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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, Ed.
Internet-Draft                              ETRI/University of Minnesota
Expires: April 25, 2006                                          S. Park
                                                     SAMSUNG Electronics
                                                              L. Beloeil
                                                      France Telecom R&D
                                                          S. Madanapalli
                                                             SAMSUNG ISO
                                                        October 22, 2005


         IPv6 Router Advertisement Option for DNS Configuration
              draft-jeong-dnsop-ipv6-dns-discovery-06.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
   Task Force (IETF), its areas, and its working groups.  Note that
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   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 25, 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
     1.1   Applicability Statements . . . . . . . . . . . . . . . . .  3
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   4.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   5.  Neighbor Discovery Extension . . . . . . . . . . . . . . . . .  4
     5.1   Recursive DNS Server Option  . . . . . . . . . . . . . . .  5
     5.2   Procedure of DNS Configuration . . . . . . . . . . . . . .  6
       5.2.1   Procedure in IPv6 Router . . . . . . . . . . . . . . .  6
       5.2.2   Procedure in IPv6 Host . . . . . . . . . . . . . . . .  7
   6.  Implementation Considerations  . . . . . . . . . . . . . . . .  7
     6.1   DNS Server Cache Management  . . . . . . . . . . . . . . .  7
     6.2   Synchronization between DNS Server Cache and Resolver
           Repository . . . . . . . . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   10.   References . . . . . . . . . . . . . . . . . . . . . . . . . 10
     10.1  Normative References . . . . . . . . . . . . . . . . . . . 10
     10.2  Informative References . . . . . . . . . . . . . . . . . . 11
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 12
       Intellectual Property and Copyright Statements . . . . . . . . 13



























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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.

   It is infeasible for nomadic hosts, such as laptops, to have to enter
   a DNS resolver each time they connect to a different wireless LAN
   (WLAN) such as IEEE 802.11 a/b/g [10]-[13].  This document provides a
   new way which uses a new IPv6 Router Advertisement option to allow
   IPv6 routers to advertise DNS recursive server addresses to IPv6
   hosts.

1.1  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, cellular networks
   (e.g., 3GPP), MIPv6 (especially, HMIPv6), NEMO and MANET connected to
   the Internet.  Especially, the new RA option may be useful in some
   mobile environments where the addresses of the RDNSSes are added or
   deleted according to a mobile node's movement because the RA option
   includes a lifetime field that allows the mobile node to delete the
   expired entries for RDNSSes.  This lifetime field can be configured
   to a value that will require the mobile node to time out the RDNSS
   address entry in the previous network and to switch over to another
   RDNSS address in the same network.  Therefore, the lifetime field can
   allow the mobile node to use the RDNSSes announced in the network
   where it is placed.  As a result, the local RDNSS may provide the
   mobile node with quicker recursive DNS resolution service than the
   remote RDNSSes.  Using the lifetime field differentiate RA approach
   from DHCPv6 approach in that it allows mobile nodes to use local
   RDNSSes rather than remote RDNSSes in order to being able to reduce
   the DNS resolution delay [6]-[8].

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].

3.  Terminology

   This document uses the terminology described in [4][5].  In addition,



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   three new terms are defined below:

   o  Recursive DNS Server (RDNSS): Server which provides a recursive
      DNS resolution service.

   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 Repository: Configuration repository with RDNSS addresses
      which DNS resolver on the host uses for DNS name resolution, such
      as Unix resolver file (i.e., /etc/resolv.conf) and Windows
      registry.

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 hosts 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 by manual configuration.  The
   automatic configuration or redistribution of RDNSS information is
   possible by running a DHCPv6 client running on the router [6]-[8].
   The automatic configuration of RDNSS addresses in the routers is out
   of scope in this document.

   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.

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.






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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 |S|      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.
                      Every additional RDNSS address increases the
                      length by 0x02.  The length field is used by
                      the receiver to determine the number of IPv6
                      addresses in the option.  The maximum number of
                      RDNSSes advertised in one option is three.  The
                      recipient MUST NOT process more than the first
                      three RDNSS addresses.

        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



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                      unspecified.  The default value of preference
                      may be from 8 to 11 for manually configured or
                      RA-derived RDNSSes.  A preference less than 8
                      means less preferred than manual configured
                      RDNSS and a preference greater than 11 means
                      more preferred.

        S             1-bit "Service open" flag.  When set, it indicates
                      that RDNSS(es) in the option can be available for
                      IPv6 hosts, which are located in the different
                      network with RDNSS(es).  This flag SHOULD be set
                      only if the routers or firewalls in the network
                      allow DNS Query messages to be routed to the
                      destination RDNSS without being filtered out.

        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 MAY send a Router Solicitation
                      to ensure the RDNSS information is fresh before
                      the interval expires.  In order to provide stable
                      DNS service, the default value of lifetime SHOULD
                      be 30 seconds or greater.  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].

5.2.1  Procedure in IPv6 Router

   An IPv6 router SHOULD include RDNSS option(s) in every solicited RA.
   For unsolicited RA, when the router participates in routing by
   forwarding data packets, RDNSS option SHOULD be sent along with
   Prefix Information option.  Otherwise, RDNSS option SHOULD be able to
   be sent without Prefix Information option.

   Since one RDNSS option is allowed to have at most three RDNSSes, the



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   router SHOULD send more than one RDNSS option if it would like to
   advertise more than three RDNSSes.

5.2.2  Procedure in IPv6 Host

   When an IPv6 host receives RDNSS option through RA, it checks whether
   the option is valid;

   o  If the RDNSS option is present, the host SHOULD copy the option's
      value into DNS Server Cache and Resolver Repository as long as the
      value of Length field is greater than or equal to the minimum
      value (0x03).  The recipient MUST process the first three RDNSS
      addresses in the case where the RDNSS option has more than three
      RDNSSes.

   o  If the RDNSS option is present but invalid (e.g., it has the
      length less than 0x03), the host SHOULD discard the option.

6.  Implementation Considerations

Note

   This non-normative section gives some hints for implementing the
   processing of RDNSS option in IPv6 host.


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

   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 Repository in
   user space.  For the synchronization, the implementation where ND
   works in the kernel should provide write operation for updating RDNSS
   information from the kernel to the Resolver Repository.  One simple
   approach to perform 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.  Whenever there is an expired entry
   in DNS Server Cache, the daemon can delete the corresponding entry
   from Resolver Repository.

6.1  DNS Server Cache Management

   The DNS configuration needs a new DNS Server Cache in the 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



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   follows:

   o  RDNSS address: IPv6 address of Recursive DNS Server which is
      available for recursive DNS resolution service in the network
      advertising the RDNSS option; such a network is called site in
      this document.

   o  Preference: Preference field in RDNSS option allowing IPv6 hosts
      to select a primary RDNSS among several RDNSSes; the other RDNSSes
      except for the primary one can be used as backup.

   o  Expiration-time: Expiration time field giving the time when this
      entry becomes invalid.  Expiration-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.  When
      Expiration-time becomes less than the current system time, this
      entry is regared as expired.  The decision about whether to delete
      the expired entry depends on its Service-open-flag (See the
      explanation for Service-open-flag).

   o  Service-open-flag: Flag for deciding whether to delete the expired
      entry.  It is set to the value of "Service open" flag of RDNSS
      option.  When the entry has expired and Service-open-flag is 0,
      the expired entry is deleted from DNS Server Cache.  Otherwise,
      the entry is maintained.  That is, Service-open-flag set to 1
      allows expired entry to be maintained.  It may be useful when an
      IPv6 host is nomadic or mobile node.  Service-open-flag allows an
      IPv6 host to continue to use expired RDNSSes located in other
      networks which it moved from.  When there is no available RDNSS in
      the new network (or subnet), the IPv6 host can still use the
      remote RDNSSes which it used for DNS name resolution before.  A
      host MAY delete expired entries in order to limit the storage
      needed for the DNS Server Cache.  Any least recently used (LRU)
      policy that reclaims entries that have expired with Service-open-
      flag set to 0 can be adopted for replacing the expired entries
      with the entries for newly announced RDNSSes [4].  For example,
      when the replacement is necessary, the IPv6 host can choose one of
      which Service-open-flag is turned off and of which Expiration-time
      is the least.

6.2  Synchronization between DNS Server Cache and Resolver Repository

   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
   Repository.  The processing of the RDNSS option included in RA
   message is as follows:



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      Step (a): Receive and parse RDNSS option(s).  Process only the
      first three RDNSS addresses in each RDNSS option if one RDNSS
      option has more than three RDNSS addresses.

      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
      Repository by sorting the entries, including newly added entries,
      in the descending order of preference value.  In the case where
      there are several routers advertising RDNSS option(s) in a subnet,
      "Pref" field is used to arrange the information.  When the
      preference is the same, the RDNSS announced earlier is more
      preferred.  Also, when one RDNSS option has multiple RDNSSes with
      the same preference, keep the order or the addresses in the
      option, so the first is preferred.

      Step (c): For each RDNSS option, check the following: If each
      value of "Lifetime" field is set to zero, regardless of the value
      of 'S' flag, delete the corresponding RDNSS entries from both DNS
      Server Cache and Resolver Repository in order to let the RDNSSes
      be not used any more for certain reasons 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 Repository.  However, in mobile environment, in
      order that a mobile node can still use the RDNSS of the previous
      site when the host 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
      Repository.  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 Repository
   either when it cannot get the information of RDNSSes from local
   network or when there is no valid RDNSS address in DNS Server Cache.

7.  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.



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   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.
   Also, an attacker could configure a host to send out RA with a
   fraudulent RDNSS address, which is presumably and easier avenue of
   attack than becoming a rogue router and having to process all traffic
   for the subnet.  It is necessary to disable the RA RDNSS option
   administatively to avoid this problem.  All of this can be done
   independently of implementing ND.  Therefore, the RA option for RDNSS
   does not add to the vulnerability.

   If Secure Neighbor Discovery (SEND) protocol is used as the security
   mechanism for ND, all the ND options including RDNSS option are also
   automatically included in the signatures [9], so the RDNSS transport
   is integrity-protected.  However, since any valid SEND node can still
   insert RDNSS options, SEND cannot verify who is or is not authorized
   to send the options.

8.  IANA Considerations

Note

   This section will be removed after the assignment of RDNSS option
   type.


   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

9.  Acknowledgements

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

10.  References

10.1  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.



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   [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.

10.2  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.

   [10]  ANSI/IEEE Std 802.11, "Part 11: Wireless LAN Medium Access
         Control (MAC) and Physical Layer (PHY) Specifications",
         March 1999.

   [11]  IEEE Std 802.11a, "Part 11: Wireless LAN Medium Access Control
         (MAC) and Physical Layer (PHY) specifications: High-speed
         Physical Layer in the 5 GHZ Band", September 1999.

   [12]  IEEE Std 802.11b, "Part 11: Wireless LAN Medium Access Control
         (MAC) and Physical Layer (PHY) specifications: Higher-Speed
         Physical Layer Extension in the 2.4 GHz Band", September 1999.

   [13]  IEEE P802.11g/D8.2, "Part 11: Wireless LAN Medium Access
         Control (MAC) and Physical Layer (PHY) specifications: Further
         Higher Data Rate Extension in the 2.4 GHz Band", April 2003.












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Authors' Addresses

   Jaehoon Paul Jeong (editor)
   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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Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
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   Copies of IPR disclosures made to the IETF Secretariat and any
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   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Disclaimer of Validity

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
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   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Copyright Statement

   Copyright (C) The Internet Society (2005).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


Acknowledgment

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




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