One document matched: draft-polk-dhc-uri-00.txt





DHC Working Group                                            James Polk
Internet Draft                                            Cisco Systems
Expiration: March 6th, 2006                         September 6th, 2005
File: draft-polk-dhc-uri-00.txt


          A Dynamic Host Configuration Protocol Option for
        Requesting and Receiving Uniform Resource Identifiers


Status of this Memo

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   This Internet-Draft will expire on March 6th, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document defines a new Dynamic Host Configuration Protocol 
   (DHC) Option to allow one or more URIs to be transmitted from a 
   server to a client within one or more messages, and for one or more 
   URIs, each with a unique purpose, to be specifically requested by a 
   client of a server.  Included in this Option is a purpose field to 
   identify the type of URI being requested by the client, or the type 
   of URI in the DHCP reply from the server.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .  2
     1.1  Conventions used in this document  . . . . . . . . . . . .  4
     1.2  Terms, Acronyms and Definitions  . . . . . . . . . . . . .  4
   2.  DHC Relay Option Format . . . . . . . . . . . . . . . . . . .  5
     2.1   Rules of Usage  . . . . . . . . . . . . . . . . . . . . .  5
   3.  Purposes of Different URI Types . . . . . . . . . . . . . . .  6
     3.1   Primary SIP/SIPS URI of Public Safety Answering Point . .  7
     3.2   Secondary SIP/SIPS URI of Public Safety Answering Point .  7
     3.3   Client's Location By-Reference URI  . . . . . . . . . . .  7
     3.4   SIP/SIPS URI of Emergency Services Gateway (ESGW) . . . .  8
     3.5   SIP/SIPS URI of Emergency Services Routing Proxy (ESRP) .  8
     3.6   URI of Organization Providing LCI . . . . . . . . . . . .  8
     3.7   URI for Geocoding or Reverse Geocoding Function . . . . .  8
     3.8   Primary URI for Geo Mapping Service . . . . . . . . . . .  9
     3.9   Secondary URI for Geo Mapping Service . . . . . . . . . .  9
     3.10  Primary URI for Civic Mapping Service . . . . . . . . . .  9
     3.11  Secondary URI for Civic Mapping Service . . . . . . . . .  9
   4.  Open Items for Discussion . . . . . . . . . . . . . . . . . . 10
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . 10
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 11
     8.1   Normative References  . . . . . . . . . . . . . . . . . . 11
     8.2   Informative References  . . . . . . . . . . . . . . . . . 11
       Author's Address  . . . . . . . . . . . . . . . . . . . . . . 12
       Intellectual Property and Copyright Statements  . . . . . . . 12


1.  Introduction

   There are times in which a Uniform Resource Identifier (URI) is an 
   essential part of configuration information necessary for usage by 
   an endpoint (client) for the particular purpose of contacting what 
   is at that URI.  This document defines a new Dynamic Host 
   Configuration Protocol (DHC) Option [RFC 2131] to allow URIs of 
   specific types, or purposes, to be requested by a client of a 
   server, and transmitted unrequested from a server to a client.  
   Because URIs can be used for many purposes, and to ensure 
   extensibility, this client option has a sub-option "purpose" field 
   to identify the type of URI included in the message.

   The motivation of creating the ability to have sub-options within 
   the same DHCP Option here is because there are currently 11 unique 
   URIs described within this document, and each should not take up 
   valuable option number assignments when there is a limited set of 
   DHCP Option values.  Therefore this document specifies one DHCP 
   Option for all URIs, allowing up to 255 uniquely identified URIs to 
   be defined as sub-options.  This document will IANA Register each 
   purpose URI for interoperability.  


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   This document does not limit the means of an client from gaining 
   knowledge of a URI to DHCP, but provides DHCP as a means for a 
   client to gain knowledge of a URI or series of URIs determined 
   through local configuration, that are considered essential to that 
   client for use by applications within that client.  This 
   determination MAY be made at client boot-up, or when a particular 
   application launches.  One example of this URI download would be one
   specifically for the SIP or SIPS URI of the appropriate Public 
   Safety Answer Point (PSAP) for the client when the user of that 
   client calls for emergency help (911 or 112-type of help).  This is 
   not a transaction that should take place when a voice application 
   wants to make such a critical call set-up.  It is more appropriate 
   that this information be downloaded to the client when the voice (or
   other) application boots up in case it is needed at a later time.  
   An Internet Access Provider (IAP) would be in a better position to 
   have knowledge of where the client is than an Internet Service 
   Provider (ISP); the latter becoming more divorced from the physical 
   location of the client, especially in the case of the ISP being an 
   Application Service Provider (ASP) on a regional, national or 
   international scale.  This was part of the motivation for Option 123
   (GeoConf) [RFC 3825].

   Examples of IAPs are DSL providers with known endpoints of their 
   cabling infrastructure, Hybrid Fiber Coax (HFC) Cable providers with
   knowledge of where their logical endpoints are, and small or large 
   enterprise infrastructures.  The DSL or HFC Cable provides are not 
   limited in this context to a single client at the subscriber's 
   endpoint, but could have few to many clients being served by an 
   access device of those infrastructures, all with a common need for 
   the particular URI, or series of URIs.

   A client may request more than one URI be sent to it within the same
   DHCPDISCOVER or DHCPREQUEST message.  Each URI will be inside its 
   own payload container with an Option number, a length field and a 
   purpose field.  This means that if more than one URI is being 
   requested or downloaded, there can be more than one DHCP Option XXX 
   (this document's option number) in the same IP message.  Each URI 
   will be inside the DHCP Option payload shown in section 2 of this 
   document.  There is no meaning to the order of URIs in a message.  

   Section 1.2 reviews the terminology and acronyms used in this 
   document that are fairly new to DHCP.  Section 2.1 discusses the 
   rules of usage of this Option.  Section 3 lists the unique numbering
   of the purpose fields to the purpose type that is explained in 
   section 3.1 - 3.11.  Section 4 discusses open issues to be 
   addressed. Section 5 is the IANA Considerations section of this DHCP
   Option as well as the purpose field sub-options.






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1.1  Conventions used in this document

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

1.2  Terms, Acronyms and Definitions

   The following terms and acronyms are used within this document:

   Civic Mapping - the process a server receiving the civic format 
      location of a client, processing that location to determine the 
      appropriate PSAP for that location, and returning that PSAP URI 
      to the client

   Emergency Services Gateway - The special IP to circuit-switched 
      gateway that front-ends an emergency services Selective Router 
      (which directs all TDM based 911/112 type calls to the 
      appropriate PSAP)

   Emergency Services Routing Proxy - a special instance of a SIP Proxy
      that understands emergency routing to a PSAP based on the 
      location of the caller

   ESGW - Emergency Services Gateway

   ESRP - Emergency Services Routing Proxy

   Geo Mapping - the process a server receiving the geo format location
      of a client, processing that location to determine the 
      appropriate PSAP for that location, and returning that PSAP URI 
      to the client

   IAP - Internet Access Provider 

   Internet Access Provider - typically the organization that provides 
      Internet or IP access to the client, and could be the same as the 
      ISP in certain circumstances

   Internet Service Provider - Provider of advanced services, such as 
      application layer message processing, filtering and routing, and 
      services such as voice/video/instant messaging over IP, and could
      be the same as the IAP in certain circumstances

   ISP - Internet Service Provider

   PSAP - Public Safety Answering Point

   Public Safety Answering Point - the emergency response call center 
      talking the local emergency calls from people in distress.  This 
      facility can be logical, and can transfer (reroute) any request 
      sent to it to another facility deemed more appropriate to receive


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      the request.


2.  DHC Relay Option Format

   The format for this Option is as follows:

     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 XXX    |    Length     |  URI Purpose  |      URI      +
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          URI (cont'd)                         +
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              URI (cont'd to a maximum of 254 bytes)           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Code =        The IANA Assigned Option number

   Length =      This is a variable length value of the number of bytes 
                 in the Option, including this length field

   URI Purpose = This is what the URI is used for by applications 
                 within the client

   URI =         This is a variable length field containing the URI 
                 being transmitted, to a maximum of 254 bytes in length

                 This URI may be a partial URI, with concatenation-
                 required if multiple Option XXXs are present in the 
                 same message with the same purpose value; see the 
                 rules section below.


2.1  Rules of Usage

   The following are the rules of usage of this DHCP Option:

   - Each URI requested for by a client, or transmitted by the server, 
     MUST have a purpose identifier indicating the intended usage for 
     this URI by applications within the client

   - there MAY be more than one URI requested by the client in the same
     message

   - If more than one URI is requested for by the client, or 
     transmitted by the server, each MUST be in separate Option fields 
     (i.e. there is no provision for multiple URIs within the same 
     Option as there is no length field for an individual URI)

   - The certain URI fields MAY be populated with a URL of a server



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   - Purpose=6 "URI of Organization Providing Location Configuration 
     Information" SHOULD be included when Option 123 (GeoConf) or the 
     Option for [ID-CIVIC] is downloaded to the client.

   - URIs that denote public identifiers, such as for a PSAP, are not 
     as much at risk as other URIs transmitted to the client.  That 
     said, URIs with specific information of the client, such as its 
     location by-reference URI SHOULD NOT be transmitted by the server 
     without being requested by the client first, and SHOULD only be 
     requested by the client once it learns the specific IP address of 
     the server.

   In keeping with established rules of option lengths [RFC2131], the 
   length of a single option containing one URI MUST NOT exceed 255 
   bytes, unless following the rules established in [RFC3396] for 
   "concatenation-required" values, which states clearly that if the 
   same option appears more than once in the same message, to consider 
   that a split option value, to be concatenated prior to processing at
   the receiving end.  

   This document provides a unique, therefore modified, usage of this 
   rule in DHCP, in which the literal meaning of [RFC3396] does not 
   apply, as this Option has sub-options (called 'purposes' here). 
   However, this [RFC3396] rule is modified here to state that:

   - if the same purpose field value appears in the same message more 
     than once, the receiving entity MUST concatenate the URI values 
     prior to processing as a single value.  This procedure MUST only 
     to be done when the URI value is longer than 255 bytes (per the 
     rules of [RFC2131] and [RFC3396]), therefore MUST NOT be done 
     otherwise.

   The rest of [RFC3396] applies as written, as long as the reader 
   adjusts their understanding of that RFC to mean the purpose field in
   this document, and not the Option field.

   - multiple instances of this Option XXX in the same message with 
     different purpose values MUST NOT be considered for [RFC3396] 
     concatenation.


3.  Purposes of Different URI Types

   This section lists the initial set of purpose fields which can be 
   used by a client for different requests, or a server for different 
   transmissions:

   Purpose = 1  (Primary PSAP URI)
   Purpose = 2  (Secondary PSAP URI)
   Purpose = 3  (Location By-Reference of Client)
   Purpose = 4  (ESGW URI of Client)
   Purpose = 5  (ESRP URI of Client)


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   Purpose = 6  (Location Providing Location for Client)
   Purpose = 7  (URI of Geocoding/Reverse Geocoding)
   Purpose = 8  (Primary URI of Geo Mapping Service)
   Purpose = 9  (Secondary URI of Geo Mapping Service)
   Purpose = 10 (Primary URI of Civic Mapping Service)
   Purpose = 11 (Secondary URI of Civic Mapping Service)

   Others can be added based on discussion of this document.


3.1  Primary SIP/SIPS URI of Public Safety Answering Point (PSAP)

   This purpose=1 URI is the primary URI used by a SIP [RFC3261] 
   enabled element in the Request-URI field for the appropriate PSAP 
   for this client when the SIP user agent (UA) is attempting to call 
   for emergency help (such as the police or ambulance).  


3.2  Secondary SIP/SIPS URI of Public Safety Answering Point (PSAP)

   Related to Purpose=1.  This purpose=2 URI is the secondary or backup
   SIP or SIPS URI of same PSAP facility or of another PSAP facility to
   be used when the primary URI fails to connect, due to a timeout or a
   SIP final failure message.  This SHOULD NOT be used if the initial 
   attempt to contact the PSAP fails for any reason, as many failures 
   are recoverable within SIP [RFC 3261].  In fact, many non-successful
   responses are not uncommon in SIP before a transaction is 
   successfully responded to.  


3.3  Client's Location By-Reference URI

   This purpose=3 URI is the pointer to the client's by-reference 
   location on a server external to the client [ID-SIP-LOC].  Location 
   of a client can be signified in two ways: 

      by-value - meaning the client possesses its location information 
                 locally, and

      by-reference - meaning the client's location information is 
                 stored on a remote element such as a server.  

   Storing location information by-reference external to the client may
   be for many reasons, including because the client does not know how 
   to store its location, because the client chooses to store it 
   remotely for a URI reference to be given to others to save bandwidth
   during transmission, or because a service provider may decide to 
   keep this information from the client by-value.  If the client knows
   where its location is by-reference, it merely needs to provide that 
   reference to another entity when it decides to reveal where it is.  
   This URI is the retrieval identifier for a protocol to fetch the 
   client's location from.  Examples of usable protocols are: HTTP, 


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   SIP, etc.


3.4  SIP/SIPS URI of Emergency Services Gateway (ESGW)

   This purpose=4 URI is for the Emergency Services Gateway that an IP 
   client would contact when setting up an emergency call with a PSAP 
   that is not IP enabled.  Having this information locally in the
   client will allow it to contact the ESGW directly and not have to 
   rely on an intermediary to determine which ESGW is the right one for
   this client, and possibly fail the call set-up during that 
   determination.


3.5  SIP/SIPS URI of Emergency Services Routing Proxy (ESRP)

   This purpose=5 URI is for the Emergency Services Routing Proxy that 
   is tasked with determining which PSAP the client needs to contact 
   when attempting to establish a call with a PSAP.  In SIP for 
   example, not all SIP Proxies or intermediaries are expected to have 
   knowledge of how to determine which is the appropriate PSAP of a 
   client based on where the client is located.  There may be difficult
   in a non-updated SIP intermediary in this determination, even in 
   determining which SIP intermediary knows how to do this function.  
   This SIP/SIPS URI is the Request-URI of such a SIP intermediary that
   knows how to determine which is the correct PSAP given the included 
   PIDF-LO [ID-SIP-LOC] in the session set-up message (the SIP INVITE) 
   to that intermediary.


3.6  URI of Organization Providing Location Configuration Information 

   This purpose=6 URI is the organization that provided location 
   configuration information (LCI) to the DHCP client.  In building a 
   proper XML Location Message Body [ID-PIDF-LO], the location 
   generator [RFC 3693] will include a <provided-by> element indicating
   which organization was responsible for delivering this location 
   information to the client.  This URI is used to populate this 
   <provided-by> element without further interaction.  


3.7  URI for Geocoding or Reverse Geocoding Function

   This purpose=7 URI of a server that can perform a geocoding or 
   reverse geocoding function.  DHCP has the ability to provide 
   Location Configuration Information to a client in the geo format 
   using Option 123 [RFC 3825] or the civic format [ID-CIVIC], or the 
   client can learn is location through manual configuration or an 
   internal GPS process.  Various applications on a client MAY prefer 
   one format over another and not possess the ability to geocode or 
   reverse geocode the available location information.  This URI 
   (purpose=7) provides the client with the server known to have this 


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   ability prior to the client requiring the new format.


3.8  Primary URI for Geo Mapping Service

   This purpose=8 URI gives the client the ability to transmit its 
   location, perhaps downloaded from DHCP Option 123 [RFC3825], and 
   contact a "primary" server at this URI to perform a location-to-
   PSAP-URI mapping function before the client attempts to contact a 
   PSAP.  

   This transmission of client location to the primary mapping server 
   that includes the request to map this location to the appropriate 
   PSAP for that location is done with another protocol, and not DHCP.


3.9  Secondary URI for Geo Mapping Service

   This purpose=9 URI gives the client the ability to transmit its 
   location, perhaps downloaded from DHCP Option 123 [RFC3825], and 
   contact a "secondary" server at this URI to perform a location-to-
   PSAP-URI mapping function before the client attempts to contact a 
   PSAP.  

   This transmission of client location to the secondary mapping server
   that includes the request to map this location to the appropriate 
   PSAP for that location is done with another protocol, and not DHCP.


3.10 Primary URI for Civic Mapping Service

   This purpose=10 URI gives the client the ability to transmit its 
   location, perhaps downloaded from the civic format DHCP Option [ID-
   CIVIC], and contact a "primary" server at this URI to perform a 
   location-to-PSAP-URI mapping function before the client attempts to 
   contact a PSAP.  

   This transmission of client location to the primary mapping server 
   that includes the request to map this location to the appropriate 
   PSAP for that location is done with another protocol, and not DHCP.


3.11 Secondary URI for Civic Mapping Service

   This purpose=11 URI gives the client the ability to transmit its 
   location, perhaps downloaded from the civic format DHCP Option [ID-
   CIVIC], and contact a "secondary" server at this URI to perform a 
   location-to-PSAP-URI mapping function before the client attempts to 
   contact a PSAP.  

   This transmission of client location to the secondary mapping server
   that includes the request to map this location to the appropriate 


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   PSAP for that location is done with another protocol, and not DHCP.


4.  Open Items for Discussion

   There are several open items that need to be addressed in following 
   versions of this ID (if it moves forward).

   #1 - Does Purpose=5 (URI of the ESRP) need to be pulled into two 
        separate URIs, one for a Routing Proxy that knows geo format 
        mapping, and the other that knows civic format mapping? This 
        may be too granular at this point.


5.  IANA Considerations

   IANA has assigned a DHCP option code of [XXX] for the URI option
   defined in this document.

   This URI Option defines one field for which IANA maintains a 
   registry: the Purpose field (see Section 2).  The initial values of 
   the Purpose registry are as follows:

   Purpose   Description                              Reference
   -------   ------------                             ---------
      1      Primary PSAP URI                         [This RFC]
      2      Secondary PSAP URI                       [This RFC]
      3      Location By-Reference of Client          [This RFC]
      4      ESGW URI of Client                       [This RFC]
      5      ESRP URI of Client                       [This RFC]
      6      Location Providing Location for Client   [This RFC]
      7      URI of Geocoding/Reverse Geocoding       [This RFC]
      8      Primary URI of Geo Mapping Service       [This RFC]
      9      Secondary URI of Geo Mapping Service     [This RFC]
      10     Primary URI of Civic Mapping Service     [This RFC]
      11     Secondary URI of Civic Mapping Service   [This RFC]


   IANA registration of new purpose field values MUST be done in a 
   standards track RFC. 


6.  Security Considerations

   Where critical decisions might be based on the value of this URI
   option, DHCP authentication in [RFC3118] SHOULD be used to protect 
   the integrity of the DHCP options.

   Since there is no privacy protection for DHCP messages, an
   eavesdropper who can monitor the link between the client and
   destination DHCP server to capture any URIs in transit.



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   When implementing a DHC server that will serve clients across an
   uncontrolled network, one should consider the potential security
   risks.


7.  Acknowledgements

   To Andy Newton and Ralph Droms for guidance and assistance in the 
   shaping of this effort.  To Josh Littlefield for his help.


8.  References

8.1  Normative References

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

 [RFC3825] J. Polk, J. Schnizlein, M. Linsner, "Dynamic Host
           Configuration Protocol Option for Coordinate-based Location
           Configuration Information", RFC 3825, July 2004

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

 [RFC3261] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J.
           Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP:
           Session Initiation Protocol", RFC 3261, May 2002.

 [RFC3396] T. Lemon, S. Cheshire, "Encoding Long Options in the Dynamic
           Host Configuration Protocol (DHCPv4)", RFC 3396, November 
           2002

 [RFC3693] J. Cuellar, J. Morris, D. Mulligan, J. Peterson. J. Polk, 
           "Geopriv Requirements", RFC 3693, February 2004

 [RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP 
           Messages", RFC 3118, June 2001.

 [ID-PIDF-LO] J. Peterson, "Presence Information Data Format - Location
           Object", draft-ietf-Geopriv-pidf-lo-03, "work in progress",
           Sept 2004


8.2  Informative References

 [RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC 
           3046, January 2001.

 [ID-SIP-LOC] J. Polk, B. Rosen, "SIP Location Conveyance", draft-ietf-
           sip-location-conveyance-01.txt, "work in progress", June 
           2005


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 [ID-CIVIC] H. Schulzrinne, " Dynamic Host Configuration Protocol 
            (DHCPv4 and DHCPv6) Option for Civic Addresses Configuration
            Information ", draft-ietf-geopriv-dhcp-civil-06, "work in 
            progress", May 2005


Author's Address

   James M. Polk
   3913 Treemont Circle
   Colleyville, Texas  76034
   USA

   Phone: +1-817-271-3552
   Fax:   none
   Email: jmpolk@cisco.com


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   This document and the information contained herein are provided on 
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   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Copyright Statement

   Copyright (C) The Internet Society (2005).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


Acknowledgment

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








































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