RFC8917: The LoST-Validation Straightforward-Naming Authority PoinTeR (S-NAPTR) Application Service Tag

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Internet Engineering Task Force (IETF)                        R. Gellens
Request for Comments: 8917                    Core Technology Consulting
Updates: 5222                                                   B. Rosen
Category: Standards Track                                   October 2020
ISSN: 2070-1721

 The LoST-Validation Straightforward-Naming Authority PoinTeR (S-NAPTR)
                        Application Service Tag


   This document adds the 'LoST-Validation' service tag to the
   Straightforward-Naming Authority PoinTeR (S-NAPTR) Application
   Service Tag IANA registry.  This tag can appear in a Naming Authority
   Pointer (NAPTR) Domain Name System (DNS) record to assist clients of
   the Location-to-Service Translation (LoST) Protocol in identifying
   LoST servers designated for location validation.  This tag and the
   information about its use update RFC 5222, which enables the explicit
   discovery of a server that supports location validation.

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 in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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   document authors.  All rights reserved.

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Table of Contents

   1.  Document Scope
   2.  Introduction
     2.1.  Requirements Language
   3.  The LoST-Validation Application Service Tag
   4.  Backwards Compatibility
   5.  Security Considerations
   6.  IANA Considerations
     6.1.  S-NAPTR Registration
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Authors' Addresses

1.  Document Scope

   This document adds 'LoST-Validation' to the S-NAPTR Application
   Service Tag IANA registry and describes how this tag fits in the LoST
   server discovery procedure described in [RFC5222].  This tag is used
   with Naming Authority Pointer (NAPTR) Domain Name System (DNS)
   records so that clients of the Location-to-Service Translation (LoST)
   Protocol [RFC5222] can identify servers designated for location
   validation.  This tag and the information on its use is an update to
   [RFC5222] that enables the explicit discovery of a server that
   supports location validation.

2.  Introduction

   The LoST Protocol [RFC5222] defines a mapping service with the
   additional ability for a client to request that a civic address be
   validated.  The LoST protocol allows servers to ignore a request to
   perform location validation.  The National Emergency Number
   Association (NENA) has defined an architecture for all-IP emergency
   services (known as "i3" [NENA-i3]), which defines the mapping
   (routing) and validation functions as two distinct functional
   elements, defined as an Emergency Call Routing Function (ECRF) and a
   Location Validation Function (LVF).  NENA i3 requires that the
   mapping (ECRF) and validation (LVF) functions be separable; an entity
   responsible for a LoST server cluster can decide to provide mapping
   and validation services using consolidated or separate server
   clusters (i.e., using the same or separate boxes).  The rationale is
   that the mapping service is used in real time during emergency call
   routing, while the validation service is used in advance, typically
   when data is provisioned; therefore, the mapping service has much
   higher availability and response-time requirements than the
   validation service.  An organization might choose to deploy these
   services using different server clusters to make it easier to provide
   higher levels of service for the mapping function while shielding it
   from the potentially bursty load of validation.  Another organization
   might choose to use the same sets of servers for both services,
   configured and deployed to offer the high service level demanded of
   the mapping service.

   In order to permit this separability, any entity querying a LoST
   server needs to be able to resolve an Application Unique String (AUS)
   into a URL for a LoST server designated for the required service
   (mapping or validation).  This separability needs to be maintained
   throughout the LoST tree structure, from forest guide to leaf node
   (LoST architecture is described in [RFC5582]).  Because LoST
   referrals return an AUS rather than a URL, either a different service
   tag or a DNS name convention (e.g., "ecrf.example.org" and
   "lvf.example.org") is needed to differentiate between the services.
   DNS name conventions are inflexible and fragile, making a different
   service tag the preferred approach.

   Because LoST servers may ignore a request to perform location
   validation, a service tag explicitly for location validation also
   reduces the likelihood (which has existed since [RFC5582]) that a
   client needing location validation will reach servers that are not
   doing so (due to configuration and/or conditions).

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  The LoST-Validation Application Service Tag

   This document adds 'LoST-Validation' to the "S-NAPTR Application
   Service Tags" registry created by [RFC3958].  The 'LoST-Validation'
   tag serves as a counterpart to the 'LoST' tag added by [RFC5222]: the
   'LoST' tag identifies servers able to perform the core mapping
   function, while 'LoST-Validation' identifies servers designated for
   the validation function.

   Because some servers might be configured to provide both mapping and
   validation functions, a server identified using the 'LoST' service
   tag might also perform the validation function (and resolving the two
   tags might result in the same URL).  Because the two functions might
   be separate, clients seeking a LoST server for location validation
   can first try a URI-Enabled NAPTR (U-NAPTR) resolution using the
   'LoST-Validation' service tag and can fall back to the 'LoST' service
   tag if this does not resolve to a usable LoST server.

   LoST [RFC5222] specifies that LoST servers are located by resolving
   an AUS using U-NAPTR/DDDS (URI-Enabled NAPTR / Dynamic Delegation
   Discovery Service) [RFC4848] and defines the 'LoST' application
   service tag.  In order to permit separability of the mapping and
   validation services performed using LoST, this document defines the
   'LoST-Validation' service tag.  This tag also reduces the likelihood
   that a client needing location validation might reach servers that
   are not performing validation (due to configuration and/or
   conditions).  NAPTR records for LoST servers available for location
   validation contain the 'LoST-Validation' service tag.  An entity
   needing to perform location validation using LoST performs the
   discovery procedure as described in [RFC5222], except that the 'LoST-
   Validation' service tag is used in preference to the 'LoST' service
   tag.  For both service tags, the HTTP and HTTPS URL schemes are used.
   In the absence of any NAPTR records containing the 'LoST-Validation'
   service tag, the 'LoST' service tag is used.  Fallback to the 'LoST'
   service tag may follow if the 'LoST-Validation' service tag fails to
   result in a usable LoST server.  The discovery procedure with the
   'LoST-Validation' service tag might result in the same URL as the
   'LoST' service tag, or it may result in a different URL.  When the
   URLs are different, they could lead to the same physical servers or
   different servers.

4.  Backwards Compatibility

   The primary use of LoST in general, and the location validation
   functionality in particular, is within the emergency services area.
   Within North America, the NENA i3 [NENA-i3] document specifies how
   protocols including LoST are used.  The i3 document is expected to
   reference the 'LoST-Validation' service tag and specify its use in
   both server NAPTR DNS records and client resolution of AUS.

   LoST allows a server to refuse to perform location validation and
   defines the 'locationValidationUnavailable' warning.  LoST also
   allows a server to refer to another server rather than answering
   itself.  So, in a deployment where a LoST tree has separate server
   clusters for mapping and for validation, mapping servers receiving a
   request for validation could either perform the validation as
   requested or return the 'locationValidationUnavailable' warning and
   potentially also include a <redirect> element to redirect to a
   validation server.  However, the <redirect> element contains an AUS,
   so unless the AUSs for validation and mapping are different (e.g.,
   'ecrf.example.org' and 'lvf.example.org'), we still need a different
   service tag to allow for flexible deployment choices (i.e., not
   requiring a DNS name convention).

   LoST clients performing emergency services operations in North
   America are expected to comply with the NENA i3 specification and
   hence support the 'LoST-Validation' service tag when defined.  A LoST
   client implemented prior to the addition of the 'LoST-Validation' tag
   would use the 'LoST' tag to resolve an AUS.  Such a client might not
   be performing location validation, but if it is, the LoST server it
   contacts may perform the service.  Even in a deployment where mapping
   and validation are split, the data is identical; the split is a load
   and deployment optimization strategy.  Servers designated for mapping
   might perform validation when requested (potentially depending on
   load or other factors).  If an older client attempts validation using
   a designated mapping server that refuses the request, the client will
   retry later, at which point the server might provide the function
   (e.g., if its load or other conditions have changed).  Even in the
   case of a designated mapping server that refuses to perform
   validation at any time, the server could return a redirect with a
   different AUS (e.g., "lvf.example.com") that resolves to a designated
   validation server.  In the worst case, the client will be unable to
   reach a server willing to perform validation and will follow up
   (e.g., submit a discrepancy report as specified in NENA i3).  The
   resolution may be to update the client with the 'LoST-Validation'
   service tag, update the AUS returned in a redirect and DNS to use a
   different DNS host name, or permit the server to perform validation
   when not under stress (or a combination).  Note that, because LoST
   does not require servers to perform validation, the situation
   described can exist regardless of the addition of the 'LoST-
   Validation' service tag.  Use of the tag improves the likelihood that
   a client is able to validate a location when needed.

5.  Security Considerations

   The security considerations described in [RFC3958], [RFC4848], and
   [RFC5222] apply here.  No additional security aspects are foreseen by
   the addition of an extra tag.  Separation of services might be
   desired, for example, to be able to allocate different levels of
   resources (such as server capacity, attack mitigation, bandwidth,
   etc.) to the mapping and validation services, in which case separate
   tags are needed to allow LoST clients (which may include other LoST
   servers) to identify the correct server cluster.

   [RFC5222] descriptively discusses the use of DNS security [RFC4033]
   to mitigate the risk of DNS-based attacks.  Because DNS security has
   become more widely deployed since the publication of [RFC5222], such
   measures SHOULD be used when performing NAPTR resolution.  Note that,
   while there are valid reasons to proceed with a LoST mapping query
   despite security failures while initiating or processing an emergency
   call, these concerns generally do not apply to a LoST validation
   query done in advance of an emergency call.

6.  IANA Considerations

   IANA has added 'LoST-Validation' to the "S-NAPTR Application Service
   Tags" registry created by [RFC3958].  This tag serves as a
   counterpart to the 'LoST' tag added by [RFC5222].

   (Note that IANA and [RFC3958] call this registry "S-NAPTR Application
   Service Tags", while [RFC5222] calls it "U-NAPTR application service

6.1.  S-NAPTR Registration

   This document registers an S-NAPTR application service tag:

   Application Service Tag:  LoST-Validation

   Defining Publication:  This document

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC3958]  Daigle, L. and A. Newton, "Domain-Based Application
              Service Location Using SRV RRs and the Dynamic Delegation
              Discovery Service (DDDS)", RFC 3958, DOI 10.17487/RFC3958,
              January 2005, <https://www.rfc-editor.org/info/rfc3958>.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,

   [RFC4848]  Daigle, L., "Domain-Based Application Service Location
              Using URIs and the Dynamic Delegation Discovery Service
              (DDDS)", RFC 4848, DOI 10.17487/RFC4848, April 2007,

   [RFC5222]  Hardie, T., Newton, A., Schulzrinne, H., and H.
              Tschofenig, "LoST: A Location-to-Service Translation
              Protocol", RFC 5222, DOI 10.17487/RFC5222, August 2008,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

7.2.  Informative References

   [NENA-i3]  National Emergency Number Association (NENA)
              Interconnection and Security Committee, i3 Architecture
              Working Group, "Detailed Functional and Interface
              Standards for the NENA i3 Solution", 2016,

   [RFC5582]  Schulzrinne, H., "Location-to-URL Mapping Architecture and
              Framework", RFC 5582, DOI 10.17487/RFC5582, September
              2009, <https://www.rfc-editor.org/info/rfc5582>.


   Many thanks to Ted Hardie, Ben Campbell, Dan Banks, Pete Resnick,
   Shawn Emery, Robert Wilton, Roman Danyliw, and Benjamin Kaduk for
   their helpful reviews and suggestions and to Barry Leiba for
   shepherding the document.

Authors' Addresses

   Randall Gellens
   Core Technology Consulting
   United States of America

   Email: rg+ietf@coretechnologyconsulting.com
   URI:   http://www.coretechnologyconsulting.com

   Brian Rosen
   470 Conrad Dr.
   Mars, PA 16046
   United States of America

   Email: br@brianrosen.net