GEOPRIV                                                       M. Thomson
Internet-Draft                                        Andrew Corporation
Intended status: Informational                                 R. Bellis
Expires: March 15, 2012                                       Nominet UK
                                                      September 12, 2011

Location Information Server (LIS) Discovery using IP address and Reverse


   The residential gateway is a device that has become an integral part
   of home networking equipment.  Discovering a Location Information
   Server (LIS) is a necessary part of acquiring location information
   for location-based services.  However, discovering a LIS when a
   residential gateway is present poses a configuration challenge,
   requiring a method that is able to work around the obstacle presented
   by the gateway.

   This document describes a solution to this problem.  The solution
   provides alternative domain names as input to the LIS discovery
   process based on the network addresses assigned to a Device.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 15, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal

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   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions used in this document  . . . . . . . . . . . . . .  4
   3.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Residential Gateway  . . . . . . . . . . . . . . . . . . .  6
     3.2.  Residential Gateway Security Features  . . . . . . . . . .  7
   4.  IP-based DNS Solution  . . . . . . . . . . . . . . . . . . . .  8
     4.1.  Identification of IP Addresses . . . . . . . . . . . . . .  8
     4.2.  Domain Name Selection  . . . . . . . . . . . . . . . . . .  9
     4.3.  When To Use This Method  . . . . . . . . . . . . . . . . .  9
     4.4.  Private Address Spaces . . . . . . . . . . . . . . . . . . 10
     4.5.  Necessary Assumptions and Restrictions . . . . . . . . . . 11
     4.6.  Failure Modes  . . . . . . . . . . . . . . . . . . . . . . 11
     4.7.  Deployment Considerations  . . . . . . . . . . . . . . . . 11
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   7.  IAB Considerations . . . . . . . . . . . . . . . . . . . . . . 15
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 17
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19

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1.  Introduction

   A Location Information Server (LIS) is a service provided by an
   access network.  The LIS uses knowledge of the access network
   topology and other information to generate location for Devices.
   Devices within an access network are able to acquire location
   information from a LIS.

   The relationship between a Device and an access network might be
   transient.  Configuration of the correct LIS at the Device ensures
   that accurate location information is available.  Without location
   information, some network services are not available.

   The configuration of a LIS address on a Device requires some
   automated configuration process.  This is particularly relevant when
   it is considered that Devices might move between different access
   networks.  LIS Discovery [RFC5986] describes a method that employs
   the Dynamic Host Configuration Protocol (DHCPv4 [RFC2131], DHCPv6
   [RFC3315]) as input to U-NAPTR [RFC4848] discovery.

   A residential gateway, or home router, provides a range of networking
   functions for Devices within the network it serves.  In most cases,
   these functions effectively prevent the successful use of DHCP for
   LIS discovery.

   The drawback with DHCP is that universal deployment of a new option
   takes a considerable amount of time.  Often, networking equipment
   needs to be updated in order to support the new option.  Of
   particular concern are the millions of residential gateway devices
   used to provide Internet access to homes and businesses.  While
   [RFC5986] describes functions that can be provided by residential
   gateways to support LIS discovery, gateways built before the
   publication of this specification do not (and cannot) provide these

   This document explores the problem of configuring Devices with a LIS
   address when a residential gateway is interposed between the Device
   and access network.  Section 3 defines the problem and Section 4
   describes a method for determining a domain name that can be used for
   discovery of the LIS.

   In some cases, the solution described in this document is based on a
   UNilateral Self-Address Fixing (UNSAF) [RFC3424] method.  For those
   cases, this solution is considered transitional until such time as
   the recommendations for residential gateways in [RFC5986] are more
   widely deployed.  Considerations relating to UNSAF applications are
   described in Section 7.

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2.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   This document uses terminology established in [RFC3693] and

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3.  Problem Statement

   Figure 1 shows a simplified network topology for fixed wire-line
   Internet access.  This arrangement is typical when wired Internet
   access is provided.  The diagram shows two network segments: the
   access network provided by an internet service provider (ISP), and
   the residential network served by the residential gateway.

   There are a number of variations on this arrangement, as documented
   in Section 3.1 of [RFC5687].  In each of these variations the goal of
   LIS discovery is to identify the LIS in the access network.

                  (/        \)
                 (( Internet ))
                 .- - -|- - - - - - - - - - - -.
                (      |                        )
               (   +--------+       +-------+    )
     Access    (   | Access |. . . .|  LIS  |    )
     Network   (   |  Node  |       |       |    )
      (ISP)    (   +--------+       +-------+    )
                (       \               \       )
                 `- - - -\- - - - - - - -\- - -'
                          \               \
                           \               |
                  .- - - - -\- - - - - - - + -.
                 (           \             |   )
                (      +-------------+     :    )
                (      | Residential |     |    )
    Residential (      |   Gateway   |     :    )
      Network   (      +-------------+     |    )
                (         /        \      /     )
                (        /          \    /      )
                (   +--------+    +--------+    )
                (   | Device |    | Device |    )
                (   +--------+    +--------+    )
                 (                             )
                  `- - - - - - - - - - - - - -'

                   Figure 1: Simplified Network Topology

   A particularly important characteristic of this arrangement is the
   relatively small area served by the residential gateway.  Given a
   small enough area, it is reasonable to delegate the responsibility
   for providing Devices within the residential network with location

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   information to the ISP.  The ISP is able to provide location
   information that identifies the residence, which should be adequate
   for a wide range of purposes.

   A residential network that covers a larger area might require a
   dedicated LIS, a case that is outside the scope of this document.

   The goal of LIS discovery is to identify a LIS that is able to
   provide the Device with accurate location information.  In the
   network topology described, this means identifying the LIS in the
   access network.  The residential gateway is a major obstacle in
   achieving this goal.

3.1.  Residential Gateway

   A residential gateway can encompass several different functions
   including: modem, Ethernet switch, wireless access point, router,
   network address translation (NAT), DHCP server, DNS relay and
   firewall.  Of the common functions provided, the NAT function of a
   residential gateway has the greatest impact on LIS discovery.

   An ISP is typically parsimonious about their IP address allocations;
   each customer is allocated a limited number of IP addresses.
   Therefore, NAT is an extremely common function of gateways.  NAT
   enables the use of multiple Devices within the residential network.
   However NAT also means that Devices within the residence are not
   configured by the ISP directly.

   When it comes to discovering a LIS, the fact that Devices are not
   configured by the ISP causes a significant problem.  Configuration is
   the ideal method of conveying the information necessary for
   discovery.  Devices attached to residential gateways are usually
   given a generic configuration that includes no information about the
   ISP network.  For instance, DNS configuration typically points to a
   DNS relay on the gateway device.  This approach ensures that the
   local network served by the gateway is able to operate without a
   connection to the ISP, but it also means that Devices are effectively
   ignorant of the ISP network.

   [RFC5986] describes several methods that can be applied by a
   residential gateway to assist Devices in acquiring location
   information.  For instance, the residential gateway could forward LIS
   address information to hosts within the network it serves.  Such an
   active involvement in the discovery process only works for new
   residential gateway devices that implement these recommendations.

   Where residential gateways already exist, direct involvement of the
   gateway in LIS discovery requires that the residential gateway be

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   updated or replaced.  The cost of replacement is difficult to justify
   to the owner of the gateway, especially when it is considered that
   the gateway still fills its primary function: Internet access.

   Existing residential gateways have proven to be quite reliable
   devices, some operating continuously for many years without failure.
   As a result, there are many operational gateways that are of a
   considerable age, some well outside the period of manufacturer
   support.  Updating the software in such devices is not feasible in
   many cases.  Even if software updates were made available, many
   residential gateways cannot be updated remotely, inevitably leading
   to some proportion that is not updated.

   This document therefore describes a method which can be used by
   Devices to discover their LIS without any assistance from the

3.2.  Residential Gateway Security Features

   A network firewall function is often provided by residential gateways
   as a security measure.  Security features like intrusion detection
   systems help protect users from attacks.  Amongst these protections
   is a port filter that prevents both inbound and outbound traffic on
   certain TCP and UDP ports.  Therefore, any solution needs to consider
   the likelihood of traffic being blocked.

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4.  IP-based DNS Solution

   LIS discovery [RFC5986] uses a DNS-based Dynamic Delegation Discovery
   Service (DDDS) system as the basis of discovery.  Input to this
   process is a domain name.  Use of DHCP for acquiring the domain name
   is specified, but alternative methods of acquisition are permitted.

   This document specifies a means for a device to discover several
   alternative domain names that can be used as input to the DDDS
   process.  These domain names are based on the IP address of the
   Device.  Specifically, the domain names are a portion of the reverse
   DNS trees - either the "" or "" tree.

   A Device might be reachable at one of a number of IP addresses.  In
   the process described, a Device first identifies each IP address that
   it is potentially reachable from.  From each of these addresses, the
   Device then selects up to three domain names for use in discovery.
   These domain names are then used as input to the DDDS process.

4.1.  Identification of IP Addresses

   A Device identifies a set of potential IP addresses that currently
   result in packets being routed to it.  These are ordered by
   proximity, with those addresses that are used in adjacent network
   segments being favoured over those used in public or remote networks.
   The first addresses in the set are those that are assigned to local
   network interfaces.

   A Device can use the Session Traversal Utilities for NAT (STUN)
   [RFC5389] to determine its public reflexive transport address.  The
   host uses the "Binding Request" message and the resulting
   "XOR-MAPPED-ADDRESS" parameter that is returned in the response.

   Alternative methods for determining other IP addresses MAY be used by
   the host.  Universal Plug and Play (UPnP) [UPnP-IGD-WANIPConnection1]
   and NAT Port Mapping Protocol (NAT-PMP) [I-D.cheshire-nat-pmp] are
   both able to provide the external address of a residential gateway
   device when enabled.  These as well as proprietary methods for
   determining other addresses might also be available.  Because there
   is no assurance that these methods will be supported by any access
   network these methods are not mandated.  Note also that in some
   cases, methods that rely on the view of the network from the
   residential gateway device could reveal an address in a private
   address range (see Section 4.5).

   In many instances, the IP address produced might be from a private
   address range.  For instance, the address on a local network
   interface could be from a private range allocated by the residential

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   gateway.  In other cases, methods that rely on the view of the
   network (UPnP, NAT-PMP) from the residential gateway device could
   reveal an address in a private address range if the access network
   also uses NAT.  For a private IP address, the derived domain name is
   only usable where the DNS server used contains data for the
   corresponding private IP address range.

4.2.  Domain Name Selection

   The domain name selected for each resulting IP address is the name
   that would be used for a reverse DNS lookup.  The domain name derived
   from an IP version 4 address is in the "" tree and
   follows the construction rules in Section 3.5 of [RFC1035].  The
   domain name derived from an IP version 6 address is in the
   "" tree and follows the construction rules in Section 2.5
   of [RFC3596].

   Additional domain names are added to allow for a single record to
   cover a larger set of addresses.  If the search on the domain derived
   from the full IP address does not produce a NAPTR record with the
   desired service tag (e.g., "LIS:HELD"), a similar search is repeated
   based on a shorter domain name, using a part of the IP address:

   o  For IP version 4, the resulting domain name SHOULD be shortened
      successively by one and two labels and the query repeated.  This
      corresponds to a search on a /24 or /16 network prefix.  This
      allows for fewer DNS records in the case where a single access
      network covering an entire /24 or /16 network is served by the
      same LIS.

   o  For IP version 6, the resulting domain SHOULD be shortened
      sucessively by 16, 18, 20 and 24 labels and the query repeated.
      This corresponds to a search on a /64, /56, /48 or /32 network

   DNS queries on other prefixes than those listed above SHOULD NOT be
   performed to limit the number of DNS queries performed by Devices.
   If no LIS is discovered by this method, no more than four U-NAPTR
   resolutions are invoked for each IP address.

4.3.  When To Use This Method

   The DHCP method described in [RFC5986] SHOULD be attempted on all
   local network interfaces before attempting this method.  This method
   is employed either because DHCP is unavailable, when the DHCP server
   does not provide a value for the access network domain name option,
   or if a request to the resulting LIS results in a HELD "notLocatable"
   error or equivalent.

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4.4.  Private Address Spaces

   Addresses from a private use address space can be used as input to
   this method.  In many cases, this applies to addresses defined in
   [RFC1918], though other address ranges could have limited
   reachability where this advice also applies.  This is only possible
   if a DNS server with a view of the same address space is used.
   Public DNS servers cannot provide useful records for private

   Using an address from a private space in discovery can provide a more
   specific answer if the DNS server has records for that space.
   Figure 2 shows a network configuration where addresses from an ISP
   network could better indicate the correct LIS.  Records in DNS B can
   be provided for the range, potentially dividing that range
   so that a more local LIS can be selected.

     _____        ________
    ( DNS ).....(/        \)      Public
    (__A__)    (( Internet ))     Address
                (\________/)      Space
     _____       _____|_____
    ( DNS )....(/           \)    Private
    (__B__)   (( ISP Network ))   Address Space
               (\___________/)    (e.g.
                (/         \)     Private
               (( Residence ))    Address Space
                (\_________/)     (e.g.

                      Figure 2: Address Space Example

   The goal of automatic DNS configuration is usually to select a local
   DNS, which suits configurations like the one shown.  However, use of
   public DNS or STUN servers means that a public IP address is likely
   to be found.  For STUN in particular, selecting a public server
   minimizes the need for reconfiguration when a Device moves.  Adding
   records for the public address space used by an access network
   ensures that the discovery process succeeds when a public address is

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4.5.  Necessary Assumptions and Restrictions

   When used by a Device for LIS discovery this is an UNSAF application
   and is subject to the limitations described in Section 7.

   It is not necessary that the IP address used is unique to the Device,
   only that the address can be somehow related to the Device or the
   access network that serves the Device.  This allows a degree of
   flexibility in determining this value, although security
   considerations (Section 6) might require that the address be verified
   to limit the chance of falsification.

   This solution assumes that the public reflexive transport address
   used by a Device is in some way controlled by the access network
   provider, or some other related party.  This implies that the
   corresponding "" or "" record can be updated
   by that entity to include a useful value for the LIS address.

4.6.  Failure Modes

   Successful use of private addresses relies on a DNS server that has
   records for the address space that is used.  Using a public IP
   address increases the likelihood of this.  This document relies on
   STUN to provide the Device with a public reflexive transport address.
   Configuration of STUN server is necessary to ensure that this is

   Alternative methods for discovering external IP addresses are
   possible, including UPnP and NAT-PMP.  These methods might not be
   supported by the residential gateway and cannot be relied upon in all

   In cases where a virtual private network (VPN) or other tunnel is
   used, the entity providing a public IP address might not be able to
   provide the Device with location information.  It is assumed that
   this entity is able to identify this problem and indicate this to the
   Device (using the "notLocatable" HELD error, or similar).  This
   problem is described in more detail in [RFC5985].

4.7.  Deployment Considerations

   An access network provider SHOULD provide NAPTR records for each
   public IP address that is used for Devices within the access network.
   If the access network provider uses NAT, any DNS internal to that NAT
   SHOULD also include records for the private address range.

   NAPTR records can be provided for individual IP addresses.  To limit
   the proliferation of identical records, a single record can be placed

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   at a the higher nodes of the tree (corresponding to /24 and /16 for
   IPv4; /64, /48 and /32 for IPv6).  A record at a higher point in the
   tree (those with a shorter prefix) applies to all addresses lower in
   the tree (those with a longer prefix); records at the lower point
   override those at higher points, allowing for exceptions to be
   provided for at the lower point.

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5.  IANA Considerations

   [RFC Editor: please remove this section prior to publication.]

   This document has no IANA actions.

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6.  Security Considerations

   The security considerations described in [RFC5986] apply to the
   discovery process as a whole.  The primary security concern is with
   the potential for an attacker to impersonate a LIS.

   The added ability for a third party to discover the identity of a LIS
   does not add any concerns, since the identity of a LIS is considered
   public information.

   In addition to existing considerations, this document introduces
   further security considerations relating to the identification of the
   IP address.  It is possible that an attacker could attempt to provide
   a falsified IP addresses in an attempt to subvert the rest of the

   [RFC5389] describes attacks where an attacker is able to ensure that
   a Device receives a falsified reflexive address.  Even if the STUN
   server is trusted, an attacker might be able to ensure that a
   falsified address is provided to the Device.

   This attack is an effective means of denial of service, or a means to
   provide a deliberately misleading service.  Notably, any LIS that is
   identified based on a falsified IP address could still be a valid LIS
   for the given IP address, just not one that is useful for providing
   the Device with location information.  In this case, the LIS provides
   a HELD "notLocatable" error, or an equivalent.  If the falsified IP
   address is under the control of the attacker, it is possible that
   misleading (but verifiable) DNS records could indicate a malicious
   LIS that provides false location information.

   In all cases of falsification, the best remedy is to perform some
   form of independent verification of the result.  No specific
   mechanism is currently available to prevent attacks based on
   falsification of reflexive addresses; it is suggested that Devices
   attempt to independently verify that the reflexive transport address
   provided is accurate.

   Use of private address space effectively prevents use of the usual
   set of trust anchors for DNSSEC.  Only a DNS server that is able to
   see the same private address space can provide useful records.  A
   Device that relies on DNS records in the private address space
   portion of the "" or "" trees MUST either use
   an alternative trust anchor for these records or rely on other means
   of ensuring the veracity of the DNS records.

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7.  IAB Considerations

   The IAB has studied the problem of Unilateral Self-Address Fixing
   (UNSAF) [RFC3424], which is the general process by which a client
   attempts to determine its address in another realm on the other side
   of a NAT through a collaborative protocol reflection mechanism, such
   as STUN.

   This section only applies to the use of this method of LIS discovery
   by Devices and does not apply to its use for third-party LIS

   The IAB requires that protocol specifications that define UNSAF
   mechanisms document a set of considerations.

   1.  Precise definition of a specific, limited-scope problem that is
       to be solved with the UNSAF proposal.

       Section 3 describes the limited scope of the problem addressed in
       this document.

   2.  Description of an exit strategy/transition plan.

       [RFC5986] describes behaviour that residential gateways require
       in order for this short term solution to be rendered unnecessary.
       When implementations of the recommendations in LIS discovery are
       widely available, this UNSAF mechanism can be made obsolete.

   3.  Discussion of specific issues that may render systems more

       A description of the necessary assumptions and limitations of
       this solution are included in Section 4.5.

       Use of STUN for discovery of a reflexive transport address is
       inherently brittle in the presence of multiple NATs or address
       realms.  In particular, brittleness is added by the requirement
       of using a DNS server that is able to view the address realm that
       contains the IP address in question.  If address realms use
       overlapping addressing space, then there is a risk that the DNS
       server provides information that is not useful to the Device.

   4.  Identify requirements for longer term, sound technical solutions;
       contribute to the process of finding the right longer term

       A longer term solution is already provided in [RFC5986].
       However, that solution relies on widespread deployment.  The

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       UNSAF solution provided here is provided as an interim solution
       that enables LIS access for Devices that are not able to benefit
       from deployment of the recommendations in [RFC5986].

   5.  Discussion of the impact of the noted practical issues with
       existing deployed NATs and experience reports.

       The UNSAF mechanism depends on the experience in deployment of
       STUN [RFC5389].  On the whole, existing residential gateway
       devices are able to provide access to STUN and DNS service
       reliably, although regard should be given to the size of the DNS
       response (see [RFC5625]).

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8.  References

8.1.  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", BCP 14, RFC 2119, March 1997.

   [RFC3424]  Daigle, L. and IAB, "IAB Considerations for UNilateral
              Self-Address Fixing (UNSAF) Across Network Address
              Translation", RFC 3424, November 2002.

   [RFC3596]  Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
              "DNS Extensions to Support IP Version 6", RFC 3596,
              October 2003.

   [RFC5985]  Barnes, M., "HTTP-Enabled Location Delivery (HELD)",
              RFC 5985, September 2010.

   [RFC5986]  Thomson, M. and J. Winterbottom, "Discovering the Local
              Location Information Server (LIS)", RFC 5986,
              September 2010.

8.2.  Informative References

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

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

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

   [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.

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   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              October 2008.

   [RFC5687]  Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7
              Location Configuration Protocol: Problem Statement and
              Requirements", RFC 5687, March 2010.

              Polk, J., Rosen, B., and J. Peterson, "Location Conveyance
              for the Session Initiation Protocol",
              draft-ietf-sipcore-location-conveyance-09 (work in
              progress), September 2011.

              UPnP Forum, "Internet Gateway Device (IGD) Standardized
              Device Control Protocol V 1.0: WANIPConnection:1 Service
              Template Version 1.01 For UPnP Version 1.0", DCP 05-001,
              Nov 2001.

              Cheshire, S., "NAT Port Mapping Protocol (NAT-PMP)",
              draft-cheshire-nat-pmp-03 (work in progress), April 2008.

   [RFC6155]  Winterbottom, J., Thomson, M., Tschofenig, H., and R.
              Barnes, "Use of Device Identity in HTTP-Enabled Location
              Delivery (HELD)", RFC 6155, March 2011.

   [RFC5625]  Bellis, R., "DNS Proxy Implementation Guidelines",
              BCP 152, RFC 5625, August 2009.

Thomson & Bellis         Expires March 15, 2012                [Page 18]

Internet-Draft             LIS Discovery by IP            September 2011

Authors' Addresses

   Martin Thomson
   Andrew Corporation
   PO Box U40
   Wollongong University Campus, NSW  2500

   Phone: +61 2 4221 2915

   Ray Bellis
   Nominet UK
   Edmund Halley Road
   Oxford  OX4 4DQ
   United Kingdom

   Phone: +44 1865 332211

Thomson & Bellis         Expires March 15, 2012                [Page 19]