| Network Working Group | R. Gellens |
| Internet-Draft | Core Technology Consulting |
| Intended status: Informational | B. Rosen |
| Expires: August 24, 2020 | February 21, 2020 |
The LoST-Validation S-NAPTR Application Service Tag
draft-gellens-lost-validation-05
This document adds the LoST-Validation service tag to the S-NAPTR Application Service Tag IANA registry. This tag is used by clients of the Location-to-Service Translation Protocol (LoST).
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This document only adds an additional entry for 'LoST-Validation' to the S-NAPTR Application Service Tag IANA registry. This tag is used by clients of the Location-to-Service Translation Protocol (LoST) [RFC5222].
The Location-to-Service Translation Protocol, LoST [RFC5222] defines a mapping service with the additional ability to request that a civic address be validated. 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, so that 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, and 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, while another organization might choose to use the same sets of servers for both, 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 server that offers the required service (mapping or validation). This separability needs to be maintained throughout the LoST tree structure, from forest guide to leaf node. 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 the different services. DNS name conventions are inflexible and fragile, so a different service tag is the preferred approach.
This document adds 'LoST-Validation' to the S-NAPTR Application Service Tag 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 explicitly willing to perform 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 should first try U-NAPTR resolution using the 'Lost-Validation' service tag, and may fallback to the 'LoST' service tag if the 'Lost-Validation' service tag cannot be resolved to a usable LoST server.
LoST [RFC5222] specifies that LoST servers are located by resolving an application Unique String (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. 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 absense 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. Using the 'LoST-Validation' service tag might result in the same URL as the 'LoST' service tag, or it may result in a different URL. The URLs might result in the same physical servers being contacted, or different servers.
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 DNS records and client resolution of Application Unique Strings (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, the mapping servers could either perform the validation as requested, or return the 'locationValidationUnavailable' warning, and potentially also include a <redirect> element to redirect to the validation server. However, the <redirect> element contains an Application Unique String, 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 are expected to comply with the latest 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. The server designated for mapping is likely to perform validation when requested, potentially unless it is under load. 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 may no longer be under load and may provide the function. Even in the (unlikely) case of a designated mapping server that refuses to perform validation at any time, the server is likely to return a redirect with a different AUS (e.g., "lvf.example.com") that resolves to a designated validation server. In the (unlikely) worst case, the client will be unable to reach a server willing to perform validation, and will submit a discrepancy report, as specified in NENA i3. The discrepancy report resolution would 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 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. The addition of the tag improves the situation.
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.
IANA is requested to add 'LoST-Validation' to the S-NAPTR Application Service Tag 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 tag".)
This document registers an S-NAPTR application service tag:
Many thanks to Ted Hardie and Ben Campbell for their helpful reviews and suggestions.
| [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. |
| [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. |