   EMail: syam@samsung.com










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