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rfc:rfc5855

Internet Engineering Task Force (IETF) J. Abley Request for Comments: 5855 T. Manderson BCP: 155 ICANN Category: Best Current Practice May 2010 ISSN: 2070-1721

            Nameservers for IPv4 and IPv6 Reverse Zones

Abstract

 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 in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://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 to BCP 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 2010

Table of Contents

 1. Introduction ....................................................2
 2. Nameservers for IN-ADDR.ARPA ....................................3
 3. Nameservers for IP6.ARPA ........................................3
 4. IAB Statement ...................................................4
 5. IANA Considerations .............................................4
 6. Security Considerations .........................................4
 7. References ......................................................4
    7.1. Normative References .......................................4
    7.2. Informative References .....................................5
 Appendix A.  Existing NS RRSets ....................................6
 Appendix B.  Performance Characteristics ...........................7
   B.1.  Label Compression ..........................................7
   B.2.  Query Patterns .............................................9
     B.2.1.  QNAME under IN-ADDR.ARPA ..............................10
     B.2.2.  QNAME under IP6.ARPA ..................................10

1. 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 (see Appendix 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 of Section 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 2010

4. 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 (see Section 4),
 the IANA has delegated:
 1. IN-ADDR-SERVERS.ARPA to the nameservers listed in Section 2;
 2. IP6-SERVERS.ARPA to the nameservers listed in Section 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 of Section 4 of the MoU between the IETF and ICANN [RFC2860].

6. Security Considerations

 This document introduces no additional security risks for the
 Internet.

7. References

7.1. 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 2010

7.2. 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 2010

Appendix 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 2010

Appendix B. Performance Characteristics

B.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 Sections 2 and 3 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 to Section 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 to Section 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 in Appendix 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 2010

B.2.1. QNAME under IN-ADDR.ARPA

 Consider the IN-ADDR.ARPA NS RRSet (described in Appendix 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 in
 Section 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 in Appendix 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 in
 Section 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 2010

Authors' 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.org

Abley & Manderson Best Current Practice [Page 12]

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