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Versions: 00 01 02 03 04 RFC 3646

Network Working Group                                     R. Droms (ed.)
Internet-Draft                                             Cisco Systems
Expires: September 30, 2002                                     Apr 2002


                  DNS Configuration options for DHCPv6
               draft-ietf-dhc-dhcpv6-opt-dnsconfig-01.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   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.

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   This Internet-Draft will expire on September 30, 2002.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This document describes DHCPv6 options for passing a list of
   available DNS Servers and a domain search list to a client.

1. Introduction

   This document describes three options for configuration information
   related to Domain Name Service (DNS) [1, 2] in DHCPv6 [4].

2. Requirements

   The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be



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   interpreted as described in RFC2119 [3].

3. Terminology

   This document uses terminology specific to IPv6 and DHCPv6 as defined
   in section "Terminology" of the DHCP specification.

4. Domain Name Server option

   The Domain Name Server option provides a list of one or more IP
   addresses of DNS servers to which a client's DNS resolver MAY send
   DNS queries [2].  The DNS servers are listed in the order of
   preference for use by the client resolver.

   The format of the Domain Name Server option is:


       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      OPTION_DNS_SERVERS       |         option-len            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                   DNS-server (IP address)                     |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                   DNS-server (IP address)                     |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   option-code:   OPTION_DNS_SERVERS (tbd)

   option-length: Length of the 'options' field in octets; must be a
      multiple of 16

   DNS-server:    IP address of DNS server


5. Domain Search List option

   A server sends a Domain Search List option to the DHCP client to
   specify the domain search list the client is to use when resolving



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   hostnames with DNS.  This option does not apply to other name
   resolution mechanisms.

   The format of the Domain Search option is:


       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      OPTION_DOMAIN_LIST       |         option-len            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         searchstring                          |
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   option-code:   OPTION_DOMAIN_LIST (tbd)

   option-length: Length of the 'searchstring' field in octets

   searchstring:  The specification of the list of domain names in the
      Domain Search List

   The list of domain names in the 'searchstring' MUST be encoded as
   specified in section "Representation and use of domain names" of the
   DHCPv6 specification [4].

6. Appearance of these options

   The Domain Name Server option MUST appear only in the following
   messages: Solicit, Advertise, Request, Confirm, Renew, Rebind,
   Information-Request, Reply

   The Domain Search List option MUST appear only in the following
   messages: Solicit, Advertise, Request, Confirm, Renew, Rebind,
   Information-Request, Reply

7. Security Considerations

   The Domain Name Server option may be used by an intruder DHCP server
   to cause DHCP clients to send DNS queries to an intruder DNS server.
   The results of these misdirected DNS queries may be used to spoof DNS
   names.

   The Domain Name option may be used by an intruder DHCP server to
   configure a DHCP client with an invalid domain name, which could be
   used as a denial of service attack.




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   The Domain Search List option may be used by an intruder DHCP server
   to cause DHCP clients to search through invalid domains for
   incompletely specified domain names.  The results of these
   misdirected searches may be used to spoof DNS names.

   To avoid attacks through the Domain Name Server option and the Domain
   Name option, the DHCP client SHOULD use authenticated DHCP (see
   section "Authentication of DHCP messages" in the DHCPv6
   specification).

   Because the Domain Search List option may be used to spoof DNS name
   resolution in a way that cannot be detected by DNS security
   mechanisms like DNSSEC [5], DHCP clients and servers MUST use
   authenticated DHCP when a Domain Search List option is included in a
   DHCP message.

8. IANA Considerations

   IANA is requested to assign an option code to these options from the
   option-code space defined in section "DHCPv6 Options" of the DHCPv6
   specification [4].

References

   [1]  Mockapetris, P., "Domain names - concepts and facilities", STD
        13, RFC 1034, November 1987.

   [2]  Mockapetris, P., "Domain names - implementation and
        specification", STD 13, RFC 1035, November 1987.

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

   [4]  Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
        Droms (ed.), "Dynamic Host Configuration Protocol for IPv6
        (DHCPv6)", draft-ietf-dhc-dhcpv6-23 (work in progress), February
        2002.

   [5]  Eastlake, D., "Domain Name System Security Extensions", RFC
        2535, March 1999.











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Author's Address

   Ralph Droms (ed.)
   Cisco Systems
   250 Apollo Drive
   Chelmsford, MA  01824
   USA

   Phone: +1 978 497 4733
   EMail: rdroms@cisco.com









































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Full Copyright Statement

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
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   followed, or as required to translate it into languages other than
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   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

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



















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