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'7') (Obsoleted by RFC 3966) ** Obsolete normative reference: RFC 1959 (ref. '8') (Obsoleted by RFC 2255) ** Obsolete normative reference: RFC 2535 (ref. '9') (Obsoleted by RFC 4033, RFC 4034, RFC 4035) Summary: 8 errors (**), 0 flaws (~~), 5 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group P Faltstrom 2 Internet-Draft Cisco Systems Inc 3 Expires: January 31, 2001 August 2, 2000 5 E.164 number and DNS 6 draft-ietf-enum-e164-dns-03 8 Status of this Memo 10 This document is an Internet-Draft and is in full conformance with 11 all provisions of Section 10 of RFC2026. 13 Internet-Drafts are working documents of the Internet Engineering 14 Task Force (IETF), its areas, and its working groups. Note that 15 other groups may also distribute working documents as 16 Internet-Drafts. 18 Internet-Drafts are draft documents valid for a maximum of six 19 months and may be updated, replaced, or obsoleted by other documents 20 at any time. It is inappropriate to use Internet-Drafts as reference 21 material or to cite them other than as "work in progress." 23 The list of current Internet-Drafts can be accessed at 24 http://www.ietf.org/ietf/1id-abstracts.txt. 26 The list of Internet-Draft Shadow Directories can be accessed at 27 http://www.ietf.org/shadow.html. 29 This Internet-Draft will expire on January 31, 2001. 31 Copyright Notice 33 Copyright (C) The Internet Society (2000). All Rights Reserved. 35 Abstract 37 This document discusses the use of DNS for storage of E.164 numbers. 38 More specifically, how DNS can be used for identifying available 39 services connected to one E.164 number. Routing of the actual 40 connection using the service selected using these methods is not 41 discussed. 43 1. Introduction 45 Through transformation of E.164 numbers into DNS names and the use 46 of existing DNS services like delegation through NS records, and use 47 of NAPTR[1] records in DNS[2][3], one can look up what services are 48 available for a specific domainname in a decentralized way with 49 distributed management of the different levels in the lookup 50 process. 52 1.1 Terminology 54 The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY" 55 in this document are to be interpreted as described in RFC2119[4] 57 2. E.164 numbers and DNS 59 The domain "e164.arpa." is being populated in order to provide the 60 infrastructure in DNS for storage of E.164 numbers. In order to 61 facilitate distributed operations, this domain is divided into 62 subdomains. Holders of E.164 numbers which want to be listed in DNS 63 should contact the appropriate zone administrator in order to be 64 listed, by examining the SOA resource record associated with the 65 zone, just like in normal DNS operations. 67 Of course, as with other domains, policies for such listings will be 68 controlled on a subdomain basis and may differ in different parts of 69 the world. 71 To find the DNS names for a specific E.164 number, the following 72 procedure is to be followed: 74 1. See that the E.164 number is written in its full form, including 75 the countrycode IDDD. Example: +46-8-9761234 77 2. Remove all non-digit characters with the exception of the 78 leading '+'. Example: +4689761234 80 3. Remove all characters with the exception of the digits. Example: 81 4689761234 83 4. Put dots (".") between each digit. Example: 4.6.8.9.7.6.1.2.3.4 85 5. Reverse the order of the digits. Example: 4.3.2.1.6.7.9.8.6.4 87 6. Append the string ".e164.arpa" to the end. Example: 88 4.3.2.1.6.7.9.8.6.4.e164.arpa 90 3. Fetching URIs given an E.164 number 92 For a record in DNS, the NAPTR record is used for identifying 93 available ways of contacting a specific node identified by that 94 name. Specifically it can be used for knowing what services exists 95 for a specific domainname, including phone numbers by the use of the 96 e164.arpa domain as described above. 98 The identification is using the NAPTR resource record defined for 99 use in the URN resolution process, but it can be generalized in a 100 way that suits the needs specified in this document. 102 It is the string which is the result of step 2 in section 2 above 103 which is input to the NAPTR algorithm. 105 3.1 The NAPTR record 107 The key fields in the NAPTR RR are order, preference, service, 108 flags, regexp, and replacement. For a detailed description, see: 110 o The order field specifies the order in which records MUST be 111 processed when multiple NAPTR records are returned in response to 112 a single query. 114 o The preference field specifies the order in which records SHOULD 115 be processed when multiple NAPTR records have the same value of 116 "order". 118 o The service field specifies the resolution protocol and 119 resolution service(s) that will be available if the rewrite 120 specified by the regexp or replacement fields is applied. 122 o The flags field contains modifiers that affect what happens in 123 the next DNS lookup, typically for optimizing the process. 125 o The regexp field is one of two fields used for the rewrite rules, 126 and is the core concept of the NAPTR record. 128 o The replacement field is the other field that may be used for the 129 rewrite rule. 131 Note that the client applies all the substitutions and performs all 132 lookups, they are not performed in the DNS servers. Note that URIs 133 are stored in the regexp field. 135 3.1.1 Specification for use of NAPTR Resource Records 137 The input is an E.164 encoded telephone number. The output is a 138 Uniform Resource Identifier in its absolute form according to the 139 'absoluteURI' production in the Collected ABNF found in RFC2396[5] 141 An E.164 number, without any characters but leading '+' and digits, 142 (result of step 2 in section 2 above) is the input to the NAPTR 143 algorithm. 145 The service supported for a call is E2U. 147 3.1.2 Specification of Service E2U (E.164 to URI) 149 * Name: E.164 to URI 150 * Mnemonic: E2U 151 * Number of Operands: 1 152 * Type of Each Operand: First operand is an E.164 number. 153 * Format of Each Operand: First operand is the E.164 number in the 154 form as specified in step 2 in section 2 in this document. 155 * Algorithm: Opaque 156 * Output: One or more URLs 157 * Error Conditions: 158 o E.164 number not in the numbering plan 159 o E.164 number in the numbering plan, but no URLs exist for that number 160 o Service unavailable 162 * Security Considerations: 163 o Malicious Redirection 164 One of the fundamental dangers related to any service such 165 as this is that a malicious entry in a resolver's database 166 will cause clients to resolve the E.164 into the wrong URL. 167 The possible intent may be to cause the client to retrieve 168 a resource containing fraudulent or damaging material. 169 o Denial of Service 170 By removing the URL to which the E.164 maps, a malicious 171 intruder may remove the client's ability to access the 172 resource. 174 This operation is used to map a one E.164 number to a list of URIs. 175 The first well-known step in the resolution process is to remove all 176 non-digits apart from the leading '+' from the E.164 number as 177 described in step 1 and 2 in section 2 of this document. 179 3.2 Examples 181 3.2.1 Example 1 183 $ORIGIN 4.3.2.1.6.7.9.8.6.4.e164.arpa. 184 IN NAPTR 100 10 "u" "sip+E2U" "!^.*$!sip:information@tele2.se!" . 185 IN NAPTR 102 10 "u" "mailto+E2U" "!^.*$!mailto:information@tele2.se!" . 187 This describes that the domain 4.3.2.1.6.7.9.8.6.4.e164.arpa is 188 preferably contacted by SIP, and secondly by SMTP. 190 In both cases, the next step in the resolution process is to use the 191 resolution mechanism for each of the protocols, (SIP and SMTP) to 192 know what node to contact for each. 194 3.2.2 Example 2 196 $ORIGIN 4.3.2.1.6.7.9.8.6.4.e164.arpa. 197 IN NAPTR 10 10 "u" "sip+E2U" "!^.*$!sip:paf@swip.net!" . 198 IN NAPTR 102 10 "u" "mailto+E2U" "!^.*$!mailto:paf@swip.net!" . 199 IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:+4689761234!" . 201 Note that the preferred method is to use the SIP protocol, but the 202 result of the rewrite of the NAPTR record is a URI (the "u" flag in 203 the NAPTR record). In the case of the protocol SIP, the URI might be 204 a SIP URI, which is resolved as described in RFC 2543[6]. In the 205 case of the "tel" URI scheme[7], the procedure is restarted with 206 this new E.164 number. The client is responsible for loop detection. 208 The rest of the resolution of the routing is done as described 209 above. 211 3.2.3 Example 3 213 $ORIGIN 6.4.e164.arpa. 214 * IN NAPTR 100 10 "u" "ldap+E2U" "!^+46(.*)$!ldap://ldap.example.se/cn=0\1!" . 216 We see in this example that information about all E.164 numbers in 217 the 46 countrycode (for Sweden) exists in an LDAP server, and the 218 search to do is specified by the LDAP URI[8]. 220 4. IANA considerations 222 This memo requests that the IANA delegate the E164.ARPA domain 223 following instructions to be provided by the IAB. Names within this 224 zone are to be delegated to parties according to the ITU 225 recommendation E.164. The names allocated should be hierarchic in 226 accordance with ITU Recommendation E.164, and the codes should 227 assigned in accordance with that Recommendation. 229 Delegations should be done after Expert Review, and the IESG will 230 appoint a designated expert. 232 5. Security Considerations 234 As this system is built on top of DNS, one can not be sure that the 235 information one get back from DNS is more secure than any DNS query. 236 To solve that, the use of DNSSEC[9] for securing and verifying zones 237 is to be recommended. 239 The caching in DNS can make the propagation time for a change take 240 the same amount of time as the time to live for the NAPTR and 241 SRV[10] records in the zone that is changed. The TTL should because 242 of that be kept to a minimum. The use of this in an environment 243 where IP-addresses are for hire (for example when using DHCP[11]) 244 must therefore be done very carefully. 246 There are a number of countries (and other numbering environments) 247 in which there are multiple providers of call routing and 248 number/name-translation services. In these areas, any system that 249 permits users, or putative agents for users, to change routing or 250 supplier information may provide incentives for changes that are 251 actually unauthorized (and, in some cases, for denial of legitimate 252 change requests). Such environments should be designed with 253 adequate mechanisms for identification and authentication of those 254 requesting changes and for authorization of those changes. 256 6. Acknowledgement 258 Support and ideas has come from people at Ericsson, Bjorn Larsson 259 and the group which implemented this scheme in their lab to see that 260 it worked. Input has also come from ITU-T SG2, Working Party 1/2 261 (Numbering, Routing, Global Mobility and Service Definition), the 262 ENUM working group in the IETF, John Klensin and Leif Sunnegardh. 264 References 266 [1] Mealling, M and R Daniel, "The Naming Authority Pointer (NAPTR) 267 DNS Resource Record", draft-ietf-urn-naptr-rr-03.txt (work in 268 progress), June 1998. 270 [2] Mockapetris, P.V., "Domain names - concepts and facilities", 271 RFC 1034, STD 13, Nov 1987. 273 [3] Mockapetris, P.V., "Domain names - implementation and 274 specification", RFC 1035, STD 13, Nov 1987. 276 [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement 277 Levels", RFC 2119, BCP 14, March 1997. 279 [5] Berners-Lee, T., Fielding, R.T. and L. Masinter, "Uniform 280 Resource Identifiers (URI): Generic Syntax", RFC 2396, August 281 1998. 283 [6] Handley, M., Schulzrinne, H., Schooler, E. and J. Rosenberg, 284 "SIP: Session Initiation Protocol", RFC 2543, March 1999. 286 [7] Vaha-Sipila, A., "URLs for Telephone Calls", RFC 2806, April 287 2000. 289 [8] Howes, T. and M. Smith, "An LDAP URL Format", RFC 1959, June 290 1996. 292 [9] Eastlake, D., "Domain Name System Security Extensions", RFC 293 2535, March 1999. 295 [10] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for 296 specifying the location of services (DNS SRV)", RFC 2782, 297 February 2000. 299 [11] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, 300 March 1997. 302 Author's Address 304 Patrik Faltstrom 305 Cisco Systems Inc 306 170 W Tasman Drive SJ-13/2 307 San Jose CA 95134 308 USA 310 EMail: paf@cisco.com 311 URI: http://www.cisco.com 313 Appendix A. Scenario 315 Say that the content of the e164.arpa zone is the following: 317 $ORIGIN e164.arpa. 318 6.4 IN NS ns.regulator-e164.example.se. 320 The regulator has in turn given a series of 10000 numbers to the 321 telco with the name Telco-A. The regulator because of that has in 322 his DNS. 324 $ORIGIN 6.4.e164.arpa. 325 6.7.9.8 IN NS ns.telco-a.example.se. 327 A user named Sven Svensson has from Telco A got the phone number 328 +46-8-9761234. The user gets the service of running DNS from the 329 company Redirection Service. Sven Svensson has asked Telco A to 330 point out Redirection Service as the authoritative source for 331 information about the number +46-8-9761234. Telco A because of this 332 puts in his DNS the following. 334 $ORIGIN 6.7.9.8.6.4.e164.arpa. 335 4.3.2.1 IN NS ns.redirection-service.example.se. 337 Sven Svensson has already plain telephony from Telco A, but also a 338 SIP service from the company Sip Service which provides Sven with 339 the SIP URI "sip:sven@sipservice.example.se". The ISP with the name 340 ISP A runs email and webpages for Sven, under the emailaddress 341 sven@ispa.example.se, and URL http://svensson.ispa.example.se. 343 The DNS for the redirection service because of this contains the 344 following. 346 $ORIGIN 4.3.2.1.6.7.9.8.6.4.e164.arpa. 347 IN NAPTR 10 10 "u" "sip+E2U" "!^.*$!sip:sven@sipservice.example.se!" . 348 IN NAPTR 10 10 "u" "mailto+E2U" "!^.*$!mailto:sven@ispa.example.se!" . 349 IN NAPTR 10 10 "u" "http+E2U" "!^.*$!http://svensson.ispa.example.se!" . 350 IN NAPTR 10 10 "u" "tel+E2U" "!^.*$!tel:+46-8-9761234!" . 352 A user, John Smith, want to contact Sven Svensson, he to start with 353 only has the E.164 number of Sven, i.e. +46-8-9761234. He takes the 354 number, and enters the number in his communication client, which 355 happen to know how to handle the SIP protocol. The client removes 356 the dashes, and ends up with the E.164 number +4689761234. That is 357 what is used in the algorithm for NAPTR records, which is as 358 follows. 360 The client converts the E.164 number into the domainname 361 4.3.2.1.6.7.9.8.6.4.e164.arpa., and queries for NAPTR records for 362 this domainname. Using DNS mechanisms which includes following the 363 NS record referals, the following records are returned: 365 $ORIGIN 4.3.2.1.6.7.9.8.6.4.e164.arpa. 366 IN NAPTR 10 10 "u" "sip+E2U" "!^.*$!sip:sven@sipservice.example.se" . 367 IN NAPTR 10 10 "u" "mailto+E2U" "!^.*$!mailto:sven@ispa.example.se" . 368 IN NAPTR 10 10 "u" "http+E2U" "!^.*$!http://svensson.ispa.example.se" . 369 IN NAPTR 10 10 "u" "tel+E2U" "!^.*$!tel:+46-8-9761234" . 371 Because this client know sip, the first record above is selected, 372 and the SIP URI is extracted, and used according to SIP resolution. 374 Full Copyright Statement 376 Copyright (C) The Internet Society (2000). 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