ENUM -- Telephone Number Mapping O. Lendl Working Group enum.at Internet-Draft December 12, 2006 Intended status: Standards Track Expires: June 15, 2007 The ENUM Branch Location Record draft-ietf-enum-branch-location-record-02 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on June 15, 2007. Copyright Notice Copyright (C) The IETF Trust (2006). Abstract This documents defines the ENUM Branch Location record (EBL) which is used to indicate where the ENUM tree for special ENUM application is located. The primary application for the EBL record is to provide a temporary solution for the Infrastructure ENUM tree location. Lendl Expires June 15, 2007 [Page 1] Internet-Draft ENUM Branch Location Record December 2006 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Context . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. The generalized ENUM Application . . . . . . . . . . . . . . . 4 4. The EBL Resource Record . . . . . . . . . . . . . . . . . . . . 5 4.1. The EBL RDATA Format . . . . . . . . . . . . . . . . . . . 5 4.2. The EBL Presentation Format . . . . . . . . . . . . . . . . 5 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . . 7 9.2. Informative References . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . . . 9 Lendl Expires June 15, 2007 [Page 2] Internet-Draft ENUM Branch Location Record December 2006 1. Introduction ENUM (E.164 Number Mapping) as defined in RFC 3761 [1] (User-ENUM) is based on the concept of a single "golden" tree (e164.arpa) which stores telephone number to URI mappings. Experience has shown that this single tree is not suitable for all applications and usage scenarios. The rules regarding administrative control of domains, opt-in requirements, and delegation hierarchy can vary between applications. See e.g. Infrastructure ENUM [5]. While non-terminal NAPTRs (see [3]) can redirect the ENUM resolution algorithm to another DNS tree, their semantics are not powerful enough to support an integration of Infrastructure ENUM into User ENUM at the number level. A more generic application-specific redirection mechanism is thus needed. The ENUM Branch Location (EBL) Record as defined by this document contains information to drive a generalized algorithm which transforms a telephone number into a domain name. This extends the original algorithm as defined in section 2.4 of RFC 3761 [1] for specific use-cases. 2. Context RFC 3761 defines ENUM as a Dynamic Delegation Discovery System (DDDS) application according to RFC 3401 ff [2]. As such, ENUM defines the following components of the DDDS algorithm: 1. Application Unique String 2. First Well Known Rule 3. Expected Output 4. Valid Databases The generalized ENUM application as based on EBL records extends only the definition of the "Valid Databases" part of the DDDS algorithm. All other aspects of ENUM (e.g. further processing, valid enum- service types) are not affected. The terminology can be confusing: ENUM is a DDDS Application. This draft generalizes ENUM to allow specific applications (e.g. Infrastructure ENUM) to use EBL records to tailor the ENUM algorithm to their individual needs. To distinguish these two layers of "applications", this document uses the term "use-case" for specific applications of the EBL-enabled ENUM algorithm. Lendl Expires June 15, 2007 [Page 3] Internet-Draft ENUM Branch Location Record December 2006 This document does not define where EBL records are located in the DNS, that is left to documents which describe an actual use-case of the generalized ENUM application. 3. The generalized ENUM Application To recap, RFC 3761 (section 2.4) uses the following steps for the "Valid Databases" part of the DDDS Algorithm: 1. Remove all characters with the exception of the digits. 2. Put dots (".") between each digit. 3. Reverse the order of the digits. 4. Append the string ".e164.arpa" to the end. This small algorithm translates the "Application Unique String" (AUS, the E.164 telephone number) to a fully qualified domain name (FQDN) which is then used to query for NAPTR (Naming Authority Pointer, [3]) records containing rewriting rules. Any use-case which uses EBL records to generalize the basic ENUM algorithm needs to define where EBLs for this use-case are located in the DNS. The EBL itself contains three parameters which affect the translation algorithm: SEPERATOR, POSITION, and APEX. The generalized algorithm to derive the initial FQDN for the NAPTR lookup (thus replacing steps 1-4 from above) is defined as: 1. Apply the use-case specific algorithm to translate the AUS (the E.164 telephone number) to the location of the EBL record in the DNS. This needs to yields a fully qualified domain name (FQDN). 2. Query the DNS for an EBL record at the location of this FQDN, and retrieve the triple (SEPERATOR, POSITION, APEX) from this record. If multiple records are present, take any one and ignore the others. If no EBL record was found, use the triple ("", 0, "e164.arpa") as default. This corresponds to the RFC 3671 "golden tree". 3. Build an ordered list of single-digit strings from all digits appearing in the AUS. All non-digit characters will be ignored. 4. If SEPERATOR is not the empty string, then insert a string consisting of SEPERATOR after POSITION strings into this list. If the list of strings was shorter than POSITION elements, then report an error. Lendl Expires June 15, 2007 [Page 4] Internet-Draft ENUM Branch Location Record December 2006 5. Reverse the order of the list. 6. Append a string containing APEX to the end of the list. 7. Create a single domain-name by joining the list together with dots (".") between each string. Further processing is done according to RFC 3271: This domain-name is used to request NAPTR records which may contain the end result or, if the flags field is blank, produce new keys in the form of domain- names from the DNS. Section 5 contains examples. 4. The EBL Resource Record The RR type code for the EBL RR is /IANA-ACTION/. 4.1. The EBL RDATA Format The RDATA for a EBL RR consists of a position number, separator string and an apex domain. and refer to the definitions of RFC 1035 [4]. 0 1 2 3 4 5 6 7 +--+--+--+--+--+--+--+--+ | POSITION | +--+--+--+--+--+--+--+--+ / SEPARATOR / +--+--+--+--+--+--+--+--+ / APEX / +--+--+--+--+--+--+--+--+ where POSITION is a single byte, SEPARATOR is a and APEX is a and must not be empty. Name-compression is not to be used for the APEX field. 4.2. The EBL Presentation Format The master file format follows the standard rules in RFC 1035. POSITION is represented as decimal integer. SEPARATOR is a quoted string, APEX is a domain name and thus does not require quoting. 5. Examples This example shows the use of EBL records as defined by the interim Lendl Expires June 15, 2007 [Page 5] Internet-Draft ENUM Branch Location Record December 2006 solution to Infrastructure ENUM as defined by draft-ietf-enum-combined-01 [6]. This application defines that the EBL resides at "infrastructure"..e164.arpa. Thus for example: infrastructure.3.4.e164.arpa. IN EBL 2 "i" e164.arpa. infrastructure.1.e164.arpa. IN EBL 4 "i" example.com. infrastructure.9.4.e164.arpa. IN EBL 0 "" ie164.arpa. These records indicate how the transformation from E.164 number to ENUM domains for the application "Infrastructure ENUM" should be done for numbers in country code +43, +1, and +49. This leads to the following mappings: +43 15056416 6.1.4.6.5.0.5.1.i.3.4.e164.arpa +1 5551234567 7.6.5.4.3.2.1.i.5.5.5.1.example.com +49 891234567 7.6.5.4.3.2.1.9.8.9.4.ie164.arpa Here is the list of the intermediate steps for the first example to visualize how the algorithm as defined in Section 3 operates on "+43 15056416": 1. According to the interim, combined I-ENUM specification, retrieve the country-code from the number and build a FQDN using "infrastructure", the reversed, dot-separated country-code and "e164.arpa", yielding "infrastructure.3.4.e164.arpa". 2. The EBL lookup for this domain sets SEPERATOR to "i", POSITION to "2" and APEX to "e164.arpa". 3. The list of strings is ("4","3","1","5","0","5","6","4","1","6"). 4. The SEPERATOR is "i", POSITION is 2, thus "i" is inserted between the second and the third string, yielding: ("4","3","i","1","5","0","5","6","4","1","6") 5. Reversing the list gives: ("6","3","4","6","5","0","5","1","i","3","4") 6. Appending APEX yields: ("6","3","4","6","5","0","5","1","i","3","4","e164.arpa") 7. Concatenation with dots: "6.3.4.6.5.0.5.1.i.3.4.e164.arpa" Lendl Expires June 15, 2007 [Page 6] Internet-Draft ENUM Branch Location Record December 2006 6. Security Considerations EBLs are used to direct ENUM resolvers to other places in the DNS. The security of DNS in both the location of the EBLs and wherever they point to needs to be maintained. Use-case specifications need to be careful when designing their EBL location: Information concerning which numbers have been dialed could be leaked to the nameserver hosting the EBL records. 7. IANA Considerations This documents allocates the Resource Records Type field for the EBL record according to the definition in Section 4. 8. Acknowledgements The author would like to thank Alexander Mayrhofer, Michael Haberler, Richard Stastny, Klaus Nieminen, Richard Shockey, and Karsten Fleischhauer for their contributions. 9. References 9.1. Normative References [1] Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)", RFC 3761, April 2004. [2] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part One: The Comprehensive DDDS", RFC 3401, October 2002. [3] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part Three: The Domain Name System (DNS) Database", RFC 3403, October 2002. [4] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. 9.2. Informative References [5] Lind, S. and P. Pfautz, "Infrastrucure ENUM Requirements", draft-ietf-enum-infrastructure-enum-reqs-02 (work in progress), April 2006. Lendl Expires June 15, 2007 [Page 7] Internet-Draft ENUM Branch Location Record December 2006 [6] Haberler, M. and R. Stastny, "Combined User and Infrastructure ENUM in the e164.arpa tree", draft-ietf-enum-combined-01 (work in progress), October 2006. Author's Address Otmar Lendl enum.at GmbH Karlsplatz 1/9 Wien A-1010 Austria Phone: +43 1 5056416 33 Email: otmar.lendl@enum.at URI: http://www.enum.at/ Lendl Expires June 15, 2007 [Page 8] Internet-Draft ENUM Branch Location Record December 2006 Full Copyright Statement Copyright (C) The IETF Trust (2006). 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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Lendl Expires June 15, 2007 [Page 9]