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Versions: 00

Network Working Group                                 A.K. Vijayabhaskar
Internet-Draft                                           Hewlett-Packard
Expires: April 17, 2004                                      16 Oct 2003


                 The Name Service Search Option for DHCPv6
                   draft-ietf-dhc-dhcpv6-opt-nss-00.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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   This Internet-Draft will expire on April 17, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document describes a new option called Name Service Search Option
   to specify the order in which name services should be consulted by the
   client when resolving host names and other information.

1. Introduction

   DHCPv6 specification [1] allows DHCPv6 server to convey various kinds
   of name services to the DHCPv6 clients through the options like DNS
   Servers Option [2], NIS Servers Option [3] and NIS+ Servers Option [3].
   The clients can use multiple name services. Currently, there is no
   way by which the client can be notified with the search order for the
   name services. This document defines a new option by which the server
   can pass the search order for the name services to the clients.






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2. Requirements

   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
   document, are to be interpreted as described in RFC 2119 [5]


3. Terminology

   This document uses terminology specific to IPv6 and DHCPv6 as defined
   in "Terminology" section of the DHCPv6 specification [1].

4. Name Service Search Option

   The Name Service Search Option lists the one or more option codes of
   the name services in the order of preference. The first listed name
   service will be first used for resolution.

   The format of the Name Service Search Option is as shown below:

       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_NSS         |         option-len            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         NS Option code        |       NS Option code          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   option-code:   OPTION_NSS (tbd)

   option-len: Length of the 'NS Option code' fields in octets; It must
               be a multiple of 2.

   NS Option code: 2 bytes option code of Name service represented
               in network byte order.

   The following list gives the various name services and their
   corresponding option codes.

        Name Service                                Option code
    Domain Name Servers Option                    OPT_DNS_SERVERS
    Network Information Servers Option            OPT_NIS_SERVERS
    NetBIOS over TCP/IP Name Server Option       OPT_NBNS_SERVERS
    Network Information Service+ Servers Option  OPT_NISP_SERVERS

    The value of OPT_DNS_SERVERS is defined in [2] and the values of
    OPT_NIS_SERVERS and OPT_NISP_SERVERS are defined in [3]. Currently
    the values are `tbd`. IANA has been requested to assign a value for
    these options. Currently, there is no DHCPv6 option to deliver NetBIOS
    over TCP/IP Name Server (NBNS) [4] addresses to the clients. So, the
    value of OPT_NBNS_SERVERS is `tbd`.


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    The NS Option code of 0 is to indicate that the client should refer
    to local naming information (e.g., an /etc/hosts file on a UNIX
    machine).

    Example:

       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_NSS         |             6                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         OPT_DNS_SERVERS       |       OPT_NIS_SERVERS         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               0               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    This means, the client has to first use DNS, then NIS and then the
    local naming information like /etc/hosts for name service.

5. Client Behaviour

    The client should use this option to create search list for name
    service.

    i) If the DHCPv6 server doesn't provide the information about one or
    more name services listed in this option and these service are
    supported in the client and the client is configured to access these
    services, it can either use the information about these name services
    configured by some other mechanism external to DHCPv6 (or) it can try
    to obtain the information about these name services from the
    alternative DHCPv6 servers (or) it can ignore these name services
    and keep the remaining name services in the search list in the same
    relative order as before. For example, assume that the server provides
    the search list as (1) DNS (2) NIS+ and (3) NetBIOS and the server
    has not provided NIS+ server addresses to the client. The client
    supports NIS+ and it is configured to use NIS+. The client can
    either get the information about NIS+ servers through some other
    mechanisms like manual configuration database (or) it can contact
    alternative DHCPv6 servers to obtain NIS+ server addresses. If both
    mechanisms doesn't succeed, it can ignore NIS+ and keep (1) DNS
    and (2) NetBIOS in its search list with DNS and NetBIOS in same
    relative order as before.

    ii) The client may receive this option with some name services, which
    are not supported by client (or) it has not been configured to access.
    In this case, it can ignore these name services and create the search
    list removing these name services with relative order of the remaining
    name services not changed.

    This specification does mandate any strict rules to be followed
    for the cases i) and ii). However, it provides the guidelines
    which will be helpful for the implementors. For all these cases
    the client can interpret this option in a system-specific manner
    whose specification is outside the scope of this document.


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6. Appearance of this option

   The Name Service Search option MUST NOT appear in other than the
   following messages: Solicit, Advertise, Request, Renew, Rebind,
   Information-Request and Reply.

   The option number for this option MAY appear in the Option Request
   Option [1] in the following messages: Solicit, Request, Renew,
   Rebind, Information-Request and Reconfigure.

7. Security Considerations

   The Name Service Search Option may be used by an intruder DHCPv6
   server to provide a search list which contain only the name services
   which are not supported in the client. This will make the clients
   unable to resolve the names and other information.

   The Name Service Search Option may be used by an intruder DHCPv6
   server to provide a search list with lower precedence given to the
   service which provide better results. For example, local naming
   information like /etc/hosts, which doesn't have adequate information
   for name and other resolutions, will be given higher precedence in the
   search list. This will degrade the performance of the applications
   running on the client as they have to perform lookup multiple times
   with different name services to resolve the names and other
   information. If these applications are very critical like banking
   services, which require higher throughput, this will result in Denial
   Of Service.

   To avoid attacks through this option, the DHCP client SHOULD use
   authenticated DHCP (see section "Authentication of DHCP messages"
   in the DHCPv6 specification [1]).

8. IANA Considerations

   IANA is requested to assign an option code to the following options
   from the option-code space defined in "DHCPv6 Options" section of the
   DHCPv6 specification [1].



      Option Name            Value    Described in
       OPTION_NSS             tbd       Section 4
   OPTION_NBNS_SERVERS        tbd       Section 4


9. Normative References

   [1]  Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
        Droms (ed.), "Dynamic Host Configuration Protocol for IPv6
        (DHCPv6)", RFC 3315, July 2003.





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10. Informative References

   [2]  R. (ed.) Droms.  DNS Configuration options for DHCPv6.  Internet
        Draft, Internet Engineering Task Force, August 2003.  Work in
        progress.

   [3]  A. K. Vijayabhaskar.  NIS Configuration Options for DHCPv6.
        Internet Draft, Internet Engineering Task Force, Oct 2003. Work
        in progress.

   [4]  NetBIOS Working Group, "Protocol Standard for a NetBIOS Service
        on a TCP/UDP transport: Detailed Specifications", STD 19, RFC
        1002, March 1987.

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

Author's Address

   Vijayabhaskar A K
   Hewlett-Packard STSD-I
   29, Cunningham Road
   Bangalore - 560052
   India

   Phone: +91-80-2053085
   E-Mail: vijayak@india.hp.com






























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Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society. The idea of this specification is based on
   RFC 2937, September 2000.

























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