1 Internet Engineering Task Force (IETF)                        P. Hoffman   
    2 Request for Comments: 7719                                         ICANN   
    3 Category: Informational                                      A. Sullivan   
    4 ISSN: 2070-1721                                                      Dyn   
    5                                                              K. Fujiwara   
    6                                                                     JPRS   
    7                                                            December 2015   
   10                             DNS Terminology                                
   12 Abstract                                                                   
   14    The DNS is defined in literally dozens of different RFCs.  The          
   15    terminology used by implementers and developers of DNS protocols, and   
   16    by operators of DNS systems, has sometimes changed in the decades       
   17    since the DNS was first defined.  This document gives current           
   18    definitions for many of the terms used in the DNS in a single           
   19    document.                                                               
   21 Status of This Memo                                                        
   23    This document is not an Internet Standards Track specification; it is   
   24    published for informational purposes.                                   
   26    This document is a product of the Internet Engineering Task Force       
   27    (IETF).  It represents the consensus of the IETF community.  It has     
   28    received public review and has been approved for publication by the     
   29    Internet Engineering Steering Group (IESG).  Not all documents          
   30    approved by the IESG are a candidate for any level of Internet          
   31    Standard; see Section 2 of RFC 5741.                                    
   33    Information about the current status of this document, any errata,      
   34    and how to provide feedback on it may be obtained at                    
   35    http://www.rfc-editor.org/info/rfc7719.                                 
   52 Hoffman, et al.               Informational                     [Page 1]   

   53 RFC 7719                     DNS Terminology               December 2015   
   56 Copyright Notice                                                           
   58    Copyright (c) 2015 IETF Trust and the persons identified as the         
   59    document authors.  All rights reserved.                                 
   61    This document is subject to BCP 78 and the IETF Trust's Legal           
   62    Provisions Relating to IETF Documents                                   
   63    (http://trustee.ietf.org/license-info) in effect on the date of         
   64    publication of this document.  Please review these documents            
   65    carefully, as they describe your rights and restrictions with respect   
   66    to this document.  Code Components extracted from this document must    
   67    include Simplified BSD License text as described in Section 4.e of      
   68    the Trust Legal Provisions and are provided without warranty as         
   69    described in the Simplified BSD License.                                
   71 Table of Contents                                                          
   73    1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2   
   74    2.  Names . . . . . . . . . . . . . . . . . . . . . . . . . . . .   4   
   75    3.  DNS Header and Response Codes . . . . . . . . . . . . . . . .   6   
   76    4.  Resource Records  . . . . . . . . . . . . . . . . . . . . . .   7   
   77    5.  DNS Servers and Clients . . . . . . . . . . . . . . . . . . .   9   
   78    6.  Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . .  13   
   79    7.  Registration Model  . . . . . . . . . . . . . . . . . . . . .  17   
   80    8.  General DNSSEC  . . . . . . . . . . . . . . . . . . . . . . .  18   
   81    9.  DNSSEC States . . . . . . . . . . . . . . . . . . . . . . . .  20   
   82    10. Security Considerations . . . . . . . . . . . . . . . . . . .  22   
   83    11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22   
   84      11.1.  Normative References . . . . . . . . . . . . . . . . . .  22   
   85      11.2.  Informative References . . . . . . . . . . . . . . . . .  24   
   86    Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  27   
   87    Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27   

The IETF is responsible for the creation and maintenance of the DNS RFCs. The ICANN DNS RFC annotation project provides a forum for collecting community annotations on these RFCs as an aid to understanding for implementers and any interested parties. The annotations displayed here are not the result of the IETF consensus process.

This RFC is included in the DNS RFCs annotation project whose home page is here.

Obsoleted by RFC8499
   89 1.  Introduction                                                           
   91    The Domain Name System (DNS) is a simple query-response protocol        
   92    whose messages in both directions have the same format.  The protocol   
   93    and message format are defined in [RFC1034] and [RFC1035].  These       
   94    RFCs defined some terms, but later documents defined others.  Some of   
   95    the terms from RFCs 1034 and 1035 now have somewhat different           
   96    meanings than they did in 1987.                                         
   98    This document collects a wide variety of DNS-related terms.  Some of    
   99    them have been precisely defined in earlier RFCs, some have been        
  100    loosely defined in earlier RFCs, and some are not defined in any        
  101    earlier RFC at all.                                                     
  107 Hoffman, et al.               Informational                     [Page 2]   

  108 RFC 7719                     DNS Terminology               December 2015   
  111    Most of the definitions here are the consensus definition of the DNS    
  112    community -- both protocol developers and operators.  Some of the       
  113    definitions differ from earlier RFCs, and those differences are         
  114    noted.  In this document, where the consensus definition is the same    
  115    as the one in an RFC, that RFC is quoted.  Where the consensus          
  116    definition has changed somewhat, the RFC is mentioned but the new       
  117    stand-alone definition is given.                                        
  119    It is important to note that, during the development of this            
  120    document, it became clear that some DNS-related terms are interpreted   
  121    quite differently by different DNS experts.  Further, some terms that   
  122    are defined in early DNS RFCs now have definitions that are generally   
  123    agreed to, but that are different from the original definitions.        
  124    Therefore, the authors intend to follow this document with a            
  125    substantial revision in the not-distant future.  That revision will     
  126    probably have more in-depth discussion of some terms as well as new     
  127    terms; it will also update some of the RFCs with new definitions.       
  129    The terms are organized loosely by topic.  Some definitions are for     
  130    new terms for things that are commonly talked about in the DNS          
  131    community but that never had terms defined for them.                    
  133    Other organizations sometimes define DNS-related terms their own way.   
  134    For example, the W3C defines "domain" at                                
  135    https://specs.webplatform.org/url/webspecs/develop/.                    
  137    Note that there is no single consistent definition of "the DNS".  It    
  138    can be considered to be some combination of the following: a commonly   
  139    used naming scheme for objects on the Internet; a distributed           
  140    database representing the names and certain properties of these         
  141    objects; an architecture providing distributed maintenance,             
  142    resilience, and loose coherency for this database; and a simple         
  143    query-response protocol (as mentioned below) implementing this          
  144    architecture.                                                           
  146    Capitalization in DNS terms is often inconsistent among RFCs and        
  147    various DNS practitioners.  The capitalization used in this document    
  148    is a best guess at current practices, and is not meant to indicate      
  149    that other capitalization styles are wrong or archaic.  In some         
  150    cases, multiple styles of capitalization are used for the same term     
  151    due to quoting from different RFCs.                                     
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  163 RFC 7719                     DNS Terminology               December 2015   
section-1 Scott Corcoran(Technical Erratum #5542) [Rejected]
based on outdated version
It should say:

The RFC should be edited to reflect the intended content. Unfortunately,
although I am technical, I do not have knowledge of the original. There
are also other dead references.... and a reference to a "dead project"
which is still living, here, but with little reference to DNS or

RFC Editor note: Errata are typically not used to correct URLs that were
functioning at the time of publication. For this case, please see RFC
8499 (which obsoleted RFC 7719) for the current information.
Thank you for submitting this. RFC 7719 has been updated by RFC8499
(published after your errata was submitted), which doesn't contain the

Thanks again
  166 2.  Names                                                                  
  168    Domain name:  Section 3.1 of [RFC1034] talks of "the domain name        
  169       space" as a tree structure.  "Each node has a label, which is zero   
  170       to 63 octets in length. ... The domain name of a node is the list    
  171       of the labels on the path from the node to the root of the tree.     
  172       ... To simplify implementations, the total number of octets that     
  173       represent a domain name (i.e., the sum of all label octets and       
  174       label lengths) is limited to 255."  Any label in a domain name can   
  175       contain any octet value.                                             
  177    Fully qualified domain name (FQDN):  This is often just a clear way     
  178       of saying the same thing as "domain name of a node", as outlined     
  179       above.  However, the term is ambiguous.  Strictly speaking, a        
  180       fully qualified domain name would include every label, including     
  181       the final, zero-length label of the root: such a name would be       
  182       written "www.example.net." (note the terminating dot).  But          
  183       because every name eventually shares the common root, names are      
  184       often written relative to the root (such as "www.example.net") and   
  185       are still called "fully qualified".  This term first appeared in     
  186       [RFC819].  In this document, names are often written relative to     
  187       the root.                                                            
  189       The need for the term "fully qualified domain name" comes from the   
  190       existence of partially qualified domain names, which are names       
  191       where some of the right-most names are left off and are understood   
  192       only by context.                                                     
  194    Label:  The identifier of an individual node in the sequence of nodes   
  195       identified by a fully qualified domain name.                         
  197    Host name:  This term and its equivalent, "hostname", have been         
  198       widely used but are not defined in [RFC1034], [RFC1035],             
  199       [RFC1123], or [RFC2181].  The DNS was originally deployed into the   
  200       Host Tables environment as outlined in [RFC952], and it is likely    
  201       that the term followed informally from the definition there.  Over   
  202       time, the definition seems to have shifted.  "Host name" is often    
  203       meant to be a domain name that follows the rules in Section 3.5 of   
  204       [RFC1034], the "preferred name syntax".  Note that any label in a    
  205       domain name can contain any octet value; hostnames are generally     
  206       considered to be domain names where every label follows the rules    
  207       in the "preferred name syntax", with the amendment that labels can   
  208       start with ASCII digits (this amendment comes from Section 2.1 of    
  209       [RFC1123]).                                                          
  211       People also sometimes use the term hostname to refer to just the     
  212       first label of an FQDN, such as "printer" in                         
  213       "printer.admin.example.com".  (Sometimes this is formalized in       
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  218 RFC 7719                     DNS Terminology               December 2015   
  221       configuration in operating systems.)  In addition, people            
  222       sometimes use this term to describe any name that refers to a        
  223       machine, and those might include labels that do not conform to the   
  224       "preferred name syntax".                                             
  226    TLD:  A Top-Level Domain, meaning a zone that is one layer below the    
  227       root, such as "com" or "jp".  There is nothing special, from the     
  228       point of view of the DNS, about TLDs.  Most of them are also         
  229       delegation-centric zones, and there are significant policy issues    
  230       around their operation.  TLDs are often divided into sub-groups      
  231       such as Country Code Top-Level Domains (ccTLDs), Generic Top-Level   
  232       Domains (gTLDs), and others; the division is a matter of policy,     
  233       and beyond the scope of this document.                               
  235    IDN:  The common abbreviation for "Internationalized Domain Name".      
  236       The IDNA protocol is the standard mechanism for handling domain      
  237       names with non-ASCII characters in applications in the DNS.  The     
  238       current standard, normally called "IDNA2008", is defined in          
  239       [RFC5890], [RFC5891], [RFC5892], [RFC5893], and [RFC5894].  These    
  240       documents define many IDN-specific terms such as "LDH label",        
  241       "A-label", and "U-label".  [RFC6365] defines more terms that         
  242       relate to internationalization (some of which relate to IDNs), and   
  243       [RFC6055] has a much more extensive discussion of IDNs, including    
  244       some new terminology.                                                
  246    Subdomain:  "A domain is a subdomain of another domain if it is         
  247       contained within that domain.  This relationship can be tested by    
  248       seeing if the subdomain's name ends with the containing domain's     
  249       name."  (Quoted from [RFC1034], Section 3.1).  For example, in the   
  250       host name "nnn.mmm.example.com", both "mmm.example.com" and          
  251       "nnn.mmm.example.com" are subdomains of "example.com".               
  253    Alias:  The owner of a CNAME resource record, or a subdomain of the     
  254       owner of a DNAME resource record [RFC6672].  See also "canonical     
  255       name".                                                               
  257    Canonical name:  A CNAME resource record "identifies its owner name     
  258       as an alias, and specifies the corresponding canonical name in the   
  259       RDATA section of the RR."  (Quoted from [RFC1034], Section 3.6.2)    
  260       This usage of the word "canonical" is related to the mathematical    
  261       concept of "canonical form".                                         
  263    CNAME:  "It is traditional to refer to the owner of a CNAME record as   
  264       'a CNAME'.  This is unfortunate, as 'CNAME' is an abbreviation of    
  265       'canonical name', and the owner of a CNAME record is an alias, not   
  266       a canonical name."  (Quoted from [RFC2181], Section 10.1.1)          
  272 Hoffman, et al.               Informational                     [Page 5]   

  273 RFC 7719                     DNS Terminology               December 2015   
  276    Public suffix:  "A domain that is controlled by a public registry."     
  277       (Quoted from [RFC6265], Section 5.3) A common definition for this    
  278       term is a domain under which subdomains can be registered, and on    
  279       which HTTP cookies ([RFC6265]) should not be set.  There is no       
  280       indication in a domain name whether it is a public suffix; that      
  281       can only be determined by outside means.  In fact, both a domain     
  282       and a subdomain of that domain can be public suffixes.  At the       
  283       time this document is published, the IETF DBOUND Working Group       
  284       [DBOUND] is dealing with issues concerning public suffixes.          
  286       There is nothing inherent in a domain name to indicate whether it    
  287       is a public suffix.  One resource for identifying public suffixes    
  288       is the Public Suffix List (PSL) maintained by Mozilla                
  289       (http://publicsuffix.org/).                                          
  291       For example, at the time this document is published, the "com.au"    
  292       domain is listed as a public suffix in the PSL.  (Note that this     
  293       example might change in the future.)                                 
  295       Note that the term "public suffix" is controversial in the DNS       
  296       community for many reasons, and may be significantly changed in      
  297       the future.  One example of the difficulty of calling a domain a     
  298       public suffix is that designation can change over time as the        
  299       registration policy for the zone changes, such as the case of the    
  300       "uk" TLD around the time this document is published.                 
  302 3.  DNS Header and Response Codes                                          
  304    The header of a DNS message is its first 12 octets.  Many of the        
  305    fields and flags in the header diagram in Sections 4.1.1 through        
  306    4.1.3 of [RFC1035] are referred to by their names in that diagram.      
  307    For example, the response codes are called "RCODEs", the data for a     
  308    record is called the "RDATA", and the authoritative answer bit is       
  309    often called "the AA flag" or "the AA bit".                             
  311    Some of response codes that are defined in [RFC1035] have gotten        
  312    their own shorthand names.  Some common response code names that        
  313    appear without reference to the numeric value are "FORMERR",            
  314    "SERVFAIL", and "NXDOMAIN" (the latter of which is also referred to     
  315    as "Name Error").  All of the RCODEs are listed at                      
  316    http://www.iana.org/assignments/dns-parameters, although that site      
  317    uses mixed-case capitalization, while most documents use all-caps.      
  319    NODATA:  "A pseudo RCODE which indicates that the name is valid for     
  320       the given class, but there are no records of the given type.  A      
  321       NODATA response has to be inferred from the answer."  (Quoted from   
  322       [RFC2308], Section 1.)  "NODATA is indicated by an answer with the   
  323       RCODE set to NOERROR and no relevant answers in the answer           
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  328 RFC 7719                     DNS Terminology               December 2015   
  331       section.  The authority section will contain an SOA record, or       
  332       there will be no NS records there."  (Quoted from [RFC2308],         
  333       Section 2.2.)  Note that referrals have a similar format to NODATA   
  334       replies; [RFC2308] explains how to distinguish them.                 
  336       The term "NXRRSET" is sometimes used as a synonym for NODATA.        
  337       However, this is a mistake, given that NXRRSET is a specific error   
  338       code defined in [RFC2136].                                           
  340    Negative response:  A response that indicates that a particular RRset   
  341       does not exist, or whose RCODE indicates the nameserver cannot       
  342       answer.  Sections 2 and 7 of [RFC2308] describe the types of         
  343       negative responses in detail.                                        
  345    Referrals:  Data from the authority section of a non-authoritative      
  346       answer.  [RFC1035] Section 2.1 defines "authoritative" data.         
  347       However, referrals at zone cuts (defined in Section 6) are not       
  348       authoritative.  Referrals may be zone cut NS resource records and    
  349       their glue records.  NS records on the parent side of a zone cut     
  350       are an authoritative delegation, but are normally not treated as     
  351       authoritative data.  In general, a referral is a way for a server    
  352       to send an answer saying that the server does not know the answer,   
  353       but knows where the query should be directed in order to get an      
  354       answer.  Historically, many authoritative servers answered with a    
  355       referral to the root zone when queried for a name for which they     
  356       were not authoritative, but this practice has declined.              
  358 4.  Resource Records                                                       
  360    RR:  An acronym for resource record.  ([RFC1034], Section 3.6.)         
  362    RRset:  A set of resource records with the same label, class and        
  363       type, but with different data.  (Definition from [RFC2181]) Also     
  364       spelled RRSet in some documents.  As a clarification, "same label"   
  365       in this definition means "same owner name".  In addition,            
  366       [RFC2181] states that "the TTLs of all RRs in an RRSet must be the   
  367       same".  (This definition is definitely not the same as "the          
  368       response one gets to a query for QTYPE=ANY", which is an             
  369       unfortunate misunderstanding.)                                       
  371    EDNS:  The extension mechanisms for DNS, defined in [RFC6891].          
  372       Sometimes called "EDNS0" or "EDNS(0)" to indicate the version        
  373       number.  EDNS allows DNS clients and servers to specify message      
  374       sizes larger than the original 512 octet limit, to expand the        
  375       response code space, and potentially to carry additional options     
  376       that affect the handling of a DNS query.                             
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  383 RFC 7719                     DNS Terminology               December 2015   
  386    OPT:  A pseudo-RR (sometimes called a "meta-RR") that is used only to   
  387       contain control information pertaining to the question-and-answer    
  388       sequence of a specific transaction.  (Definition from [RFC6891],     
  389       Section 6.1.1) It is used by EDNS.                                   
  391    Owner:  The domain name where a RR is found ([RFC1034], Section 3.6).   
  392       Often appears in the term "owner name".                              
  394    SOA field names:  DNS documents, including the definitions here,        
  395       often refer to the fields in the RDATA of an SOA resource record     
  396       by field name.  Those fields are defined in Section 3.3.13 of        
  397       [RFC1035].  The names (in the order they appear in the SOA RDATA)    
  399       Note that the meaning of MINIMUM field is updated in Section 4 of    
  400       [RFC2308]; the new definition is that the MINIMUM field is only      
  401       "the TTL to be used for negative responses".  This document tends    
  402       to use field names instead of terms that describe the fields.        
  404    TTL:  The maximum "time to live" of a resource record.  "A TTL value    
  405       is an unsigned number, with a minimum value of 0, and a maximum      
  406       value of 2147483647.  That is, a maximum of 2^31 - 1.  When          
  407       transmitted, the TTL is encoded in the less significant 31 bits of   
  408       the 32 bit TTL field, with the most significant, or sign, bit set    
  409       to zero."  (Quoted from [RFC2181], Section 8) (Note that [RFC1035]   
  410       erroneously stated that this is a signed integer; that was fixed     
  411       by [RFC2181].)                                                       
  413       The TTL "specifies the time interval that the resource record may    
  414       be cached before the source of the information should again be       
  415       consulted".  (Quoted from [RFC1035], Section 3.2.1) Also: "the       
  416       time interval (in seconds) that the resource record may be cached    
  417       before it should be discarded".  (Quoted from [RFC1035],             
  418       Section 4.1.3).  Despite being defined for a resource record, the    
  419       TTL of every resource record in an RRset is required to be the       
  420       same ([RFC2181], Section 5.2).                                       
  422       The reason that the TTL is the maximum time to live is that a        
  423       cache operator might decide to shorten the time to live for          
  424       operational purposes, such as if there is a policy to disallow TTL   
  425       values over a certain number.  Also, if a value is flushed from      
  426       the cache when its value is still positive, the value effectively    
  427       becomes zero.  Some servers are known to ignore the TTL on some      
  428       RRsets (such as when the authoritative data has a very short TTL)    
  429       even though this is against the advice in RFC 1035.                  
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  438 RFC 7719                     DNS Terminology               December 2015   
  441       There is also the concept of a "default TTL" for a zone, which can   
  442       be a configuration parameter in the server software.  This is        
  443       often expressed by a default for the entire server, and a default    
  444       for a zone using the $TTL directive in a zone file.  The $TTL        
  445       directive was added to the master file format by [RFC2308].          
  447    Class independent:  A resource record type whose syntax and semantics   
  448       are the same for every DNS class.  A resource record type that is    
  449       not class independent has different meanings depending on the DNS    
  450       class of the record, or the meaning is undefined for classes other   
  451       than IN (class 1, the Internet).                                     
  453 5.  DNS Servers and Clients                                                
  455    This section defines the terms used for the systems that act as DNS     
  456    clients, DNS servers, or both.                                          
  458    Resolver:  A program "that extract[s] information from name servers     
  459       in response to client requests."  (Quoted from [RFC1034],            
  460       Section 2.4) "The resolver is located on the same machine as the     
  461       program that requests the resolver's services, but it may need to    
  462       consult name servers on other hosts."  (Quoted from [RFC1034],       
  463       Section 5.1) A resolver performs queries for a name, type, and       
  464       class, and receives answers.  The logical function is called         
  465       "resolution".  In practice, the term is usually referring to some    
  466       specific type of resolver (some of which are defined below), and     
  467       understanding the use of the term depends on understanding the       
  468       context.                                                             
  470    Stub resolver:  A resolver that cannot perform all resolution itself.   
  471       Stub resolvers generally depend on a recursive resolver to           
  472       undertake the actual resolution function.  Stub resolvers are        
  473       discussed but never fully defined in Section 5.3.1 of [RFC1034].     
  474       They are fully defined in Section of [RFC1123].              
  476    Iterative mode:  A resolution mode of a server that receives DNS        
  477       queries and responds with a referral to another server.              
  478       Section 2.3 of [RFC1034] describes this as "The server refers the    
  479       client to another server and lets the client pursue the query".  A   
  480       resolver that works in iterative mode is sometimes called an         
  481       "iterative resolver".                                                
  483    Recursive mode:  A resolution mode of a server that receives DNS        
  484       queries and either responds to those queries from a local cache or   
  485       sends queries to other servers in order to get the final answers     
  486       to the original queries.  Section 2.3 of [RFC1034] describes this    
  487       as "The first server pursues the query for the client at another     
  488       server".  A server operating in recursive mode may be thought of     
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  493 RFC 7719                     DNS Terminology               December 2015   
  496       as having a name server side (which is what answers the query) and   
  497       a resolver side (which performs the resolution function).  Systems   
  498       operating in this mode are commonly called "recursive servers".      
  499       Sometimes they are called "recursive resolvers".  While strictly     
  500       the difference between these is that one of them sends queries to    
  501       another recursive server and the other does not, in practice it is   
  502       not possible to know in advance whether the server that one is       
  503       querying will also perform recursion; both terms can be observed     
  504       in use interchangeably.                                              
  506    Full resolver:  This term is used in [RFC1035], but it is not defined   
  507       there.  RFC 1123 defines a "full-service resolver" that may or may   
  508       not be what was intended by "full resolver" in [RFC1035].  This      
  509       term is not properly defined in any RFC.                             
  511    Full-service resolver:  Section of [RFC1123] defines this       
  512       term to mean a resolver that acts in recursive mode with a cache     
  513       (and meets other requirements).                                      
  515    Priming:  The mechanism used by a resolver to determine where to send   
  516       queries before there is anything in the resolver's cache.  Priming   
  517       is most often done from a configuration setting that contains a      
  518       list of authoritative servers for the root zone.                     
  520    Negative caching:  "The storage of knowledge that something does not    
  521       exist, cannot give an answer, or does not give an answer."           
  522       (Quoted from [RFC2308], Section 1)                                   
  524    Authoritative server:  "A server that knows the content of a DNS zone   
  525       from local knowledge, and thus can answer queries about that zone    
  526       without needing to query other servers."  (Quoted from [RFC2182],    
  527       Section 2.)  It is a system that responds to DNS queries with        
  528       information about zones for which it has been configured to answer   
  529       with the AA flag in the response header set to 1.  It is a server    
  530       that has authority over one or more DNS zones.  Note that it is      
  531       possible for an authoritative server to respond to a query without   
  532       the parent zone delegating authority to that server.                 
  533       Authoritative servers also provide "referrals", usually to child     
  534       zones delegated from them; these referrals have the AA bit set to    
  535       0 and come with referral data in the Authority and (if needed) the   
  536       Additional sections.                                                 
  538    Authoritative-only server:  A name server that only serves              
  539       authoritative data and ignores requests for recursion.  It will      
  540       "not normally generate any queries of its own.  Instead, it          
  541       answers non-recursive queries from iterative resolvers looking for   
  542       information in zones it serves."  (Quoted from [RFC4697],            
  543       Section 2.4)                                                         
  547 Hoffman, et al.               Informational                    [Page 10]   

  548 RFC 7719                     DNS Terminology               December 2015   
  551    Zone transfer:  The act of a client requesting a copy of a zone and     
  552       an authoritative server sending the needed information.  (See        
  553       Section 6 for a description of zones.)  There are two common         
  554       standard ways to do zone transfers: the AXFR ("Authoritative         
  555       Transfer") mechanism to copy the full zone (described in             
  556       [RFC5936], and the IXFR ("Incremental Transfer") mechanism to copy   
  557       only parts of the zone that have changed (described in [RFC1995]).   
  558       Many systems use non-standard methods for zone transfer outside      
  559       the DNS protocol.                                                    
  561    Secondary server:  "An authoritative server which uses zone transfer    
  562       to retrieve the zone" (Quoted from [RFC1996], Section 2.1).          
  563       [RFC2182] describes secondary servers in detail.  Although early     
  564       DNS RFCs such as [RFC1996] referred to this as a "slave", the        
  565       current common usage has shifted to calling it a "secondary".        
  566       Secondary servers are also discussed in [RFC1034].                   
  568    Slave server:  See secondary server.                                    
  570    Primary server:  "Any authoritative server configured to be the         
  571       source of zone transfer for one or more [secondary] servers"         
  572       (Quoted from [RFC1996], Section 2.1) or, more specifically, "an      
  573       authoritative server configured to be the source of AXFR or IXFR     
  574       data for one or more [secondary] servers" (Quoted from [RFC2136]).   
  575       Although early DNS RFCs such as [RFC1996] referred to this as a      
  576       "master", the current common usage has shifted to "primary".         
  577       Primary servers are also discussed in [RFC1034].                     
  579    Master server:  See primary server.                                     
  581    Primary master:  "The primary master is named in the zone's SOA MNAME   
  582       field and optionally by an NS RR".  (Quoted from [RFC1996],          
  583       Section 2.1).  [RFC2136] defines "primary master" as "Master         
  584       server at the root of the AXFR/IXFR dependency graph.  The primary   
  585       master is named in the zone's SOA MNAME field and optionally by an   
  586       NS RR.  There is by definition only one primary master server per    
  587       zone."  The idea of a primary master is only used by [RFC2136],      
  588       and is considered archaic in other parts of the DNS.                 
  590    Stealth server:  This is "like a slave server except not listed in an   
  591       NS RR for the zone."  (Quoted from [RFC1996], Section 2.1)           
  602 Hoffman, et al.               Informational                    [Page 11]   

  603 RFC 7719                     DNS Terminology               December 2015   
  606    Hidden master:  A stealth server that is a master for zone transfers.   
  607       "In this arrangement, the master name server that processes the      
  608       updates is unavailable to general hosts on the Internet; it is not   
  609       listed in the NS RRset."  (Quoted from [RFC6781], Section 3.4.3.)    
  610       An earlier RFC, [RFC4641], said that the hidden master's name        
  611       appears in the SOA RRs MNAME field, although in some setups, the     
  612       name does not appear at all in the public DNS.  A hidden master      
  613       can be either a secondary or a primary master.                       
  615    Forwarding:  The process of one server sending a DNS query with the     
  616       RD bit set to 1 to another server to resolve that query.             
  617       Forwarding is a function of a DNS resolver; it is different than     
  618       simply blindly relaying queries.                                     
  620       [RFC5625] does not give a specific definition for forwarding, but    
  621       describes in detail what features a system that forwards need to     
  622       support.  Systems that forward are sometimes called "DNS proxies",   
  623       but that term has not yet been defined (even in [RFC5625]).          
  625    Forwarder:  Section 1 of [RFC2308] describes a forwarder as "a          
  626       nameserver used to resolve queries instead of directly using the     
  627       authoritative nameserver chain".  [RFC2308] further says "The        
  628       forwarder typically either has better access to the internet, or     
  629       maintains a bigger cache which may be shared amongst many            
  630       resolvers."  That definition appears to suggest that forwarders      
  631       normally only query authoritative servers.  In current use,          
  632       however, forwarders often stand between stub resolvers and           
  633       recursive servers.  [RFC2308] is silent on whether a forwarder is    
  634       iterative-only or can be a full-service resolver.                    
  636    Policy-implementing resolver:  A resolver acting in recursive mode      
  637       that changes some of the answers that it returns based on policy     
  638       criteria, such as to prevent access to malware sites or              
  639       objectionable content.  In general, a stub resolver has no idea      
  640       whether upstream resolvers implement such policy or, if they do,     
  641       the exact policy about what changes will be made.  In some cases,    
  642       the user of the stub resolver has selected the policy-implementing   
  643       resolver with the explicit intention of using it to implement the    
  644       policies.  In other cases, policies are imposed without the user     
  645       of the stub resolver being informed.                                 
  647    Open resolver:  A full-service resolver that accepts and processes      
  648       queries from any (or nearly any) stub resolver.  This is sometimes   
  649       also called a "public resolver", although the term "public           
  650       resolver" is used more with open resolvers that are meant to be      
  651       open, as compared to the vast majority of open resolvers that are    
  652       probably misconfigured to be open.                                   
  657 Hoffman, et al.               Informational                    [Page 12]   

  658 RFC 7719                     DNS Terminology               December 2015   
  661    View:  A configuration for a DNS server that allows it to provide       
  662       different answers depending on attributes of the query.              
  663       Typically, views differ by the source IP address of a query, but     
  664       can also be based on the destination IP address, the type of query   
  665       (such as AXFR), whether it is recursive, and so on.  Views are       
  666       often used to provide more names or different addresses to queries   
  667       from "inside" a protected network than to those "outside" that       
  668       network.  Views are not a standardized part of the DNS, but they     
  669       are widely implemented in server software.                           
  671    Passive DNS:  A mechanism to collect large amounts of DNS data by       
  672       storing DNS responses from servers.  Some of these systems also      
  673       collect the DNS queries associated with the responses; this can      
  674       raise privacy issues.  Passive DNS databases can be used to answer   
  675       historical questions about DNS zones such as which records were      
  676       available for them at what times in the past.  Passive DNS           
  677       databases allow searching of the stored records on keys other than   
  678       just the name, such as "find all names which have A records of a     
  679       particular value".                                                   
  681    Anycast:  "The practice of making a particular service address          
  682       available in multiple, discrete, autonomous locations, such that     
  683       datagrams sent are routed to one of several available locations."    
  684       (Quoted from [RFC4786], Section 2)                                   
  686 6.  Zones                                                                  
  688    This section defines terms that are used when discussing zones that     
  689    are being served or retrieved.                                          
  691    Zone:  "Authoritative information is organized into units called        
  692       'zones', and these zones can be automatically distributed to the     
  693       name servers which provide redundant service for the data in a       
  694       zone."  (Quoted from [RFC1034], Section 2.4)                         
  696    Child:  "The entity on record that has the delegation of the domain     
  697       from the Parent."  (Quoted from [RFC7344], Section 1.1)              
  699    Parent:  "The domain in which the Child is registered."  (Quoted from   
  700       [RFC7344], Section 1.1) Earlier, "parent name server" was defined    
  701       in [RFC882] as "the name server that has authority over the place    
  702       in the domain name space that will hold the new domain".  (Note      
  703       that [RFC882] was obsoleted by [RFC1034] and [RFC1035].)  [RFC819]   
  704       also has some description of the relationship between parents and    
  705       children.                                                            
  712 Hoffman, et al.               Informational                    [Page 13]   

  713 RFC 7719                     DNS Terminology               December 2015   
  716    Origin:                                                                 
  718       (a) "The domain name that appears at the top of a zone (just below   
  719       the cut that separates the zone from its parent).  The name of the   
  720       zone is the same as the name of the domain at the zone's origin."    
  721       (Quoted from [RFC2181], Section 6.)  These days, this sense of       
  722       "origin" and "apex" (defined below) are often used                   
  723       interchangeably.                                                     
  725       (b) The domain name within which a given relative domain name        
  726       appears in zone files.  Generally seen in the context of             
  727       "$ORIGIN", which is a control entry defined in [RFC1035],            
  728       Section 5.1, as part of the master file format.  For example, if     
  729       the $ORIGIN is set to "example.org.", then a master file line for    
  730       "www" is in fact an entry for "www.example.org.".                    
  732    Apex:  The point in the tree at an owner of an SOA and corresponding    
  733       authoritative NS RRset.  This is also called the "zone apex".        
  734       [RFC4033] defines it as "the name at the child's side of a zone      
  735       cut".  The "apex" can usefully be thought of as a data-theoretic     
  736       description of a tree structure, and "origin" is the name of the     
  737       same concept when it is implemented in zone files.  The              
  738       distinction is not always maintained in use, however, and one can    
  739       find uses that conflict subtly with this definition.  [RFC1034]      
  740       uses the term "top node of the zone" as a synonym of "apex", but     
  741       that term is not widely used.  These days, the first sense of        
  742       "origin" (above) and "apex" are often used interchangeably.          
  744    Zone cut:  The delimitation point between two zones where the origin    
  745       of one of the zones is the child of the other zone.                  
  747       "Zones are delimited by 'zone cuts'.  Each zone cut separates a      
  748       'child' zone (below the cut) from a 'parent' zone (above the cut).   
  749       (Quoted from [RFC2181], Section 6; note that this is barely an       
  750       ostensive definition.)  Section 4.2 of [RFC1034] uses "cuts" as      
  751       'zone cut'."                                                         
  753    Delegation:  The process by which a separate zone is created in the     
  754       name space beneath the apex of a given domain.  Delegation happens   
  755       when an NS RRset is added in the parent zone for the child origin.   
  756       Delegation inherently happens at a zone cut.  The term is also       
  757       commonly a noun: the new zone that is created by the act of          
  758       delegating.                                                          
  767 Hoffman, et al.               Informational                    [Page 14]   

  768 RFC 7719                     DNS Terminology               December 2015   
  771    Glue records:  "[Resource records] which are not part of the            
  772       authoritative data [of the zone], and are address resource records   
  773       for the [name servers in subzones].  These RRs are only necessary    
  774       if the name server's name is 'below' the cut, and are only used as   
  775       part of a referral response."  Without glue "we could be faced       
  776       with the situation where the NS RRs tell us that in order to learn   
  777       a name server's address, we should contact the server using the      
  778       address we wish to learn."  (Definition from [RFC1034],              
  779       Section 4.2.1)                                                       
  781       A later definition is that glue "includes any record in a zone       
  782       file that is not properly part of that zone, including nameserver    
  783       records of delegated sub-zones (NS records), address records that    
  784       accompany those NS records (A, AAAA, etc), and any other stray       
  785       data that might appear" ([RFC2181], Section 5.4.1).  Although glue   
  786       is sometimes used today with this wider definition in mind, the      
  787       context surrounding the [RFC2181] definition suggests it is          
  788       intended to apply to the use of glue within the document itself      
  789       and not necessarily beyond.                                          
  791    In-bailiwick:                                                           
  793       (a) An adjective to describe a name server whose name is either      
  794       subordinate to or (rarely) the same as the zone origin.  In-         
  795       bailiwick name servers require glue records in their parent zone     
  796       (using the first of the definitions of "glue records" in the         
  797       definition above).                                                   
  799       (b) Data for which the server is either authoritative, or else       
  800       authoritative for an ancestor of the owner name.  This sense of      
  801       the term normally is used when discussing the relevancy of glue      
  802       records in a response.  For example, the server for the parent       
  803       zone "example.com" might reply with glue records for                 
  804       "ns.child.example.com".  Because the "child.example.com" zone is a   
  805       descendant of the "example.com" zone, the glue records are in-       
  806       bailiwick.                                                           
  808    Out-of-bailiwick:  The antonym of in-bailiwick.                         
  810    Authoritative data:  "All of the RRs attached to all of the nodes       
  811       from the top node of the zone down to leaf nodes or nodes above      
  812       cuts around the bottom edge of the zone."  (Quoted from [RFC1034],   
  813       Section 4.2.1) It is noted that this definition might                
  814       inadvertently also include any NS records that appear in the zone,   
  815       even those that might not truly be authoritative because there are   
  816       identical NS RRs below the zone cut.  This reveals the ambiguity     
  822 Hoffman, et al.               Informational                    [Page 15]   

  823 RFC 7719                     DNS Terminology               December 2015   
  826       in the notion of authoritative data, because the parent-side NS      
  827       records authoritatively indicate the delegation, even though they    
  828       are not themselves authoritative data.                               
  830    Root zone:  The zone whose apex is the zero-length label.  Also         
  831       sometimes called "the DNS root".                                     
  833    Empty non-terminals:  "Domain names that own no resource records but    
  834       have subdomains that do."  (Quoted from [RFC4592], Section 2.2.2.)   
  835       A typical example is in SRV records: in the name                     
  836       "_sip._tcp.example.com", it is likely that "_tcp.example.com" has    
  837       no RRsets, but that "_sip._tcp.example.com" has (at least) an SRV    
  838       RRset.                                                               
  840    Delegation-centric zone:  A zone that consists mostly of delegations    
  841       to child zones.  This term is used in contrast to a zone that        
  842       might have some delegations to child zones, but also has many data   
  843       resource records for the zone itself and/or for child zones.  The    
  844       term is used in [RFC4956] and [RFC5155], but is not defined there.   
  846    Wildcard:  [RFC1034] defined "wildcard", but in a way that turned out   
  847       to be confusing to implementers.  Special treatment is given to      
  848       RRs with owner names starting with the label "*".  "Such RRs are     
  849       called 'wildcards'.  Wildcard RRs can be thought of as               
  850       instructions for synthesizing RRs."  (Quoted from [RFC1034],         
  851       Section 4.3.3) For an extended discussion of wildcards, including    
  852       clearer definitions, see [RFC4592].                                  
  854    Occluded name:  "The addition of a delegation point via dynamic         
  855       update will render all subordinate domain names to be in a limbo,    
  856       still part of the zone, but not available to the lookup process.     
  857       The addition of a DNAME resource record has the same impact.  The    
  858       subordinate names are said to be 'occluded'."  (Quoted from          
  859       [RFC5936], Section 3.5)                                              
  861    Fast flux DNS:  This "occurs when a domain is found in DNS using A      
  862       records to multiple IP addresses, each of which has a very short     
  863       Time-to-Live (TTL) value associated with it.  This means that the    
  864       domain resolves to varying IP addresses over a short period of       
  865       time."  (Quoted from [RFC6561], Section 1.1.5, with typo             
  866       corrected) It is often used to deliver malware.  Because the         
  867       addresses change so rapidly, it is difficult to ascertain all the    
  868       hosts.  It should be noted that the technique also works with AAAA   
  869       records, but such use is not frequently observed on the Internet     
  870       as of this writing.                                                  
  877 Hoffman, et al.               Informational                    [Page 16]   

  878 RFC 7719                     DNS Terminology               December 2015   
  881 7.  Registration Model                                                     
  883    Registry:  The administrative operation of a zone that allows           
  884       registration of names within that zone.  People often use this       
  885       term to refer only to those organizations that perform               
  886       registration in large delegation-centric zones (such as TLDs); but   
  887       formally, whoever decides what data goes into a zone is the          
  888       registry for that zone.  This definition of "registry" is from a     
  889       DNS point of view; for some zones, the policies that determine       
  890       what can go in the zone are decided by superior zones and not the    
  891       registry operator.                                                   
  893    Registrant:  An individual or organization on whose behalf a name in    
  894       a zone is registered by the registry.  In many zones, the registry   
  895       and the registrant may be the same entity, but in TLDs they often    
  896       are not.                                                             
  898    Registrar:  A service provider that acts as a go-between for            
  899       registrants and registries.  Not all registrations require a         
  900       registrar, though it is common to have registrars involved in        
  901       registrations in TLDs.                                               
  903    EPP:  The Extensible Provisioning Protocol (EPP), which is commonly     
  904       used for communication of registration information between           
  905       registries and registrars.  EPP is defined in [RFC5730].             
  907    WHOIS:  A protocol specified in [RFC3912], often used for querying      
  908       registry databases.  WHOIS data is frequently used to associate      
  909       registration data (such as zone management contacts) with domain     
  910       names.  The term "WHOIS data" is often used as a synonym for the     
  911       registry database, even though that database may be served by        
  912       different protocols, particularly RDAP.  The WHOIS protocol is       
  913       also used with IP address registry data.                             
  915    RDAP:  The Registration Data Access Protocol, defined in [RFC7480],     
  916       [RFC7481], [RFC7482], [RFC7483], [RFC7484], and [RFC7485].  The      
  917       RDAP protocol and data format are meant as a replacement for         
  918       WHOIS.                                                               
  920    DNS operator:  An entity responsible for running DNS servers.  For a    
  921       zone's authoritative servers, the registrant may act as their own    
  922       DNS operator, or their registrar may do it on their behalf, or       
  923       they may use a third-party operator.  For some zones, the registry   
  924       function is performed by the DNS operator plus other entities who    
  925       decide about the allowed contents of the zone.                       
  932 Hoffman, et al.               Informational                    [Page 17]   

  933 RFC 7719                     DNS Terminology               December 2015   
  936 8.  General DNSSEC                                                         
  938    Most DNSSEC terms are defined in [RFC4033], [RFC4034], [RFC4035], and   
  939    [RFC5155].  The terms that have caused confusion in the DNS community   
  940    are highlighted here.                                                   
  942    DNSSEC-aware and DNSSEC-unaware:  These two terms, which are used in    
  943       some RFCs, have not been formally defined.  However, Section 2 of    
  944       [RFC4033] defines many types of resolvers and validators,            
  945       including "non-validating security-aware stub resolver", "non-       
  946       validating stub resolver", "security-aware name server",             
  947       "security-aware recursive name server", "security-aware resolver",   
  948       "security-aware stub resolver", and "security-oblivious              
  949       'anything'".  (Note that the term "validating resolver", which is    
  950       used in some places in DNSSEC-related documents, is also not         
  951       defined.)                                                            
  953    Signed zone:  "A zone whose RRsets are signed and that contains         
  954       properly constructed DNSKEY, Resource Record Signature (RRSIG),      
  955       Next Secure (NSEC), and (optionally) DS records."  (Quoted from      
  956       [RFC4033], Section 2.)  It has been noted in other contexts that     
  957       the zone itself is not really signed, but all the relevant RRsets    
  958       in the zone are signed.  Nevertheless, if a zone that should be      
  959       signed contains any RRsets that are not signed (or opted out),       
  960       those RRsets will be treated as bogus, so the whole zone needs to    
  961       be handled in some way.                                              
  963       It should also be noted that, since the publication of [RFC6840],    
  964       NSEC records are no longer required for signed zones: a signed       
  965       zone might include NSEC3 records instead.  [RFC7129] provides        
  966       additional background commentary and some context for the NSEC and   
  967       NSEC3 mechanisms used by DNSSEC to provide authenticated denial-     
  968       of-existence responses.                                              
  970    Unsigned zone:  Section 2 of [RFC4033] defines this as "a zone that     
  971       is not signed".  Section 2 of [RFC4035] defines this as "A zone      
  972       that does not include these records [properly constructed DNSKEY,    
  973       Resource Record Signature (RRSIG), Next Secure (NSEC), and           
  974       (optionally) DS records] according to the rules in this section".    
  975       There is an important note at the end of Section 5.2 of [RFC4035]    
  976       that defines an additional situation in which a zone is considered   
  977       unsigned: "If the resolver does not support any of the algorithms    
  978       listed in an authenticated DS RRset, then the resolver will not be   
  979       able to verify the authentication path to the child zone.  In this   
  980       case, the resolver SHOULD treat the child zone as if it were         
  981       unsigned."                                                           
  987 Hoffman, et al.               Informational                    [Page 18]   

  988 RFC 7719                     DNS Terminology               December 2015   
  991    NSEC:  "The NSEC record allows a security-aware resolver to             
  992       authenticate a negative reply for either name or type non-           
  993       existence with the same mechanisms used to authenticate other DNS    
  994       replies."  (Quoted from [RFC4033], Section 3.2.)  In short, an       
  995       NSEC record provides authenticated denial of existence.              
  997       "The NSEC resource record lists two separate things: the next        
  998       owner name (in the canonical ordering of the zone) that contains     
  999       authoritative data or a delegation point NS RRset, and the set of    
 1000       RR types present at the NSEC RR's owner name."  (Quoted from         
 1001       Section 4 of RFC 4034)                                               
 1003    NSEC3:  Like the NSEC record, the NSEC3 record also provides            
 1004       authenticated denial of existence; however, NSEC3 records mitigate   
 1005       against zone enumeration and support Opt-Out.  NSEC3 resource        
 1006       records are defined in [RFC5155].                                    
 1008       Note that [RFC6840] says that [RFC5155] "is now considered part of   
 1009       the DNS Security Document Family as described by Section 10 of       
 1010       [RFC4033]".  This means that some of the definitions from earlier    
 1011       RFCs that only talk about NSEC records should probably be            
 1012       considered to be talking about both NSEC and NSEC3.                  
 1014    Opt-out:  "The Opt-Out Flag indicates whether this NSEC3 RR may cover   
 1015       unsigned delegations."  (Quoted from [RFC5155], Section    
 1016       Opt-out tackles the high costs of securing a delegation to an        
 1017       insecure zone.  When using Opt-Out, names that are an insecure       
 1018       delegation (and empty non-terminals that are only derived from       
 1019       insecure delegations) don't require an NSEC3 record or its           
 1020       corresponding RRSIG records.  Opt-Out NSEC3 records are not able     
 1021       to prove or deny the existence of the insecure delegations.          
 1022       (Adapted from [RFC7129], Section 5.1)                                
 1024    Zone enumeration:  "The practice of discovering the full content of a   
 1025       zone via successive queries."  (Quoted from [RFC5155],               
 1026       Section 1.3.)  This is also sometimes called "zone walking".  Zone   
 1027       enumeration is different from zone content guessing where the        
 1028       guesser uses a large dictionary of possible labels and sends         
 1029       successive queries for them, or matches the contents of NSEC3        
 1030       records against such a dictionary.                                   
 1032    Key signing key (KSK):  DNSSEC keys that "only sign the apex DNSKEY     
 1033       RRset in a zone."(Quoted from [RFC6781], Section 3.1)                
 1042 Hoffman, et al.               Informational                    [Page 19]   

 1043 RFC 7719                     DNS Terminology               December 2015   
 1046    Zone signing key (ZSK):  "DNSSEC keys that can be used to sign all      
 1047       the RRsets in a zone that require signatures, other than the apex    
 1048       DNSKEY RRset."  (Quoted from [RFC6781], Section 3.1) Note that the   
 1049       roles KSK and ZSK are not mutually exclusive: a single key can be    
 1050       both KSK and ZSK at the same time.  Also note that a ZSK is          
 1051       sometimes used to sign the apex DNSKEY RRset.                        
 1053    Combined signing key (CSK):  "In cases where the differentiation        
 1054       between the KSK and ZSK is not made, i.e., where keys have the       
 1055       role of both KSK and ZSK, we talk about a Single-Type Signing        
 1056       Scheme."  (Quoted from [RFC6781], Section 3.1) This is sometimes     
 1057       called a "combined signing key" or CSK.  It is operational           
 1058       practice, not protocol, that determines whether a particular key     
 1059       is a ZSK, a KSK, or a CSK.                                           
 1061    Secure Entry Point (SEP):  A flag in the DNSKEY RDATA that "can be      
 1062       used to distinguish between keys that are intended to be used as     
 1063       the secure entry point into the zone when building chains of         
 1064       trust, i.e., they are (to be) pointed to by parental DS RRs or       
 1065       configured as a trust anchor.  Therefore, it is suggested that the   
 1066       SEP flag be set on keys that are used as KSKs and not on keys that   
 1067       are used as ZSKs, while in those cases where a distinction between   
 1068       a KSK and ZSK is not made (i.e., for a Single-Type Signing           
 1069       Scheme), it is suggested that the SEP flag be set on all keys."      
 1070       (Quoted from [RFC6781], Section 3.2.3.)  Note that the SEP flag is   
 1071       only a hint, and its presence or absence may not be used to          
 1072       disqualify a given DNSKEY RR from use as a KSK or ZSK during         
 1073       validation.                                                          
 1075    DNSSEC Policy (DP):  A statement that "sets forth the security          
 1076       requirements and standards to be implemented for a DNSSEC-signed     
 1077       zone."  (Quoted from [RFC6841], Section 2)                           
 1079    DNSSEC Practice Statement (DPS):  "A practices disclosure document      
 1080       that may support and be a supplemental document to the DNSSEC        
 1081       Policy (if such exists), and it states how the management of a       
 1082       given zone implements procedures and controls at a high level."      
 1083       (Quoted from [RFC6841], Section 2)                                   
 1085 9.  DNSSEC States                                                          
 1087    A validating resolver can determine that a response is in one of four   
 1088    states: secure, insecure, bogus, or indeterminate.  These states are    
 1089    defined in [RFC4033] and [RFC4035], although the two definitions        
 1090    differ a bit.  This document makes no effort to reconcile the two       
 1091    definitions, and takes no position as to whether they need to be        
 1092    reconciled.                                                             
 1097 Hoffman, et al.               Informational                    [Page 20]   

 1098 RFC 7719                     DNS Terminology               December 2015   
 1101    Section 5 of [RFC4033] says:                                            
 1103       A validating resolver can determine the following 4 states:          
 1105       Secure: The validating resolver has a trust anchor, has a chain      
 1106          of trust, and is able to verify all the signatures in the         
 1107          response.                                                         
 1109       Insecure: The validating resolver has a trust anchor, a chain        
 1110          of trust, and, at some delegation point, signed proof of the      
 1111          non-existence of a DS record.  This indicates that subsequent     
 1112          branches in the tree are provably insecure.  A validating         
 1113          resolver may have a local policy to mark parts of the domain      
 1114          space as insecure.                                                
 1116       Bogus: The validating resolver has a trust anchor and a secure       
 1117          delegation indicating that subsidiary data is signed, but         
 1118          the response fails to validate for some reason: missing           
 1119          signatures, expired signatures, signatures with unsupported       
 1120          algorithms, data missing that the relevant NSEC RR says           
 1121          should be present, and so forth.                                  
 1123       Indeterminate: There is no trust anchor that would indicate that a   
 1124          specific portion of the tree is secure.  This is the default      
 1125          operation mode.                                                   
 1127    Section 4.3 of [RFC4035] says:                                          
 1129       A security-aware resolver must be able to distinguish between four   
 1130       cases:                                                               
 1132       Secure: An RRset for which the resolver is able to build a chain     
 1133           of signed DNSKEY and DS RRs from a trusted security anchor to    
 1134           the RRset.  In this case, the RRset should be signed and is      
 1135           subject to signature validation, as described above.             
 1137       Insecure: An RRset for which the resolver knows that it has no       
 1138          chain of signed DNSKEY and DS RRs from any trusted starting       
 1139          point to the RRset.  This can occur when the target RRset lies    
 1140          in an unsigned zone or in a descendent [sic] of an unsigned       
 1141          zone.  In this case, the RRset may or may not be signed, but      
 1142          the resolver will not be able to verify the signature.            
 1152 Hoffman, et al.               Informational                    [Page 21]   

 1153 RFC 7719                     DNS Terminology               December 2015   
 1156       Bogus: An RRset for which the resolver believes that it ought to     
 1157          be able to establish a chain of trust but for which it is         
 1158          unable to do so, either due to signatures that for some reason    
 1159          fail to validate or due to missing data that the relevant         
 1160          DNSSEC RRs indicate should be present.  This case may indicate    
 1161          an attack but may also indicate a configuration error or some     
 1162          form of data corruption.                                          
 1164       Indeterminate: An RRset for which the resolver is not able to        
 1165          determine whether the RRset should be signed, as the resolver     
 1166          is not able to obtain the necessary DNSSEC RRs.  This can occur   
 1167          when the security-aware resolver is not able to contact           
 1168          security-aware name servers for the relevant zones.               
 1170 10.  Security Considerations                                               
 1172    These definitions do not change any security considerations for the     
 1173    DNS.                                                                    
 1175 11.  References                                                            
 1177 11.1.  Normative References                                                
 1179    [RFC882]   Mockapetris, P., "Domain names: Concepts and facilities",    
 1180               RFC 882, DOI 10.17487/RFC0882, November 1983,                
 1181               <http://www.rfc-editor.org/info/rfc882>.                     
 1183    [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",   
 1184               STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,       
 1185               <http://www.rfc-editor.org/info/rfc1034>.                    
 1187    [RFC1035]  Mockapetris, P., "Domain names - implementation and          
 1188               specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,      
 1189               November 1987, <http://www.rfc-editor.org/info/rfc1035>.     
 1191    [RFC1123]  Braden, R., Ed., "Requirements for Internet Hosts -          
 1192               Application and Support", STD 3, RFC 1123,                   
 1193               DOI 10.17487/RFC1123, October 1989,                          
 1194               <http://www.rfc-editor.org/info/rfc1123>.                    
 1196    [RFC1996]  Vixie, P., "A Mechanism for Prompt Notification of Zone      
 1197               Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,       
 1198               August 1996, <http://www.rfc-editor.org/info/rfc1996>.       
 1200    [RFC2136]  Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,      
 1201               "Dynamic Updates in the Domain Name System (DNS UPDATE)",    
 1202               RFC 2136, DOI 10.17487/RFC2136, April 1997,                  
 1203               <http://www.rfc-editor.org/info/rfc2136>.                    
 1207 Hoffman, et al.               Informational                    [Page 22]   

 1208 RFC 7719                     DNS Terminology               December 2015   
 1211    [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS              
 1212               Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,   
 1213               <http://www.rfc-editor.org/info/rfc2181>.                    
 1215    [RFC2182]  Elz, R., Bush, R., Bradner, S., and M. Patton, "Selection    
 1216               and Operation of Secondary DNS Servers", BCP 16, RFC 2182,   
 1217               DOI 10.17487/RFC2182, July 1997,                             
 1218               <http://www.rfc-editor.org/info/rfc2182>.                    
 1220    [RFC2308]  Andrews, M., "Negative Caching of DNS Queries (DNS           
 1221               NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,        
 1222               <http://www.rfc-editor.org/info/rfc2308>.                    
 1224    [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.      
 1225               Rose, "DNS Security Introduction and Requirements",          
 1226               RFC 4033, DOI 10.17487/RFC4033, March 2005,                  
 1227               <http://www.rfc-editor.org/info/rfc4033>.                    
 1229    [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.      
 1230               Rose, "Resource Records for the DNS Security Extensions",    
 1231               RFC 4034, DOI 10.17487/RFC4034, March 2005,                  
 1232               <http://www.rfc-editor.org/info/rfc4034>.                    
 1234    [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.      
 1235               Rose, "Protocol Modifications for the DNS Security           
 1236               Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,     
 1237               <http://www.rfc-editor.org/info/rfc4035>.                    
 1239    [RFC4592]  Lewis, E., "The Role of Wildcards in the Domain Name         
 1240               System", RFC 4592, DOI 10.17487/RFC4592, July 2006,          
 1241               <http://www.rfc-editor.org/info/rfc4592>.                    
 1243    [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS      
 1244               Security (DNSSEC) Hashed Authenticated Denial of             
 1245               Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,      
 1246               <http://www.rfc-editor.org/info/rfc5155>.                    
 1248    [RFC5730]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",    
 1249               STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,         
 1250               <http://www.rfc-editor.org/info/rfc5730>.                    
 1252    [RFC5936]  Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol    
 1253               (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,          
 1254               <http://www.rfc-editor.org/info/rfc5936>.                    
 1262 Hoffman, et al.               Informational                    [Page 23]   

 1263 RFC 7719                     DNS Terminology               December 2015   
 1266    [RFC6561]  Livingood, J., Mody, N., and M. O'Reirdan,                   
 1267               "Recommendations for the Remediation of Bots in ISP          
 1268               Networks", RFC 6561, DOI 10.17487/RFC6561, March 2012,       
 1269               <http://www.rfc-editor.org/info/rfc6561>.                    
 1271    [RFC6672]  Rose, S. and W. Wijngaards, "DNAME Redirection in the        
 1272               DNS", RFC 6672, DOI 10.17487/RFC6672, June 2012,             
 1273               <http://www.rfc-editor.org/info/rfc6672>.                    
 1275    [RFC6781]  Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC             
 1276               Operational Practices, Version 2", RFC 6781,                 
 1277               DOI 10.17487/RFC6781, December 2012,                         
 1278               <http://www.rfc-editor.org/info/rfc6781>.                    
 1280    [RFC6840]  Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and      
 1281               Implementation Notes for DNS Security (DNSSEC)", RFC 6840,   
 1282               DOI 10.17487/RFC6840, February 2013,                         
 1283               <http://www.rfc-editor.org/info/rfc6840>.                    
 1285    [RFC6841]  Ljunggren, F., Eklund Lowinder, AM., and T. Okubo, "A        
 1286               Framework for DNSSEC Policies and DNSSEC Practice            
 1287               Statements", RFC 6841, DOI 10.17487/RFC6841, January 2013,   
 1288               <http://www.rfc-editor.org/info/rfc6841>.                    
 1290    [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms    
 1291               for DNS (EDNS(0))", STD 75, RFC 6891,                        
 1292               DOI 10.17487/RFC6891, April 2013,                            
 1293               <http://www.rfc-editor.org/info/rfc6891>.                    
 1295    [RFC7344]  Kumari, W., Gudmundsson, O., and G. Barwood, "Automating     
 1296               DNSSEC Delegation Trust Maintenance", RFC 7344,              
 1297               DOI 10.17487/RFC7344, September 2014,                        
 1298               <http://www.rfc-editor.org/info/rfc7344>.                    
 1300 11.2.  Informative References                                              
 1302    [DBOUND]   IETF, "Domain Boundaries (dbound) Working Group", 2015,      
 1303               <https://datatracker.ietf.org/wg/dbound/charter/>.           
 1305    [RFC819]   Su, Z. and J. Postel, "The Domain Naming Convention for      
 1306               Internet User Applications", RFC 819,                        
 1307               DOI 10.17487/RFC0819, August 1982,                           
 1308               <http://www.rfc-editor.org/info/rfc819>.                     
 1310    [RFC952]   Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet    
 1311               host table specification", RFC 952, DOI 10.17487/RFC0952,    
 1312               October 1985, <http://www.rfc-editor.org/info/rfc952>.       
 1317 Hoffman, et al.               Informational                    [Page 24]   

 1318 RFC 7719                     DNS Terminology               December 2015   
 1321    [RFC1995]  Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,      
 1322               DOI 10.17487/RFC1995, August 1996,                           
 1323               <http://www.rfc-editor.org/info/rfc1995>.                    
 1325    [RFC3912]  Daigle, L., "WHOIS Protocol Specification", RFC 3912,        
 1326               DOI 10.17487/RFC3912, September 2004,                        
 1327               <http://www.rfc-editor.org/info/rfc3912>.                    
 1329    [RFC4641]  Kolkman, O. and R. Gieben, "DNSSEC Operational Practices",   
 1330               RFC 4641, DOI 10.17487/RFC4641, September 2006,              
 1331               <http://www.rfc-editor.org/info/rfc4641>.                    
 1333    [RFC4697]  Larson, M. and P. Barber, "Observed DNS Resolution           
 1334               Misbehavior", BCP 123, RFC 4697, DOI 10.17487/RFC4697,       
 1335               October 2006, <http://www.rfc-editor.org/info/rfc4697>.      
 1337    [RFC4786]  Abley, J. and K. Lindqvist, "Operation of Anycast            
 1338               Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786,          
 1339               December 2006, <http://www.rfc-editor.org/info/rfc4786>.     
 1341    [RFC4956]  Arends, R., Kosters, M., and D. Blacka, "DNS Security        
 1342               (DNSSEC) Opt-In", RFC 4956, DOI 10.17487/RFC4956, July       
 1343               2007, <http://www.rfc-editor.org/info/rfc4956>.              
 1345    [RFC5625]  Bellis, R., "DNS Proxy Implementation Guidelines",           
 1346               BCP 152, RFC 5625, DOI 10.17487/RFC5625, August 2009,        
 1347               <http://www.rfc-editor.org/info/rfc5625>.                    
 1349    [RFC5890]  Klensin, J., "Internationalized Domain Names for             
 1350               Applications (IDNA): Definitions and Document Framework",    
 1351               RFC 5890, DOI 10.17487/RFC5890, August 2010,                 
 1352               <http://www.rfc-editor.org/info/rfc5890>.                    
 1354    [RFC5891]  Klensin, J., "Internationalized Domain Names in              
 1355               Applications (IDNA): Protocol", RFC 5891,                    
 1356               DOI 10.17487/RFC5891, August 2010,                           
 1357               <http://www.rfc-editor.org/info/rfc5891>.                    
 1359    [RFC5892]  Faltstrom, P., Ed., "The Unicode Code Points and             
 1360               Internationalized Domain Names for Applications (IDNA)",     
 1361               RFC 5892, DOI 10.17487/RFC5892, August 2010,                 
 1362               <http://www.rfc-editor.org/info/rfc5892>.                    
 1364    [RFC5893]  Alvestrand, H., Ed. and C. Karp, "Right-to-Left Scripts      
 1365               for Internationalized Domain Names for Applications          
 1366               (IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010,        
 1367               <http://www.rfc-editor.org/info/rfc5893>.                    
 1372 Hoffman, et al.               Informational                    [Page 25]   

 1373 RFC 7719                     DNS Terminology               December 2015   
 1376    [RFC5894]  Klensin, J., "Internationalized Domain Names for             
 1377               Applications (IDNA): Background, Explanation, and            
 1378               Rationale", RFC 5894, DOI 10.17487/RFC5894, August 2010,     
 1379               <http://www.rfc-editor.org/info/rfc5894>.                    
 1381    [RFC6055]  Thaler, D., Klensin, J., and S. Cheshire, "IAB Thoughts on   
 1382               Encodings for Internationalized Domain Names", RFC 6055,     
 1383               DOI 10.17487/RFC6055, February 2011,                         
 1384               <http://www.rfc-editor.org/info/rfc6055>.                    
 1386    [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,      
 1387               DOI 10.17487/RFC6265, April 2011,                            
 1388               <http://www.rfc-editor.org/info/rfc6265>.                    
 1390    [RFC6365]  Hoffman, P. and J. Klensin, "Terminology Used in             
 1391               Internationalization in the IETF", BCP 166, RFC 6365,        
 1392               DOI 10.17487/RFC6365, September 2011,                        
 1393               <http://www.rfc-editor.org/info/rfc6365>.                    
 1395    [RFC7129]  Gieben, R. and W. Mekking, "Authenticated Denial of          
 1396               Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129,       
 1397               February 2014, <http://www.rfc-editor.org/info/rfc7129>.     
 1399    [RFC7480]  Newton, A., Ellacott, B., and N. Kong, "HTTP Usage in the    
 1400               Registration Data Access Protocol (RDAP)", RFC 7480,         
 1401               DOI 10.17487/RFC7480, March 2015,                            
 1402               <http://www.rfc-editor.org/info/rfc7480>.                    
 1404    [RFC7481]  Hollenbeck, S. and N. Kong, "Security Services for the       
 1405               Registration Data Access Protocol (RDAP)", RFC 7481,         
 1406               DOI 10.17487/RFC7481, March 2015,                            
 1407               <http://www.rfc-editor.org/info/rfc7481>.                    
 1409    [RFC7482]  Newton, A. and S. Hollenbeck, "Registration Data Access      
 1410               Protocol (RDAP) Query Format", RFC 7482,                     
 1411               DOI 10.17487/RFC7482, March 2015,                            
 1412               <http://www.rfc-editor.org/info/rfc7482>.                    
 1414    [RFC7483]  Newton, A. and S. Hollenbeck, "JSON Responses for the        
 1415               Registration Data Access Protocol (RDAP)", RFC 7483,         
 1416               DOI 10.17487/RFC7483, March 2015,                            
 1417               <http://www.rfc-editor.org/info/rfc7483>.                    
 1419    [RFC7484]  Blanchet, M., "Finding the Authoritative Registration Data   
 1420               (RDAP) Service", RFC 7484, DOI 10.17487/RFC7484, March       
 1421               2015, <http://www.rfc-editor.org/info/rfc7484>.              
 1427 Hoffman, et al.               Informational                    [Page 26]   

 1428 RFC 7719                     DNS Terminology               December 2015   
 1431    [RFC7485]  Zhou, L., Kong, N., Shen, S., Sheng, S., and A. Servin,      
 1432               "Inventory and Analysis of WHOIS Registration Objects",      
 1433               RFC 7485, DOI 10.17487/RFC7485, March 2015,                  
 1434               <http://www.rfc-editor.org/info/rfc7485>.                    
 1436 Acknowledgements                                                           
 1438    The authors gratefully acknowledge all of the authors of DNS-related    
 1439    RFCs that proceed this one.  Comments from Tony Finch, Stephane         
 1440    Bortzmeyer, Niall O'Reilly, Colm MacCarthaigh, Ray Bellis, John         
 1441    Kristoff, Robert Edmonds, Paul Wouters, Shumon Huque, Paul Ebersman,    
 1442    David Lawrence, Matthijs Mekking, Casey Deccio, Bob Harold, Ed Lewis,   
 1443    John Klensin, David Black, and many others in the DNSOP Working Group   
 1444    have helped shape this document.                                        
 1446 Authors' Addresses                                                         
 1448    Paul Hoffman                                                            
 1449    ICANN                                                                   
 1451    Email: paul.hoffman@icann.org                                           
 1454    Andrew Sullivan                                                         
 1455    Dyn                                                                     
 1456    150 Dow Street, Tower 2                                                 
 1457    Manchester, NH  03101                                                   
 1458    United States                                                           
 1460    Email: asullivan@dyn.com                                                
 1463    Kazunori Fujiwara                                                       
 1464    Japan Registry Services Co., Ltd.                                       
 1465    Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda                         
 1466    Chiyoda-ku, Tokyo  101-0065                                             
 1467    Japan                                                                   
 1469    Phone: +81 3 5215 8451                                                  
 1470    Email: fujiwara@jprs.co.jp                                              
 1482 Hoffman, et al.               Informational                    [Page 27]   
section-2 Nikolai Malykh(Technical Erratum #4611) [Rejected]
based on outdated version
CNAME:  "It is traditional to refer to the owner of a CNAME record as
   'a CNAME'.  This is unfortunate, as 'CNAME' is an abbreviation of
   'canonical name', and the owner of a CNAME record is most certainly
   not a canonical name."  (Quoted from [RFC2181], Section 10.1.1)

It should say:
CNAME:  "It is traditional to refer to the label of a CNAME record as
   'a CNAME'.  This is unfortunate, as 'CNAME' is an abbreviation of
   'canonical name', and the label of a CNAME record is an alias, not
   a canonical name."  (Quoted from [RFC2181], Section 10.1.1)

Incorrect quote from RFC 2181.
Not a technical erratum.

is corrected already in


which  should be examined for consistency