IETF ENUM WG R. Stastny Internet Draft OeFEG L. Conroy Document:draft-ietf-enum-void-00.txt Siemens Roke Manor Research Expires: March 2005 October 2004 IANA Registration for Enumservice VOID Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, or will be disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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 a "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This document registers the Enumservice 'void' using the URI schemes 'mailto:' and 'http:' as per the IANA registration process defined in the ENUM specification, RFC3761. This Enumservice may be used to indicate that the E.164 number (or E.164 number range) tied to the domain in which the enclosing NAPTR is published is not assigned for communications service. When such an indication is provided, an ENUM client can detect calls that will fail "early". 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 RFC-2119 [1]. 1. Introduction The Circuit Switched Network (CSN) of which the Public Switched Telephone Network, Integrated Services Digital Network, and Public Land Mobile Network are part is designed to use E.164 numbers [2] as native global addresses. If a potential caller has an E.164 number, then to place a call using this address has needed a way to pass the request either directly or indirectly to systems "in" the CSN for them to forward. ENUM has introduced a mechanism to find other contact addresses when given an E.164 number. Thus, if the caller (or an agent somewhere in the call path) has access to the global DNS, they can use ENUM [3] to find alternative contacts to the E.164 number and place the call using whatever system was indicated in those contacts. However, ENUM entries may not exist for a given E.164 number for two reasons. Either the assignee who is entitled to register an ENUM domain associated with the E.164 number they hold has chosen not to request this registration, or the number is not currently assigned for communications service. In either situation, the caller has no other information and so no alternative to placing the call via the system that uses E.164 numbers as global identifiers; at present, this is the CSN. 2. The problem At present, from the ENUM client's perspective, two possibilities exist: there is an ENUM domain that potentially holds alternative contacts, or there is no ENUM domain, in which case a query on ENUM will return a DNS response showing 'no such domain' (NXDOMAIN, code 3)[4]. This latter response is ambiguous. There are two potential reasons for the lack of an ENUM domain holding alternative contacts; either the assignee has chosen not to register the domain, or the E.164 number is not assigned for communications service at present. If the number is assigned, then the caller can use the E.164 number to place the call via a network that uses such identifiers as global addresses (i.e. the CSN). If however, there is no domain because the associated E.164 number is not assigned for communications service, then any attempt to place the call via the CSN will fail. What would be useful is a mechanism "between" a registration holding NAPTRs with URIs and the lack of a domain registration. In this way, an entity who is responsible for E.164 numbers in a range can indicate that a particular number has not been assigned to anyone for communications service. For example, if a communications service provider has been allocated responsibility for delivering calls to endpoints identified with E.164 numbers in a block, then they may have some numbers in that block that are currently unused. These E.164 numbers are not used to terminate calls to end users. An originating user agent cannot differentiate this state from the one in which there is an end user as a number assignee, but that end user has have chosen not to "publish" other contacts. In effect, it would be more useful if the originating end user could receive a response that states "there is no service via this number", as opposed to "there may be service via this number, but there are no alternative contacts available". 3. The proposed solution We propose an explicit indication of this "number unassigned" state. This uses a NAPTR in the "enclosing" zone, with an Enumservice called VOID that should be taken as an assertion that the associated E.164 number is not assigned to an end user for communications service; it's an unused number. This NAPTR can also be used by an NRA to indicate number blocks that it has reserved or has not allocated, or has not assigned to a service provider. It is a matter for individual Countries whether or not they will support (or require) information giving the identity of the current "owner" of an E.164 number within their responsibility to be made available via IRIS/Whois. Thus it may not be possible to use these protocols to find out the entity responsible for a number or number range, particularly where that number or range is not currently "in use". For this reason, we propose that the VOID indication also includes a contact address (an email address or a web address) by which the authority responsible for this number (or range) can be contacted. This may not be the same entity as the one that maintains the DNS service for that "enclosing zone"; often the NRA will sub-contract a Registry Operator to maintain the DNS, but it is the NRA who is the authority for the E.164 number range, not that Registry Operator. 4. ENUM Service Registration - VOID As defined in [3], the following is a template covering information needed for the registration of the Enumservice specified in this document. Enumservice Name: "VOID" Type(s): "void" Subtype(s): "mailto", "http", "https" URI Scheme(s): "mailto:", "http:", "https:" Functional Specification: The proposed solution in section 3. Definition of expected action: If a NAPTR with this Enumservice is received, it indicates that the queried E.164 number is currently unassigned to an end user for communications service. The recipient SHOULD treat this response as if they had received a "number not in service" indication from a terminating network. Note that, whatever subtype exists for this Enumservice, the generated URI is not a potential target for any current call. This contact (mailto:[5], http:[6], or https:[7]) MUST NOT be used in normal call processing but only if there is a non-call related reason to contact the number holder or authority. Security considerations: see section 6 Intended usage: COMMON Authors: Lawrence Conroy, Richard Stastny (for authors contact details see Authors' Addresses section) Any other information that the author deems interesting: There are three possible subtypes (each with an associated URI scheme). In the first case, the subtype is "mailto" and has a generated URI scheme of "mailto:". This can be used to hold an email address of the entity responsible for the unassigned number or number range (such as the NRA, or the CSP to whom they have allocated a block of numbers, of which the current number is unused). The second case has a sub-type of "http" and has a generated URI scheme of "http:". The last case has a sub-type of "https" and an associated generated URI scheme of "https:". In both these, the URI can be used to indicate a web site holding information on the number (or number range) associated with the domain holding this NAPTR. They differ only in whether or not the URL "points to" a web site using either a standard or TLS-secured connection. 5. Examples (i) VOID:mailto $ORIGIN 0.6.9.2.3.6.1.4.4.e164.arpa. 3.8.0 NAPTR 10 100 "u" "E2U+void:mailto" "!^.*$!mailto:num-drama-info@nra.foo!" This indicates that the controller of the number block +441632960xxx does not provide telephony service via the number +441632960083; it is not assigned to an end user. Information on the status of this number may be obtainable by contacting the email address held in the regexp field. (ii) VOID:http and VOID:https $ORIGIN 0.6.9.2.3.6.1.4.4.e164.arpa. 4.8.0 NAPTR 10 100 "u" "E2U+void:http" "!^.*$!http:\/\/www.nra.foo\/drama-numbers\/index.html!" $ORIGIN 0.6.9.2.3.6.1.4.4.e164.arpa. 4.8.0 NAPTR 10 100 "u" "E2U+void:https" "!^.*$!https:\/\/connect.nra.foo\/drama-numbers\/secure.html!" Both of these examples indicate that the controller of the number block +441632960xxx does not provide communication service via the number +441632960084; it is not assigned to an end user. Information on the status of this number may be obtained by making an HTTP connection to the web URL shown in the regexp field of the former example, or making a connection using TLS to the secure web URL held in the regexp field of the latter example. 6. Security considerations DNS does not make policy decisions about the records that it shares with an inquirer. All DNS records must be assumed to be available to all inquirers at all times. The information provided within an ENUM record set must therefore be considered to be open to the public. An analysis of threats specific to the dependence of ENUM on the DNS, and the applicability of DNSSEC[8] to these, is provided in[3]. The specific issues applicable to this registration are: (i) by including an email address, the responsible authority is making this available globally. They should expect that the published email address will be used to send unsolicited commercial email to them. (ii) by publishing the email address, they expose the identity of the entity that has authority over this E.164 number (or range of numbers. This may also be the case if a web URL is used. (iii) by constructing a DNS response holding a VOID NAPTR, a third party could initiate a denial of service attack on the assignee of a number (or number range). The recipient of a "spoofed" response would react by assuming that the associated E.164 number is not in service, so denying calls to that number. 7. IANA Considerations This document requests registration of the E2U+void Enumservice with three sub-types (void:mailto, void:http and void:https) according to the guidelines and specifications in RFC 3761 [3] and the definitions in this document. 8. Normative References 1 Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 2 ITU-T, "The International Public Telecommunication Number Plan", Recommendation E.164 , May 1997. 3 Faltstrom, P. and Mealling M., "The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)", RFC 3761, April 2004. 4 Mockapetris, P., "Domain Names - Concepts and Facilities", STD 13, RFC 1034, November 1987. 5 Hofmann, P., Masinter, L., Zawinski, J, "The mailto URL scheme", RFC2368, July 1998. 6 Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol - HTTP/1.1", RFC 2616, June 1999; 7 Rescola, E., "HTTP Over TLS", RFC 2818, May 2000. 9. Informative References 8 Eastlake, D.,"Domain Name System Security Extensions", RFC 2535, March 1999 9 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. 10 Bradner, S., "Intellectual Property Rights in IETF Technology", BCP 78, RFC3667, February 2004 11 Bradner, S., "IETF Rights in Contributions", BCP 79, RFC3668, February 2004 10. Acknowledgments Thanks to Jim Reid for the substantial inputs regarding the mechanism to query the enclosed zone and to Patrik Faltstrom and Michael Mealling for their feedback. 11. Author's Addresses Lawrence Conroy Siemens Roke Manor Research Roke Manor Romsey United Kingdom Phone: +44-1794-833666 Email: lwc@roke.co.uk Richard Stastny OeFEG Arsenal Objekt 24, Postbox 147 1140 Vienna Austria Phone: +43 664 420 4100 Email: richard.stastny@oefeg.at This draft expires in March 2005 Full Copyright Statement Copyright (C) The Internet Society (2004). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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