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

Network Working Group                                           J. Jeong
Internet-Draft                              ETRI/University of Minnesota
Expires: January 16, 2006                                        S. Park
                                                     SAMSUNG Electronics
                                                              L. Beloeil
                                                      France Telecom R&D
                                                          S. Madanapalli
                                                             SAMSUNG ISO
                                                           July 15, 2005


         IPv6 Router Advertisement Option for DNS Configuration
              draft-jeong-dnsop-ipv6-dns-discovery-05.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on January 16, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document specifies a new IPv6 Router Advertisement option to
   allow IPv6 routers to advertise DNS recursive server addresses to
   IPv6 hosts.



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Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Definitions  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.   Terminology  . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.   Overview . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.   Neighbor Discovery Extension . . . . . . . . . . . . . . . .   7
     5.1  Recursive DNS Server Option  . . . . . . . . . . . . . . .   7
     5.2  Procedure of DNS Configuration . . . . . . . . . . . . . .   8
   6.   Implementation Considerations  . . . . . . . . . . . . . . .   9
     6.1  DNS Server Cache Management  . . . . . . . . . . . . . . .   9
     6.2  Synchronization between DNS Server Cache and Resolver
          File . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.   Applicability Statements . . . . . . . . . . . . . . . . . .  11
   8.   Security Considerations  . . . . . . . . . . . . . . . . . .  12
   9.   IANA Considerations  . . . . . . . . . . . . . . . . . . . .  13
   10.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  14
   11.  References . . . . . . . . . . . . . . . . . . . . . . . . .  15
     11.1   Normative References . . . . . . . . . . . . . . . . . .  15
     11.2   Informative References . . . . . . . . . . . . . . . . .  15
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  15
        Intellectual Property and Copyright Statements . . . . . . .  17





























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1.  Introduction

   Neighbor Discovery (ND) for IP Version 6 and IPv6 Stateless Address
   Autoconfiguration provide ways to configure either fixed or mobile
   nodes with one or more IPv6 addresses, default routes and some other
   parameters [4][5].  To support the access to additional services in
   the Internet that are identified by a DNS name, such as a web server,
   the configuration of at least one recursive DNS server is also needed
   for DNS name resolution.

   Due to the difficulty of manually entering IPv6 addresses because of
   their length, it is important for host to be able to automatically
   configure the addresses of IPv6 recursive DNS servers.  This document
   provides a new way to do this which uses a new IPv6 Router
   Advertisement option to allow IPv6 routers to advertise DNS recursive
   server addresses to IPv6 hosts.



































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2.  Definitions

   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 [3].














































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3.  Terminology

   This document uses the terminology described in [4][5].  In addition,
   three new terms are defined below:

   o  Recursive DNS Server (RDNSS): DNS recursive server that offers the
      recursive service of DNS name resolution.

   o  DNS Server Cache: Data structure for managing DNS Server
      Information existing in IPv6 protocol stack in addition to
      Neighbor Cache and Destination Cache for Neighbor Discovery [4].

   o  Resolver File: Configuration file with RDNSS addresses which DNS
      resolver on the host uses for DNS name resolution, e.g., /etc/
      resolv.conf in UNIX.




































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4.  Overview

   This document defines a new ND option called RDNSS option that
   contains the addresses of recursive DNS servers.  Existing ND
   transport mechanisms (i.e., advertisements and solicitations) are
   used.  This works in the same way that nodes learn about routers and
   prefixes.  An IPv6 host can configure the IPv6 addresses of one or
   more RDNSSes via RA message periodically sent by router or solicited
   by a Router Solicitation (RS).

   Through ND protocol and RDNSS option along with prefix information
   option, an IPv6 host can perform its network configuration of its
   IPv6 address and RDNSS simultaneously [4][5].  The RA option for
   RDNSS can be used on any network that supports the use of ND.

   This approach requires RDNSS information to be configured in the
   routers sending the advertisements.  The configuration of RDNSS
   addresses in the routers can be done in a variety of ways, for
   example manual configuration or automatically by running a DHCPv6
   client running on the router [6]-[8].

   The new RA option is useful in some mobile environments where the
   addresses of the RDNSSes are changing because the RA option includes
   a lifetime field that allows client to use RDNSSes nearer to the
   client.  This lifetime field can be configured to a value that will
   require the client to time out the entry and switch over to another
   RDNSS address.

   The preference field of RDNSS option allows IPv6 hosts to select a
   primary RDNSS among several RDNSSes; this can be used for load
   balancing of RDNSSes.




















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5.  Neighbor Discovery Extension

   The IPv6 DNS configuration mechanism in this document needs a new ND
   option in Neighbor Discovery, Recursive DNS Server (RDNSS) option.

5.1  Recursive DNS Server Option

   RDNSS option contains one or more IPv6 addresses of recursive DNS
   servers.  All of the addresses share the same preference and lifetime
   values.  If it is desirable to have different preference and lifetime
   values, multiple RDNSS options can be used.



      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                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     :            Addresses of IPv6 Recursive DNS Servers            :
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


           Figure 1: Recursive DNS Server (RDNSS) Option Format


   Figure 1 shows the format of RDNSS option.

   Fields:

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

        Length        8-bit unsigned integer.  The length of the
                      option (including the type and length fields)
                      in units of 8 octets.  The minimum value is 0x03
                      if one IPv6 address is contained in the option.
                      Additional addresses add 0x02 to the length.  The
                      length field is used by the receiver to determine
                      the number of IPv6 addresses in the option.






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        Pref          The preference of an RDNSS.  A 4-bit unsigned
                      integer.  A decimal value of 15 indicates the
                      highest preference.  A value of zero means
                      unspecified.  The field MAY 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 (relative to the time the packet is sent),
                      over which this RDNSS is used for name
                      resolution.  Hosts SHOULD contact the source
                      of this information, router, before this time
                      interval expires.  A value of all one bits
                      (0xffffffff) represents infinity.  A value of
                      zero means that the RDNSS MUST no longer be used.

        Addresses of IPv6 Recursive DNS Servers
                      One or more 128-bit IPv6 addresses of the
                      recursive DNS servers.  The number of addresses
                      is determined by the Length field.  That is,
                      the number of addresses is equal to
                      (Length - 1) / 2.


5.2  Procedure of DNS Configuration

   The procedure of DNS configuration through RDNSS option is the same
   as any other ND option [4].























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6.  Implementation Considerations

   For the configuration and management of RDNSS information, the
   advertised RDNSS addresses can be stored and managed in both DNS
   Server Cache and Resolver File.

   In environments where the RDNSS information is stored in user space
   and ND runs in the kernel, it is necessary to synchronize the DNS
   Server Cache for RDNSSes in kernel space and Resolver File for the
   RDNSS information in user space.  For the synchronization, the
   current ND framework should be modified because it is unacceptable to
   write and rewrite the Resolver file (e.g., resolv.conf) from the
   kernel.  One simple approach to solve this is to have a daemon around
   (or a program that is called at the defined intervals) that keeps
   monitoring the lifetime of RDNSSes all the time.  However, such a
   daemon is not necessary with the current ND framework.

6.1  DNS Server Cache Management

   The DNS configuration needs a new DNS Server Cache in IPv6 protocol
   stack in addition to Neighbor Cache and Destination Cache for
   Neighbor Discovery [4].  Each entry of DNS Server Cache consists of
   RDNSS address, Preference, Expire-time, and Onsite-flag as follows:

   o  RDNSS address: Recursive DNS Server's IPv6 address in the site.

   o  Preference: Preference field in RDNSS option used for an IPv6 host
      to decide which RDNSS it will use as a primary RDNSS among the
      announced RDNSSes.  This field can be used for load balancing of
      DNS queries with multiple RDNSSes within an autonomous site.

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

   o  Onsite-flag: Flag for checking this entry's validity.  That is,
      Onsite-flag is set on while Expire-time is greater than the
      current system time; in other words, while this entry is valid.
      When Expire-time becomes less than the current system time, this
      flag is set off.  When Expire-time becomes greater than the
      current system time again through the receipt of another RDNSS
      option, the flag is set on again.  The entry of which Onsite-flag
      is off is not deleted immediately, but MAY be used for DNS
      resolution in the site where the IPv6 host is a mobile node and no
      RDNSS is provided.  Therefore, the IPv6 host MAY use the RDNSS of
      the previous site even though the RDNSS is in the remote network.



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      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 [4].  For example, when the replacement
      is necessary, the 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 RDNSS option(s), it stores the
   RDNSS addresses in order into both DNS Server Cache and Resolver
   File.  The processing of the RDNSS option included in RA message is
   as follows:

      Step (a): Receive and parse RDNSS option(s).

      Step (b): Arrange the addresses of RDNSSes in a descending order,
      starting with the biggest value of "Pref" field of the RDNSS
      option and store them in both DNS Server Cache and Resolver File.
      In the case where there are several routers advertising RDNSS
      option(s) in a subnet, "Pref" field is used to arrange the
      information.

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

      Step (d): Delete each entry of which Onsite-flag is set off from
      DNS Server Cache and the RDNSS address corresponding to the entry
      from Resolver File.  However, in mobile environment, in order that
      a mobile node can still use the RDNSS of the previous site when
      the node moves into another site and no RDNSS is available there,
      it MAY be allowed to maintain the entry of which Onsite-flag is
      off in both DNS Server Cache and Resolver File.  In this case,
      invalid entries can be deleted according to LRU-based policy.

   As a last resort of DNS name resolution, an IPv6 host can use the
   RDNSSes manually configured by its user in its Resolver File either
   when it cannot get the information of RDNSSes from local network or
   when there is no valid RDNSS address in DNS Server Cache.




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7.  Applicability Statements

   RA-based DNS configuration is useful in the networks where IPv6
   address is autoconfigured through IPv6 stateless address
   autoconfiguration, such as SOHO, home networks, celluar networks
   (e.g., 3GPP), MIPv6 (especially, HMIPv6), NEMO and MANET connected to
   the Internet.  Especially, the RA approach is useful in some mobile
   environments where the addresses of the RDNSSes are changing because
   the RA option includes a lifetime field that allows client to use
   RDNSSes nearer to the client.  This can be configured to a value that
   will require the client to time out the entry and switch over to
   another RDNSS in current local network.







































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8.  Security Considerations

   The security of RA option for RDNSS is the same as ND protocol
   security [4].  The RA option does not add any new vulnerability.

   It should be noted that the vulnerability of ND is not worse and is a
   subset of the attacks that any node attached to a LAN can do
   independently of ND.  A malicious node on a LAN can promiscuously
   receive packets for any router's MAC address and send packets with
   the router's MAC address as the source MAC address in the L2 header.
   As a result, the L2 switches send packets addressed to the router to
   the malicious node.  Also, this attack can send redirects that tell
   the hosts to send their traffic somewhere else.  The malicious node
   can send unsolicited RA or NA replies, answer RS or NS requests, etc.
   All of this can be done independently of implementing ND.  Therefore,
   the RA option for RDNSS does not add to the vulnerability.

   For the security mechanisms for ND, Secure Neighbor Discovery (SEND)
   protocol can be used [9].  SEND is also applicable in environments
   where physical security on the link is not assured (such as over
   wireless) and attacks on ND protocol are a concern.






























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9.  IANA Considerations

   The IANA should assign a new IPv6 Neighbor Discovery Option type for
   the RDNSS option defined in this document.  The IANA registry for
   these options is:

   http://www.iana.org/assignments/icmpv6-parameters












































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10.  Acknowledgements

   This draft has greatly benefited from inputs by Robert Hinden, Pekka
   Savola, and Tim Chown.  The authors appreciate their contribution.















































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11.  References

11.1  Normative References

   [1]  Bradner, S., "IETF Rights in Contributions", RFC 3978,
        March 2005.

   [2]  Bradner, S., "Intellectual Property Rights in IETF Technology",
        RFC 3668, February 2004.

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

   [4]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
        for IP Version 6 (IPv6)", RFC 2461, December 1998.

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

11.2  Informative References

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

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

   [8]  Droms, R., Ed., "DNS Configuration options for Dynamic Host
        Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
        December 2003.

   [9]  Arkko, J., Ed., "SEcure Neighbor Discovery (SEND)", RFC 3971,
        March 2005.


















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Authors' Addresses

   Jaehoon Paul Jeong
   ETRI/Department of Computer Science and Engineering
   University of Minnesota
   117 Pleasant Street SE
   Minneapolis, MN  55455
   US

   Phone: +1 651 587 7774
   Fax:   +1 612 625 2002
   Email: jjeong@cs.umn.edu
   URI:   http://www.cs.umn.edu/~jjeong/


   Soohong Daniel Park
   Mobile Platform Laboratory
   SAMSUNG Electronics
   416 Maetan-3dong, Yeongtong-Gu
   Suwon, Gyeonggi-Do  443-742
   Korea

   Phone: +82 31 200 4508
   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
   AMSUNG India Software Operations
   J. P. Techno Park, 3/1
   Millers Road
   Bangalore  560052
   India

   Phone: +91 80 51197777
   Email: syam@samsung.com





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Copyright Statement

   Copyright (C) The Internet Society (2005).  This document is subject
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Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.




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