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Internet Engineering Task Force (IETF)                        M. ThomsonRequest for Comments: 7216                                       MozillaCategory: Standards Track                                      R. BellisISSN: 2070-1721                                               Nominet UK                                                              April 2014Location Information Server (LIS) DiscoveryUsing IP Addresses and Reverse DNSAbstract   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 is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7216.Thomson & Bellis             Standards Track                    [Page 1]

RFC 7216                   LIS Discovery by IP                April 2014Copyright Notice   Copyright (c) 2014 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) 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 Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .32.  Conventions Used in This Document . . . . . . . . . . . . . .43.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .43.1.  Residential Gateway . . . . . . . . . . . . . . . . . . .63.2.  Security Features of Residential Gateways . . . . . . . .74.  IP-based DNS Solution . . . . . . . . . . . . . . . . . . . .74.1.  Identification of IP Addresses  . . . . . . . . . . . . .84.2.  Domain Name Selection . . . . . . . . . . . . . . . . . .94.3.  Shortened DNS Names . . . . . . . . . . . . . . . . . . .94.4.  When To Use the Reverse DNS Method  . . . . . . . . . . .104.5.  Private Address Spaces  . . . . . . . . . . . . . . . . .104.6.  Necessary Assumptions and Restrictions  . . . . . . . . .114.7.  Failure Modes . . . . . . . . . . . . . . . . . . . . . .124.8.  Deployment Considerations . . . . . . . . . . . . . . . .125.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .136.  Security Considerations . . . . . . . . . . . . . . . . . . .137.  IAB Considerations  . . . . . . . . . . . . . . . . . . . . .158.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .169.  References  . . . . . . . . . . . . . . . . . . . . . . . . .169.1.  Normative References  . . . . . . . . . . . . . . . . . .169.2.  Informative References  . . . . . . . . . . . . . . . . .16Thomson & Bellis             Standards Track                    [Page 2]

RFC 7216                   LIS Discovery by IP                April 20141.  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 information 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 IP address on a Device requires some   automated process.  This is particularly relevant when one considers   that Devices might move between different access networks served by   different LISs.  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.  Unfortunately,   in most cases these functions effectively prevent the successful use   of DHCP for LIS discovery.   One 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 are not expected (and are likely   not able) to provide these functions.   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, andSection 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 inSection 7.Thomson & Bellis             Standards Track                    [Page 3]

RFC 7216                   LIS Discovery by IP                April 20142.  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 [RFC2119].   This document uses terminology established in [RFC6280] and   [RFC5012].  The terms "Device" and "LIS" are capitalized throughout   when they are used to identify the roles defined in [RFC6280].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   inSection 3.1 of [RFC5687].  In each of these variations, the goal   of LIS discovery is to identify the LIS in the access network.Thomson & Bellis             Standards Track                    [Page 4]

RFC 7216                   LIS Discovery by IP                April 2014                    ________                  (/        \)                 (( 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 geographical 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 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 geographical area might   require a dedicated LIS, a case that is outside the scope of this   document.Thomson & Bellis             Standards Track                    [Page 5]

RFC 7216                   LIS Discovery by IP                April 2014   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.   Unfortunately, such an active involvement in the discovery process   only works for new residential gateway devices that implement those   recommendations.   Where residential gateways already exist, direct involvement of the   gateway in LIS discovery requires that the residential gateway be   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.   Furthermore, updating the software in such devices is not feasible inThomson & Bellis             Standards Track                    [Page 6]

RFC 7216                   LIS Discovery by IP                April 2014   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 that can be used by   Devices to discover their LIS without any assistance from the   network.3.2.  Security Features of Residential Gateways   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.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 ".in-addr.arpa." or ".ip6.arpa." tree.   The goal of this process is to make a small number of DDDS queries in   order to find a LIS.  After LIS discovery using the DHCP-based   process in [RFC5986] has failed, a Device can:   1.  Collect a set of IP addresses that refer to the Device       (Section 4.1).   2.  Convert each IP address into DNS names in the "in-addr.arpa." or       "ip6.arpa." tree (Section 4.2).   3.  Perform the DDDS process for LIS discovery on those DNS names       ([RFC5986]).   4.  Shorten the DNS names by some number of labels and repeat the       DDDS process (Section 4.3).Thomson & Bellis             Standards Track                    [Page 7]

RFC 7216                   LIS Discovery by IP                April 2014   A Device might be reachable at one of a number of IP addresses.  In   the process described, a Device first identifies each IP address from   which it is potentially reachable.  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 favored 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] mechanism 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 Device.  If enabled, the Port Control Protocol (PCP) [RFC6887],   Universal Plug and Play (UPnP) [UPnP-IGD-WANIPConnection1], and NAT   Port Mapping Protocol (NAT-PMP) [RFC6886] are each able to provide   the external address of a residential gateway device.  These, as well   as proprietary methods for determining other addresses, might 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 (seeSection 4.6).   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   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 employed DNS server contains data for the   corresponding private IP address range.Thomson & Bellis             Standards Track                    [Page 8]

RFC 7216                   LIS Discovery by IP                April 20144.2.  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 ".in-addr.arpa." tree and   follows the construction rules inSection 3.5 of [RFC1035].  The   domain name derived from an IP version 6 address is in the   ".ip6.arpa." tree and follows the construction rules inSection 2.5   of [RFC3596].4.3.  Shortened DNS Names   Additional domain names are added to allow for a single DNS 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      successively by 16, 18, 20, and 24 labels, and the query repeated.      This corresponds to a search on a /64, /56, /48, or /32 network      prefix.   This set of labels is intended to provide network operators with a   degree of flexibility in where LIS discovery records can be placed   without significantly increasing the number of DNS names that are   searched.  This does not attach any other significance to these   specific zone cuts or create a classful addressing hierarchy based on   the reverse DNS tree.   For example, the IPv4 address "192.0.2.75" could result in queries   to:   o  75.2.0.192.in-addr.arpa.   o  2.0.192.in-addr.arpa.   o  0.192.in-addr.arpa.Thomson & Bellis             Standards Track                    [Page 9]

RFC 7216                   LIS Discovery by IP                April 2014   Similarly, the IPv6 address "2001:DB8::28e4:3a93:4429:dfb5" could   result in queries to:   o  5.b.f.d.9.2.4.4.3.9.a.3.4.e.8.2.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2      .ip6.arpa.   o  0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.   o  0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.   o  0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.   o  8.b.d.0.1.0.0.2.ip6.arpa.   The limited number of labels by which each name is shortened is   intended to limit the number of DNS queries performed by Devices.  If   no LIS is discovered by this method, the result will be that no more   than five U-NAPTR resolutions are invoked for each IP address.4.4.  When To Use the Reverse DNS Method   The DHCP method described in [RFC5986] MUST 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 because a request to the resulting LIS results in a HELD   "notLocatable" error or equivalent.4.5.  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   addresses.   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 10.0.0.0/8 range, potentially dividing that range   so that a more local LIS can be selected.Thomson & Bellis             Standards Track                   [Page 10]

RFC 7216                   LIS Discovery by IP                April 2014     _____        ________    ( DNS ).....(/        \)      Public    (__A__)    (( Internet ))     Address                (\________/)      Space                      |                    [NAT]     _____       _____|_____    ( DNS )....(/           \)    Private    (__B__)   (( ISP Network ))   Address Space               (\___________/)    (e.g., 10.0.0.0/8)                      |                  [Gateway]                  ____|____                (/         \)     Private               (( Residence ))    Address Space                (\_________/)     (e.g., 192.168.0.0/16)                      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   used.4.6.  Necessary Assumptions and Restrictions   When used by a Device for LIS discovery, this is an UNSAF application   and is subject to the limitations described inSection 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 ".in-addr.arpa." or ".ip6.arpa." record can be updated   by that entity to include a useful value for the LIS address.Thomson & Bellis             Standards Track                   [Page 11]

RFC 7216                   LIS Discovery by IP                April 20144.7.  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 a STUN server is necessary to ensure that   this is successful.   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].4.8.  Deployment Considerations   An access network provider SHOULD provide NAPTR records for each   public IP address that is used for Devices within the access network.   Any DNS server internal to a NAT SHOULD also include records for the   private address range.  These records might only be provided to   clients making requests from the private address range.  Doing so   allows clients within the private address range to discover a LIS   based on their IP address prior to any address translation.  In   geographically distributed networks that use a private address range,   this enables the use of a different LIS for different locations,   based on the IP address range used at each location.  Use of a   public, translated IP address for the network can still work, but it   might result in a suboptimal LIS selection.   A network that operates network address translation SHOULD provide   NAPTR records that reference a LIS endpoint with a public address.   This requires the reservation of an IP address and port for the LIS.   To ensure requests toward the LIS from within the private address   space do not traverse the NAT and have source addresses mapped by the   NAT, networks can provide a direct route to the LIS.  Clients that   perform discovery based on public DNS or STUN servers are thereby   easier to trace based on source address information.   NAPTR records can be provided for individual IP addresses.  To limit   the proliferation of identical records, a single record can be placed   at higher nodes of the tree (corresponding to /24 and /16 for IPv4;   /64, /56, /48, and /32 for IPv6).  A record at a higher point in the   tree (those with a shorter prefix) applies to all addresses lower inThomson & Bellis             Standards Track                   [Page 12]

RFC 7216                   LIS Discovery by IP                April 2014   the tree (those with a longer prefix); records at the lower point   override those at higher points, thus allowing for exceptions to be   specified.5.  Privacy Considerations   As with all uses of geolocation information, it is very important   that measures be taken to ensure that location information is not   provided to unauthorized parties.  The mechanism defined in this   document is focused on the case where a device is learning its own   location so that it can provide that location information to   applications.  We assume that the device learning its own location is   not a privacy risk.  There are then two remaining privacy risks: the   use of geolocation by applications, and the abuse of the location   configuration protocol.   The privacy considerations around the use of geolocation by   applications vary considerably by application context.  A framework   for location privacy in applications is provided in [RFC6280].   The mechanism specified in this document allows a device to discover   its local LIS, from which it then acquires its location using a   Location Configuration Protocol (LCP) [RFC5687].  If an unauthorized   third party can spoof the LCP to obtain a target's location   information, then the mechanism in this document could allow them to   discover the proper server to attack for a given IP address.  Thus,   it is important that a LIS meet the security requirements of the LCP   it implements.  For HELD, these requirements are laid out inSection 9 of [RFC5985].   A Device that discovers a LIS using the methods in this document MUST   NOT provide that LIS with additional information that might reveal   its position, such as the location measurements described in   [RFC7105], unless it has a secondary method for determining the   authenticity of the LIS, such as a white list.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.Thomson & Bellis             Standards Track                   [Page 13]

RFC 7216                   LIS Discovery by IP                April 2014   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 address in an attempt to subvert the rest of the   process.   [RFC5389] describes attacks where an attacker is able to ensure that   a Device receives a falsified reflexive address.  An on-path attacker   might be able to ensure that a falsified address is provided to the   Device.  Even though STUN messages are protected by a STUN MESSAGE-   INTEGRITY attribute, which is an HMAC that uses a shared secret, an   on-path attacker can capture and modify packets, altering source and   destination addresses to provide falsified addresses.   This attack could result in 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.  An independent, trusted source of location   information could aid in verification, even if the trusted source is   unable to provide information with the same degree of accuracy as the   discovered LIS.   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 ".in-addr.arpa." or ".ip6.arpa." trees MUST either use   an alternative trust anchor for these records or rely on other means   of ensuring the veracity of the DNS records.   DNS queries that are not blocked as [RFC6303] demands, or directed to   servers outside the network, can cause the addresses that are in use   within the network to be exposed outside of the network.  For   resolvers within the network, implementing [RFC6303] avoids this   issue; otherwise, the problem cannot be avoided without blocking DNS   queries to external servers.Thomson & Bellis             Standards Track                   [Page 14]

RFC 7216                   LIS Discovery by IP                April 20147.  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   discovery.   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 behavior 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       "brittle".       A description of the necessary assumptions and limitations of       this solution are included inSection 4.6.       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       solution.Thomson & Bellis             Standards Track                   [Page 15]

RFC 7216                   LIS Discovery by IP                April 2014       A longer-term solution is already provided in [RFC5986].       However, that solution relies on widespread deployment.  The       UNSAF solution provided here is 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]).8.  Acknowledgements   Richard Barnes provided the text inSection 5.9.  References9.1.  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.   [RFC3596]  Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,              "DNS Extensions to Support IP Version 6",RFC 3596,              October 2003.   [RFC5986]  Thomson, M. and J. Winterbottom, "Discovering the Local              Location Information Server (LIS)",RFC 5986, September              2010.   [RFC7105]  Thomson, M. and J. Winterbottom, "Using Device-Provided              Location-Related Measurements in Location Configuration              Protocols",RFC 7105, January 2014.9.2.  Informative References   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and              E. Lear, "Address Allocation for Private Internets",BCP5,RFC 1918, February 1996.Thomson & Bellis             Standards Track                   [Page 16]

RFC 7216                   LIS Discovery by IP                April 2014   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",RFC2131, 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.   [RFC3424]  Daigle, L. and IAB, "IAB Considerations for UNilateral              Self-Address Fixing (UNSAF) Across Network Address              Translation",RFC 3424, November 2002.   [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.   [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.   [RFC6280]  Barnes, R., Lepinski, M., Cooper, A., Morris, J.,              Tschofenig, H., and H. Schulzrinne, "An Architecture for              Location and Location Privacy in Internet Applications",BCP 160,RFC 6280, July 2011.   [RFC6303]  Andrews, M., "Locally Served DNS Zones",BCP 163,RFC6303, July 2011.   [RFC6887]  Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.              Selkirk, "Port Control Protocol (PCP)",RFC 6887, April              2013.   [UPnP-IGD-WANIPConnection1]              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, <http://upnp.org/specs/gw/UPnP-gw-WANIPConnection-v1-Service.pdf>.   [RFC6886]  Cheshire, S. and M. Krochmal, "NAT Port Mapping Protocol              (NAT-PMP)",RFC 6886, April 2013.Thomson & Bellis             Standards Track                   [Page 17]

RFC 7216                   LIS Discovery by IP                April 2014   [RFC5625]  Bellis, R., "DNS Proxy Implementation Guidelines",BCP152,RFC 5625, August 2009.   [RFC5985]  Barnes, M., "HTTP-Enabled Location Delivery (HELD)",RFC5985, September 2010.Authors' Addresses   Martin Thomson   Mozilla   Suite 300   650 Castro Street   Mountain View, CA  94041   US   EMail: martin.thomson@gmail.com   Ray Bellis   Nominet UK   Edmund Halley Road   Oxford  OX4 4DQ   United Kingdom   Phone: +44 1865 332211   EMail: ray.bellis@nominet.org.uk   URI:http://www.nominet.org.uk/Thomson & Bellis             Standards Track                   [Page 18]

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