





Network Working Group                                     H. Schulzrinne
Request for Comments: 5223                           Columbia University
Category: Standards Track                                        J. Polk
                                                                   Cisco
                                                           H. Tschofenig
                                                  Nokia Siemens Networks
                                                             August 2008


  Discovering Location-to-Service Translation (LoST) Servers Using the
               Dynamic Host Configuration Protocol (DHCP)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   The Location-to-Service Translation (LoST) Protocol describes an XML-
   based protocol for mapping service identifiers and geospatial or
   civic location information to service contact Uniform Resource
   Locators (URLs).  LoST servers can be located anywhere, but a
   placement closer to the end host, e.g., in the access network, is
   desirable.  In disaster situations with intermittent network
   connectivity, such a LoST server placement provides benefits
   regarding the resiliency of emergency service communication.

   This document describes how a LoST client can discover a LoST server
   using the Dynamic Host Configuration Protocol (DHCP).


















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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 2
   3.  Domain Name Encoding  . . . . . . . . . . . . . . . . . . . . . 3
   4.  LoST Server DHCPv4 Option . . . . . . . . . . . . . . . . . . . 3
   5.  LoST Server DHCPv6 Option . . . . . . . . . . . . . . . . . . . 4
   6.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
     7.1.  DHCPv4 Option . . . . . . . . . . . . . . . . . . . . . . . 5
     7.2.  DHCPv6 Option . . . . . . . . . . . . . . . . . . . . . . . 5
   8.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     10.1. Normative References  . . . . . . . . . . . . . . . . . . . 6
     10.2. Informative References  . . . . . . . . . . . . . . . . . . 6

1.  Introduction

   The Location-to-Service Translation (LoST) Protocol [RFC5222]
   describes an XML-based protocol for mapping service identifiers and
   geospatial or civic location information to service contact Uniform
   Resource Locators (URLs).

   In order to interact with a LoST server, the LoST client needs to
   discover the server's IP address.  Several mechanisms can be used to
   learn this address, including manual configuration.  In environments
   where the access network itself either deploys a LoST server or knows
   a third party that operates a LoST server, DHCP can provide the end
   host with a domain name.  This domain name is then used as input to
   the DNS-based resolution mechanism described in LoST [RFC5222] that
   reuses the URI-enabled NAPTR specification (see [RFC4848]).

   This document specifies a DHCPv4 and a DHCPv6 option that allows LoST
   clients to discover local LoST servers.

   Section 2 provides terminology.  Section 3 shows the encoding of the
   domain name.  Section 4 describes the DHCPv4 option while Section 5
   describes the DHCPv6 option, with the same functionality.  IANA and
   Security Considerations complete the document in Sections 7 and 8.

2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in RFC 2119
   [RFC2119].




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   Within this document, we use terminology from [RFC5012] and
   [RFC5222].

3.  Domain Name Encoding

   This section describes the encoding of the domain name used in the
   DHCPv4 option shown in Section 4 and also used in the DHCPv6 option
   shown in Section 5.

   The domain name is encoded according to Section 3.1 of RFC 1035
   [RFC1035] whereby each label is represented as a one-octet length
   field followed by that number of octets.  Since every domain name
   ends with the null label of the root, a domain name is terminated by
   a length byte of zero.  The high-order two bits of every length octet
   MUST be zero, and the remaining six bits of the length field limit
   the label to 63 octets or less.  To simplify implementations, the
   total length of a domain name (i.e., label octets and label length
   octets) is restricted to 255 octets or less.

4.  LoST Server DHCPv4 Option

   The LoST server DHCPv4 option carries a DNS (RFC 1035 [RFC1035])
   fully-qualified domain name (FQDN) to be used by the LoST client to
   locate a LoST server.

   The DHCP option for this encoding has the following format:

         Code    Len   LoST Server Domain Name
         +-----+-----+-----+-----+-----+-----+-----+----
         | 137 |  n  |  s1 |  s2 |  s3 |  s4 | s5  |  ...
         +-----+-----+-----+-----+-----+-----+-----+----

                     Figure 1: LoST FQDN DHCPv4 Option

   The values s1, s2, s3, etc. represent the domain name labels in the
   domain name encoding.  Note that the length field in the DHCPv4
   option represents the length of the entire domain name encoding,
   whereas the length fields in the domain name encoding (see Section 3)
   is the length of a single domain name label.

      Code: OPTION_V4_LOST (137)

      Len: Length of the 'LoST Server Domain Name' field
           in octets; variable.

      LoST Server Domain Name: The domain name of the LoST
           server for the client to use.




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   A DHCPv4 client MAY request a LoST server domain name in a Parameter
   Request List option, as described in [RFC2131].

   The encoding of the domain name is described in Section 3.

   This option contains a single domain name and, as such, MUST contain
   precisely one root label.

5.  LoST Server DHCPv6 Option

   This section defines a DHCPv6 option to carry a domain name.

   The DHCPv6 option has the format shown in Figure 2.

       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_V6_LOST           |         option-length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                LoST Server Domain Name                        |
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      option-code: OPTION_V6_LOST (51)

      option-length: Length of the 'LoST Server Domain Name' field
           in octets; variable.

      LoST Server Domain Name: The domain name of the LoST
           server for the client to use.

         Figure 2: DHCPv6 Option for LoST Server Domain Name List

   A DHCPv6 client MAY request a LoST server domain name in an Options
   Request Option (ORO), as described in [RFC3315].

   The encoding of the domain name is described in Section 3.

   This option contains a single domain name and, as such, MUST contain
   precisely one root label.

6.  Example

   This section shows an example of a DHCPv4 option where the DHCP
   server wants to offer the "example.com" domain name to the client as
   input to the U-NAPTR LoST discovery procedure.  This domain name
   would be encoded as follows:




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      +----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      |137 |13 | 7 | e | x | a | m | p | l | e | 3 | c | o | m | 0 |
      +----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

              Figure 3: Example for a LoST FQDN DHCPv4 Option

7.  IANA Considerations

7.1.  DHCPv4 Option

   The following DHCPv4 option code for the Location-to-Service
   Translation (LoST) Protocol server option has been assigned by IANA:

       Option  Name            Value       Described in
       -----------------------------------------------
       OPTION_V4_LOST            137         Section 4

7.2.  DHCPv6 Option

   IANA has assigned the following DHCPv6 option code for the Location-
   to-Service Translation (LoST) Protocol option:

       Option  Name            Value       Described in
       ------------------------------------------------
       OPTION_V6_LOST             51         Section 5

8.  Security Considerations

   If an adversary manages to modify the response from a DHCP server or
   insert its own response, a LoST client could be led to contact a
   rogue LoST server under the control of the adversary or be given an
   invalid address.  These threats are documented in [RFC5069].  The
   security considerations in [RFC2131], [RFC2132], and [RFC3315] are
   applicable to this document.

   [RFC5222] enumerates the LoST security mechanisms.

9.  Acknowledgements

   Andrew Newton reviewed the document and helped simplify the
   mechanism.  Other helpful input was provided by Jari Arkko, Leslie
   Daigle, Vijay K. Gurbani (Gen-ART Review), David W. Hankins, Russ
   Housley, Tim Polk, Mark Stapp, and Christian Vogt.








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10.  References

10.1.  Normative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

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

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.

   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
              Extensions", RFC 2132, March 1997.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

10.2.  Informative References

   [RFC4848]  Daigle, L., "Domain-Based Application Service Location
              Using URIs and the Dynamic Delegation Discovery Service
              (DDDS)", RFC 4848, April 2007.

   [RFC5012]  Schulzrinne, H. and R. Marshall, "Requirements for
              Emergency Context Resolution with Internet Technologies",
              RFC 5012, January 2008.

   [RFC5069]  Taylor, T., Tschofenig, H., Schulzrinne, H., and M.
              Shanmugam, "Security Threats and Requirements for
              Emergency Call Marking and Mapping", RFC 5069,
              January 2008.

   [RFC5222]  Hardie, T., Newton, A., Schulzrinne, H., and H.
              Tschofenig, "LoST: A Location-to-Service Translation
              Protocol", RFC 5222, August 2008.













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Authors' Addresses

   Henning Schulzrinne
   Columbia University
   Department of Computer Science
   450 Computer Science Building
   New York, NY  10027
   US

   EMail: hgs+ecrit@cs.columbia.edu
   URI:   http://www.cs.columbia.edu

   James Polk
   Cisco
   2200 East President George Bush Turnpike
   Richardson, TX  75082
   US

   EMail: jmpolk@cisco.com


   Hannes Tschofenig
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600
   Finland

   Phone: +358 (50) 4871445
   EMail: Hannes.Tschofenig@nsn.com
   URI:   http://www.tschofenig.priv.at





















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