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Internet Engineering Task Force                               C. Perkins
INTERNET DRAFT                                                       IBM
                                                           14 March 1997


               DHCP Options for Service Location Protocol
                       draft-ietf-dhc-slp-01.txt


Status of This Memo

   This document is a submission to the Dynamic Host Configuration
   Working Group of the Internet Engineering Task Force (IETF). Comments
   should be submitted to the dhcp@bucknell.edu mailing list.

   Distribution of this memo is unlimited.

   This document is an Internet-Draft.  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.

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   To learn the current status of any Internet-Draft, please check
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Abstract

   The Dynamic Host Configuration Protocol provides a framework for
   passing configuration information to hosts on a TCP/IP network.
   Entities using the Service Location Protocol need to find out the
   address of Directory Agents in order to transact messages.  In
   certain other instances they may need to discover the correct scope
   to be used in conjunction with the service attributes and URLS which
   are exchanged using the Service Location Protocol.











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1. Introduction

   The Dynamic Host Configuration Protocol [2] provides a framework
   for passing configuration information to hosts on a TCP/IP network.
   Entities using the Service Location Protocol [3] need to find out
   the address of Directory Agents in order to transact messages.  In
   certain other instances they may need to discover the correct scope
   to be used in conjunction with the service attributes and URLs [1]
   which are exchanged using the Service Location Protocol.

   The scope MAY be denoted in any standardized character set.  Values
   for character encoding can be found in IANA's database
         http://www.isi.edu/in-notes/iana/assignments/character-sets
   and have the values referred by the MIBEnum value.

   Note that each option listed below may be included multiple times in
   the same DHCPOFFER or DHCPREQUEST. If so, then the options SHOULD be
   included in order of decreasing preference.


2. Directory Agent Option

   This option requests or specifies a Directory Agent (DA), along with
   zero or more scopes supported by that DA.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Code     |     Length    |D|S|          reserved         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              (if present) Directory Agent address             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Char Encoding         |            scope ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Code     78

      Length   variable

      D        If the 'D' bit is set, the Directory Agent address is
               present.

      S        If the 'S' bit is set, the scope is present, encoded in
               the indicated character set.

      Char Encoding
               The standardized encoding for the characters making up
               the string denoting the scope.



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Internet Draft      DHCP Options for Service Location      14 March 1997


      scope    A string denoting the scope.

   Note that more than one Directory Agent option may be present in a
   DHCP message.  Each such option may have the same or different scope.
   The client may request any Directory Agent with a particular scope,
   by including the Directory Agent option in a DHCP Request message
   with no Directory Agent address included (the 'D' bit set to zero),
   and the string denoting the scope.  The length of the scope string is
   only indicated implicitly by the overall length of the option.


3. Service Scope Option

   This option indicates a scope that should be used by a Service Agent
   (SA) [3], when responding to Service Request messages as specified by
   the Service Location Protocol.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Code     |     Length    |         Char Encoding         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           scope ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Code     79

      Length   variable

      Char Encoding
               The standardized encoding for the characters making up
               the string denoting the scope.

      scope    A string denoting the scope.

   Note that more than one Service Scope option may be present in a DHCP
   message.  The length of the scope string is only indicated implicitly
   by the overall length of the option.


4. Security Considerations

   If a malicious host is able to insert fraudulent information in
   DHCPOFFER packets sent to a prospective client of the Service
   Location Protocol, then the client will be unable to obtain service,
   and vulnerable to disclosing information to unauthorized service
   agents.  Likewise, a service agent would find that it might rely on




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Internet Draft      DHCP Options for Service Location      14 March 1997


   fraudulent or otherwise malicious directory agents to advertise its
   services.  Many opportunities for denial of service exist.

   This difficulty is inherited from the much larger and more serious
   problem, viz.  securing or authenticating any information whatsoever
   from a DHCP server (or client!)  is not possible in common DHCP
   deployments.


5. Acknowledgements

   Thanks to Erik Guttman for his helpful suggestions in the creation of
   this draft.


References

   [1] T. Berners-Lee, L. Masinter, and M. McCahill.  Uniform Resource
       Locators (URL).  RFC 1738, December 1994.

   [2] Ralph Droms.  Dynamic Host Configuration Protocol.  RFC 1541,
       October 1993.

   [3] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan.  Service
       Location Protocol, November 1996.  draft-ietf-svrloc-protocol-15.txt
       (work in progress).


Author's Address

   Questions about this memo can be directed to:

   Charles E. Perkins
   Sun Microsystems
   2550 Garcia Avenue
   Mountain View, CA  94043

   Phone: +1 415 336 7153
   Fax:   +1 415 336 0670

   EMail: charliep@acm.org










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