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BEST CURRENT PRACTICE
Internet Engineering Task Force (IETF) J. AbleyRequest for Comments: 5855 T. MandersonBCP: 155 ICANNCategory: Best Current Practice May 2010ISSN: 2070-1721Nameservers for IPv4 and IPv6 Reverse ZonesAbstract This document specifies a stable naming scheme for the nameservers that serve the zones IN-ADDR.ARPA and IP6.ARPA in the DNS. These zones contain data that facilitate reverse mapping (address to name).Status of This Memo This memo documents an Internet Best Current Practice. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on BCPs is available inSection 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc5855.Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject toBCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.Abley & Manderson Best Current Practice [Page 1]
RFC 5855 Nameservers for Reverse Zones May 2010Table of Contents1. Introduction ....................................................22. Nameservers for IN-ADDR.ARPA ....................................33. Nameservers for IP6.ARPA ........................................34. IAB Statement ...................................................45. IANA Considerations .............................................46. Security Considerations .........................................47. References ......................................................47.1. Normative References .......................................47.2. Informative References .....................................5Appendix A. Existing NS RRSets ....................................6Appendix B. Performance Characteristics ...........................7B.1. Label Compression ..........................................7B.2. Query Patterns .............................................9B.2.1. QNAME under IN-ADDR.ARPA ..............................10B.2.2. QNAME under IP6.ARPA ..................................101. Introduction The Domain Name System (DNS) is described in [RFC1034] and [RFC1035]. The DNS currently supports keyed data retrieval using three namespaces -- domain names, IPv4 addresses, and IPv6 addresses. Mapping of IPv4 addresses to names is accomplished using data published in the IN-ADDR.ARPA zone. For IPv6, the IP6.ARPA zone is used (see [RFC3596]). The process of mapping an address to a name is generally known as a "reverse lookup", and the IN-ADDR.ARPA and IP6.ARPA zones are said to support the "reverse DNS". The secure and stable hosting of the IN-ADDR.ARPA and IP6.ARPA zones is critical to the operation of the Internet, since many applications rely upon timely responses to reverse lookups to be able to operate normally. At the time of this writing, the IN-ADDR.ARPA zone is served by a subset of the DNS root servers, and IP6.ARPA by servers operated by APNIC, ARIN, ICANN, LACNIC, and the RIPE NCC (seeAppendix A). This document specifies a dedicated and stable set of nameserver names for each of the IN-ADDR.ARPA and IP6.ARPA zones. The naming scheme specified in this document allows IN-ADDR.ARPA and IP6.ARPA to be delegated to two different sets of nameservers, to facilitate operational separation of the infrastructure used to serve each zone. This separation might help ensure that an operational failure of IN-ADDR.ARPA servers does not impact IPv6 reverse lookups as collateral damage, for example.Abley & Manderson Best Current Practice [Page 2]
RFC 5855 Nameservers for Reverse Zones May 2010 The choice of operators for individual nameservers is beyond the scope of this document and is an IANA function that falls under the scope ofSection 4 of the Memorandum of Understanding (MoU) between the IETF and ICANN [RFC2860].2. Nameservers for IN-ADDR.ARPA This document specifies the following naming scheme for servers that host the IN-ADDR.ARPA zone: A.IN-ADDR-SERVERS.ARPA B.IN-ADDR-SERVERS.ARPA C.IN-ADDR-SERVERS.ARPA D.IN-ADDR-SERVERS.ARPA E.IN-ADDR-SERVERS.ARPA F.IN-ADDR-SERVERS.ARPA ... The IN-ADDR-SERVERS.ARPA zone has been delegated to the same set of servers as IN-ADDR.ARPA. IPv4 and IPv6 glue records for each of those servers has been added to the ARPA zone. The IN-ADDR-SERVERS.ARPA and IN-ADDR.ARPA zones are delegated to the same servers, since they are both dedicated for a single purpose and hence can reasonably share fate. All servers in the set are named under the same domain to facilitate label compression. Since glue for all servers exist in the ARPA zone, the use of a single domain does not present a practical single point of failure.3. Nameservers for IP6.ARPA This document specifies the following nameserver set for the IP6.ARPA zone: A.IP6-SERVERS.ARPA B.IP6-SERVERS.ARPA C.IP6-SERVERS.ARPA D.IP6-SERVERS.ARPA E.IP6-SERVERS.ARPA F.IP6-SERVERS.ARPA ... The IP6-SERVERS.ARPA zone has been delegated to the same set of servers as IP6.ARPA. IPv4 and IPv6 glue records for each of those servers has been added to the ARPA zone.Abley & Manderson Best Current Practice [Page 3]
RFC 5855 Nameservers for Reverse Zones May 20104. IAB Statement In its capacity as the body that provides technical guidance to ICANN for the administration of the ARPA top-level domain as described in [RFC3172], the IAB has reviewed this proposal and supports it as an operational change that is in line with the respective roles of ICANN and the IAB.5. IANA Considerations With due consideration to the approval of the IAB (seeSection 4), the IANA has delegated: 1. IN-ADDR-SERVERS.ARPA to the nameservers listed inSection 2; 2. IP6-SERVERS.ARPA to the nameservers listed inSection 3. Additionally, IANA has installed IPv4 and IPv6 glue records for the nameservers concerned in the ARPA zone. The choice of operators for all nameservers concerned is beyond the scope of this document and is an IANA function that falls under the scope ofSection 4 of the MoU between the IETF and ICANN [RFC2860].6. Security Considerations This document introduces no additional security risks for the Internet.7. References7.1. Normative References [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13,RFC 1034, November 1987. [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13,RFC 1035, November 1987. [RFC3172] Huston, G., Ed., "Management Guidelines & Operational Requirements for the Address and Routing Parameter Area Domain ("arpa")",BCP 52,RFC 3172, September 2001.Abley & Manderson Best Current Practice [Page 4]
RFC 5855 Nameservers for Reverse Zones May 20107.2. Informative References [RFC2860] Carpenter, B., Baker, F., and M. Roberts, "Memorandum of Understanding Concerning the Technical Work of the Internet Assigned Numbers Authority",RFC 2860, June 2000. [RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, "DNS Extensions to Support IP Version 6",RFC 3596, October 2003.Abley & Manderson Best Current Practice [Page 5]
RFC 5855 Nameservers for Reverse Zones May 2010Appendix A. Existing NS RRSets The NS RRSet for the IN-ADDR.ARPA zone at the time of this writing is as follows: IN-ADDR.ARPA. 86400 IN NS A.ROOT-SERVERS.NET. IN-ADDR.ARPA. 86400 IN NS B.ROOT-SERVERS.NET. IN-ADDR.ARPA. 86400 IN NS C.ROOT-SERVERS.NET. IN-ADDR.ARPA. 86400 IN NS D.ROOT-SERVERS.NET. IN-ADDR.ARPA. 86400 IN NS E.ROOT-SERVERS.NET. IN-ADDR.ARPA. 86400 IN NS F.ROOT-SERVERS.NET. IN-ADDR.ARPA. 86400 IN NS G.ROOT-SERVERS.NET. IN-ADDR.ARPA. 86400 IN NS H.ROOT-SERVERS.NET. IN-ADDR.ARPA. 86400 IN NS I.ROOT-SERVERS.NET. IN-ADDR.ARPA. 86400 IN NS K.ROOT-SERVERS.NET. IN-ADDR.ARPA. 86400 IN NS L.ROOT-SERVERS.NET. IN-ADDR.ARPA. 86400 IN NS M.ROOT-SERVERS.NET. The NS RRSet for the IP6.ARPA zone at the time of this writing is as follows: IP6.ARPA. 84600 IN NS NS-SEC.RIPE.NET. IP6.ARPA. 86400 IN NS SEC1.APNIC.NET. IP6.ARPA. 86400 IN NS NS2.LACNIC.NET. IP6.ARPA. 86400 IN NS NS.ICANN.ORG. IP6.ARPA. 86400 IN NS TINNIE.ARIN.NET. For completeness, the NS RRSet for the ARPA zone at the time of this writing is as follows: ARPA. 86400 IN NS A.ROOT-SERVERS.NET. ARPA. 86400 IN NS B.ROOT-SERVERS.NET. ARPA. 86400 IN NS C.ROOT-SERVERS.NET. ARPA. 86400 IN NS D.ROOT-SERVERS.NET. ARPA. 86400 IN NS E.ROOT-SERVERS.NET. ARPA. 86400 IN NS F.ROOT-SERVERS.NET. ARPA. 86400 IN NS G.ROOT-SERVERS.NET. ARPA. 86400 IN NS H.ROOT-SERVERS.NET. ARPA. 86400 IN NS I.ROOT-SERVERS.NET. ARPA. 86400 IN NS K.ROOT-SERVERS.NET. ARPA. 86400 IN NS L.ROOT-SERVERS.NET. ARPA. 86400 IN NS M.ROOT-SERVERS.NET.Abley & Manderson Best Current Practice [Page 6]
RFC 5855 Nameservers for Reverse Zones May 2010Appendix B. Performance CharacteristicsB.1. Label Compression The choice of names for the respective NS RRSets of the IN-ADDR.ARPA and IP6.ARPA zones have a relatively minor impact on the delegation response sizes from their parent zones, given other anticipated contributors such as DNSSEC. However, it is still considered good practice to use a naming scheme that is reasonably compressible: doing so for frequently queried zones such as these is likely to have at least measurable impact on aggregate DNS traffic in the Internet as a whole, and has potential transport benefits to clients whose queries will not result in secure replies. The naming schemes described in Sections2 and3 are highly compressible. That is, once a single nameserver name has been encoded in a DNS message, subsequent nameservers can be specified with substantially smaller encoding. In the DNS, a complete encoding of an a-label involves a one-byte length field, plus a one-byte-per-character encoding of the a-label itself. A domain name's encoding consists of one or more a-labels, so-encoded, plus a single terminating zero byte. Where a terminating series of a-labels has already been encoded as described above, subsequent terminating references to the same series can be made using a two-byte pointer to that full encoding. The non-compressed representation of the nameserver A.IN-ADDR- SERVERS.ARPA fills (1 + 1) + (15 + 1) + (4 + 1) + 1 = 24 bytes. The non-compressed representation of A.IP6-SERVERS.ARPA fills (1 + 1) + (10 + 1) + (4 + 1) + 1 = 19 bytes. Subsequent nameservers under either domain are encoded with the initial label, plus two bytes for a pointer to the repeated domain elsewhere in the message, i.e., (1 + 1) + 2 = 4 bytes.Abley & Manderson Best Current Practice [Page 7]
RFC 5855 Nameservers for Reverse Zones May 2010 The encoded size of the a-labels in a twelve-record NS RRSet named according toSection 2 for IN-ADDR.ARPA is as follows: +------------------------+---------------------------------------+ | Nameserver | Encoded Size | +------------------------+---------------------------------------+ | A.IN-ADDR-SERVERS.ARPA | (1 + 1) + (15 + 1) + (4 + 1) + 1 = 24 | | | | | B.IN-ADDR-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | C.IN-ADDR-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | D.IN-ADDR-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | E.IN-ADDR-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | F.IN-ADDR-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | G.IN-ADDR-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | H.IN-ADDR-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | I.IN-ADDR-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | J.IN-ADDR-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | K.IN-ADDR-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | L.IN-ADDR-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | Total | 68 bytes | +------------------------+---------------------------------------+Abley & Manderson Best Current Practice [Page 8]
RFC 5855 Nameservers for Reverse Zones May 2010 The encoded size of the a-labels in a six-record NS RRSet named according toSection 3 for IP6.ARPA is, hence, as follows: +--------------------+---------------------------------------+ | Nameserver | Encoded Size | +--------------------+---------------------------------------+ | A.IP6-SERVERS.ARPA | (1 + 1) + (10 + 1) + (4 + 1) + 1 = 19 | | | | | B.IP6-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | C.IP6-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | D.IP6-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | E.IP6-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | F.IP6-SERVERS.ARPA | (1 + 1) + 2 = 4 | | | | | Total | 39 bytes | +--------------------+---------------------------------------+ By way of comparison, the encoded size of the labels in the NS RRSet for IP6.ARPA (shown inAppendix A) is as follows: +-----------------+--------------------------------------+ | Nameserver | Encoded Size | +-----------------+--------------------------------------+ | NS-SEC.RIPE.NET | (6 + 1) + (4 + 1) + (3 + 1) + 1 = 17 | | | | | SEC1.APNIC.NET | (4 + 1) + (5 + 1) + 2 + 1 = 14 | | | | | NS2.LANIC.NET | (3 + 1) + (6 + 1) + 2 + 1 = 14 | | | | | NS.ICANN.ORG | (2 + 1) + (5 + 1) + (3 + 1) + 1 = 14 | | | | | TINNIE.ARIN.NET | (6 + 1) + (4 + 1) + 2 + 1 = 15 | | | | | Total | 74 bytes | +-----------------+--------------------------------------+B.2. Query Patterns A brief description of likely query patterns for an empty cache with the existing and new NS RRSets follows.Abley & Manderson Best Current Practice [Page 9]
RFC 5855 Nameservers for Reverse Zones May 2010B.2.1. QNAME under IN-ADDR.ARPA Consider the IN-ADDR.ARPA NS RRSet (described inAppendix A) and a QNAME that is delegated beneath the IN-ADDR.ARPA zone: 1. Query sent to root server that is also authoritative for IN-ADDR.ARPA; response is a referral from the IN-ADDR.ARPA zone. In the case where the initial query is sent to the J root server: 1. Query sent to J.ROOT-SERVERS.NET (which is not authoritative for the IN-ADDR.ARPA zone); response is a referral to an ARPA server with additional-section glue. 2. Query sent to an ARPA server (all of which are also authoritative in this case for IN-ADDR.ARPA); response is a referral from the IN-ADDR.ARPA zone. Consider the same query with the IN-ADDR.ARPA NS RRSet (described inSection 2): 1. Query sent to a root server that is also authoritative for ARPA; response is a referral to an IN-ADDR.ARPA server, with additional- section glue. 2. Query sent to an IN-ADDR.ARPA server; response is a referral from the IN-ADDR.ARPA zone. In the case where the first query is sent to the J root server: 1. Query sent to J.ROOT-SERVERS.NET (which is not authoritative for ARPA); response is a referral to an ARPA server, with additional- section glue. 2. Query sent to an ARPA server; response is a referral to an IN-ADDR.ARPA server, with additional-section glue. 3. Query sent to an IN-ADDR.ARPA server; response is a referral from the IN-ADDR.ARPA zone.B.2.2. QNAME under IP6.ARPA Consider the IP6.ARPA NS RRSet (described inAppendix A) and a QNAME that is delegated beneath the IP6.ARPA zone: 1. Query sent to root server that is also authoritative for ARPA; response is a referral from the ARPA zone to an IP6.ARPA server with no additional-section glue.Abley & Manderson Best Current Practice [Page 10]
RFC 5855 Nameservers for Reverse Zones May 2010 2. A recursive lookup for one of the nameservers specified in the referral must now be performed in order to obtain an address for an IP6.ARPA server. In all cases, three queries are required. Successive recursive lookups may be performed in the event that a server is unresponsive. 3. Query sent to IP6.ARPA server; response is a referral from the IP6.ARPA zone. In the case where the first query is sent to the J root server: 1. Query sent to J.ROOT-SERVERS.NET; response is a referral to an ARPA server with additional-section glue. 2. Query sent to an ARPA server; response is a referral from the ARPA zone to an IP6.ARPA server with no additional-section glue. 3. A recursive lookup for one of the nameservers specified in the referral must now be performed in order to obtain an address for an IP6.ARPA server. In all cases, three queries are required. Successive recursive lookups may be performed in the event that a server is unresponsive. 4. Query sent to IP6.ARPA server; response is a referral from the IP6.ARPA zone. Consider the same query with the IP6.ARPA NS RRSet (described inSection 3): 1. Query sent to a root server that is also authoritative for ARPA; response is a referral to an IP6.ARPA server, with additional- section glue. 2. Query sent to an IP6.ARPA server; response is a referral from the IP6.ARPA zone. In the case where the first query is sent to the J root server: 1. Query sent to J.ROOT-SERVERS.NET (which is not authoritative for ARPA); response is a referral to an ARPA server, with additional- section glue. 2. Query sent to an ARPA server; response is a referral to an IP6.ARPA server with additional-section glue. 3. Query sent to an IP6.ARPA server; response is a referral from the IP6.ARPA zone.Abley & Manderson Best Current Practice [Page 11]
RFC 5855 Nameservers for Reverse Zones May 2010Authors' Addresses Joe Abley ICANN 4676 Admiralty Way, Suite 330 Marina del Rey, CA 90292 USA Phone: +1 310 463 9062 EMail: joe.abley@icann.org Terry Manderson ICANN 4676 Admiralty Way, Suite 330 Marina del Rey, CA 90292 USA Phone: +61 4 1127 5673 EMail: terry.manderson@icann.orgAbley & Manderson Best Current Practice [Page 12]
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