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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
Intended status: Standards Track                                 S. Park
Expires: November 17, 2007                           SAMSUNG Electronics
                                                              L. Beloeil
                                                      France Telecom R&D
                                                          S. Madanapalli
                                                             SAMSUNG ISO
                                                            May 16, 2007


         IPv6 Router Advertisement Option for DNS Configuration
              draft-jeong-dnsop-ipv6-dns-discovery-12.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 November 17, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

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
     1.2.  Coexistence of RDNSS Option and DHCP Option  . . . . . . .  3
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   5.  Neighbor Discovery Extension . . . . . . . . . . . . . . . . .  5
     5.1.  Recursive DNS Server Option  . . . . . . . . . . . . . . .  5
     5.2.  Procedure of DNS Configuration . . . . . . . . . . . . . .  6
       5.2.1.  Procedure in IPv6 Host . . . . . . . . . . . . . . . .  6
   6.  Implementation Considerations  . . . . . . . . . . . . . . . .  7
     6.1.  DNS Server List Management . . . . . . . . . . . . . . . .  7
     6.2.  Synchronization between DNS Server List and Resolver
           Repository . . . . . . . . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
     10.2. Informative References . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
   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 [2][3].  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 [12]-[15].  Normally, DHCP [6]-[8]
   is used to locate such resolvers.  This document provides an
   alternate, experimental mechanism which uses a new IPv6 Router
   Advertisement (RA) option to allow IPv6 routers to advertise DNS
   recursive server addresses to IPv6 hosts.

1.1.  Applicability Statements

   The only standards-track DNS configuration mechanism in the IETF is
   DHCP, and its support in hosts and routers is necessary for reasons
   of interoperability.

   RA-based DNS configuration is a useful, optional alternative in
   networks where an IPv6 host's address is autoconfigured through IPv6
   stateless address autoconfiguration, and where the delays in
   acquiring server addresses and communicating with the servers are
   critical.  RA-based DNS configuration allows the host to acquire the
   nearest server addresses on every link.  Furthermore, it learns these
   addresses from the same RA message that provides configuration
   information for the link, thereby avoiding an additional protocol
   run.  This can be beneficial in some mobile environments, such as
   with Mobile IPv6 [10].

   The advantages and disadvantages of the RA-based approach are
   discussed in [9] along with other approaches, such as the DHCP and
   Well-known anycast addresses approaches.

1.2.  Coexistence of RDNSS Option and DHCP Option

   The RDNSS option and DHCP option can be used together [9].  To order
   the RA and DHCP approaches, the O (Other stateful configuration) flag
   can be used in the RA message [2].  If no RDNSS option is included,
   an IPv6 host may perform DNS configuration through DHCPv6 [6]-[8]
   regardless of whether the O flag is set or not.





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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 [1].


3.  Terminology

   This document uses the terminology described in [2] and [3].  In
   addition, four new terms are defined below:

   o  Recursive DNS Server (RDNSS): Server which provides a recursive
      DNS resolution service for translating domain names into IP
      addresses as defined in [4] and [5].

   o  RDNSS Option: IPv6 RA Option to deliver the RDNSS information to
      the IPv6 hosts [2].

   o  DNS Server List: Data structure for managing DNS Server
      Information existing in IPv6 protocol stack in addition to
      Neighbor Cache and Destination Cache for Neighbor Discovery [2].

   o  Resolver Repository: Configuration repository with RDNSS addresses
      which a 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 the RDNSS option along with the prefix information option
   based on the ND protocol ([2] and [3]), an IPv6 host can perform its
   network configuration of its IPv6 address and RDNSS simultaneously
   without needing a separate message exchange for the RDNSS
   information.  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



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   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.


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 lifetime value.  If it
   is desirable to have different lifetime values, multiple RDNSS
   options can be used.  Figure 1 shows the format of RDNSS 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    |           Reserved            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Lifetime                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     :            Addresses of IPv6 Recursive DNS Servers            :
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 1: Recursive DNS Server (RDNSS) Option Format

   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.




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        Lifetime      32-bit unsigned integer.  The maximum time, in
                      seconds (relative to the time the packet is sent),
                      over which this RDNSS MAY be 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 fixed
                      hosts with the stable DNS service and allow mobile
                      hosts to prefer local RDNSSes to remote RDNSSes,
                      the value of lifetime should be at least as long
                      as the Maximum RA Interval (MaxRtrAdvInterval) in
                      RFC 2461, and be at most as long as two times
                      MaxRtrAdvInterval; Lifetime SHOULD be bounded as
                      follows:
                      MaxRtrAdvInterval<=Lifetime<=2*MaxRtrAdvInterval.
                      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 [2].

5.2.1.  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 the DNS Server List and the Resolver Repository as long
      as the value of Length field is greater than or equal to the
      minimum value (0x03).  The host MAY ignore additional RDNSS
      addresses within an RDNSS option and/or additional RDNSS options
      within an RA when it has gathered a sufficient number of 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.







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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 the DNS
   Server List and the 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 List for RDNSSes in kernel space and the Resolver Repository
   in user space.  For the synchronization, the implementation where ND
   works in the kernel should provide the 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 the DNS Server List, the daemon can delete the
   corresponding entry from the Resolver Repository.

6.1.  DNS Server List Management

   The kernel or user-space process (depending on where RAs are
   processed) should maintain a data structure called DNS Server List
   which keeps the list of RDNSSes.  Each entry of DNS Server List
   consists of RDNSS address and Expiration-time as 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  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.


Note

   An RDNSS MUST be used only as long as both the RA router lifetime and



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   the RDNSS option lifetime have not expired.  The reason is that the
   RDNSS may not be currently reachable or may not provide service to
   the host's current address (e.g., due to the network ingress
   filtering [16][17]).

6.2.  Synchronization between DNS Server List 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 the DNS Server List and the
   Resolver Repository.  The processing of the RDNSS option included in
   RA message is as follows:

      Step (a): Receive and parse RDNSS option(s).  For the RDNSS
      addresses in each RDNSS option, perform Step (b) through Step (d).
      Note that Step (e) is performed whenever an entry expires in the
      DNS Server List.

      Step (b): For each RDNSS address, check the following: If the
      RDNSS address already exists in the DNS Server List and the RDNSS
      option's "Lifetime" field is set to zero, delete the corresponding
      RDNSS entry from both the DNS Server List and the Resolver
      Repository in order to let the RDNSS be not used any more for
      certain reasons in network management, e.g., the breakdown of the
      RDNSS or a renumbering situation.  The processing of this RDNSS
      address is finished here.  Otherwise, go to Step (c).

      Step (c): For each RDNSS address, if it already exists in the DNS
      Server List, then just update the value of "Expiration-time" field
      to have a new expiration time with the RDNSS option's "Lifetime"
      field and the current system time.  Otherwise, go to Step (d).

      Step (d): For each RDNSS address, if it does not exist in the DNS
      Server List, register the RDNSS address and lifetime with the DNS
      Server List and then insert the RDNSS address in front of the
      Resolver Repository.  In the case where the data structure for the
      DNS Server List is full of RDNSS entries, delete from the DNS
      Server List the entry with the smallest expiration time that will
      expire first.  The corresponding RDNSS address is also deleted
      from the Resolver Repository.  In the order in the RDNSS option,
      position the newly added RDNSS addresses in the front of the
      Resolver Repository so that the RDNSS addresses may be preferred
      according to their order in the RDNSS option for the DNS name
      resolution.  The processing of these RDNSS addresses is finished
      here.  Note that, in the case where there are several routers
      advertising RDNSS option(s) in a subnet, the RDNSSes announced
      lately are more preferred.




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      Step (e): Delete each expired entry from DNS Server List and the
      RDNSS address corresponding to the entry from the Resolver
      Repository.


7.  Security Considerations

   The security of RA option for RDNSS might be worse than ND protocol
   security [2].  However, any new vulnerability is not known yet in
   this RA option.  In this context, it can be claimed 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.  Also, an attacker could
   configure a host to send out RA with a fraudulent RDNSS address,
   which is presumably an 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 in both routers and clients
   administratively to avoid this problem.  All of this can be done
   independently of implementing ND.  Therefore, it can be claimed that
   the RA option for RDNSS has vulnerabilities similar to those existing
   in current mechanisms.

   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 [11], 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

   The IANA is requested to assign a new IPv6 Neighbor Discovery Option
   type for the RDNSS option defined in this document.

                 Option Name               Type
                 RDNSS option              (TBD)


   The IANA registry for these options is:

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



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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., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

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

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

10.2.  Informative References

   [4]   Mockapetris, P., "Domain Names - Concepts and Facilities",
         RFC 1034, November 1987.

   [5]   Mockapetris, P., "Domain Names - Implementation and
         Specification", RFC 1035, November 1987.

   [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]   Jeong, J., Ed., "IPv6 Host Configuration of DNS Server
         Information Approaches", RFC 4339, February 2006.

   [10]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
         IPv6", RFC 3775, June 2004.

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

   [12]  ANSI/IEEE Std 802.11, "Part 11: Wireless LAN Medium Access



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         Control (MAC) and Physical Layer (PHY) Specifications",
         March 1999.

   [13]  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.

   [14]  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.

   [15]  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.

   [16]  Damas, J. and F. Neves, "Preventing Use of Nameservers in
         Reflector Attacks",
         draft-ietf-dnsop-reflectors-are-evil-03.txt (Work in Progress),
         February 2007.

   [17]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
         Defeating Denial of Service Attacks which employ IP Source
         Address Spoofing", BCP 38, RFC 2827, May 2000.


Authors' Addresses

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

   Phone: +1 651 587 7774
   Fax:   +1 612 625 0572
   Email: jjeong@cs.umn.edu
   URI:   http://www.cs.umn.edu/~jjeong/













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   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
   SAMSUNG India Software Operations
   J. P. Techno Park, 3/1
   Millers Road
   Bangalore  560052
   India

   Phone: +91 80 51197777
   Email: smadanapalli@gmail.com




















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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
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Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





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