Network Working Group                                           J. Jeong
Internet-Draft                                              Brocade/ETRI
Obsoletes: 5006 (if approved)                                    S. Park
Intended status: Standards Track                     SAMSUNG Electronics
Expires: December 11, 2010                                    L. Beloeil
                                                      France Telecom R&D
                                                          S. Madanapalli
                                                      Ordyn Technologies
                                                            June 9, 2010


  IPv6 Router Advertisement Options for DNS Configuration RFC 5006-bis
                   draft-ietf-6man-dns-options-bis-03

Abstract

   This document specifies IPv6 Router Advertisement options to allow
   IPv6 routers to advertise a list of DNS recursive server addresses
   and a DNS search list to IPv6 hosts.

Status of This Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   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.

   This Internet-Draft will expire on December 11, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Applicability Statements . . . . . . . . . . . . . . . . .  3
     1.2.  Coexistence of RA Options and DHCP Options for DNS
           Configuration  . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Neighbor Discovery Extension . . . . . . . . . . . . . . . . .  5
     5.1.  Recursive DNS Server Option  . . . . . . . . . . . . . . .  5
     5.2.  DNS Search List Option . . . . . . . . . . . . . . . . . .  7
     5.3.  Procedure of DNS Configuration . . . . . . . . . . . . . .  8
       5.3.1.  Procedure in IPv6 Host . . . . . . . . . . . . . . . .  8
   6.  Implementation Considerations  . . . . . . . . . . . . . . . .  9
     6.1.  DNS Repository Management  . . . . . . . . . . . . . . . .  9
     6.2.  Synchronization between DNS Server List and Resolver
           Repository . . . . . . . . . . . . . . . . . . . . . . . . 10
     6.3.  Synchronization between DNS Search List and Resolver
           Repository . . . . . . . . . . . . . . . . . . . . . . . . 11
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 13
     10.2. Informative References . . . . . . . . . . . . . . . . . . 14
   Appendix A.  Changes from RFC 5006 . . . . . . . . . . . . . . . . 15














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1.  Introduction

   The purpose of this document is to standardize IPv6 Router
   Advertisement (RA) option for DNS configuration in IPv6 hosts
   specified in an earlier experimental specification [RFC5006] and also
   to define a new RA option for Domain Name Search lists.

   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 routers and some other
   parameters [RFC4861][RFC4862].  Most Internet services are identified
   by using a DNS name.  The two RA options defined in this document
   provide the DNS information needed for an IPv6 host to reach Internet
   services.

   It is infeasible to manually configure nomadic hosts each time they
   connect to a different network.  While a one-time static
   configuration is possible, it is generally not desirable on general-
   purpose hosts such as laptops.  For instance, locally defined name
   spaces would not be available to the host if it were to run its own
   name server software directly connected to the global DNS.

   The DNS information can also be provided through DHCP
   [RFC3315][RFC3736][RFC3646].  However, the access to DNS is a
   fundamental requirement for almost all hosts, so IPv6 stateless
   autoconfiguration cannot stand on its own as an alternative
   deployment model in any practical network without any support for DNS
   configuration.

   These issues are not pressing in dual stack networks as long as a DNS
   server is available on the IPv4 side, but become more critical with
   the deployment of IPv6-only networks.  As a result, this document
   defines a mechanism based on IPv6 RA options to allow IPv6 hosts to
   perform the automatic DNS configuration.

1.1.  Applicability Statements

   RA-based DNS configuration is a useful alternative in networks where
   an IPv6 host's address is autoconfigured through IPv6 stateless
   address autoconfiguration, and where there is either no DHCPv6
   infrastructure at all or some hosts do not have a DHCPv6 client.  The
   intention is to enable the full configuration of basic networking
   information for hosts without requiring DHCPv6.  However, when in
   many networks some additional information needs to be distributed,
   those networks are likely to employ DHCPv6.  In these networks RA-
   based DNS configuration may not be needed.

   RA-based DNS configuration allows an IPv6 host to acquire the DNS



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   configuration (i.e., DNS recursive server addresses and DNS search
   list) for the link(s) to which the host is connected.  Furthermore,
   the host learns this DNS configuration from the same RA message that
   provides configuration information for the link, thereby avoiding
   also running DHCPv6.

   The advantages and disadvantages of the RA-based approach are
   discussed in [RFC4339] along with other approaches, such as the DHCP
   and well-known anycast addresses approaches.

1.2.  Coexistence of RA Options and DHCP Options for DNS Configuration

   Two protocols exist to configure the DNS information on a host, the
   Router Advertisement options described in this document and the
   DHCPv6 options described in [RFC3646].  They can be used together.
   The rules governing the decision to use stateful configuration
   mechanisms are specified in [RFC4861].  Hosts conforming to this
   specification MUST extract DNS information from Router Advertisement
   messages, unless static DNS configuration has been specified by the
   user.  If there is DNS information available from multiple Router
   Advertisements and/or from DHCP, the host MUST maintain an ordered
   list of this information as specified in Section 5.3.1.

2.  Requirements Language

   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 [RFC2119].

3.  Terminology

   This document uses the terminology described in [RFC4861] and
   [RFC4862].  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 [RFC1034] and [RFC1035].

   o  RDNSS Option: IPv6 RA option to deliver the RDNSS information to
      IPv6 hosts [RFC4861].

   o  DNS Search List (DNSSL): The list of DNS suffix domain names used
      by IPv6 hosts when they perform DNS query searches for short,
      unqualified domain names.

   o  DNSSL Option: IPv6 RA option to deliver the DNSSL information to
      IPv6 hosts.




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   o  DNS Repository: Two data structures for managing DNS Configuration
      Information in the IPv6 protocol stack in addition to Neighbor
      Cache and Destination Cache for Neighbor Discovery [RFC4861].  The
      first data structure is the DNS Server List for RDNSS addresses
      and the second is the DNS Search List for DNS search domain names.

   o  Resolver Repository: Configuration repository with RDNSS addresses
      and a DNS search list that a DNS resolver on the host uses for DNS
      name resolution; for example, the Unix resolver file (i.e., /etc/
      resolv.conf) and Windows registry.

4.  Overview

   This document standardizes the ND option called RDNSS option defined
   in [RFC5006] that contains the addresses of recursive DNS servers.
   This document also defines a new ND option called DNSSL option for
   Domain Search List.  This is to maintain parity with the DHCPv6
   options and to ensure that there is necessary functionality to
   determine the search domains.

   Existing ND message (i.e., Router Advertisement) is used to carry
   this information.  An IPv6 host can configure the IPv6 addresses of
   one or more RDNSSes via RA messages.  Through the RDNSS and DNSSL
   options, along with the prefix information option based on the ND
   protocol ([RFC4861] and [RFC4862]), an IPv6 host can perform the
   network configuration of its IPv6 address and the DNS information
   simultaneously without needing DHCPv6 for the DNS configuration.  The
   RA options for RDNSS and DNSSL can be used on any network that
   supports the use of ND.

   This approach requires the manual configuration or other automatic
   mechanisms (e.g., DHCPv6 or vendor proprietary configuration
   mechanisms) to configure the DNS information in routers sending the
   advertisements.  The automatic configuration of RDNSS addresses and a
   DNS search list in routers is out of scope for this document.

5.  Neighbor Discovery Extension

   The IPv6 DNS configuration mechanism in this document needs two new
   ND options in Neighbor Discovery: (i) the Recursive DNS Server
   (RDNSS) option and (ii) the DNS Search List (DNSSL) option.

5.1.  Recursive DNS Server Option

   The 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 the RDNSS option.



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      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 RDNSS option type as assigned
                   by the IANA: 25

     Length        8-bit unsigned integer.  The length of the option
                   (including the Type and Length fields) is in units of
                   8 octets.  The minimum value is 3 if one IPv6 address
                   is contained in the option.  Every additional RDNSS
                   address increases the length by 2.  The Length field
                   is used by the receiver to determine the number of
                   IPv6 addresses in the option.

     Lifetime      32-bit unsigned integer.  The maximum time, in
                   seconds (relative to the time the packet is sent),
                   over which this RDNSS address 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 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 [RFC4861], 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 address 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



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                   addresses is equal to (Length - 1) / 2.

5.2.  DNS Search List Option

   The DNSSL option contains one or more domain names of DNS suffixes.
   All of the domain names share the same lifetime value.  If it is
   desirable to have different lifetime values, multiple DNSSL options
   can be used.  Figure 2 shows the format of the DNSSL 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                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     :                Domain Names of DNS Search List                :
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 2: DNS Search List (DNSSL) Option Format


   Fields:
     Type          8-bit identifier of the RDNSS option type as assigned
                   by the IANA: (TBD)

     Length        8-bit unsigned integer.  The length of the option
                   (including the Type and Length fields) is in units of
                   8 octets.  The minimum value is 2 if at least one
                   domain name is contained in the option.  The Length
                   field is set to a multiple of 8 octets to accommodate
                   all the domain names in the field of Domain Names of
                   DNS Search List.

     Lifetime      32-bit unsigned integer.  The maximum time, in
                   seconds (relative to the time the packet is sent),
                   over which this DNSSL domain name MAY be used for
                   name resolution.  The Lifetime value has the same
                   semantics as with RDNSS option.  That is, 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 DNSSL domain name MUST no longer
                   be used.





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     Domain Names of DNS Search List
                   One or more domain names of DNS search list that MUST
                   be encoded using the technique described in Section
                   3.1 of [RFC1035].  By this technique, each domain
                   name is represented as a sequence of labels ending in
                   a zero octet, defined as domain name representation.
                   For more than one domain name, the corresponding
                   domain name representations are concatenated as they
                   are.  Note that for the simple decoding, the domain
                   names MUST NOT be encoded in a compressed form, as
                   described in Section 4.1.4 of [RFC1035].  Because the
                   size of this field MUST be a multiple of 8 octets,
                   for the minimum multiple including the domain name
                   representations, the remaining octets other than the
                   encoding parts of the domain name representations
                   MUST be padded with zeros.

   Note:  An RDNSS address or a DNSSL domain name MUST be used only as
      long as both the RA router lifetime and the option lifetime have
      not expired.  The reason is that in the current network to which
      an IPv6 host is connected, the RDNSS may not be currently
      reachable, that the DNSSL domain name is not valid any more, or
      that these options do not provide service to the host's current
      address (e.g., due to network ingress filtering
      [RFC2827][RFC5358]).

5.3.  Procedure of DNS Configuration

   The procedure of DNS configuration through the RDNSS and DNSSL
   options is the same as with any other ND option [RFC4861].

5.3.1.  Procedure in IPv6 Host

   When an IPv6 host receives DNS options (i.e., RDNSS option and DNSSL
   option) through RA messages, it checks whether the options are valid
   or not as follow:

   o  If the DNS options are valid, the host SHOULD copy the values of
      the options into the DNS Repository and the Resolver Repository in
      order; the value of the Length field in the RDNSS option is
      greater than or equal to the minimum value (3) and also the value
      of the Length field in the DNSSL option is greater than or equal
      to the minimum value (2).

   o  If the DNS options are invalid, the host MUST discard the options;
      for example, the Length field in the RDNSS option has a value less
      than 3 or the Length field in the DNSSL option has a value less
      than 2.



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   When the IPv6 host has gathered a sufficient number (e.g., three) of
   RDNSS addresses (or DNS search domain names), it MAY ignore
   additional RDNSS addresses (or DNS search domain names) within an
   RDNSS (or DNSSL) option and/or additional RDNSS (or DNSSL) options
   within an RA.

   In the case where the DNS options of RDNSS and DNSSL can be obtained
   from multiple sources, such as RA and DHCP, the IPv6 host can keep
   some DNS options from RA and some from DHCP; for example, two RDNSS
   addresses (or DNS search domain names) from RA and one RDNSS address
   (or DNS search domain name) from DHCP.

6.  Implementation Considerations

   Note:  This non-normative section gives some hints for implementing
      the processing of the RDNSS and DNSSL options in an IPv6 host.

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

   In environments where the DNS information is stored in user space and
   ND runs in the kernel, it is necessary to synchronize the DNS
   information (i.e., RDNSS addresses and DNS search domain names) in
   kernel space and the Resolver Repository in user space.  For the
   synchronization, an implementation where ND works in the kernel
   should provide a write operation for updating DNS information from
   the kernel to the Resolver Repository.  One simple approach is to
   have a daemon (or a program that is called at defined intervals) that
   keeps monitoring the lifetimes of RDNSS addresses and DNS search
   domain names all the time.  Whenever there is an expired entry in the
   DNS Repository, the daemon can delete the corresponding entry from
   the Resolver Repository.

6.1.  DNS Repository Management

   For DNS repository management, the kernel or user-space process
   (depending on where RAs are processed) should maintain two data
   structures: (i) DNS Server List that keeps the list of RDNSS
   addresses and (ii) DNS Search List that keeps the list of DNS search
   domain names.  Each entry in these two lists consists of a pair of an
   RDNSS address (or DNSSL domain name) and Expiration-time as follows:

   o  RDNSS address for DNS Server List: IPv6 address of the Recursive
      DNS Server, which is available for recursive DNS resolution
      service in the network advertising the RDNSS option.





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   o  DNSSL domain name for DNS Search List: DNS suffix domain names,
      which is used to perform DNS query searches for short, unqualified
      domain names in the network advertising the DNSSL option.

   o  Expiration-time for DNS Server List or DNS Search List: The time
      when this entry becomes invalid.  Expiration-time is set to the
      value of the Lifetime field of the RDNSS option or DNSSL option
      plus the current system time.  Whenever a new RDNSS option with
      the same address (or DNSSL option with the same domain name) is
      received on the same interface as a previous RDNSS option (or
      DNSSL option), this field is updated to have a new expiration
      time.  When Expiration-time becomes less than the current system
      time, this entry is regarded as expired.

6.2.  Synchronization between DNS Server List and Resolver Repository

   When an IPv6 host receives the information of multiple RDNSS
   addresses within a network (e.g., campus network and company network)
   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(s) included in an RA
   message is as follows:

      Step (a): Receive and parse the 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 prevent the RDNSS address from being used
      any more for certain reasons in network management, e.g., the
      termination 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 the Expiration-time
      field according to the procedure specified in the second bullet of
      Section 6.1.  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



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      Server List the entry with the shortest expiration time (i.e., the
      entry 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 front of
      the Resolver Repository so that the new 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 that
      have been announced recently are preferred.

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

6.3.  Synchronization between DNS Search List and Resolver Repository

   When an IPv6 host receives the information of multiple DNSSL domain
   names within a network (e.g., campus network and company network)
   through an RA message with DNSSL option(s), it stores the DNSSL
   domain names (in order) into both the DNS Search List and the
   Resolver Repository.  The processing of the DNSSL option(s) included
   in an RA message is as follows:

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

      Step (b): For each DNSSL domain name, check the following: If the
      DNSSL domain name already exists in the DNS Search List and the
      DNSSL option's Lifetime field is set to zero, delete the
      corresponding DNSSL entry from both the DNS Search List and the
      Resolver Repository in order to prevent the DNSSL domain name from
      being used any more for certain reasons in network management,
      e.g., the termination of the RDNSS or a renaming situation.  The
      processing of this DNSSL domain name is finished here.  Otherwise,
      go to Step (c).

      Step (c): For each DNSSL domain name, if it already exists in the
      DNS Server List, then just update the value of the Expiration-time
      field according to the procedure specified in the second bullet of
      Section 6.1.  Otherwise, go to Step (d).

      Step (d): For each DNSSL domain name, if it does not exist in the
      DNS Search List, register the DNSSL domain name and lifetime with
      the DNS Search List and then insert the DNSSL domain name in front
      of the Resolver Repository.  In the case where the data structure



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      for the DNS Search List is full of DNSSL domain name entries,
      delete from the DNS Server List the entry with the shortest
      expiration time (i.e., the entry that will expire first).  The
      corresponding DNSSL domain name is also deleted from the Resolver
      Repository.  In the order in the DNSSL option, position the newly
      added DNSSL domain names in front of the Resolver Repository so
      that the new DNSSL domain names may be preferred according to
      their order in the DNSSL option for the DNS domain name used by
      the DNS query.  The processing of these DNSSL domain name is
      finished here.  Note that, in the case where there are several
      routers advertising DNSSL option(s) in a subnet, the DNSSL domain
      names that have been announced recently are preferred.

      Step (e): Delete each expired entry from the DNS Search List, and
      delete the DNSSL domain name corresponding to the entry from the
      Resolver Repository.

7.  Security Considerations

   The security of the RA options for DNS configuration does not affect
   ND protocol security [RFC4861].  This is because learning DNS
   information via the RA options cannot be worse than learning bad
   router information via the RA options.  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, 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 Neighbor
   Advertisement (NA) replies, answer RS or Neighbor Solicitation (NS)
   requests, etc.  Also, an attacker could configure a host to send out
   an 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 or DNSSL 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 options
   for RDNSS and DNSSL has vulnerabilities similar to those existing in
   unauthenticated DHCPv6.

   It is common for network devices such as switches to include
   mechanisms to block unauthorized ports from running a DHCPv6 server
   to provide protection from rogue DHCP servers.  That means that an
   attacker on other ports cannot insert bogus DNS servers using DHCPv6.
   The corresponding technique for network devices is recommended to
   block rogue Router Advertisement messages including the RDNSS and



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   DNSSL options from unauthorized nodes.

   An attacker may provide a bogus DNS Search List option in order to
   cause the victim to send DNS queries to a specific DNS server when
   the victim queries non-fully qualified domain names.  For this
   attack, the DNS resolver in IPv6 hosts can mitigate the vulnerability
   with the recommendations in [RFC1535], [RFC1536], and [RFC3646].

   If the Secure Neighbor Discovery (SEND) protocol is used as a
   security mechanism for ND, all the ND options including the RDNSS and
   DNSSL options are automatically included in the signatures [RFC3971],
   so the transport for the RA options is integrity-protected.  However,
   since any valid SEND router can still insert RDNSS and DNSSL options,
   SEND cannot verify which one is or is not authorized to send the
   options.

8.  IANA Considerations

   The RDNSS option defined in this document is using the IPv6 Neighbor
   Discovery Option type in RFC 5006 [RFC5006] assigned by the IANA as
   follows:

                 Option Name               Type
                 RDNSS option              25

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

                 Option Name               Type
                 DNSSL option              (TBD)

   The IANA registry for these options is:

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

9.  Acknowledgements

   This document has greatly benefited from inputs by Robert Hinden,
   Pekka Savola, Iljitsch van Beijnum, Brian Haberman, Tim Chown, Erik
   Nordmark, Dan Wing, and Jari Arkko.  The authors sincerely appreciate
   their contributions.

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.



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   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP Version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [RFC1035]  Mockapetris, P., "Domain Names - Implementation and
              Specification", RFC 1035, November 1987.

10.2.  Informative References

   [RFC1034]  Mockapetris, P., "Domain Names - Concepts and Facilities",
              RFC 1034, November 1987.

   [RFC3315]  Droms, R., Ed., "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3736]  Droms, R., "Stateless Dynamic Host Configuration Protocol
              (DHCP) Service for IPv6", RFC 3736, April 2004.

   [RFC3646]  Droms, R., Ed., "DNS Configuration options for Dynamic
              Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
              December 2003.

   [RFC5006]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
              "IPv6 Router Advertisement Option for DNS Configuration",
              RFC 5006, September 2007.

   [RFC4339]  Jeong, J., Ed., "IPv6 Host Configuration of DNS Server
              Information Approaches", RFC 4339, February 2006.

   [RFC3971]  Arkko, J., Ed., "SEcure Neighbor Discovery (SEND)",
              RFC 3971, March 2005.

   [RFC5358]  Damas, J. and F. Neves, "Preventing Use of Recursive
              Nameservers in Reflector Attacks", BCP 140, RFC 5358,
              October 2008.

   [RFC2827]  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.

   [RFC1535]  Gavron, E., "A Security Problem and Proposed Correction
              With Widely Deployed DNS Software", RFC 1535,
              October 1993.

   [RFC1536]  Kumar, A., Postel, J., Neuman, C., Danzig, P., and S.



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              Miller, "Common DNS Implementation Errors and Suggested
              Fixes", RFC 1536, October 1993.

Appendix A.  Changes from RFC 5006

   The following changes were made from RFC 5006 "IPv6 Router
   Advertisement Option for DNS Configuration":

   o  Added DNS Search List (DNSSL) Option to support the advertisement
      of DNS suffixes used in the DNS search along with RDNSS Option in
      RFC 5006.

   o  Clarified the coexistence of RA options and DHCP options for DNS
      configuration.

   o  Modified the procedure in IPv6 host:

      *  Clarified the procedure for DNS options in an IPv6 host.

      *  Specified a sufficient number of RDNSS addresses or DNS search
         domain names as three.

      *  Specified a way to deal with DNS options from multiple sources,
         such as RA and DHCP.

   o  Modified implementation considerations for DNSSL Option handling.

   o  Modified security considerations to consider more attack scenarios
      and the corresponding possible solutions.

   o  Modified IANA considerations to require another IPv6 Neighbor
      Discovery Option type for DNSSL option.

Authors' Addresses

   Jaehoon Paul Jeong
   Brocade Communications Systems/ETRI
   6000 Nathan Ln N
   Plymouth, MN  55442
   USA

   Phone: +1 763 268 7173 begin_of_the_skype_highlighting              +1 763 268 7173      end_of_the_skype_highlighting
   Fax:   +1 763 268 6800
   EMail: pjeong@brocade.com
   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 begin_of_the_skype_highlighting              +82 31 200 4508      end_of_the_skype_highlighting
   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 begin_of_the_skype_highlighting              +33 02 3175 9391      end_of_the_skype_highlighting
   EMail: luc.beloeil@orange-ftgroup.com


   Syam Madanapalli
   Ordyn Technologies
   1st Floor, Creator Building, ITPL
   Bangalore - 560066
   India

   Phone: +91-80-40383000 begin_of_the_skype_highlighting              +91-80-40383000      end_of_the_skype_highlighting
   EMail: smadanapalli@gmail.com





















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