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Solving Technical Issues with ENUM and DNS

This article discusses the technical issues with ENUM and DNS and presents a solution to solve them. It explores the background, problem statements, and provides a technical solution using NAPTR records in DNS. The conclusion highlights the benefits of using ENUM for PSTN/IP convergence.

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Solving Technical Issues with ENUM and DNS

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  1. ENUM Technical issues / DNS Patrik FältströmArea Director, Applications Area, IETFpaf@cisco.com

  2. Agenda • Background • Problem we want to solve • Technical solution • Conclusion

  3. Background ENUM 3

  4. The Domain Name System • It is a distributed database • It is a protocol • Often the two get mixed up

  5. DNS as distributed database Central server, “root server” Server for “com” Server for “se” Local resolver Client Server for “jp”

  6. Ask “se”! Query a.paf.se? Query a.paf.se? Ask “paf.se”! Query a.paf.se? Query a.paf.se? 192.168.1.11 192.168.1.11 Recursion Root-server Server “se” Local resolver Server “paf.se”

  7. zone "a.se." domain "a.se." domain/zone "b.a.se." Domains and zones "root" se a c b ns ns ns

  8. Delegations Root server se. IN NS ns.nic-se.se ns.nic-se.se. IN A 192.168.0.1 ns.nic-se.se ns.se. IN NS ns.nic-se.se. a.se. IN NS ns.a.se. c.se. IN NS ns.c.se. ns.nic-se.se. IN A 192.168.0.1 ns.a.se. IN A 192.168.1.1 ns.c.se. IN A 192.168.3.1 ns.a.se a.se. IN NS ns.c.se. b.a.se. IN NS ns.b.se. ns.a.se. IN A 192.168.1.1 ns.b.se. IN A 192.168.2.1 ns.c.se. c.se. IN NS ns.c.se. ns.c.se. IN A 192.168.3.1 ns.b.a.se. b.a.se. IN N S ns.b.a.se. ns.b.a.se. IN A 192.168.3.1

  9. Allocation at CC level by the ITU, SG2/WP1/2 (from an IETF perspective) E.164 provides the number structure and functionality of numbers used for international public telecommunicationsHierarchically allocated E.164 numbers

  10. Structure to use for geographic areas Structure of E.164 CC NDC SN 1-3 digits N digits Max (15-N) digits National (significant) number International public telecommunication Number for geographical areas

  11. Problem we want to solve ENUM 11

  12. Problem statements 1(2) • How do network elements find services on the Internet if you only have a telephone (E.164) number? • How can subscribers (as opposed to carriers) define their preferences for incoming communications? • How can we (IETF/ITU) enable new services while enabling competition, consumer choice and consumer protection?

  13. Problem statements 2(2) • How can consumers, carriers and new players have equal access to these new opportunities? • How do we (IETF/ITU) make this simple and easy to use without reinventing the wheel?

  14. Technical solution ENUM 14

  15. Solution in short • Put telephone numbers* in the global domain name system, DNS • ENUM Working Group created to solve the problem of using the DNS for: • Domainname in • [Numbers reformatted as domain names] • URI out • [mailto, sip, tel, http or other URI scheme] • Solution was to use NAPTR records * Maybe not in the original E.164 format

  16. Example • $ORIGIN 4.3.2.1.7.9.8.6.4.e164.arpa.IN NAPTR 10 10 "U""sip+E2U""!^.*$!sip:spam@paf.se!"IN NAPTR 20 10 "U""ldap+E2U""!^.*$!mailto:spam@paf.se!"

  17. Why DNS? • It’s there • It works… It’s global… It scales… It’s fast… It’s open… • Grandfather existing DNS delegation mechanisms, which looks like delegation in E.164 world • ENUM enabled DNS provides a low cost, shared SCP-like infrastructure for IP infrastructure • ENUM facilitates PSTN/IP convergence

  18. The input to the NAPTR algorithm Step 1 • Take an E.164 number and create a fully qualified domain name in a single highly defined and structured domain • +46-8-971234 • +468971234 • 4.3.2.1.7.9.8.6.4.e164.arpa.

  19. Step 1 Explanation • Each digit becomes a definable and distributed “zone” in DNS terms • Delegation can (doesn’t have to) happen at every digit, including at last digit • Zones such as country codes, area codes or primary delegated blocks of numbers can be delegated as well as individual numbers • DNS defines authoritative nameservers for NAPTR/service resource records (RR’s)

  20. Step 2 • Lookup NAPTR RR’s in DNS, and apply NAPTR/ENUM algorithm • 4.3.2.1.7.9.8.6.4.e164.arpa. • !^.*$!mailto:spam@paf.se!!^+46(.*)$!ldap://ldap.telco.se/cn=0\1! • Use rewrite rules using regular expressions which operate on the E.164 number (+468971234)

  21. Regular expressions • For ENUM, the NAPTR regexp field may yield an (unchanged) URL • !<regexp>!<string>! • “Match <regexp> on original E.164, and apply rewrite rule <string>” ^ - Match beginning $ - Match end . - Match any character .* - Match any number of any character () - Grouping, \n in <string> is replaced with group number ‘n’ in <regexp>

  22. Step 2 in detail • $ORIGIN 4.3.2.1.7.9.8.6.4.e164.arpa. • IN NAPTR 10 10 “U” “mailto+E2U” “!^.*$!mailto:spam@paf.se!” • IN NAPTR 20 10 “U” “ldap+E2U” “!^+46(.*)$!ldap://ldap.telco.se/cn=0\1” • Note that no line break should be in the records

  23. e164.arpa 6.4.e164.arpa 7.9.8.6.4.e164.arpa 4.3.2.1.7.9.8.6.4.e164.arpa ENUM DNS Hierarchy Alternative 1 Alternative 2

  24. +46-8-976123 ns.ripe.net e164.arpa. IN NS ns.ripe.net. 6.4.e164.arpa. IN NS ns.e164.se. ns.ns.e164.se. IN A 192.168.0.1 Root server e164.arpa. IN NS. ns.ripe.net ns.ripe.net. IN A 193.0.0.193 ns.e164.se 6.4.e164.arpa IN NS ns.e164.se. 7.9.8.6.4.e164.se. IN NS e164.telco.se. e164.telia.se. IN A 192.168.1.1 e164.telco.se. 7.9.8.6.4.e164.se. IN NS e164.telco.se. 3.2.1.6.7.9.8.6.4.e164.arpa. IN NS ns.eservice.net. ns.eservice.net. 3.2.1.6.7.9.8.6.4.e164.arpa. IN NS eservice.net. 3.2.1.6.7.9.8.6.4.e164.arpa. IN NAPTR …….

  25. DNS Hierarchy • Strictly delegated • One authoritative server for each name, and only one • Have led to the registry/registrar model • One responsible registry, but many registrars which talk with customers

  26. Registrar for .com interQ Incorporated Registrar for .com Active ISP Registrar for .se Tele2 Registrar for .com Network Solutions Registrars for .se Today 227 Registrars for .com Today 77 Registry/registrar Root server Server for .com Verisign Global Registry Server for .se NIC-SE AB

  27. Conclusion ENUM 27

  28. DNS-Server Sip proxy Sip proxy ENUM example flow/usage Query 4.3.2.1.7.9.8.6.4.e164.arpa? Response sip:spam@paf.se “Call setup” Dial +468971234 Sip sip:spam@paf.se

  29. ENUM and VoIP • ENUM allows VoIP proxies and servers to find each other • Intra and inter domain call setup • Only for declaring ability to accept certain applications • ENUM is an opt-in system (also on country code level)

  30. ENUM in Universal Messaging • IETF Voice Profile for Internet Mail • ENUM enables carrier and enterprise voice mail systems to find each other, interoperate and exchange messages • Linkage to directory gives access to “spoken name” as well as authenticated access to sensitive information (privacy)

  31. ENUM in Internet Fax • IETF RFC 2305 / ITU-T Rec. T.37 • ENUM enables internet aware fax machines to find each other, interoperate and exchange messages

  32. Detailed example of Fax • Person X wants to send a fax to Person Y; she knows Y's E.164 number. • Person Y has many IP applications tied to her own (Y's) E.164 number. • Device C became responsible for delivering the fax. Device C is Internet Aware, is ENUM-enhanced, can do SMTP and SIP, but can't do H.323 yet. • Device C does a DNS query on the E.164 number. Device C discovers from the response that Person Y prefers real-time to store-and-forward fax delivery, likes SIP and H.323 equally, and has SMTP, too. • Device C tries SIP first. If SIP fails, Device C does not try H.323. Instead, Device C then tries SMTP. • Note: Device C uses ENUM in its application selection logic. ENUM is an enabler and not the same sort of thing as SMTP, SIP, H.323, voice/fax/data, etc.

  33. From RFC 2916 • 4. IANA Considerations • This memo requests that the IANA delegate the E164.ARPA domain following instructions to be provided by the IAB. Names within this zone are to be delegated to parties according to the ITU recommendation E.164. The names allocated should be hierarchic in accordance with ITU Recommendation E.164, and the codes should assigned in accordance with that Recommendation. • Delegations in the zone e164.arpa (not delegations in delegated domains of e164.arpa) should be done after Expert Review, and the IESG will appoint a designated expert.

  34. Status as of Jan 10, 2001 (done) • Base spec published as RFC 2916 • e164.arpa delegated to RIPE-NCC • ITU SG2/WP1/2 liaison statement: • Member state can inform ITU on entry of numbers in DNS, provision of E.164 information

  35. Status as of Jan 10, 2001 (not done) • Delegation of domains below e164.arpa to managing entities that are appointed by member states • National issues

  36. Resources • NAPTR Resource Records (RFC 2915) • http://www.ietf.org/rfc/rfc2915.txt • ENUM Specification (RFC 2916) • http://www.ietf.org/rfc/rfc2916.txt • Liaison Statement (RFC 3026) • http://www.ietf.org/rfc/rfc3026.txt • IAB on need for unique root (RFC 2826) • http://www.ietf.org/rfc/rfc2826.txt • IAB Statement on ARPA • http://www.iab.org/iab/DOCUMENTS/statement-on-infrastructure-domains.txt • My email address: paf@cisco.com

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