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Versions: 00 01 02 draft-ietf-dnsop-dns-terminology

Network Working Group                                         P. Hoffman
Internet-Draft                                            VPN Consortium
Intended status: Best Current Practice                       A. Sullivan
Expires: June 1, 2015                                                Dyn
                                                             K. Fujiwara
                                                       November 28, 2014

                            DNS Terminology


   The DNS is defined in literally dozens of different RFCs.  The
   terminology used in by implementers and developers of DNS protocols,
   and by operators of DNS systems, has sometimes changed in the decades
   since the DNS was first defined.  This document gives current
   definitions for many of the terms used in the DNS in a single

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on June 1, 2015.

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   Copyright (c) 2014 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

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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  DNS Message Format  . . . . . . . . . . . . . . . . . . . . .   3
   3.  Resource Records  . . . . . . . . . . . . . . . . . . . . . .   4
   4.  DNS Servers . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  DNSSEC  . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The DNS is a simple query-response protocol whose messages in both
   directions have the same format.  The protocol and message format are
   defined in [RFC1034] and [RFC1035].  These RFCs defined some terms,
   but later documents defined others.  Some of the terms from RFCs 1034
   and 1035 now have somewhat different meanings than they did in 1987.

   This document collects a wide variety of DNS-related terms.  Some of
   them have been precisely defined in earlier RFCs, some have been
   loosely defined in earlier RFCs, and some are not defined in any
   earlier RFC at all.

   The definitions here are believed to be the consensus definition of
   the DNS community, both protocol developers and operators.  Some of
   the definitions differ from earlier RFCs, and those differences are
   noted.  The terms are organized loosely by topic.  Some definitions
   are for new terms for things that are commonly talked about in the
   DNS community but that never had terms defined for them.

   In this document, where the consensus definition is the same as the
   one in an RFC, that RFC is quoted.  Where the consensus definition
   has changed somewhat, the RFC is mentioned but the new stand-alone
   definition is given.

   Note that capitalization in DNS terms is often inconsistent between
   RFCs and between DNS practitioners.  The capitalization used in this

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   document is a best guess at current practices, and is not meant to
   indicate that other capitalization styles are wrong or archaic.

   (Note: the formatting of this early draft is a bit funky.  It will
   improve in later drafts.  Bikeshedding the format, as compared to the
   content, of this draft is probably premature.)

2.  DNS Message Format

   Header -- The first 12 octets of a DNS message.  Many of the fields
   and flags in the header diagram in section 4.1.1 of RFC 1035 are
   referred to by their names in that diagram.  For example, the
   response codes are called "RCODEs", and the authoritative answer bit
   is often called "the AA flag" or "the AA bit".

   Some of response codes that are defined in RFC 1035 have gotten their
   own shorthand names.  Some common ones are:

     FORMERR -- A response message whose header has an RCODE of 1

     SERVFAIL -- A response message whose header has an RCODE of 2

     NXDOMAIN -- A response message whose header has an RCODE of 3.
     NXDOMAIN is defined as an official synonym for Name Error in
     RFC 2308, section 1.

   TTL -- The "time to live" of a resource record.  A TTL value is an
   unsigned number, with a minimum value of 0, and a maximum value of
   2147483647.  That is, a maximum of 2^31 - 1.  When transmitted, the
   TTL is encoded in the less significant 31 bits of the 32 bit TTL
   field, with the most significant, or sign, bit set to zero.  (Quoted
   from [RFC2181], section 8) (Note that RFC 1035 erroneously stated
   that this is a signed integer; it is fixed in an erratum.)

   The TTL "specifies the time interval that the resource record may be
   cached before the source of the information should again be
   consulted".  (Quoted from RFC 1035, section 3.2.1) Also: "the time
   interval (in seconds) that the resource record may be cached before
   it should be discarded".  (Quoted from RFC 1035, section 4.1.3).
   Despite being defined for a resource record, the TTL of every
   resource record in an RRset is required to be the same (RFC2181,
   section 5.2).

   Glue records -- Resource records which are not part of the
   authoritative data, and are address resource records for the servers
   listed in the message.  They contain data that allows access to name
   servers for subzones.  (Definition from RFC 1034, section 4.2.1)

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   Referrals -- Data from the authority section of a non-authoritative
   answer.  RFC 1035 section 2.1 defines "authoritative" data.  However,
   referrals at zone cuts are not authoritative.  Referrals may be a
   zone cut NS resource records and their glue.  NS records on the
   parent side of a zone cut are an authoritative delegation, but are
   not treated as authoritative data by the client.  [[ A more complete
   and precise definition will be needed here. ]]

3.  Resource Records

   RR -- A short form for resource record.  (RFC 1034, section 3.6.)

   RRset -- A set of resource records with the same label, class and
   type, but with different data.  (Definition from RFC 2181).  Also
   spelled RRSet in some documents.

   OPT -- A pseudo-RR (sometimes called a meta-RR) that is used only to
   contain control information pertaining to the question-and-answer
   sequence of a specific transaction. contains control information
   pertaining to the question-and-answer sequence of a specific
   transaction.  (Definition from [RFC6891], section 6.1.1)

   Owner -- The domain name where a RR is found (RFC 1034, section 3.6).
   Often appears in the term "owner name".

4.  DNS Servers

   This section defines the terms used for the systems that act as DNS
   clients, DNS servers, or both.  Some terms about servers describe
   servers that do and do not use DNSSEC; see Section 6 for those

   Resolver -- Programs that interface user programs to domain name
   servers.  (Quoted from RFC 1034, section 5.1) A resolver performs
   queries for a name, type, and class, and receives answers.  The
   logical function is called "resolution".  In practice, the term is
   usually referring to some specific type of resolver (some of which
   are defined below), and understanding the use of the term depends on
   understanding the context.

   Stub resolver -- A resolver that cannot perform all resolution
   itself.  Stub resolvers generally depend on a recursive resolver to
   undertake the actual resolution function.  Stub resolvers are
   discussed but never fully defined in RFC 1034, section 5.3.1.

   Iterative resolver -- A system that receives DNS queries and responds
   with a referral to another server.  RFC 1034 (section 2.3) describes

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   this as, "The server refers the client to another server and lets the
   client pursue the query."

   Recursive resolver -- A system that receives DNS queries and either
   responds to those queries from a local cache or sends queries to
   authoritative servers in order to get the final answers to the
   original queries.  RFC 1034 (section 2.3) describes this as, "The
   first server pursues the query for the client at another server."
   Recursive resolvers may be thought of as having a name server side
   (which is what answers the query) and a resolver side (which performs
   the resolution function).  A recursive resolver is responsible for
   resolving domain names for clients by following the domain's
   delegation chain, starting at the DNS root.  These systems are also
   commonly called "recursive servers".

   Authoritative server -- A system that responds to DNS queries with
   information about zones for which it has been configured to answer
   with the AA flag in the response header set to 1.  It is a server
   that has authority over one or more DNS zones.  Note that it is
   possible for an authoritative server to respond to a query without
   the parent zone delegating authority to that server.

   DNS forwarder -- A system receives a DNS query, possibly changes the
   query, sends the resulting query to a recursive resolver, receives
   the response from a resolver, possibly changes the response, and
   sends the resulting response to the stub resolver.  Section 1 of
   [RFC2308] describes a forwarder as "a nameserver used to resolve
   queries instead of directly using the authoritative nameserver
   chain".  [RFC5625] does not give a specific definition for DNS
   forwarder, but describes in detail what features they need to
   support.  The protocol interfaces for DNS forwarders are exactly the
   same as those for recursive resolvers (for interactions with DNS
   stubs) and as those for stub resolvers (for interactions with
   recursive resolvers).

   Full resolver -- This term is used in RFC 1035, but it is not defined
   there.  RFC 1123 defines a "full-service resolver" that may or may
   not be what was intended by "full resolver" in RFC 1035.  In the
   vernacular, a full-service resolver is usually one that would be
   suitable for use by a stub resolver.

   Consensual policy-implementing resolver -- A resolver that changes
   some answers it returns based on policy criteria, such as to prevent
   access to malware sites.  These policy criteria are agreed to by
   systems that query this resolver through some out of band mechanism
   (such as finding out about the resolver from a web site and reading
   the policy).

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   Non-consensual policy-implementing resolver -- A resolver that is not
   a consensual policy-implementing resolver that changes the answers it
   returns.  The difference between this and a consensual policy-
   implementing resolver is that users of this resolver are not expected
   to know that there is a policy to change the answers it returns.

5.  Zones

   This section defines terms that are used when discussing zones that
   are being served or retrieved.

   Zone -- A unit of organization of authoritative data.  Zones can be
   automatically distributed to the name servers which provide redundant
   service for the data in a zone.  (Quoted from RFC 1034, section 2.4).

   Child -- The entity on record that has the delegation of the domain
   from the Parent.  (Quoted from [RFC7344], section 1.1)

   Parent -- The domain in which the Child is registered.  (Quoted from
   RFC 7344, section 1.1)

   Zone cut -- The delimitation point between two zones where the origin
   of one of the zones is the child of the other zone.  (Section 6 of
   RFC 2181 uses this term extensively, although never actually defines

   In-bailiwick response -- A response in which the name server
   answering is authoritative for an ancestor of the owner name in the
   response.  The term normally is used when discussing the relevancy of
   glue records.  For example, the parent zone example.com might reply
   with glue records for ns.child.example.com.  Because the
   child.example.com zone is a descendant of the example.com zone, the
   glue is in-bailiwick.

   Out-of-bailiwick response -- A response in which the name server
   answering is not authoritative for an ancestor of the owner name in
   the response.

   Origin -- 1.  The domain name within which a given relative domain
   name appears.  Generally seen in the context of "$ORIGIN", which is a
   control entry defined in RFC 1035, section 5.1, as part of the master
   file format.  For example, if the $ORIGIN is set to "example.org.",
   then a master file line for "www" is in fact an entry for
   "www.example.org.".  2.  The domain name that appears at the top of a
   zone, that is, the owner name of the apex records.

   Authoritative data -- RRsets in a DNS response that has the AA bit in
   the response header set to 1.

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   Delegation -- The process by which a separate zone is created in the
   name space beneath a given domain.  Delegation happens when an NS
   RRset is added in the parent zone for the child origin, and a
   corresponding zone apex is created at the child origin.

   Apex -- The SOA and NS RRsets at the origin of a zone.  This is also
   called the "zone apex".

   Root zone -- The zone whose origin is the zero-length label.  Also
   sometimes called "the DNS root".


   This section will mostly be populated with direct quotes from RFC
   4033.  For some terms, there will be additional commentary.

   [[ The four types of validation states ]]

   [[ The many types of DNSSEC-aware and -unaware resolvers and
   validators ]]

   NSEC -- [[ Definition goes here ]]

   NSEC3 -- [[ Definition goes here ]]

7.  IANA Considerations

   This document has no effect on IANA registries.

8.  Security Considerations

   These definitions do not change any security considerations for the

9.  Acknowledgements

   The authors gratefully acknowledge all of the authors of DNS-related
   RFCs that proceed this one. [[ More acks will go here as people point
   out new terms to add and changes to the ones we have listed here. ]]

10.  References

10.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

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   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS
              Specification", RFC 2181, July 1997.

   [RFC2308]  Andrews, M., "Negative Caching of DNS Queries (DNS
              NCACHE)", RFC 2308, March 1998.

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891, April 2013.

   [RFC7344]  Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
              DNSSEC Delegation Trust Maintenance", RFC 7344, September

10.2.  Informative References

   [RFC5625]  Bellis, R., "DNS Proxy Implementation Guidelines", BCP
              152, RFC 5625, August 2009.

Authors' Addresses

   Paul Hoffman
   VPN Consortium
   127 Segre Place
   Santa Cruz, CA  95060

   Email: paul.hoffman@vpnc.org

   Andrew Sullivan
   150 Dow St, Tower 2
   Manchester, NH  1604

   Email: asullivan@dyn.com

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   Kazunori Fujiwara
   Japan Registry Services Co., Ltd.
   Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda
   Chiyoda-ku, Tokyo  101-0065

   Phone: +81 3 5215 8451
   Email: fujiwara@jprs.co.jp

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