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rfc:rfc5223

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).

Schulzrinne, et al. Standards Track [Page 1] RFC 5223 DHCP-Based LoST Discovery August 2008

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].

Schulzrinne, et al. Standards Track [Page 2] RFC 5223 DHCP-Based LoST Discovery August 2008

 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.

Schulzrinne, et al. Standards Track [Page 3] RFC 5223 DHCP-Based LoST Discovery August 2008

 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:

Schulzrinne, et al. Standards Track [Page 4] RFC 5223 DHCP-Based LoST Discovery August 2008

    +----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
    |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.

Schulzrinne, et al. Standards Track [Page 5] RFC 5223 DHCP-Based LoST Discovery August 2008

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.

Schulzrinne, et al. Standards Track [Page 6] RFC 5223 DHCP-Based LoST Discovery August 2008

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

Schulzrinne, et al. Standards Track [Page 7] RFC 5223 DHCP-Based LoST Discovery August 2008

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 contained in BCP 78, and except as set forth therein, the authors
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Schulzrinne, et al. Standards Track [Page 8]

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