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

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-01.txt
Expires: August 2004                                   13 February 2004


             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 the address of recursive DNS server for DNS name
   resolution.  The way of discovering recursive DNS server is based on
   Router Advertisement message.

Conventions used in this document






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   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].

Table of Contents

   1. Terminology.....................................................2
   2. Introduction....................................................2
   3. Overview........................................................3
   4. Neighbor Discovery Extension....................................3
      4.1 DNS Server Option...........................................3
   5. Procedure of DNS Discovery......................................4
   6. Autoconfiguration of DNS Information............................5
      6.1 DNS Server Cache Management.................................5
      6.2 Synchronization between DNS Server Cache and Resolver File..6
      6.3 DNS Resolution..............................................7
   7. Applicability Statements........................................7
   8. Open Issues.....................................................7
   9. Security Considerations.........................................8
   10. Changes from Previous Version of the Draft.....................8
   11. Copyright......................................................8
   12. Normative References...........................................9
   13. Informative References.........................................9
   14. Authors' Addresses............................................10

1. Terminology

   This memo uses the terminology described in [3][4].  In addition,
   three new terms are defined below:

   Recursive DNS Server (RDNSS)

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

   DNS Server Cache

      DNS Server Cache is a data structure for managing DNS Server
      Information existing in IPv6 protocol stack in addition to
      Neighbor Cache and Destination Cache for Neighbor Discovery [3].

   Resolver File

      Resolver File is a configuration file which DNS resolver on the
      host uses for DNS name resolution, e.g., /etc/resolv.conf in UNIX.

2. Introduction



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   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 the address of recursive DNS
   server within the local network.

3. Overview

   An IPv6 host can autoconfigure DNS information via RA message sent
   periodically by router.  Namely, an IPv6 host can autoconfigure the
   IPv6 address of RDNSS for DNS name resolution through DNS Server
   option included in RA message.

4. Neighbor Discovery Extension

   The DNS discovery mechanism in this document needs a new RA option in
   Neighbor Discovery, DNS Server option.

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, an RA
   message includes as many DNS Server options as DNS servers.  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       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           Lifetime                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                                                               +
    |                                                               |
    +                   IPv6 Address of DNS Server                  +
    |                                                               |
    +                                                               +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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        Figure 1. DNS Server Option Format

    Fields:

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

                               Option Name               Type

                               DNS Server                (TBD)

      Length          8-bit unsigned integer.  The length of the
                      option (including the type and length fields)
                      in units of 8 octets SHOULD be 0x03 (3 x 8 = 24
                      octets).

      Pref            The preference of a DNS server.  A 4 bit unsigned
                      integer.  A decimal value of 15 indicates the
                      highest preference.  A value of zero means
                      unspecified.  The field can be used for load
                      balancing of DNS queries with multiple RDNSSes
                      according to local policy.

      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.  A value of
                      zero means that the DNS server must not be used
                      any more.

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

5. Procedure of DNS Discovery

     IPv6 Host                                                 Router
         |                                                       |
      (a)|(-------------------------RS------------------------->)|
      (b)|<------------------RA w/ DNS option(s)-----------------|
      (c)|                    Processing of RA                   |
      (d)|          Stateless Address Autoconfiguration          |
      (e)|             Stateless DNS Autoconfiguration           |
      (f)|       (Stateful Address or DNS Autoconfiguration)     |

      Figure 2. Procedure of DNS Discovery



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   Figure 2 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
              stateless address autoconfiguration and DNS Server options
              for DNS server's addresses.

   Step (c) : If there are not any Prefix Information option and DNS
              Server option in RA message, IPv6 Host goes to Step (f).

   Step (d) : If there is Prefix Information option in RA message, IPv6
              Host performs stateless address autoconfiguration based on
              the prefix included in the option.  If the auto-
              configuration fails, IPv6 Host goes to Step (f).

   Step (e) : If there is DNS Server option in RA message, IPv6 Host
              stores the DNS server's address in its DNS Server Cache
              and resolver configuration file.

   Step (f) : If M (Managed address configuration) flag is set on, IPv6
              Host MUST perform stateful address autoconfiguration
              Through DHCPv6 [3-5].  If O (Other stateful configuration)
              flag is set on, IPv6 Host MAY perform stateful DNS auto-
              configuration through DHCPv6, too [3-5].

6. Autoconfiguration of DNS Information

   The addresses of DNS servers are announced by DNS Server options in
   RA message.  These addresses can be used for recursive DNS service
   providing DNS name resolution.  The newly discovered DNS information,
   i.e., RDNSS's address, is stored and managed in both DNS Server Cache
   and Resolver File.

6.1 DNS Server Cache Management

   DNS Discovery in this document needs a new DNS Server Cache in IPv6
   protocol stack in addition to Neighbor Cache and Destination Cache
   for Neighbor Discovery [3].  Each entry of DNS Server Cache consists
   of DNS Server's IPv6 address, Preference, Expire-time, and Onsite-
   flag as follows:

   - DNS Server's IPv6 address:
     DNS Server's IPv6 address indicates the recursive DNS server in
     the site.


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   - Preference:
     Preference, delivered in DNS Server option, is used to give the
     usage preference to the announced DNS servers; e.g., the value of
     two of preference field may indicate a primary DNS server and that
     of one a secondary one.  Like this, this field can be
     used for load balancing of DNS queries with multiple RDNSSes
     within a autonomous site.

   - Expire-time:
     Lifetime, delivered in DNS Server option, is used to give the time
     when this entry becomes invalid.  Expire-time is set to the value
     of Lifetime field of DNS Server option plus the current system
     time.  Whenever a new DNS Server option with the same address is
     received, it is updated.

   - Onsite-flag:
     Onsite-flag is set on while Expire-time is less than the current
     system time, namely this entry is valid.  When Expire-time becomes
     greater than the current system time, this flag is set to off.
     When Expire-time becomes less than the current system time again
     through a receipt of another DNS Server option, the flag is set on.
     The entry of which Onsite-flag is off is not deleted immediately,
     but used for DNS resolution in the site where IPv6 host is mobile
     node and recursive DNS server is not provided.  In such a site,
     IPv6 host MAY use the DNS server of the previous site.  To limit
     the storage needed for the DNS Server Cache, a node may need to
     garbage-collect old entries.  However, care must be taken to
     insure that sufficient space is always present to hold the working
     set of active entries.  Any LRU-based policy that only reclaims
     entries that have expired should be adequate for garbage-
     collecting unused entries [3].  For example, when the replacement
     is necessary, IPv6 host can choose one of which Onsite-flag is off
     and of which Expire-time is the least.

6.2 Synchronization between DNS Server Cache and Resolver File

   When an IPv6 host receives the information of multiple RDNSSes within
   a site through an RA message with DNS Server options, it stores the
   RDNSS addresses in order into both DNS Server Cache and Resolver File.
   The processing of the DNS Server option included in RA message is as
   follows:

   Step (a) : Receive and parse 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 both DNS Server Cache


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              and Resolver File. In the case where there are several
              routers advertising DNS Server option(s) in a subnet,
              "Pref" field is used to arrange the information.

   Step (c) : For each DNS Server option, check the following: If the
              value of "Pref" and "Lifetime" fields is set to zero,
              delete the corresponding RDNSS entry from both DNS Server
              Cache and Resolver File in order to let the RDNSS not used
              any more for certain reason in network management, e.g.,
              the breakdown of the DNS server and a renumbering
              situation.

   Step (d) : Delete each entry of which Onsite-flag is set off from DNS
              Server Cache and the address of DNS server corresponding
              to the entry from Resolver File.  In mobile environments,
              in order that a mobile node still uses a DNS server of the
              previous site when the node moves into another site and no
              DNS server is available there, it MAY be allowed to
              maintain the entry of which Onsite-flag is off, not to
              delete it from both DNS Server Cache and Resolver File.

   The actual synchronization between the above two storages is
   performed through a DNS API dependent on operating system.  Whenever
   DNS resolver should resolve a DNS name which is not cached in its
   local DNS cache, it can use DNS servers listed in Resolver File,
   which is synchronized with DNS Server Cache.

6.3 DNS Resolution

   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 Resolver File.

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, MIPv6
   (especially, HMIPv6), NEMO and MANET connected to the Internet.

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?


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   o  What about the use of "Pref" or "Lifetime" field?

   o  What about several routers on the same link advertising
      distinct parameters, such as Prefix Information options and DNS
      Server options? (Multihoming considerations)

   o  What about advertising DHCPv6 Server's address through RA message
      as indirect DNS discovery?  DHCP-lite or Stateless DHCP can be
      considered together [6].

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 to the 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 [7].

10. Changes from Previous Version of the Draft

   This section briefly lists some of the major changes in this
   draft relative to the previous version of this same draft,
   draft-jeong-dnsop-ipv6-dns-discovery-00.txt:

   - excluded DNS Zone Suffix Option.

   - introduced DNS Server Cache in order to store the list of DNS
     Server addresses in part of IPv6 Neighbor Discovery.

   - clarified the use of M and O flag in RA message to explain the
     cooperation between Stateless and Stateful Autoconfigurations.

11. 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.




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   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
   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.

12. 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, "Neighbor Discovery for IP
       version 6 (IPv6)", RFC 2461, December 1998.

   [4] S. Thomson and T. Narten, "IPv6 Stateless Address
       Autoconfiguration", RFC 2462, December 1998.

13. Informative References

   [5] R. Droms et al., "Dynamic Host Configuration Protocol for IPv6
       (DHCPv6)", RFC 3315, July 2003.

   [6] R. Droms, "Stateless DHCP Service for IPv6", draft-ietf-dhc-
       dhcpv6-stateless-04.txt, January 2004.

   [7] J. Arkko et al., "SEcure Neighbor Discovery (SEND)", draft-ietf-
       send-ndopt-03.txt, January 2004.


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14. 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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