Network Working Group                                      H. Tschofenig
Internet-Draft                                    Nokia Siemens Networks
Intended status:  Informational                           H. Schulzrinne
Expires:  May 22, 2008                               Columbia University
                                                       November 19, 2007

 GEOPRIV Layer 7 Location Configuration Protocol; Problem Statement and

Status of this Memo

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   Copyright (C) The IETF Trust (2007).

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   This document provides a problem statement, lists requirements and
   captures design aspects for a Geopriv Layer 7 Location Configuration
   Protocol L7 (LCP).  This protocol aims to allow an end host to obtain
   location information, by value or by reference, from a Location
   Information Server (LIS) that is located in the access network.  The
   obtained location information can then be used for a variety of
   different protocols and purposes.  For example, it can be used as
   input to the Location-to-Service Translation Protocol (LoST) or to
   convey location within SIP to other entities.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Scenarios  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Fixed Wired Environment  . . . . . . . . . . . . . . . . .  5
     3.2.  Moving Network . . . . . . . . . . . . . . . . . . . . . .  7
     3.3.  Wireless Access  . . . . . . . . . . . . . . . . . . . . .  9
   4.  Discovery of the Location Information Server . . . . . . . . . 11
   5.  Identifier for Location Determination  . . . . . . . . . . . . 13
   6.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 16
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   9.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 20
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 22
     11.2. Informative References . . . . . . . . . . . . . . . . . . 22
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
   Intellectual Property and Copyright Statements . . . . . . . . . . 25

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1.  Introduction

   This document provides a problem statement, lists requirements and
   captures design aspects for a Geopriv Layer 7 Location Configuration
   Protocol L7 (LCP).  The protocol has two purposes:

   o  It is used to obtain location information (referred as "Location
      by Value" or LbyV) from a dedicated node, called the Location
      Information Server (LIS).

   o  It enables the Target to obtain a reference to location
      information (referred as "Location by Reference" or LbyR).  This
      reference can take the form of a subscription URI, such as a SIP
      presence URI, a HTTP/HTTPS URI, or another URI.  The requirements
      related to the task of obtaining a LbyR are described in a
      separate document, see [4].

   The need for these two functions can be derived from the scenarios
   presented in Section 3.

   For this document we assume that the GEOPRIV Layer 7 LCP runs between
   the end host (i.e., the Target in [1] terminology) and the LIS.

   This document is structured as follows.  Section 4 discusses the
   challenge of discovering the LIS in the access network.  Section 5
   compares different types of identifiers that can be used to retrieve
   location information.  A list of requirements for the L7 LCP can be
   found in Section 6.

   This document does not describe how the access network provider
   determines the location of the end host since this is largely a
   matter of the capabilities of specific link layer technologies or
   certain deployment environments.

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2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 [2],
   with the qualification that unless otherwise stated these words apply
   to the design of the GEOPRIV Layer 7 Location Configuration Protocol.

   The term Location Information Server (LIS) refers to an entity
   capable of determining the location of a Target and of providing that
   location information, a reference to it, or both via the Location
   Configuration Protocol (LCP) to the requesting party.  In most cases
   the requesting party is the Target itself but it may also be an
   authorized entity that acts on behalf of it, such as a SIP proxy or
   another LIS.

   This document also uses terminology from [1] (such as Target) and [3]
   (such as Internet Access Provider (IAP), Internet Service Provider
   (ISP), and Application Service Provider (ASP)).

   With the term "Access Network Provider" we refer to the Internet
   Access Provider (IAP) and the Internet Service Provider (ISP) without
   further distinguishing these two entities as it is not relevant for
   the purpose of this document.  An additional requirements document on
   LIS-to-LIS [5] shows scenario where the separation between IAP and
   ISP is important.

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3.  Scenarios

   This section describes a few network scenarios where the L7 LCP may
   be used.  Note that this section does not aim to exhaustively list
   all possible deployment environments.  Instead we focus on the
   following environments:

   o  DSL/Cable networks, WiMax-like fixed access

   o  Airport, City, Campus Wireless Networks, such as 802.11a/b/g,

   o  3G networks

   o  Enterprise networks

   We illustrate a few examples below.

3.1.  Fixed Wired Environment

   Figure 1 shows a DSL network scenario with the Access Network
   Provider and the customer premises.  The Access Network Provider
   operates link and network layer devices (represented as Node) and the

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   |                           |
   |  Access Network Provider  |
   |                           |
   |   +--------+              |
   |   | Node   |              |
   |   +--------+ +----------+ |
   |       |  |   | LIS      | |
   |       |  +---|          | |
   |       |      +----------+ |
   |       |                   |
           | Wired Network
   <----------------> Access Network Provider demarc
   |       |                   |
   |   +-------------+         |
   |   | NTE         |         |
   |   +-------------+         |
   |       |                   |
   |       |                   |
   |   +--------------+        |
   |   | Device with  | Home   |
   |   | NAPT and     | Router |
   |   | DHCP server  |        |
   |   +--------------+        |
   |       |                   |
   |       |                   |
   |    +------+               |
   |    | End  |               |
   |    | Host |               |
   |    +------+               |
   |                           |
   |Customer Premises Network  |
   |                           |

                          Figure 1: DSL Scenario

   The customer premises consists of a router with a Network Address
   Translator with Port Address Translation (NAPT) and a DHCP server as
   used in most Customer Premises Networks (CPN) and the Network
   Termination Equipment (NTE) where Layer 1 and sometimes Layer 2
   protocols are terminated.  The router in the home network (e.g.,
   broadband router, cable or DSL router) typically runs a NAPT and a
   DHCP server.  The NTE is a legacy device and in many cases cannot be
   modified for the purpose of delivering location information to the

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   end host.  The same is true of the device with the NAPT and DHCP

   It is possible for the NTE and the home router to physically be in
   the same box, or for there to be no home router, or for the NTE and
   end host to be in the same physical box (with no home router).  An
   example of this last case is where Ethernet service is delivered to
   customers' homes, and the Ethernet NIC in their PC serves as the NTE.

   Current Customer Premises Network (CPN) deployments frequently show
   the following characteristics:

   1.  CPE = Single PC

       1.  with Ethernet NIC (PPPoE or DHCP on PC); there may be a
           bridged DSL or cable modem as NTE, or the Ethernet NIC might
           be the NTE

       2.  with USB DSL or cable modem [PPPoA, PPPoE, or DHCP on PC]

       Note that the device with NAPT and DHCP of Figure 1 is not
       present in such a scenario.

   2.  One or more hosts with at least one router (DHCP Client or PPPoE,
       DHCP server in router; VoIP can be soft client on PC, stand-alone
       VoIP device, or Analog Terminal Adaptor (ATA) function embedded
       in router)

       1.  combined router and NTE

       2.  separate router with NTE in bridged mode

       3.  separate router with NTE (NTE/router does PPPoE or DHCP to
           WAN, router provides DHCP server for hosts in LAN; double

   The majority of fixed access broadband customers use a router.  The
   placement of the VoIP client is mentioned to describe what sorts of
   hosts may need to be able to request location information.  Soft
   clients on PCs are frequently not launched until long after bootstrap
   is complete, and are not able to control any options that may be
   specified during bootstrap.  They also cannot control whether a VPN
   client is running on the end host.

3.2.  Moving Network

   An example of a moving network is a "WIMAX-like fixed wireless"
   scenario that is offered in several cities, like New Orleans, Biloxi,

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   etc., where much of the communications infrastructure was destroyed
   due to a natural disaster.  The customer-side antenna for this
   service is rather small (about the size of a mass market paperback
   book) and can be run off battery power.  The output of this little
   antenna is a RJ-45 Ethernet jack.  A laptop can be plugged into this
   Ethernet jack.  The user would then run a PPPoE client to connect to
   the network.  Once the network connection is established, the user
   can run a SIP client on the laptop.

   The network-side antenna is, for example, connected through ATM to
   the core network, and from there to the same BRASs that serve regular
   DSL customers.  These Broadband Remote Access Servers (BRASs)
   terminate the PPPoE sessions, just like they do for regular DSL.

   The laptop and SIP client are, in this case, unaware that they are
   "mobile".  All they see is an Ethernet connection, and the IP address
   they get from PPPoE does not change over the coverage area.  Only the
   user and the network are aware of the laptop's mobility.

   Further examples of moving networks can be found in busses, trains,
   and airplanes.

   Figure 2 shows an example topology for a moving network.

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   | Wireless                 |
   | Access Network Provider  |
   |                          |
   |              +----------+|
   |      +-------+ LIS      ||
   |      |       |          ||
   |  +---+----+  +----------+|
   |  | Node   |              |
   |  |        |              |
   |  +---+----+              |
   |      |                   |
          | Wireless Interface
   |      |    Moving Network |
   |  +---+----+              |
   |  | NTE    |   +--------+ |
   |  |        +---+ Host   | |
   |  +-+-----++   |  B     | |
   |    |     \    +--------+ |
   |    |      \              |
   |+---+----+  \  +---+----+ |
   || Host   |   \ | Host   | |
   ||  A     |    \+  B     | |
   |+--------+     +--------+ |

                         Figure 2: Moving Network

3.3.  Wireless Access

   Figure 3 shows a wireless access network where a moving end host
   obtains location information or references to location information
   from the LIS.  The access equipment uses, in many cases, link layer
   devices.  Figure 3 represents a hotspot network found, for example,
   in hotels, airports, and coffee shops.  For editorial reasons we only
   describe a single access point and do not depict how the LIS obtains
   location information since this is very deployment specific.

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   | Access Network Provider  |
   |                          |
   |              +----------+|
   |      +-------| LIS      ||
   |      |       |          ||
   |  +--------+  +----------+|
   |  | Access |              |
   |  | Point  |              |
   |  +--------+              |
   |      |                   |
        | End  |
        | Host |

                    Figure 3: Wireless Access Scenario

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4.  Discovery of the Location Information Server

   When a Target wants to retrieve location information from the LIS it
   first needs to discover it.  Based on the problem statement of
   determining the location of the Target, which is known best by
   entities close to the Target itself, we assume that the LIS is
   located in the local subnet or in access network.  Several procedures
   have been investigated that aim to discover the LIS in such an access

   DHCP-based Discovery:

      In some environments the Dynamic Host Configuration Protocol
      (DHCP) might be a good choice for discovering the FQDN or the IP
      address of the LIS.  In environments where DHCP can be used it is
      also possible to use the already defined location extensions.  In
      environments with legacy devices, such as the one shown in
      Section 3.1, a DHCP based discovery solution may not be possible.

   DNS-based Discovery:

      Before a DNS lookup can be started it is necessary to learn the
      domain name of the access network that runs a LIS.  Several ways
      to learn the domain name exist.  For example, the end host obtains
      its own public IP address, for example via STUN [6], and performs
      a reverse DNS lookup (assuming the data is provisioned into the
      DNS).  Then, the SRV or NAPTR record for that domain is retrieved.
      A more detailed description of this approach can be found in [7].

   Redirect Rule:

      A redirect rule at a device in the access network, for example at
      the AAA client, could be used to redirect the L7 LCP signalling
      messages (destined to a specific port) to the LIS.  The end host
      could then discover the LIS by sending a packet with a specific
      (registered) port number to almost any address (as long as the
      destination IP address does not target a device in the local
      network).  The packet would be redirected to the respective LIS
      being configured.  The same procedure is used by captive portals
      whereby any HTTP traffic is intercepted and redirected.

      To some extend this approach is similar to packets that are marked
      with a Router Alert option [8] and intercepted by entities that
      understand the specific marking.  In the above-mentioned case,
      however, the marking is provided via a registered port number
      instead of relying on a Router Alert option.

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   Multicast Query:

      An end node could also discover a LIS by sending a DNS query to a
      well-known address.  An example of such a mechanism is multicast
      DNS (see [9] and [10]).  Unfortunately, these mechanisms only work
      on the local link.


      With this solution an anycast address is defined (for IPv4 and
      IPv6) in the style of [11] that allows the endhost to route
      discovery packets to the nearest LIS.  Note that this procedure
      would be used purely for discovery and thereby similar to local
      Teredo server discovery approach outlined in Section 4.2 of [12].

   The LIS discovery procedure raises deployment and security issues.
   When an end host discovers a LIS it must be ensured that

   1.  it does not talk to a man-in-the-middle, and

   2.  that the discovered entity is indeed an authorized LIS.

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5.  Identifier for Location Determination

   The LIS returns location information to the end host when it receives
   a request.  Some form of identifier is therefore needed to allow the
   LIS to retrieve the Target's current location (or a good
   approximation of it) from a database.

   The chosen identifier needs to have the following properties:

   Ability for Target to learn or know the identifier:

      The Target MUST know or MUST be able to learn the identifier
      (explicitly or implicitly) in order to send it to the LIS.
      Implicitly refers to the situation where a device along the path
      between the end host and the LIS modifies the identifier, as it is
      done by a NAT when an IP address based identifier is used.

   Ability to use the identifier for location determination:

      The LIS MUST be able to use the identifier (directly or
      indirectly) for location determination.  Indirectly refers to the
      case where the LIS uses other identifiers internally for location
      determination, in addition to the one provided by the Target.

   Security properties of the identifier:

      Misuse needs to be minimized whereby off-path adversary MUST NOT
      be able to obtain location information of other Targets.  A on-
      path adversary in the same subnet SHOULD NOT be able to spoof the
      identifier of another Target in the same subnet.

   The following list discusses frequently mentioned identifiers and
   their properties:

   Host MAC Address:

      The Target's MAC address is known to the end host, but not carried
      over an IP hop and therefore not accessible to the LIS in most
      deployment environments (unless carried in the L7 LCP itself).


      The VPI/VCI is generally only seen by the DSL modem.  Almost all
      routers in the US use 1 of 2 VPI/VCI value pairs:  0/35 and 8/35.
      This VC is terminated at the DSLAM, which uses a different VPI/VCI

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      (per end customer) to connect to the ATM switch.  Only the network
      provider is able to map VPI/VCI values through its network.  With
      the arrival of VDSL, ATM will slowly be phased out in favor of

   Switch/Port Number:

      This identifier is available only in certain networks, such as
      enterprise networks, typically available via proprietary protocols
      like CDP or, in the future, 802.1ab.

   Cell ID:

      This identifier is available in cellular data networks and the
      cell ID may not be visible to the end host.

   Host Identifier:

      The Host Identifier introduced by the Host Identity Protocol [13]
      allows identification of a particular host.  Unfortunately, the
      network can only use this identifier for location determination if
      the operator already stores an mapping of host identities to
      location information.  Furthermore, there is a deployment problem
      since the host identities are not used in todays networks.

   Cryptographically Generated Address (CGA):

      The concept of a Cryptographically Generated Address (CGA) was
      introduced by [14].  The basic idea is to put the truncated hash
      of a public key into the interface identifier part of an IPv6
      address.  In addition to the properties of an IP address it allows
      a proof of ownership.  Hence, a return routability check can be
      omitted.  It is only available for IPv6 addresses.

   Network Access Identifiers:

      A Network Access Identifier [15] is used during the network access
      authentication procedure, for example in RADIUS [16] and Diameter
      [17].  In DSL networks the user credentials are, in many cases,
      only known by the home router and not configured at the Target
      itself.  To the network, the authenticated user identity is only
      available if a network access authentication procedure is
      executed.  In case of roaming the user's identity might not be

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      available to the access network since security protocols might
      offer user identity confidentiality and thereby hiding the real
      identity of the user allowing the access network to only see a
      pseudonym or a randomized string.

   Unique Client Identifier

      The DSL Forum has defined that all devices that expect to be
      managed by the TR-069 interface be able to generate an identifier
      as described in Section 3.4.4 of the TR-069v2 DSL Forum document.
      It also has a requirement that routers that use DHCP to the WAN
      use RFC 4361 [18] to provide the DHCP server with a unique client
      identifier.  This identifier is, however, not visible to the
      Target when legacy NTE device are used.

   IP Address:

      The Target's IP address may be used for location determination.
      This IP address is not visible to the LIS if the end host is
      behind one or multiple NATs.  This may not be a problem since the
      location of a host that is located behind a NAT cannot be
      determined by the access network.  The LIS would in this case only
      see the public IP address of the NAT binding allocated by the NAT,
      which is the expected behavior.  The property of the IP address
      for a return routability check is attractive to return location
      information only to the address that submitted the request.  If an
      adversary wants to learn the location of a Target (as identified
      by a particular IP address) then it does not see the response
      message (unless he is on the subnetwork or at a router along the
      path towards the LIS).

      On a shared medium an adversary could ask for location information
      of another Target.  The adversary would be able to see the
      response message since it is sniffing on the shared medium unless
      security mechanisms, such as link layer encryption, are in place.
      With a network deployment as shown in Section 3.1 with multiple
      hosts in the Customer Premise being behind a NAT the LIS is unable
      to differentiate the individual end points.  For WLAN deployments
      as found in hotels, as shown in Section 3.3, it is possible for an
      adversary to eavesdrop data traffic and subsequently to spoof the
      IP address in a query to the LIS to learn more detailed location
      information (e.g., specific room numbers).  Such an attack might,
      for example, compromise the privacy of hotel guests.

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6.  Requirements

   The following requirements and assumptions have been identified:

   Requirement L7-1: Identifier Choice

      The L7 LCP MUST be able to carry different identifiers or MUST
      define an identifier that is mandatory to implement.  Regarding
      the latter aspect, such an identifier is only appropriate if it is
      from the same realm as the one for which the location information
      service maintains identifier to location mapping.

   Requirement L7-2: Mobility Support

      The L7 LCP MUST support a broad range of mobility from devices
      that can only move between reboots, to devices that can change
      attachment points with the impact that their IP address is
      changed, to devices that do not change their IP address while
      roaming, to devices that continuously move by being attached to
      the same network attachment point.

   Requirement L7-3: ASP and Access Network Provider Relationship

      The design of the L7 LCP MUST NOT assume a business or trust
      relationship between the Application Service Provider (ASP) and
      the Access Network Provider.  Requirements for resolving a
      reference to location information are not discussed in this

   Requirement L7-4: Layer 2 and Layer 3 Provider Relationship

      The design of the L7 LCP MUST assume that there is a trust and
      business relationship between the L2 and the L3 provider.  The L3
      provider operates the LIS and needs to obtain location information
      from the L2 provider since this one is closest to the end host.
      If the L2 and L3 provider for the same host are different
      entities, they cooperate for the purposes needed to determine end
      system locations.

   Requirement L7-5: Legacy Device Considerations

      The design of the L7 LCP MUST consider legacy devices, such as
      residential NAT devices and NTEs in an DSL environment, that
      cannot be upgraded to support additional protocols, for example,

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      to pass additional information towards the Target.

   Requirement L7-6: VPN Awareness

      The design of the L7 LCP MUST assume that at least one end of a
      VPN is aware of the VPN functionality.  In an enterprise scenario,
      the enterprise side will provide the LIS used by the client and
      can thereby detect whether the LIS request was initiated through a
      VPN tunnel.

   Requirement L7-7: Network Access Authentication

      The design of the L7 LCP MUST NOT assume prior network access

   Requirement L7-8: Network Topology Unawareness

      The design of the L7 LCP MUST NOT assume end systems being aware
      of the access network topology.  End systems are, however, able to
      determine their public IP address(es) via mechanisms, such as STUN
      [6] or NSIS NATFW NSLP [19] .

   Requirement L7-9: Discovery Mechanism

      The L7 LCP MUST define a mandatory-to-implement LIS discovery

   Requirement L7-10: PIDF-LO Creation

      When a LIS creates a PIDF-LO [20] then it MUST put the <geopriv>
      element into the <device> element of the presence document (see
      [21]).  This ensures that the resulting PIDF-LO document, which is
      subsequently distributed to other entities, conforms to the rules
      outlined in [22].

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7.  Security Considerations

   This document contains security related requirements.  A discussion
   about security aspects of the HELD protocol when used in the GEOPRIV
   architecture when applied to certain usage environments, such as
   emergency services, can be found in [23].

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8.  IANA Considerations

   This document does not require actions by IANA.

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9.  Contributors

   This contribution is a joint effort of the GEOPRIV Layer 7 Location
   Configuration Requirements Design Team of the IETF GEOPRIV Working
   Group.  The contributors include Henning Schulzrinne, Barbara Stark,
   Marc Linsner, Andrew Newton, James Winterbottom, Martin Thomson,
   Rohan Mahy, Brian Rosen, Jon Peterson and Hannes Tschofenig.

   We would like to thank the GEOPRIV working group chairs, Andy Newton,
   Randy Gellens and Allison Mankin, for creating the design team.

   The design team members can be reached at:

   Marc Linsner:

   Rohan Mahy:

   Andrew Newton:

   Jon Peterson:

   Brian Rosen:

   Henning Schulzrinne:

   Barbara Stark:

   Martin Thomson:

   Hannes Tschofenig:

   James Winterbottom:

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10.  Acknowledgements

   We would like to thank the IETF GEOPRIV working group chairs, Andy
   Newton, Allison Mankin and Randall Gellens, for creating this design
   team.  Furthermore, we would like thank Andy Newton for his support
   during the design team mailing list, for setting up Jabber chat
   conferences and for participating in the phone conference

   We would also like to thank Murugaraj Shanmugam, Ted Hardie, Martin
   Dawson, Richard Barnes, James Winterbottom, Tom Taylor, Otmar Lendl,
   Marc Linsner, Brian Rosen, Roger Marshall, Guy Caron, Doug Stuard,
   Eric Arolick, Dan Romascanu, Jerome Grenier, Martin Thomson, Barbara
   Stark, Michael Haberler, and Mary Barnes for their WGLC review

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11.  References

11.1.  Normative References

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

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

   [3]   Schulzrinne, H. and R. Marshall, "Requirements for Emergency
         Context Resolution with Internet Technologies",
         draft-ietf-ecrit-requirements-13 (work in progress),
         March 2007.

11.2.  Informative References

   [4]   Marshall, R., "Requirements for a Location-by-Reference
         Mechanism", draft-ietf-geopriv-lbyr-requirements-01 (work in
         progress), October 2007.

   [5]   Winterbottom, J. and S. Norreys, "LIS to LIS Protocol
         Requirements", draft-winterbottom-geopriv-lis2lis-req-01 (work
         in progress), November 2007.

   [6]   Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy, "STUN
         - Simple Traversal of User Datagram Protocol (UDP) Through
         Network Address Translators (NATs)", RFC 3489, March 2003.

   [7]   Thomson, M. and J. Winterbottom, "Discovering the Local
         Location Information Server (LIS)",
         draft-thomson-geopriv-lis-discovery-03 (work in progress),
         September 2007.

   [8]   Katz, D., "IP Router Alert Option", RFC 2113, February 1997.

   [9]   Aboba, B., Thaler, D., and L. Esibov, "Link-local Multicast
         Name Resolution (LLMNR)", RFC 4795, January 2007.

   [10]  Cheshire, S. and M. Krochmal, "Multicast DNS",
         draft-cheshire-dnsext-multicastdns-06 (work in progress),
         August 2006.

   [11]  Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
         RFC 3068, June 2001.

   [12]  Ward, N., "Teredo Server Selection",
         draft-nward-v6ops-teredo-server-selection-00 (work in

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         progress), July 2007.

   [13]  Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson,
         "Host Identity Protocol", draft-ietf-hip-base-10 (work in
         progress), October 2007.

   [14]  Aura, T., "Cryptographically Generated Addresses (CGA)",
         RFC 3972, March 2005.

   [15]  Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The Network
         Access Identifier", RFC 4282, December 2005.

   [16]  Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote
         Authentication Dial In User Service (RADIUS)", RFC 2865,
         June 2000.

   [17]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko,
         "Diameter Base Protocol", RFC 3588, September 2003.

   [18]  Lemon, T. and B. Sommerfeld, "Node-specific Client Identifiers
         for Dynamic Host Configuration Protocol Version Four (DHCPv4)",
         RFC 4361, February 2006.

   [19]  Stiemerling, M., "NAT/Firewall NSIS Signaling Layer Protocol
         (NSLP)", draft-ietf-nsis-nslp-natfw-15 (work in progress),
         July 2007.

   [20]  Peterson, J., "A Presence-based GEOPRIV Location Object
         Format", RFC 4119, December 2005.

   [21]  Rosenberg, J., "A Data Model for Presence", RFC 4479,
         July 2006.

   [22]  Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
         PIDF-LO Usage Clarification, Considerations and
         Recommendations", draft-ietf-geopriv-pdif-lo-profile-10 (work
         in progress), October 2007.

   [23]  Barnes, R., "Threats to GEOPRIV Location Objects",
         draft-barnes-geopriv-lo-sec-00 (work in progress), July 2007.

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Authors' Addresses

   Hannes Tschofenig
   Nokia Siemens Networks
   Otto-Hahn-Ring 6
   Munich, Bavaria  81739

   Phone:  +49 89 636 40390

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

   Phone:  +1 212 939 7004

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