7Internet Engineering Task Force (IETF) P. Hoffman
8Request for Comments: 8499 ICANN
11Updates: 2308 K. Fujiwara
12Category: Best Current Practice JPRS
13ISSN: 2070-1721 January 2019
20 The Domain Name System (DNS) is defined in literally dozens of
21 different RFCs. The terminology used by implementers and developers
22 of DNS protocols, and by operators of DNS systems, has sometimes
23 changed in the decades since the DNS was first defined. This
24 document gives current definitions for many of the terms used in the
25 DNS in a single document.
27 This document obsoletes RFC 7719 and updates RFC 2308.
31 This memo documents an Internet Best Current Practice.
33 This document is a product of the Internet Engineering Task Force
34 (IETF). It represents the consensus of the IETF community. It has
35 received public review and has been approved for publication by the
36 Internet Engineering Steering Group (IESG). Further information on
37 BCPs is available in Section 2 of RFC 7841.
39 Information about the current status of this document, any errata,
40 and how to provide feedback on it may be obtained at
41 https://www.rfc-editor.org/info/rfc8499.
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60RFC 8499 DNS Terminology January 2019
65 Copyright (c) 2019 IETF Trust and the persons identified as the
66 document authors. All rights reserved.
68 This document is subject to BCP 78 and the IETF Trust's Legal
69 Provisions Relating to IETF Documents
70 (https://trustee.ietf.org/license-info) in effect on the date of
71 publication of this document. Please review these documents
72 carefully, as they describe your rights and restrictions with respect
73 to this document. Code Components extracted from this document must
74 include Simplified BSD License text as described in Section 4.e of
75 the Trust Legal Provisions and are provided without warranty as
76 described in the Simplified BSD License.
80 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
81 2. Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
82 3. DNS Response Codes . . . . . . . . . . . . . . . . . . . . . 10
83 4. DNS Transactions . . . . . . . . . . . . . . . . . . . . . . 11
84 5. Resource Records . . . . . . . . . . . . . . . . . . . . . . 14
85 6. DNS Servers and Clients . . . . . . . . . . . . . . . . . . . 16
86 7. Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
87 8. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . . . 27
88 9. Registration Model . . . . . . . . . . . . . . . . . . . . . 28
89 10. General DNSSEC . . . . . . . . . . . . . . . . . . . . . . . 30
90 11. DNSSEC States . . . . . . . . . . . . . . . . . . . . . . . . 34
91 12. Security Considerations . . . . . . . . . . . . . . . . . . . 36
92 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
93 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
94 14.1. Normative References . . . . . . . . . . . . . . . . . . 36
95 14.2. Informative References . . . . . . . . . . . . . . . . . 39
96 Appendix A. Definitions Updated by This Document . . . . . . . . 44
97 Appendix B. Definitions First Defined in This Document . . . . . 44
98 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
99 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 50
100 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50
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116RFC 8499 DNS Terminology January 2019
121 The Domain Name System (DNS) is a simple query-response protocol
122 whose messages in both directions have the same format. (Section 2
123 gives a definition of "public DNS", which is often what people mean
124 when they say "the DNS".) The protocol and message format are
125 defined in [RFC1034] and [RFC1035]. These RFCs defined some terms,
126 and later documents defined others. Some of the terms from [RFC1034]
127 and [RFC1035] have somewhat different meanings now than they did in
130 This document contains a collection of a wide variety of DNS-related
131 terms, organized loosely by topic. Some of them have been precisely
132 defined in earlier RFCs, some have been loosely defined in earlier
133 RFCs, and some are not defined in an earlier RFC at all.
135 Other organizations sometimes define DNS-related terms their own way.
136 For example, the WHATWG defines "domain" at
137 <https://url.spec.whatwg.org/>. The Root Server System Advisory
138 Committee (RSSAC) has a good lexicon [RSSAC026].
140 Most of the definitions listed here represent the consensus
141 definition of the DNS community -- both protocol developers and
142 operators. Some of the definitions differ from earlier RFCs, and
143 those differences are noted. In this document, where the consensus
144 definition is the same as the one in an RFC, that RFC is quoted.
145 Where the consensus definition has changed somewhat, the RFC is
146 mentioned but the new stand-alone definition is given. See
147 Appendix A for a list of the definitions that this document updates.
149 It is important to note that, during the development of this
150 document, it became clear that some DNS-related terms are interpreted
151 quite differently by different DNS experts. Further, some terms that
152 are defined in early DNS RFCs now have definitions that are generally
153 agreed to, but that are different from the original definitions.
154 Therefore, this document is a substantial revision to [RFC7719].
156 Note that there is no single consistent definition of "the DNS". It
157 can be considered to be some combination of the following: a commonly
158 used naming scheme for objects on the Internet; a distributed
159 database representing the names and certain properties of these
160 objects; an architecture providing distributed maintenance,
161 resilience, and loose coherency for this database; and a simple
162 query-response protocol (as mentioned below) implementing this
163 architecture. Section 2 defines "global DNS" and "private DNS" as a
164 way to deal with these differing definitions.
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172RFC 8499 DNS Terminology January 2019
175 Capitalization in DNS terms is often inconsistent among RFCs and
176 various DNS practitioners. The capitalization used in this document
177 is a best guess at current practices, and is not meant to indicate
178 that other capitalization styles are wrong or archaic. In some
179 cases, multiple styles of capitalization are used for the same term
180 due to quoting from different RFCs.
182 Readers should note that the terms in this document are grouped by
183 topic. Someone who is not already familiar with the DNS probably
184 cannot learn about the DNS from scratch by reading this document from
185 front to back. Instead, skipping around may be the only way to get
186 enough context to understand some of the definitions. This document
187 has an index that might be useful for readers who are attempting to
188 learn the DNS by reading this document.
192 Naming system: A naming system associates names with data. Naming
193 systems have many significant facets that help differentiate them
194 from each other. Some commonly identified facets include:
196 * Composition of names
200 * Administration of names
202 * Types of data that can be associated with names
204 * Types of metadata for names
206 * Protocol for getting data from a name
208 * Context for resolving a name
210 Note that this list is a small subset of facets that people have
211 identified over time for naming systems, and the IETF has yet to
212 agree on a good set of facets that can be used to compare naming
213 systems. For example, other facets might include "protocol to
214 update data in a name", "privacy of names", and "privacy of data
215 associated with names", but those are not as well defined as the
216 ones listed above. The list here is chosen because it helps
217 describe the DNS and naming systems similar to the DNS.
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231 Domain name: An ordered list of one or more labels.
233 Note that this is a definition independent of the DNS RFCs
234 ([RFC1034] and [RFC1035]), and the definition here also applies to
235 systems other than the DNS. [RFC1034] defines the "domain name
236 space" using mathematical trees and their nodes in graph theory,
237 and that definition has the same practical result as the
238 definition here. Any path of a directed acyclic graph can be
239 represented by a domain name consisting of the labels of its
240 nodes, ordered by decreasing distance from the root(s) (which is
241 the normal convention within the DNS, including this document). A
242 domain name whose last label identifies a root of the graph is
243 fully qualified; other domain names whose labels form a strict
244 prefix of a fully-qualified domain name are relative to its first
247 Also note that different IETF and non-IETF documents have used the
248 term "domain name" in many different ways. It is common for
249 earlier documents to use "domain name" to mean "names that match
250 the syntax in [RFC1035]", but possibly with additional rules such
251 as "and are, or will be, resolvable in the global DNS" or "but
252 only using the presentation format".
254 Label: An ordered list of zero or more octets that makes up a
255 portion of a domain name. Using graph theory, a label identifies
256 one node in a portion of the graph of all possible domain names.
258 Global DNS: Using the short set of facets listed in "Naming system",
259 the global DNS can be defined as follows. Most of the rules here
260 come from [RFC1034] and [RFC1035], although the term "global DNS"
261 has not been defined before now.
263 Composition of names: A name in the global DNS has one or more
264 labels. The length of each label is between 0 and 63 octets
265 inclusive. In a fully-qualified domain name, the last label in
266 the ordered list is 0 octets long; it is the only label whose
267 length may be 0 octets, and it is called the "root" or "root
268 label". A domain name in the global DNS has a maximum total
269 length of 255 octets in the wire format; the root represents one
270 octet for this calculation. (Multicast DNS [RFC6762] allows names
271 up to 255 bytes plus a terminating zero byte based on a different
272 interpretation of RFC 1035 and what is included in the 255
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284RFC 8499 DNS Terminology January 2019
287 Format of names: Names in the global DNS are domain names. There
288 are three formats: wire format, presentation format, and common
291 The basic wire format for names in the global DNS is a list of
292 labels ordered by decreasing distance from the root, with the
293 root label last. Each label is preceded by a length octet.
294 [RFC1035] also defines a compression scheme that modifies this
297 The presentation format for names in the global DNS is a list
298 of labels ordered by decreasing distance from the root, encoded
299 as ASCII, with a "." character between each label. In
300 presentation format, a fully-qualified domain name includes the
301 root label and the associated separator dot. For example, in
302 presentation format, a fully-qualified domain name with two
303 non-root labels is always shown as "example.tld." instead of
304 "example.tld". [RFC1035] defines a method for showing octets
305 that do not display in ASCII.
307 The common display format is used in applications and free
308 text. It is the same as the presentation format, but showing
309 the root label and the "." before it is optional and is rarely
310 done. For example, in common display format, a fully-qualified
311 domain name with two non-root labels is usually shown as
312 "example.tld" instead of "example.tld.". Names in the common
313 display format are normally written such that the
314 directionality of the writing system presents labels by
315 decreasing distance from the root (so, in both English and the
316 C programming language the root or Top-Level Domain (TLD) label
317 in the ordered list is rightmost; but in Arabic, it may be
318 leftmost, depending on local conventions).
320 Administration of names: Administration is specified by delegation
321 (see the definition of "delegation" in Section 7). Policies for
322 administration of the root zone in the global DNS are determined
323 by the names operational community, which convenes itself in the
324 Internet Corporation for Assigned Names and Numbers (ICANN). The
325 names operational community selects the IANA Functions Operator
326 for the global DNS root zone. At the time of writing, that
327 operator is Public Technical Identifiers (PTI). (See
328 <https://pti.icann.org/> for more information about PTI operating
329 the IANA Functions.) The name servers that serve the root zone
330 are provided by independent root operators. Other zones in the
331 global DNS have their own policies for administration.
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343 Types of data that can be associated with names: A name can have
344 zero or more resource records associated with it. There are
345 numerous types of resource records with unique data structures
346 defined in many different RFCs and in the IANA registry at
347 [IANA_Resource_Registry].
349 Types of metadata for names: Any name that is published in the DNS
350 appears as a set of resource records (see the definition of
351 "RRset" in Section 5). Some names do not, themselves, have data
352 associated with them in the DNS, but they "appear" in the DNS
353 anyway because they form part of a longer name that does have data
354 associated with it (see the definition of "empty non-terminals" in
357 Protocol for getting data from a name: The protocol described in
360 Context for resolving a name: The global DNS root zone distributed
363 Private DNS: Names that use the protocol described in [RFC1035] but
364 that do not rely on the global DNS root zone or names that are
365 otherwise not generally available on the Internet but are using
366 the protocol described in [RFC1035]. A system can use both the
367 global DNS and one or more private DNS systems; for example, see
368 "Split DNS" in Section 6.
370 Note that domain names that do not appear in the DNS, and that are
371 intended never to be looked up using the DNS protocol, are not
372 part of the global DNS or a private DNS even though they are
375 Multicast DNS (mDNS): "Multicast DNS (mDNS) provides the ability to
376 perform DNS-like operations on the local link in the absence of
377 any conventional Unicast DNS server. In addition, Multicast DNS
378 designates a portion of the DNS namespace to be free for local
379 use, without the need to pay any annual fee, and without the need
380 to set up delegations or otherwise configure a conventional DNS
381 server to answer for those names." (Quoted from [RFC6762],
382 Abstract) Although it uses a compatible wire format, mDNS is,
383 strictly speaking, a different protocol than DNS. Also, where the
384 above quote says "a portion of the DNS namespace", it would be
385 clearer to say "a portion of the domain name space". The names in
386 mDNS are not intended to be looked up in the DNS.
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399 Locally served DNS zone: A locally served DNS zone is a special case
400 of private DNS. Names are resolved using the DNS protocol in a
401 local context. [RFC6303] defines subdomains of IN-ADDR.ARPA that
402 are locally served zones. Resolution of names through locally
403 served zones may result in ambiguous results. For example, the
404 same name may resolve to different results in different locally
405 served DNS zone contexts. The context for a locally served DNS
406 zone may be explicit, such as those that are listed in [RFC6303]
407 and [RFC7793], or implicit, such as those defined by local DNS
408 administration and not known to the resolution client.
410 Fully-Qualified Domain Name (FQDN): This is often just a clear way
411 of saying the same thing as "domain name of a node", as outlined
412 above. However, the term is ambiguous. Strictly speaking, a
413 fully-qualified domain name would include every label, including
414 the zero-length label of the root: such a name would be written
415 "www.example.net." (note the terminating dot). But, because every
416 name eventually shares the common root, names are often written
417 relative to the root (such as "www.example.net") and are still
418 called "fully qualified". This term first appeared in [RFC819].
419 In this document, names are often written relative to the root.
421 The need for the term "fully-qualified domain name" comes from the
422 existence of partially qualified domain names, which are names
423 where one or more of the last labels in the ordered list are
424 omitted (for example, a domain name of "www" relative to
425 "example.net" identifies "www.example.net"). Such relative names
426 are understood only by context.
428 Host name: This term and its equivalent, "hostname", have been
429 widely used but are not defined in [RFC1034], [RFC1035],
430 [RFC1123], or [RFC2181]. The DNS was originally deployed into the
431 Host Tables environment as outlined in [RFC952], and it is likely
432 that the term followed informally from the definition there. Over
433 time, the definition seems to have shifted. "Host name" is often
434 meant to be a domain name that follows the rules in Section 3.5 of
435 [RFC1034], which is also called the "preferred name syntax". (In
436 that syntax, every character in each label is a letter, a digit,
437 or a hyphen). Note that any label in a domain name can contain
438 any octet value; hostnames are generally considered to be domain
439 names where every label follows the rules in the "preferred name
440 syntax", with the amendment that labels can start with ASCII
441 digits (this amendment comes from Section 2.1 of [RFC1123]).
443 People also sometimes use the term "hostname" to refer to just the
444 first label of an FQDN, such as "printer" in
445 "printer.admin.example.com". (Sometimes this is formalized in
446 configuration in operating systems.) In addition, people
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455 sometimes use this term to describe any name that refers to a
456 machine, and those might include labels that do not conform to the
457 "preferred name syntax".
459 Top-Level Domain (TLD): A Top-Level Domain is a zone that is one
460 layer below the root, such as "com" or "jp". There is nothing
461 special, from the point of view of the DNS, about TLDs. Most of
462 them are also delegation-centric zones (defined in Section 7), and
463 there are significant policy issues around their operation. TLDs
464 are often divided into sub-groups such as Country Code Top-Level
465 Domains (ccTLDs), Generic Top-Level Domains (gTLDs), and others;
466 the division is a matter of policy and beyond the scope of this
469 Internationalized Domain Name (IDN): The Internationalized Domain
470 Names for Applications (IDNA) protocol is the standard mechanism
471 for handling domain names with non-ASCII characters in
472 applications in the DNS. The current standard at the time of this
473 writing, normally called "IDNA2008", is defined in [RFC5890],
474 [RFC5891], [RFC5892], [RFC5893], and [RFC5894]. These documents
475 define many IDN-specific terms such as "LDH label", "A-label", and
476 "U-label". [RFC6365] defines more terms that relate to
477 internationalization (some of which relate to IDNs); [RFC6055] has
478 a much more extensive discussion of IDNs, including some new
481 Subdomain: "A domain is a subdomain of another domain if it is
482 contained within that domain. This relationship can be tested by
483 seeing if the subdomain's name ends with the containing domain's
484 name." (Quoted from [RFC1034], Section 3.1) For example, in the
485 host name "nnn.mmm.example.com", both "mmm.example.com" and
486 "nnn.mmm.example.com" are subdomains of "example.com". Note that
487 the comparisons here are done on whole labels; that is,
488 "ooo.example.com" is not a subdomain of "oo.example.com".
490 Alias: The owner of a CNAME resource record, or a subdomain of the
491 owner of a DNAME resource record (DNAME records are defined in
492 [RFC6672]). See also "canonical name".
494 Canonical name: A CNAME resource record "identifies its owner name
495 as an alias, and specifies the corresponding canonical name in the
496 RDATA section of the RR." (Quoted from [RFC1034], Section 3.6.2)
497 This usage of the word "canonical" is related to the mathematical
498 concept of "canonical form".
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511 CNAME: "It has been traditional to refer to the [owner] of a CNAME
512 record as 'a CNAME'. This is unfortunate, as 'CNAME' is an
513 abbreviation of 'canonical name', and the [owner] of a CNAME
514 record is most certainly not a canonical name." (Quoted from
515 [RFC2181], Section 10.1.1. The quoted text has been changed from
520 Some of the response codes (RCODEs) that are defined in [RFC1035]
521 have acquired their own shorthand names. All of the RCODEs are
522 listed at [IANA_Resource_Registry], although that list uses mixed-
523 case capitalization, while most documents use all caps. Some of the
524 common names for values defined in [RFC1035] are described in this
525 section. This section also includes an additional RCODE and a
526 general definition. The official list of all RCODEs is in the IANA
529 NOERROR: This RCODE appears as "No error condition" in Section 4.1.1
532 FORMERR: This RCODE appears as "Format error - The name server was
533 unable to interpret the query" in Section 4.1.1 of [RFC1035].
535 SERVFAIL: This RCODE appears as "Server failure - The name server
536 was unable to process this query due to a problem with the name
537 server" in Section 4.1.1 of [RFC1035].
539 NXDOMAIN: This RCODE appears as "Name Error [...] this code
540 signifies that the domain name referenced in the query does not
541 exist." in Section 4.1.1 of [RFC1035]. [RFC2308] established
542 NXDOMAIN as a synonym for Name Error.
544 NOTIMP: This RCODE appears as "Not Implemented - The name server
545 does not support the requested kind of query" in Section 4.1.1 of
548 REFUSED: This RCODE appears as "Refused - The name server refuses to
549 perform the specified operation for policy reasons. For example,
550 a name server may not wish to provide the information to the
551 particular requester, or a name server may not wish to perform a
552 particular operation (e.g., zone transfer) for particular data."
553 in Section 4.1.1 of [RFC1035].
555 NODATA: "A pseudo RCODE which indicates that the name is valid, for
556 the given class, but [there] are no records of the given type. A
557 NODATA response has to be inferred from the answer." (Quoted from
558 [RFC2308], Section 1) "NODATA is indicated by an answer with the
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564RFC 8499 DNS Terminology January 2019
567 RCODE set to NOERROR and no relevant answers in the Answer
568 section. The authority section will contain an SOA record, or
569 there will be no NS records there." (Quoted from [RFC2308],
570 Section 2.2) Note that referrals have a similar format to NODATA
571 replies; [RFC2308] explains how to distinguish them.
573 The term "NXRRSET" is sometimes used as a synonym for NODATA.
574 However, this is a mistake, given that NXRRSET is a specific error
575 code defined in [RFC2136].
577 Negative response: A response that indicates that a particular RRset
578 does not exist or whose RCODE indicates that the nameserver cannot
579 answer. Sections 2 and 7 of [RFC2308] describe the types of
580 negative responses in detail.
584 The header of a DNS message is its first 12 octets. Many of the
585 fields and flags in the diagrams in Sections 4.1.1 through 4.1.3 of
586 [RFC1035] are referred to by their names in each diagram. For
587 example, the response codes are called "RCODEs", the data for a
588 record is called the "RDATA", and the authoritative answer bit is
589 often called "the AA flag" or "the AA bit".
591 Class: A class "identifies a protocol family or instance of a
592 protocol". (Quoted from [RFC1034], Section 3.6) "The DNS tags all
593 data with a class as well as the type, so that we can allow
594 parallel use of different formats for data of type address."
595 (Quoted from [RFC1034], Section 2.2) In practice, the class for
596 nearly every query is "IN" (the Internet). There are some queries
597 for "CH" (the Chaos class), but they are usually for the purposes
598 of information about the server itself rather than for a different
601 QNAME: The most commonly used rough definition is that the QNAME is
602 a field in the Question section of a query. "A standard query
603 specifies a target domain name (QNAME), query type (QTYPE), and
604 query class (QCLASS) and asks for RRs which match." (Quoted from
605 [RFC1034], Section 3.7.1) Strictly speaking, the definition comes
606 from [RFC1035], Section 4.1.2, where the QNAME is defined in
607 respect of the Question section. This definition appears to be
608 applied consistently: the discussion of inverse queries in
609 Section 6.4.1 refers to the "owner name of the query RR and its
610 TTL", because inverse queries populate the Answer section and
611 leave the Question section empty. (Inverse queries are deprecated
612 in [RFC3425]; thus, relevant definitions do not appear in this
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620RFC 8499 DNS Terminology January 2019
623 However, [RFC2308] has an alternate definition that puts the QNAME
624 in the answer (or series of answers) instead of the query. It
625 defines QNAME as "...the name in the query section of an answer,
626 or where this resolves to a CNAME, or CNAME chain, the data field
627 of the last CNAME. The last CNAME in this sense is that which
628 contains a value which does not resolve to another CNAME." This
629 definition has a certain internal logic, because of the way CNAME
630 substitution works and the definition of CNAME. If a name server
631 does not find an RRset that matches a query, but does find the
632 same name in the same class with a CNAME record, then the name
633 server "includes the CNAME record in the response and restarts the
634 query at the domain name specified in the data field of the CNAME
635 record." (Quoted from [RFC1034], Section 3.6.2) This is made
636 explicit in the resolution algorithm outlined in Section 4.3.2 of
637 [RFC1034], which says to "change QNAME to the canonical name in
638 the CNAME RR, and go back to step 1" in the case of a CNAME RR.
639 Since a CNAME record explicitly declares that the owner name is
640 canonically named what is in the RDATA, then there is a way to
641 view the new name (i.e., the name that was in the RDATA of the
642 CNAME RR) as also being the QNAME.
644 However, this creates a kind of confusion because the response to
645 a query that results in CNAME processing contains in the echoed
646 Question section one QNAME (the name in the original query) and a
647 second QNAME that is in the data field of the last CNAME. The
648 confusion comes from the iterative/recursive mode of resolution,
649 which finally returns an answer that need not actually have the
650 same owner name as the QNAME contained in the original query.
652 To address this potential confusion, it is helpful to distinguish
653 between three meanings:
655 * QNAME (original): The name actually sent in the Question
656 section in the original query, which is always echoed in the
657 (final) reply in the Question section when the QR bit is set to
660 * QNAME (effective): A name actually resolved, which is either
661 the name originally queried or a name received in a CNAME chain
664 * QNAME (final): The name actually resolved, which is either the
665 name actually queried or else the last name in a CNAME chain
668 Note that, because the definition in [RFC2308] is actually for a
669 different concept than what was in [RFC1034], it would have been
670 better if [RFC2308] had used a different name for that concept.
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676RFC 8499 DNS Terminology January 2019
679 In general use today, QNAME almost always means what is defined
680 above as "QNAME (original)".
682 Referrals: A type of response in which a server, signaling that it
683 is not (completely) authoritative for an answer, provides the
684 querying resolver with an alternative place to send its query.
685 Referrals can be partial.
687 A referral arises when a server is not performing recursive
688 service while answering a query. It appears in step 3(b) of the
689 algorithm in [RFC1034], Section 4.3.2.
691 There are two types of referral response. The first is a downward
692 referral (sometimes described as "delegation response"), where the
693 server is authoritative for some portion of the QNAME. The
694 authority section RRset's RDATA contains the name servers
695 specified at the referred-to zone cut. In normal DNS operation,
696 this kind of response is required in order to find names beneath a
697 delegation. The bare use of "referral" means this kind of
698 referral, and many people believe that this is the only legitimate
699 kind of referral in the DNS.
701 The second is an upward referral (sometimes described as "root
702 referral"), where the server is not authoritative for any portion
703 of the QNAME. When this happens, the referred-to zone in the
704 authority section is usually the root zone ("."). In normal DNS
705 operation, this kind of response is not required for resolution or
706 for correctly answering any query. There is no requirement that
707 any server send upward referrals. Some people regard upward
708 referrals as a sign of a misconfiguration or error. Upward
709 referrals always need some sort of qualifier (such as "upward" or
710 "root") and are never identified simply by the word "referral".
712 A response that has only a referral contains an empty answer
713 section. It contains the NS RRset for the referred-to zone in the
714 Authority section. It may contain RRs that provide addresses in
715 the additional section. The AA bit is clear.
717 In the case where the query matches an alias, and the server is
718 not authoritative for the target of the alias but is authoritative
719 for some name above the target of the alias, the resolution
720 algorithm will produce a response that contains both the
721 authoritative answer for the alias and a referral. Such a partial
722 answer and referral response has data in the Answer section. It
723 has the NS RRset for the referred-to zone in the Authority
724 section. It may contain RRs that provide addresses in the
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732RFC 8499 DNS Terminology January 2019
735 additional section. The AA bit is set, because the first name in
736 the Answer section matches the QNAME and the server is
737 authoritative for that answer (see [RFC1035], Section 4.1.1).
741 RR: An acronym for resource record. (See [RFC1034], Section 3.6.)
743 RRset: A set of resource records "with the same label, class and
744 type, but with different data" (according to [RFC2181],
745 Section 5). Also written as "RRSet" in some documents. As a
746 clarification, "same label" in this definition means "same owner
747 name". In addition, [RFC2181] states that "the TTLs of all RRs in
748 an RRSet must be the same".
750 Note that RRSIG resource records do not match this definition.
753 An RRset MAY have multiple RRSIG RRs associated with it. Note
754 that as RRSIG RRs are closely tied to the RRsets whose
755 signatures they contain, RRSIG RRs, unlike all other DNS RR
756 types, do not form RRsets. In particular, the TTL values among
757 RRSIG RRs with a common owner name do not follow the RRset
758 rules described in [RFC2181].
760 Master file: "Master files are text files that contain RRs in text
761 form. Since the contents of a zone can be expressed in the form
762 of a list of RRs a master file is most often used to define a
763 zone, though it can be used to list a cache's contents." (Quoted
764 from [RFC1035], Section 5) Master files are sometimes called "zone
767 Presentation format: The text format used in master files. This
768 format is shown but not formally defined in [RFC1034] or
769 [RFC1035]. The term "presentation format" first appears in
772 EDNS: The extension mechanisms for DNS, defined in [RFC6891].
773 Sometimes called "EDNS0" or "EDNS(0)" to indicate the version
774 number. EDNS allows DNS clients and servers to specify message
775 sizes larger than the original 512 octet limit, to expand the
776 response code space and to carry additional options that affect
777 the handling of a DNS query.
779 OPT: A pseudo-RR (sometimes called a "meta-RR") that is used only to
780 contain control information pertaining to the question-and-answer
781 sequence of a specific transaction. (Definition paraphrased from
782 [RFC6891], Section 6.1.1.) It is used by EDNS.
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791 Owner: "The domain name where the RR is found." (Quoted from
792 [RFC1034], Section 3.6) Often appears in the term "owner name".
794 SOA field names: DNS documents, including the definitions here,
795 often refer to the fields in the RDATA of an SOA resource record
796 by field name. "SOA" stands for "start of a zone of authority".
797 Those fields are defined in Section 3.3.13 of [RFC1035]. The
798 names (in the order they appear in the SOA RDATA) are MNAME,
799 RNAME, SERIAL, REFRESH, RETRY, EXPIRE, and MINIMUM. Note that the
800 meaning of the MINIMUM field is updated in Section 4 of [RFC2308];
801 the new definition is that the MINIMUM field is only "the TTL to
802 be used for negative responses". This document tends to use field
803 names instead of terms that describe the fields.
805 TTL: The maximum "time to live" of a resource record. "A TTL value
806 is an unsigned number, with a minimum value of 0, and a maximum
807 value of 2147483647. That is, a maximum of 2^31 - 1. When
808 transmitted, this value shall be encoded in the less significant
809 31 bits of the 32 bit TTL field, with the most significant, or
810 sign, bit set to zero." (Quoted from [RFC2181], Section 8) (Note
811 that [RFC1035] erroneously stated that this is a signed integer;
812 that was fixed by [RFC2181].)
814 The TTL "specifies the time interval that the resource record may
815 be cached before the source of the information should again be
816 consulted." (Quoted from [RFC1035], Section 3.2.1) Section 4.1.3
817 of the same document states: "the time interval (in seconds) that
818 the resource record may be cached before it should be discarded".
819 Despite being defined for a resource record, the TTL of every
820 resource record in an RRset is required to be the same ([RFC2181],
823 The reason that the TTL is the maximum time to live is that a
824 cache operator might decide to shorten the time to live for
825 operational purposes, such as if there is a policy to disallow TTL
826 values over a certain number. Some servers are known to ignore
827 the TTL on some RRsets (such as when the authoritative data has a
828 very short TTL) even though this is against the advice in RFC
829 1035. An RRset can be flushed from the cache before the end of
830 the TTL interval, at which point, the value of the TTL becomes
831 unknown because the RRset with which it was associated no longer
834 There is also the concept of a "default TTL" for a zone, which can
835 be a configuration parameter in the server software. This is
836 often expressed by a default for the entire server, and a default
837 for a zone using the $TTL directive in a zone file. The $TTL
838 directive was added to the master file format by [RFC2308].
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847 Class independent: A resource record type whose syntax and semantics
848 are the same for every DNS class. A resource record type that is
849 not class independent has different meanings depending on the DNS
850 class of the record, or the meaning is undefined for some class.
851 Most resource record types are defined for class 1 (IN, the
852 Internet), but many are undefined for other classes.
854 Address records: Records whose type is A or AAAA. [RFC2181]
855 informally defines these as "(A, AAAA, etc)". Note that new types
856 of address records could be defined in the future.
8586. DNS Servers and Clients
860 This section defines the terms used for the systems that act as DNS
861 clients, DNS servers, or both. In past RFCs, DNS servers are
862 sometimes called "name servers", "nameservers", or just "servers".
863 There is no formal definition of "DNS server", but RFCs generally
864 assume that it is an Internet server that listens for queries and
865 sends responses using the DNS protocol defined in [RFC1035] and its
868 It is important to note that the terms "DNS server" and "name server"
869 require context in order to understand the services being provided.
870 Both authoritative servers and recursive resolvers are often called
871 "DNS servers" and "name servers" even though they serve different
872 roles (but may be part of the same software package).
874 For terminology specific to the public DNS root server system, see
875 [RSSAC026]. That document defines terms such as "root server", "root
876 server operator", and terms that are specific to the way that the
877 root zone of the public DNS is served.
879 Resolver: A program "that extract[s] information from name servers
880 in response to client requests." (Quoted from [RFC1034],
881 Section 2.4) A resolver performs queries for a name, type, and
882 class, and receives responses. The logical function is called
883 "resolution". In practice, the term is usually referring to some
884 specific type of resolver (some of which are defined below), and
885 understanding the use of the term depends on understanding the
888 A related term is "resolve", which is not formally defined in
889 [RFC1034] or [RFC1035]. An imputed definition might be "asking a
890 question that consists of a domain name, class, and type, and
891 receiving some sort of response". Similarly, an imputed
892 definition of "resolution" might be "the response received from
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900RFC 8499 DNS Terminology January 2019
903 Stub resolver: A resolver that cannot perform all resolution itself.
904 Stub resolvers generally depend on a recursive resolver to
905 undertake the actual resolution function. Stub resolvers are
906 discussed but never fully defined in Section 5.3.1 of [RFC1034].
907 They are fully defined in Section 6.1.3.1 of [RFC1123].
909 Iterative mode: A resolution mode of a server that receives DNS
910 queries and responds with a referral to another server.
911 Section 2.3 of [RFC1034] describes this as "The server refers the
912 client to another server and lets the client pursue the query." A
913 resolver that works in iterative mode is sometimes called an
914 "iterative resolver". See also "iterative resolution" later in
917 Recursive mode: A resolution mode of a server that receives DNS
918 queries and either responds to those queries from a local cache or
919 sends queries to other servers in order to get the final answers
920 to the original queries. Section 2.3 of [RFC1034] describes this
921 as "the first server pursues the query for the client at another
922 server". Section 4.3.1 of [RFC1034] says: "in [recursive] mode
923 the name server acts in the role of a resolver and returns either
924 an error or the answer, but never referrals." That same section
927 The recursive mode occurs when a query with RD set arrives at a
928 server which is willing to provide recursive service; the
929 client can verify that recursive mode was used by checking that
930 both RA and RD are set in the reply.
932 A server operating in recursive mode may be thought of as having a
933 name server side (which is what answers the query) and a resolver
934 side (which performs the resolution function). Systems operating
935 in this mode are commonly called "recursive servers". Sometimes
936 they are called "recursive resolvers". In practice, it is not
937 possible to know in advance whether the server that one is
938 querying will also perform recursion; both terms can be observed
939 in use interchangeably.
941 Recursive resolver: A resolver that acts in recursive mode. In
942 general, a recursive resolver is expected to cache the answers it
943 receives (which would make it a full-service resolver), but some
944 recursive resolvers might not cache.
946 [RFC4697] tried to differentiate between a recursive resolver and
947 an iterative resolver.
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959 Recursive query: A query with the Recursion Desired (RD) bit set to
960 1 in the header. (See Section 4.1.1 of [RFC1035].) If recursive
961 service is available and is requested by the RD bit in the query,
962 the server uses its resolver to answer the query. (See
963 Section 4.3.2 of [RFC1034].)
965 Non-recursive query: A query with the Recursion Desired (RD) bit set
966 to 0 in the header. A server can answer non-recursive queries
967 using only local information: the response contains either an
968 error, the answer, or a referral to some other server "closer" to
969 the answer. (See Section 4.3.1 of [RFC1034].)
971 Iterative resolution: A name server may be presented with a query
972 that can only be answered by some other server. The two general
973 approaches to dealing with this problem are "recursive", in which
974 the first server pursues the query on behalf of the client at
975 another server, and "iterative", in which the server refers the
976 client to another server and lets the client pursue the query
977 there. (See Section 2.3 of [RFC1034].)
979 In iterative resolution, the client repeatedly makes non-recursive
980 queries and follows referrals and/or aliases. The iterative
981 resolution algorithm is described in Section 5.3.3 of [RFC1034].
983 Full resolver: This term is used in [RFC1035], but it is not defined
984 there. RFC 1123 defines a "full-service resolver" that may or may
985 not be what was intended by "full resolver" in [RFC1035]. This
986 term is not properly defined in any RFC.
988 Full-service resolver: Section 6.1.3.1 of [RFC1123] defines this
989 term to mean a resolver that acts in recursive mode with a cache
990 (and meets other requirements).
992 Priming: "The act of finding the list of root servers from a
993 configuration that lists some or all of the purported IP addresses
994 of some or all of those root servers." (Quoted from [RFC8109],
995 Section 2) In order to operate in recursive mode, a resolver needs
996 to know the address of at least one root server. Priming is most
997 often done from a configuration setting that contains a list of
998 authoritative servers for the root zone.
1000 Root hints: "Operators who manage a DNS recursive resolver typically
1001 need to configure a 'root hints file'. This file contains the
1002 names and IP addresses of the authoritative name servers for the
1003 root zone, so the software can bootstrap the DNS resolution
1004 process. For many pieces of software, this list comes built into
1005 the software." (Quoted from [IANA_RootFiles]) This file is often
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1015 Negative caching: "The storage of knowledge that something does not
1016 exist, cannot or does not give an answer." (Quoted from
1017 [RFC2308], Section 1)
1019 Authoritative server: "A server that knows the content of a DNS zone
1020 from local knowledge, and thus can answer queries about that zone
1021 without needing to query other servers." (Quoted from [RFC2182],
1022 Section 2) An authoritative server is named in the NS ("name
1023 server") record in a zone. It is a system that responds to DNS
1024 queries with information about zones for which it has been
1025 configured to answer with the AA flag in the response header set
1026 to 1. It is a server that has authority over one or more DNS
1027 zones. Note that it is possible for an authoritative server to
1028 respond to a query without the parent zone delegating authority to
1029 that server. Authoritative servers also provide "referrals",
1030 usually to child zones delegated from them; these referrals have
1031 the AA bit set to 0 and come with referral data in the Authority
1032 and (if needed) the Additional sections.
1034 Authoritative-only server: A name server that only serves
1035 authoritative data and ignores requests for recursion. It will
1036 "not normally generate any queries of its own. Instead it answers
1037 non-recursive queries from iterative resolvers looking for
1038 information in zones it serves." (Quoted from [RFC4697],
1039 Section 2.4) In this case, "ignores requests for recursion" means
1040 "responds to requests for recursion with responses indicating that
1041 recursion was not performed".
1043 Zone transfer: The act of a client requesting a copy of a zone and
1044 an authoritative server sending the needed information. (See
1045 Section 7 for a description of zones.) There are two common
1046 standard ways to do zone transfers: the AXFR ("Authoritative
1047 Transfer") mechanism to copy the full zone (described in
1048 [RFC5936], and the IXFR ("Incremental Transfer") mechanism to copy
1049 only parts of the zone that have changed (described in [RFC1995]).
1050 Many systems use non-standard methods for zone transfer outside
1053 Slave server: See "Secondary server".
1055 Secondary server: "An authoritative server which uses zone transfer
1056 to retrieve the zone." (Quoted from [RFC1996], Section 2.1)
1057 Secondary servers are also discussed in [RFC1034]. [RFC2182]
1058 describes secondary servers in more detail. Although early DNS
1059 RFCs such as [RFC1996] referred to this as a "slave", the current
1060 common usage has shifted to calling it a "secondary".
1062 Master server: See "Primary server".
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1068RFC 8499 DNS Terminology January 2019
1071 Primary server: "Any authoritative server configured to be the
1072 source of zone transfer for one or more [secondary] servers."
1073 (Quoted from [RFC1996], Section 2.1) Or, more specifically,
1074 [RFC2136] calls it "an authoritative server configured to be the
1075 source of AXFR or IXFR data for one or more [secondary] servers".
1076 Primary servers are also discussed in [RFC1034]. Although early
1077 DNS RFCs such as [RFC1996] referred to this as a "master", the
1078 current common usage has shifted to "primary".
1080 Primary master: "The primary master is named in the zone's SOA MNAME
1081 field and optionally by an NS RR." (Quoted from [RFC1996],
1082 Section 2.1) [RFC2136] defines "primary master" as "Master server
1083 at the root of the AXFR/IXFR dependency graph. The primary master
1084 is named in the zone's SOA MNAME field and optionally by an NS RR.
1085 There is by definition only one primary master server per zone."
1087 The idea of a primary master is only used in [RFC1996] and
1088 [RFC2136]. A modern interpretation of the term "primary master"
1089 is a server that is both authoritative for a zone and that gets
1090 its updates to the zone from configuration (such as a master file)
1091 or from UPDATE transactions.
1093 Stealth server: This is "like a slave server except not listed in an
1094 NS RR for the zone." (Quoted from [RFC1996], Section 2.1)
1096 Hidden master: A stealth server that is a primary server for zone
1097 transfers. "In this arrangement, the master name server that
1098 processes the updates is unavailable to general hosts on the
1099 Internet; it is not listed in the NS RRset." (Quoted from
1100 [RFC6781], Section 3.4.3) An earlier RFC, [RFC4641], said that the
1101 hidden master's name "appears in the SOA RRs MNAME field",
1102 although, in some setups, the name does not appear at all in the
1103 public DNS. A hidden master can also be a secondary server for
1106 Forwarding: The process of one server sending a DNS query with the
1107 RD bit set to 1 to another server to resolve that query.
1108 Forwarding is a function of a DNS resolver; it is different than
1109 simply blindly relaying queries.
1111 [RFC5625] does not give a specific definition for forwarding, but
1112 describes in detail what features a system that forwards needs to
1113 support. Systems that forward are sometimes called "DNS proxies",
1114 but that term has not yet been defined (even in [RFC5625]).
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1127 Forwarder: Section 1 of [RFC2308] describes a forwarder as "a
1128 nameserver used to resolve queries instead of directly using the
1129 authoritative nameserver chain". [RFC2308] further says "The
1130 forwarder typically either has better access to the internet, or
1131 maintains a bigger cache which may be shared amongst many
1132 resolvers." That definition appears to suggest that forwarders
1133 normally only query authoritative servers. In current use,
1134 however, forwarders often stand between stub resolvers and
1135 recursive servers. [RFC2308] is silent on whether a forwarder is
1136 iterative-only or can be a full-service resolver.
1138 Policy-implementing resolver: A resolver acting in recursive mode
1139 that changes some of the answers that it returns based on policy
1140 criteria, such as to prevent access to malware sites or
1141 objectionable content. In general, a stub resolver has no idea
1142 whether upstream resolvers implement such policy or, if they do,
1143 the exact policy about what changes will be made. In some cases,
1144 the user of the stub resolver has selected the policy-implementing
1145 resolver with the explicit intention of using it to implement the
1146 policies. In other cases, policies are imposed without the user
1147 of the stub resolver being informed.
1149 Open resolver: A full-service resolver that accepts and processes
1150 queries from any (or nearly any) client. This is sometimes also
1151 called a "public resolver", although the term "public resolver" is
1152 used more with open resolvers that are meant to be open, as
1153 compared to the vast majority of open resolvers that are probably
1154 misconfigured to be open. Open resolvers are discussed in
1157 Split DNS: The terms "split DNS" and "split-horizon DNS" have long
1158 been used in the DNS community without formal definition. In
1159 general, they refer to situations in which DNS servers that are
1160 authoritative for a particular set of domains provide partly or
1161 completely different answers in those domains depending on the
1162 source of the query. The effect of this is that a domain name
1163 that is notionally globally unique nevertheless has different
1164 meanings for different network users. This can sometimes be the
1165 result of a "view" configuration, described below.
1167 Section 3.8 of [RFC2775] gives a related definition that is too
1168 specific to be generally useful.
1170 View: A configuration for a DNS server that allows it to provide
1171 different responses depending on attributes of the query, such as
1172 for "split DNS". Typically, views differ by the source IP address
1173 of a query, but can also be based on the destination IP address,
1174 the type of query (such as AXFR), whether it is recursive, and so
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1180RFC 8499 DNS Terminology January 2019
1183 on. Views are often used to provide more names or different
1184 addresses to queries from "inside" a protected network than to
1185 those "outside" that network. Views are not a standardized part
1186 of the DNS, but they are widely implemented in server software.
1188 Passive DNS: A mechanism to collect DNS data by storing DNS
1189 responses from name servers. Some of these systems also collect
1190 the DNS queries associated with the responses, although doing so
1191 raises some privacy concerns. Passive DNS databases can be used
1192 to answer historical questions about DNS zones such as which
1193 values were present at a given time in the past, or when a name
1194 was spotted first. Passive DNS databases allow searching of the
1195 stored records on keys other than just the name and type, such as
1196 "find all names which have A records of a particular value".
1198 Anycast: "The practice of making a particular service address
1199 available in multiple, discrete, autonomous locations, such that
1200 datagrams sent are routed to one of several available locations."
1201 (Quoted from [RFC4786], Section 2) See [RFC4786] for more detail
1202 on Anycast and other terms that are specific to its use.
1204 Instance: "When anycast routing is used to allow more than one
1205 server to have the same IP address, each one of those servers is
1206 commonly referred to as an 'instance'." It goes on to say: "An
1207 instance of a server, such as a root server, is often referred to
1208 as an 'Anycast instance'." (Quoted from [RSSAC026])
1210 Privacy-enabling DNS server: "A DNS server that implements DNS over
1211 TLS [RFC7858] and may optionally implement DNS over DTLS
1212 [RFC8094]." (Quoted from [RFC8310], Section 2) Other types of DNS
1213 servers might also be considered privacy-enabling, such as those
1214 running DNS over HTTPS [RFC8484].
1218 This section defines terms that are used when discussing zones that
1219 are being served or retrieved.
1221 Zone: "Authoritative information is organized into units called
1222 ZONEs, and these zones can be automatically distributed to the
1223 name servers which provide redundant service for the data in a
1224 zone." (Quoted from [RFC1034], Section 2.4)
1226 Child: "The entity on record that has the delegation of the domain
1227 from the Parent." (Quoted from [RFC7344], Section 1.1)
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1236RFC 8499 DNS Terminology January 2019
1239 Parent: "The domain in which the Child is registered." (Quoted from
1240 [RFC7344], Section 1.1) Earlier, "parent name server" was defined
1241 in [RFC0882] as "the name server that has authority over the place
1242 in the domain name space that will hold the new domain". (Note
1243 that [RFC0882] was obsoleted by [RFC1034] and [RFC1035].)
1244 [RFC819] also has some description of the relationship between
1245 parents and children.
1249 There are two different uses for this term:
1251 (a) "The domain name that appears at the top of a zone (just
1252 below the cut that separates the zone from its parent)... The
1253 name of the zone is the same as the name of the domain at the
1254 zone's origin." (Quoted from [RFC2181], Section 6) These
1255 days, this sense of "origin" and "apex" (defined below) are
1256 often used interchangeably.
1258 (b) The domain name within which a given relative domain name
1259 appears in zone files. Generally seen in the context of
1260 "$ORIGIN", which is a control entry defined in [RFC1035],
1261 Section 5.1, as part of the master file format. For example,
1262 if the $ORIGIN is set to "example.org.", then a master file
1263 line for "www" is in fact an entry for "www.example.org.".
1265 Apex: The point in the tree at an owner of an SOA and corresponding
1266 authoritative NS RRset. This is also called the "zone apex".
1267 [RFC4033] defines it as "the name at the child's side of a zone
1268 cut". The "apex" can usefully be thought of as a data-theoretic
1269 description of a tree structure, and "origin" is the name of the
1270 same concept when it is implemented in zone files. The
1271 distinction is not always maintained in use, however, and one can
1272 find uses that conflict subtly with this definition. [RFC1034]
1273 uses the term "top node of the zone" as a synonym of "apex", but
1274 that term is not widely used. These days, the first sense of
1275 "origin" (above) and "apex" are often used interchangeably.
1277 Zone cut: The delimitation point between two zones where the origin
1278 of one of the zones is the child of the other zone.
1280 "Zones are delimited by 'zone cuts'. Each zone cut separates a
1281 'child' zone (below the cut) from a 'parent' zone (above the
1282 cut)." (Quoted from [RFC2181], Section 6; note that this is
1283 barely an ostensive definition.) Section 4.2 of [RFC1034] uses
1284 "cuts" instead of "zone cut".
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1292RFC 8499 DNS Terminology January 2019
1295 Delegation: The process by which a separate zone is created in the
1296 name space beneath the apex of a given domain. Delegation happens
1297 when an NS RRset is added in the parent zone for the child origin.
1298 Delegation inherently happens at a zone cut. The term is also
1299 commonly a noun: the new zone that is created by the act of
1302 Authoritative data: "All of the RRs attached to all of the nodes
1303 from the top node of the zone down to leaf nodes or nodes above
1304 cuts around the bottom edge of the zone." (Quoted from [RFC1034],
1305 Section 4.2.1) Note that this definition might inadvertently also
1306 cause any NS records that appear in the zone to be included, even
1307 those that might not truly be authoritative because there are
1308 identical NS RRs below the zone cut. This reveals the ambiguity
1309 in the notion of authoritative data, because the parent-side NS
1310 records authoritatively indicate the delegation, even though they
1311 are not themselves authoritative data.
1313 [RFC4033], Section 2, defines "Authoritative RRset", which is
1314 related to authoritative data but has a more precise definition.
1316 Lame delegation: "A lame delegations exists [sic] when a nameserver
1317 is delegated responsibility for providing nameservice for a zone
1318 (via NS records) but is not performing nameservice for that zone
1319 (usually because it is not set up as a primary or secondary for
1320 the zone)." (Quoted from [RFC1912], Section 2.8) Another
1321 definition is that a lame delegation "...happens when a name
1322 server is listed in the NS records for some domain and in fact it
1323 is not a server for that domain. Queries are thus sent to the
1324 wrong servers, who don't know nothing [sic] (at least not as
1325 expected) about the queried domain. Furthermore, sometimes these
1326 hosts (if they exist!) don't even run name servers." (Quoted from
1327 [RFC1713], Section 2.3)
1329 Glue records: "...[Resource records] which are not part of the
1330 authoritative data [of the zone], and are address RRs for the
1331 [name] servers [in subzones]. These RRs are only necessary if the
1332 name server's name is 'below' the cut, and are only used as part
1333 of a referral response." Without glue "we could be faced with the
1334 situation where the NS RRs tell us that in order to learn a name
1335 server's address, we should contact the server using the address
1336 we wish to learn." (Quoted from [RFC1034], Section 4.2.1)
1338 A later definition is that glue "includes any record in a zone
1339 file that is not properly part of that zone, including nameserver
1340 records of delegated sub-zones (NS records), address records that
1341 accompany those NS records (A, AAAA, etc), and any other stray
1342 data that might appear." (Quoted from [RFC2181], Section 5.4.1)
1346Hoffman, et al. Best Current Practice [Page 24]
1348RFC 8499 DNS Terminology January 2019
1351 Although glue is sometimes used today with this wider definition
1352 in mind, the context surrounding the definition in [RFC2181]
1353 suggests it is intended to apply to the use of glue within the
1354 document itself and not necessarily beyond.
1356 Bailiwick: "In-bailiwick" is a modifier to describe a name server
1357 whose name is either a subdomain of or (rarely) the same as the
1358 origin of the zone that contains the delegation to the name
1359 server. In-bailiwick name servers may have glue records in their
1360 parent zone (using the first of the definitions of "glue records"
1361 in the definition above). (The word "bailiwick" means the
1362 district or territory where a bailiff or policeman has
1365 "In-bailiwick" names are divided into two types of names for name
1366 servers: "in-domain" names and "sibling domain" names.
1368 * In-domain: a modifier to describe a name server whose name is
1369 either subordinate to or (rarely) the same as the owner name of
1370 the NS resource records. An in-domain name server name needs
1371 to have glue records or name resolution fails. For example, a
1372 delegation for "child.example.com" may have "in-domain" name
1373 server name "ns.child.example.com".
1375 * Sibling domain: a name server's name that is either subordinate
1376 to or (rarely) the same as the zone origin and not subordinate
1377 to or the same as the owner name of the NS resource records.
1378 Glue records for sibling domains are allowed, but not
1379 necessary. For example, a delegation for "child.example.com"
1380 in "example.com" zone may have "sibling" name server name
1381 "ns.another.example.com".
1383 "Out-of-bailiwick" is the antonym of "in-bailiwick". It is a
1384 modifier to describe a name server whose name is not subordinate
1385 to or the same as the zone origin. Glue records for out-of-
1386 bailiwick name servers are useless. The following table shows
1387 examples of delegation types.
1389 Delegation |Parent|Name Server Name | Type
1390 -----------+------+------------------+-----------------------------
1391 com | . |a.gtld-servers.net|in-bailiwick / sibling domain
1392 net | . |a.gtld-servers.net|in-bailiwick / in-domain
1393 example.org| org |ns.example.org |in-bailiwick / in-domain
1394 example.org| org |ns.ietf.org |in-bailiwick / sibling domain
1395 example.org| org |ns.example.com |out-of-bailiwick
1396 example.jp | jp |ns.example.jp |in-bailiwick / in-domain
1397 example.jp | jp |ns.example.ne.jp |in-bailiwick / sibling domain
1398 example.jp | jp |ns.example.com |out-of-bailiwick
1402Hoffman, et al. Best Current Practice [Page 25]
1404RFC 8499 DNS Terminology January 2019
1407 Root zone: The zone of a DNS-based tree whose apex is the zero-
1408 length label. Also sometimes called "the DNS root".
1410 Empty non-terminals (ENT): "Domain names that own no resource
1411 records but have subdomains that do." (Quoted from [RFC4592],
1412 Section 2.2.2) A typical example is in SRV records: in the name
1413 "_sip._tcp.example.com", it is likely that "_tcp.example.com" has
1414 no RRsets, but that "_sip._tcp.example.com" has (at least) an SRV
1417 Delegation-centric zone: A zone that consists mostly of delegations
1418 to child zones. This term is used in contrast to a zone that
1419 might have some delegations to child zones but also has many data
1420 resource records for the zone itself and/or for child zones. The
1421 term is used in [RFC4956] and [RFC5155], but it is not defined in
1424 Occluded name: "The addition of a delegation point via dynamic
1425 update will render all subordinate domain names to be in a limbo,
1426 still part of the zone but not available to the lookup process.
1427 The addition of a DNAME resource record has the same impact. The
1428 subordinate names are said to be 'occluded'." (Quoted from
1429 [RFC5936], Section 3.5)
1431 Fast flux DNS: This "occurs when a domain is [found] in DNS using A
1432 records to multiple IP addresses, each of which has a very short
1433 Time-to-Live (TTL) value associated with it. This means that the
1434 domain resolves to varying IP addresses over a short period of
1435 time." (Quoted from [RFC6561], Section 1.1.5, with a typo
1436 corrected) In addition to having legitimate uses, fast flux DNS
1437 can used to deliver malware. Because the addresses change so
1438 rapidly, it is difficult to ascertain all the hosts. It should be
1439 noted that the technique also works with AAAA records, but such
1440 use is not frequently observed on the Internet as of this writing.
1442 Reverse DNS, reverse lookup: "The process of mapping an address to a
1443 name is generally known as a 'reverse lookup', and the
1444 IN-ADDR.ARPA and IP6.ARPA zones are said to support the 'reverse
1445 DNS'." (Quoted from [RFC5855], Section 1)
1447 Forward lookup: "Hostname-to-address translation". (Quoted from
1448 [RFC3493], Section 6)
1450 arpa: Address and Routing Parameter Area Domain: "The 'arpa' domain
1451 was originally established as part of the initial deployment of
1452 the DNS, to provide a transition mechanism from the Host Tables
1453 that were common in the ARPANET, as well as a home for the IPv4
1454 reverse mapping domain. During 2000, the abbreviation was
1458Hoffman, et al. Best Current Practice [Page 26]
1460RFC 8499 DNS Terminology January 2019
1463 redesignated to 'Address and Routing Parameter Area' in the hope
1464 of reducing confusion with the earlier network name." (Quoted
1465 from [RFC3172], Section 2) .arpa is an "infrastructure domain", a
1466 domain whose "role is to support the operating infrastructure of
1467 the Internet". (Quoted from [RFC3172], Section 2) See [RFC3172]
1468 for more history of this name.
1470 Service name: "Service names are the unique key in the Service Name
1471 and Transport Protocol Port Number registry. This unique symbolic
1472 name for a service may also be used for other purposes, such as in
1473 DNS SRV records." (Quoted from [RFC6335], Section 5)
1477 Wildcard: [RFC1034] defined "wildcard", but in a way that turned out
1478 to be confusing to implementers. For an extended discussion of
1479 wildcards, including clearer definitions, see [RFC4592]. Special
1480 treatment is given to RRs with owner names starting with the label
1481 "*". "Such RRs are called 'wildcards'. Wildcard RRs can be
1482 thought of as instructions for synthesizing RRs." (Quoted from
1483 [RFC1034], Section 4.3.3)
1485 Asterisk label: "The first octet is the normal label type and length
1486 for a 1-octet-long label, and the second octet is the ASCII
1487 representation [RFC20] for the '*' character. A descriptive name
1488 of a label equaling that value is an 'asterisk label'." (Quoted
1489 from [RFC4592], Section 2.1.1)
1491 Wildcard domain name: "A 'wildcard domain name' is defined by having
1492 its initial (i.e., leftmost or least significant) label, in binary
1493 format: 0000 0001 0010 1010 (binary) = 0x01 0x2a (hexadecimal)".
1494 (Quoted from [RFC4592], Section 2.1.1) The second octet in this
1495 label is the ASCII representation for the "*" character.
1497 Closest encloser: "The longest existing ancestor of a name."
1498 (Quoted from [RFC5155], Section 1.3) An earlier definition is "The
1499 node in the zone's tree of existing domain names that has the most
1500 labels matching the query name (consecutively, counting from the
1501 root label downward). Each match is a 'label match' and the order
1502 of the labels is the same." (Quoted from [RFC4592],
1505 Closest provable encloser: "The longest ancestor of a name that can
1506 be proven to exist. Note that this is only different from the
1507 closest encloser in an Opt-Out zone." (Quoted from [RFC5155],
1508 Section 1.3) See Section 10 for more on "opt-out".
1514Hoffman, et al. Best Current Practice [Page 27]
1516RFC 8499 DNS Terminology January 2019
1519 Next closer name: "The name one label longer than the closest
1520 provable encloser of a name." (Quoted from [RFC5155],
1523 Source of Synthesis: "The source of synthesis is defined in the
1524 context of a query process as that wildcard domain name
1525 immediately descending from the closest encloser, provided that
1526 this wildcard domain name exists. 'Immediately descending' means
1527 that the source of synthesis has a name of the form:
1528 <asterisk label>.<closest encloser>."
1529 (Quoted from [RFC4592], Section 3.3.1)
15319. Registration Model
1533 Registry: The administrative operation of a zone that allows
1534 registration of names within that zone. People often use this
1535 term to refer only to those organizations that perform
1536 registration in large delegation-centric zones (such as TLDs); but
1537 formally, whoever decides what data goes into a zone is the
1538 registry for that zone. This definition of "registry" is from a
1539 DNS point of view; for some zones, the policies that determine
1540 what can go in the zone are decided by zones that are
1541 superordinate and not the registry operator.
1543 Registrant: An individual or organization on whose behalf a name in
1544 a zone is registered by the registry. In many zones, the registry
1545 and the registrant may be the same entity, but in TLDs they often
1548 Registrar: A service provider that acts as a go-between for
1549 registrants and registries. Not all registrations require a
1550 registrar, though it is common to have registrars involved in
1551 registrations in TLDs.
1553 EPP: The Extensible Provisioning Protocol (EPP), which is commonly
1554 used for communication of registration information between
1555 registries and registrars. EPP is defined in [RFC5730].
1557 WHOIS: A protocol specified in [RFC3912], often used for querying
1558 registry databases. WHOIS data is frequently used to associate
1559 registration data (such as zone management contacts) with domain
1560 names. The term "WHOIS data" is often used as a synonym for the
1561 registry database, even though that database may be served by
1562 different protocols, particularly RDAP. The WHOIS protocol is
1563 also used with IP address registry data.
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1572RFC 8499 DNS Terminology January 2019
1575 RDAP: The Registration Data Access Protocol, defined in [RFC7480],
1576 [RFC7481], [RFC7482], [RFC7483], [RFC7484], and [RFC7485]. The
1577 RDAP protocol and data format are meant as a replacement for
1580 DNS operator: An entity responsible for running DNS servers. For a
1581 zone's authoritative servers, the registrant may act as their own
1582 DNS operator, their registrar may do it on their behalf, or they
1583 may use a third-party operator. For some zones, the registry
1584 function is performed by the DNS operator plus other entities who
1585 decide about the allowed contents of the zone.
1587 Public suffix: "A domain that is controlled by a public registry."
1588 (Quoted from [RFC6265], Section 5.3) A common definition for this
1589 term is a domain under which subdomains can be registered by third
1590 parties and on which HTTP cookies (which are described in detail
1591 in [RFC6265]) should not be set. There is no indication in a
1592 domain name whether it is a public suffix; that can only be
1593 determined by outside means. In fact, both a domain and a
1594 subdomain of that domain can be public suffixes.
1596 There is nothing inherent in a domain name to indicate whether it
1597 is a public suffix. One resource for identifying public suffixes
1598 is the Public Suffix List (PSL) maintained by Mozilla
1599 (http://publicsuffix.org/).
1601 For example, at the time this document is published, the "com.au"
1602 domain is listed as a public suffix in the PSL. (Note that this
1603 example might change in the future.)
1605 Note that the term "public suffix" is controversial in the DNS
1606 community for many reasons, and it may be significantly changed in
1607 the future. One example of the difficulty of calling a domain a
1608 public suffix is that designation can change over time as the
1609 registration policy for the zone changes, such as was the case
1610 with the "uk" TLD in 2014.
1612 Subordinate and Superordinate: These terms are introduced in
1613 [RFC5731] for use in the registration model, but not defined
1614 there. Instead, they are given in examples. "For example, domain
1615 name 'example.com' has a superordinate relationship to host name
1616 ns1.example.com'... For example, host ns1.example1.com is a
1617 subordinate host of domain example1.com, but it is a not a
1618 subordinate host of domain example2.com." (Quoted from [RFC5731],
1619 Section 1.1) These terms are strictly ways of referring to the
1620 relationship standing of two domains where one is a subdomain of
1626Hoffman, et al. Best Current Practice [Page 29]
1628RFC 8499 DNS Terminology January 2019
1633 Most DNSSEC terms are defined in [RFC4033], [RFC4034], [RFC4035], and
1634 [RFC5155]. The terms that have caused confusion in the DNS community
1635 are highlighted here.
1637 DNSSEC-aware and DNSSEC-unaware: These two terms, which are used in
1638 some RFCs, have not been formally defined. However, Section 2 of
1639 [RFC4033] defines many types of resolvers and validators,
1640 including "non-validating security-aware stub resolver",
1641 "non-validating stub resolver", "security-aware name server",
1642 "security-aware recursive name server", "security-aware resolver",
1643 "security-aware stub resolver", and "security-oblivious
1644 'anything'". (Note that the term "validating resolver", which is
1645 used in some places in DNSSEC-related documents, is also not
1646 defined in those RFCs, but is defined below.)
1648 Signed zone: "A zone whose RRsets are signed and that contains
1649 properly constructed DNSKEY, Resource Record Signature (RRSIG),
1650 Next Secure (NSEC), and (optionally) DS records." (Quoted from
1651 [RFC4033], Section 2) It has been noted in other contexts that the
1652 zone itself is not really signed, but all the relevant RRsets in
1653 the zone are signed. Nevertheless, if a zone that should be
1654 signed contains any RRsets that are not signed (or opted out),
1655 those RRsets will be treated as bogus, so the whole zone needs to
1656 be handled in some way.
1658 It should also be noted that, since the publication of [RFC6840],
1659 NSEC records are no longer required for signed zones: a signed
1660 zone might include NSEC3 records instead. [RFC7129] provides
1661 additional background commentary and some context for the NSEC and
1662 NSEC3 mechanisms used by DNSSEC to provide authenticated denial-
1663 of-existence responses. NSEC and NSEC3 are described below.
1665 Unsigned zone: Section 2 of [RFC4033] defines this as "a zone that
1666 is not signed". Section 2 of [RFC4035] defines this as a "zone
1667 that does not include these records [properly constructed DNSKEY,
1668 Resource Record Signature (RRSIG), Next Secure (NSEC), and
1669 (optionally) DS records] according to the rules in this
1670 section..." There is an important note at the end of Section 5.2
1671 of [RFC4035] that defines an additional situation in which a zone
1672 is considered unsigned: "If the resolver does not support any of
1673 the algorithms listed in an authenticated DS RRset, then the
1674 resolver will not be able to verify the authentication path to the
1675 child zone. In this case, the resolver SHOULD treat the child
1676 zone as if it were unsigned."
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1684RFC 8499 DNS Terminology January 2019
1687 NSEC: "The NSEC record allows a security-aware resolver to
1688 authenticate a negative reply for either name or type
1689 non-existence with the same mechanisms used to authenticate other
1690 DNS replies." (Quoted from [RFC4033], Section 3.2) In short, an
1691 NSEC record provides authenticated denial of existence.
1693 "The NSEC resource record lists two separate things: the next
1694 owner name (in the canonical ordering of the zone) that contains
1695 authoritative data or a delegation point NS RRset, and the set of
1696 RR types present at the NSEC RR's owner name." (Quoted from
1697 Section 4 of RFC 4034)
1699 NSEC3: Like the NSEC record, the NSEC3 record also provides
1700 authenticated denial of existence; however, NSEC3 records mitigate
1701 zone enumeration and support Opt-Out. NSEC3 resource records
1702 require associated NSEC3PARAM resource records. NSEC3 and
1703 NSEC3PARAM resource records are defined in [RFC5155].
1705 Note that [RFC6840] says that [RFC5155] "is now considered part of
1706 the DNS Security Document Family as described by Section 10 of
1707 [RFC4033]". This means that some of the definitions from earlier
1708 RFCs that only talk about NSEC records should probably be
1709 considered to be talking about both NSEC and NSEC3.
1711 Opt-out: "The Opt-Out Flag indicates whether this NSEC3 RR may cover
1712 unsigned delegations." (Quoted from [RFC5155], Section 3.1.2.1)
1713 Opt-out tackles the high costs of securing a delegation to an
1714 insecure zone. When using Opt-Out, names that are an insecure
1715 delegation (and empty non-terminals that are only derived from
1716 insecure delegations) don't require an NSEC3 record or its
1717 corresponding RRSIG records. Opt-Out NSEC3 records are not able
1718 to prove or deny the existence of the insecure delegations.
1719 (Adapted from [RFC7129], Section 5.1)
1721 Insecure delegation: "A signed name containing a delegation (NS
1722 RRset), but lacking a DS RRset, signifying a delegation to an
1723 unsigned subzone." (Quoted from [RFC4956], Section 2)
1725 Zone enumeration: "The practice of discovering the full content of a
1726 zone via successive queries." (Quoted from [RFC5155],
1727 Section 1.3) This is also sometimes called "zone walking". Zone
1728 enumeration is different from zone content guessing where the
1729 guesser uses a large dictionary of possible labels and sends
1730 successive queries for them, or matches the contents of NSEC3
1731 records against such a dictionary.
1738Hoffman, et al. Best Current Practice [Page 31]
1740RFC 8499 DNS Terminology January 2019
1743 Validation: Validation, in the context of DNSSEC, refers to one of
1746 * Checking the validity of DNSSEC signatures,
1748 * Checking the validity of DNS responses, such as those including
1749 authenticated denial of existence, or
1751 * Building an authentication chain from a trust anchor to a DNS
1752 response or individual DNS RRsets in a response
1754 The first two definitions above consider only the validity of
1755 individual DNSSEC components such as the RRSIG validity or NSEC
1756 proof validity. The third definition considers the components of
1757 the entire DNSSEC authentication chain; thus, it requires
1758 "configured knowledge of at least one authenticated DNSKEY or DS
1759 RR" (as described in [RFC4035], Section 5).
1761 [RFC4033], Section 2, says that a "Validating Security-Aware Stub
1762 Resolver... performs signature validation" and uses a trust anchor
1763 "as a starting point for building the authentication chain to a
1764 signed DNS response"; thus, it uses the first and third
1765 definitions above. The process of validating an RRSIG resource
1766 record is described in [RFC4035], Section 5.3.
1768 [RFC5155] refers to validating responses throughout the document,
1769 in the context of hashed authenticated denial of existence; this
1770 uses the second definition above.
1772 The term "authentication" is used interchangeably with
1773 "validation", in the sense of the third definition above.
1774 [RFC4033], Section 2, describes the chain linking trust anchor to
1775 DNS data as the "authentication chain". A response is considered
1776 to be authentic if "all RRsets in the Answer and Authority
1777 sections of the response [are considered] to be authentic" (Quoted
1778 from [RFC4035]) DNS data or responses deemed to be authentic or
1779 validated have a security status of "secure" ([RFC4035],
1780 Section 4.3; [RFC4033], Section 5). "Authenticating both DNS keys
1781 and data is a matter of local policy, which may extend or even
1782 override the [DNSSEC] protocol extensions..." (Quoted from
1783 [RFC4033], Section 3.1)
1785 The term "verification", when used, is usually a synonym for
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1796RFC 8499 DNS Terminology January 2019
1799 Validating resolver: A security-aware recursive name server,
1800 security-aware resolver, or security-aware stub resolver that is
1801 applying at least one of the definitions of validation (above), as
1802 appropriate to the resolution context. For the same reason that
1803 the generic term "resolver" is sometimes ambiguous and needs to be
1804 evaluated in context (see Section 6), "validating resolver" is a
1805 context-sensitive term.
1807 Key signing key (KSK): DNSSEC keys that "only sign the apex DNSKEY
1808 RRset in a zone." (Quoted from [RFC6781], Section 3.1)
1810 Zone signing key (ZSK): "DNSSEC keys that can be used to sign all
1811 the RRsets in a zone that require signatures, other than the apex
1812 DNSKEY RRset." (Quoted from [RFC6781], Section 3.1) Also note
1813 that a ZSK is sometimes used to sign the apex DNSKEY RRset.
1815 Combined signing key (CSK): "In cases where the differentiation
1816 between the KSK and ZSK is not made, i.e., where keys have the
1817 role of both KSK and ZSK, we talk about a Single-Type Signing
1818 Scheme." (Quoted from [RFC6781], Section 3.1) This is sometimes
1819 called a "combined signing key" or "CSK". It is operational
1820 practice, not protocol, that determines whether a particular key
1821 is a ZSK, a KSK, or a CSK.
1823 Secure Entry Point (SEP): A flag in the DNSKEY RDATA that "can be
1824 used to distinguish between keys that are intended to be used as
1825 the secure entry point into the zone when building chains of
1826 trust, i.e., they are (to be) pointed to by parental DS RRs or
1827 configured as a trust anchor.... Therefore, it is suggested that
1828 the SEP flag be set on keys that are used as KSKs and not on keys
1829 that are used as ZSKs, while in those cases where a distinction
1830 between a KSK and ZSK is not made (i.e., for a Single-Type Signing
1831 Scheme), it is suggested that the SEP flag be set on all keys."
1832 (Quoted from [RFC6781], Section 3.2.3) Note that the SEP flag is
1833 only a hint, and its presence or absence may not be used to
1834 disqualify a given DNSKEY RR from use as a KSK or ZSK during
1837 The original definition of SEPs was in [RFC3757]. That definition
1838 clearly indicated that the SEP was a key, not just a bit in the
1839 key. The abstract of [RFC3757] says: "With the Delegation Signer
1840 (DS) resource record (RR), the concept of a public key acting as a
1841 secure entry point (SEP) has been introduced. During exchanges of
1842 public keys with the parent there is a need to differentiate SEP
1843 keys from other public keys in the Domain Name System KEY (DNSKEY)
1844 resource record set. A flag bit in the DNSKEY RR is defined to
1850Hoffman, et al. Best Current Practice [Page 33]
1852RFC 8499 DNS Terminology January 2019
1855 indicate that DNSKEY is to be used as a SEP." That definition of
1856 the SEP as a key was made obsolete by [RFC4034], and the
1857 definition from [RFC6781] is consistent with [RFC4034].
1859 Trust anchor: "A configured DNSKEY RR or DS RR hash of a DNSKEY RR.
1860 A validating security-aware resolver uses this public key or hash
1861 as a starting point for building the authentication chain to a
1862 signed DNS response. In general, a validating resolver will have
1863 to obtain the initial values of its trust anchors via some secure
1864 or trusted means outside the DNS protocol." (Quoted from
1865 [RFC4033], Section 2)
1867 DNSSEC Policy (DP): A statement that "sets forth the security
1868 requirements and standards to be implemented for a DNSSEC-signed
1869 zone." (Quoted from [RFC6841], Section 2)
1871 DNSSEC Practice Statement (DPS): "A practices disclosure document
1872 that may support and be a supplemental document to the DNSSEC
1873 Policy (if such exists), and it states how the management of a
1874 given zone implements procedures and controls at a high level."
1875 (Quoted from [RFC6841], Section 2)
1877 Hardware security module (HSM): A specialized piece of hardware that
1878 is used to create keys for signatures and to sign messages without
1879 ever disclosing the private key. In DNSSEC, HSMs are often used
1880 to hold the private keys for KSKs and ZSKs and to create the
1881 signatures used in RRSIG records at periodic intervals.
1883 Signing software: Authoritative DNS servers that support DNSSEC
1884 often contain software that facilitates the creation and
1885 maintenance of DNSSEC signatures in zones. There is also stand-
1886 alone software that can be used to sign a zone regardless of
1887 whether the authoritative server itself supports signing.
1888 Sometimes signing software can support particular HSMs as part of
1889 the signing process.
1893 A validating resolver can determine that a response is in one of four
1894 states: secure, insecure, bogus, or indeterminate. These states are
1895 defined in [RFC4033] and [RFC4035], although the definitions in the
1896 two documents differ a bit. This document makes no effort to
1897 reconcile the definitions in the two documents, and takes no position
1898 as to whether they need to be reconciled.
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1908RFC 8499 DNS Terminology January 2019
1911 Section 5 of [RFC4033] says:
1913 A validating resolver can determine the following 4 states:
1915 Secure: The validating resolver has a trust anchor, has a chain
1916 of trust, and is able to verify all the signatures in the
1919 Insecure: The validating resolver has a trust anchor, a chain
1920 of trust, and, at some delegation point, signed proof of the
1921 non-existence of a DS record. This indicates that subsequent
1922 branches in the tree are provably insecure. A validating
1923 resolver may have a local policy to mark parts of the domain
1926 Bogus: The validating resolver has a trust anchor and a secure
1927 delegation indicating that subsidiary data is signed, but
1928 the response fails to validate for some reason: missing
1929 signatures, expired signatures, signatures with unsupported
1930 algorithms, data missing that the relevant NSEC RR says
1931 should be present, and so forth.
1933 Indeterminate: There is no trust anchor that would indicate that a
1934 specific portion of the tree is secure. This is the default
1937 Section 4.3 of [RFC4035] says:
1939 A security-aware resolver must be able to distinguish between four
1942 Secure: An RRset for which the resolver is able to build a chain
1943 of signed DNSKEY and DS RRs from a trusted security anchor to
1944 the RRset. In this case, the RRset should be signed and is
1945 subject to signature validation, as described above.
1947 Insecure: An RRset for which the resolver knows that it has no
1948 chain of signed DNSKEY and DS RRs from any trusted starting
1949 point to the RRset. This can occur when the target RRset lies
1950 in an unsigned zone or in a descendent [sic] of an unsigned
1951 zone. In this case, the RRset may or may not be signed, but
1952 the resolver will not be able to verify the signature.
1954 Bogus: An RRset for which the resolver believes that it ought to
1955 be able to establish a chain of trust but for which it is
1956 unable to do so, either due to signatures that for some reason
1957 fail to validate or due to missing data that the relevant
1958 DNSSEC RRs indicate should be present. This case may indicate
1962Hoffman, et al. Best Current Practice [Page 35]
1964RFC 8499 DNS Terminology January 2019
1967 an attack but may also indicate a configuration error or some
1968 form of data corruption.
1970 Indeterminate: An RRset for which the resolver is not able to
1971 determine whether the RRset should be signed, as the resolver
1972 is not able to obtain the necessary DNSSEC RRs. This can occur
1973 when the security-aware resolver is not able to contact
1974 security-aware name servers for the relevant zones.
197612. Security Considerations
1978 These definitions do not change any security considerations for the
198113. IANA Considerations
1983 This document has no IANA actions.
198714.1. Normative References
1991 <https://www.iana.org/domains/root/files>.
1993 [RFC0882] Mockapetris, P., "Domain names: Concepts and facilities",
1994 RFC 882, DOI 10.17487/RFC0882, November 1983,
1995 <https://www.rfc-editor.org/info/rfc882>.
1997 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
1998 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
1999 <https://www.rfc-editor.org/info/rfc1034>.
2001 [RFC1035] Mockapetris, P., "Domain names - implementation and
2002 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
2003 November 1987, <https://www.rfc-editor.org/info/rfc1035>.
2005 [RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
2006 Application and Support", STD 3, RFC 1123,
2007 DOI 10.17487/RFC1123, October 1989,
2008 <https://www.rfc-editor.org/info/rfc1123>.
2010 [RFC1912] Barr, D., "Common DNS Operational and Configuration
2011 Errors", RFC 1912, DOI 10.17487/RFC1912, February 1996,
2012 <https://www.rfc-editor.org/info/rfc1912>.
2018Hoffman, et al. Best Current Practice [Page 36]
2020RFC 8499 DNS Terminology January 2019
2023 [RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
2024 Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
2025 August 1996, <https://www.rfc-editor.org/info/rfc1996>.
2027 [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
2028 "Dynamic Updates in the Domain Name System (DNS UPDATE)",
2029 RFC 2136, DOI 10.17487/RFC2136, April 1997,
2030 <https://www.rfc-editor.org/info/rfc2136>.
2032 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
2033 Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
2034 <https://www.rfc-editor.org/info/rfc2181>.
2036 [RFC2182] Elz, R., Bush, R., Bradner, S., and M. Patton, "Selection
2037 and Operation of Secondary DNS Servers", BCP 16, RFC 2182,
2038 DOI 10.17487/RFC2182, July 1997,
2039 <https://www.rfc-editor.org/info/rfc2182>.
2041 [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
2042 NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,
2043 <https://www.rfc-editor.org/info/rfc2308>.
2045 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and
2046 S. Rose, "DNS Security Introduction and Requirements",
2047 RFC 4033, DOI 10.17487/RFC4033, March 2005,
2048 <https://www.rfc-editor.org/info/rfc4033>.
2050 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and
2051 S. Rose, "Resource Records for the DNS Security
2052 Extensions", RFC 4034, DOI 10.17487/RFC4034, March 2005,
2053 <https://www.rfc-editor.org/info/rfc4034>.
2055 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and
2056 S. Rose, "Protocol Modifications for the DNS Security
2057 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
2058 <https://www.rfc-editor.org/info/rfc4035>.
2060 [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name
2061 System", RFC 4592, DOI 10.17487/RFC4592, July 2006,
2062 <https://www.rfc-editor.org/info/rfc4592>.
2064 [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
2065 Security (DNSSEC) Hashed Authenticated Denial of
2066 Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,
2067 <https://www.rfc-editor.org/info/rfc5155>.
2074Hoffman, et al. Best Current Practice [Page 37]
2076RFC 8499 DNS Terminology January 2019
2079 [RFC5358] Damas, J. and F. Neves, "Preventing Use of Recursive
2080 Nameservers in Reflector Attacks", BCP 140, RFC 5358,
2081 DOI 10.17487/RFC5358, October 2008,
2082 <https://www.rfc-editor.org/info/rfc5358>.
2084 [RFC5730] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
2085 STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,
2086 <https://www.rfc-editor.org/info/rfc5730>.
2088 [RFC5731] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
2089 Domain Name Mapping", STD 69, RFC 5731,
2090 DOI 10.17487/RFC5731, August 2009,
2091 <https://www.rfc-editor.org/info/rfc5731>.
2093 [RFC5855] Abley, J. and T. Manderson, "Nameservers for IPv4 and IPv6
2094 Reverse Zones", BCP 155, RFC 5855, DOI 10.17487/RFC5855,
2095 May 2010, <https://www.rfc-editor.org/info/rfc5855>.
2097 [RFC5936] Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
2098 (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,
2099 <https://www.rfc-editor.org/info/rfc5936>.
2101 [RFC6561] Livingood, J., Mody, N., and M. O'Reirdan,
2102 "Recommendations for the Remediation of Bots in ISP
2103 Networks", RFC 6561, DOI 10.17487/RFC6561, March 2012,
2104 <https://www.rfc-editor.org/info/rfc6561>.
2106 [RFC6781] Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
2107 Operational Practices, Version 2", RFC 6781,
2108 DOI 10.17487/RFC6781, December 2012,
2109 <https://www.rfc-editor.org/info/rfc6781>.
2111 [RFC6840] Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and
2112 Implementation Notes for DNS Security (DNSSEC)", RFC 6840,
2113 DOI 10.17487/RFC6840, February 2013,
2114 <https://www.rfc-editor.org/info/rfc6840>.
2116 [RFC6841] Ljunggren, F., Eklund Lowinder, AM., and T. Okubo, "A
2117 Framework for DNSSEC Policies and DNSSEC Practice
2118 Statements", RFC 6841, DOI 10.17487/RFC6841, January 2013,
2119 <https://www.rfc-editor.org/info/rfc6841>.
2121 [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
2122 for DNS (EDNS(0))", STD 75, RFC 6891,
2123 DOI 10.17487/RFC6891, April 2013,
2124 <https://www.rfc-editor.org/info/rfc6891>.
2130Hoffman, et al. Best Current Practice [Page 38]
2132RFC 8499 DNS Terminology January 2019
2135 [RFC7344] Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
2136 DNSSEC Delegation Trust Maintenance", RFC 7344,
2137 DOI 10.17487/RFC7344, September 2014,
2138 <https://www.rfc-editor.org/info/rfc7344>.
2140 [RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
2141 Terminology", RFC 7719, DOI 10.17487/RFC7719, December
2142 2015, <https://www.rfc-editor.org/info/rfc7719>.
2144 [RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
2145 for DNS over TLS and DNS over DTLS", RFC 8310,
2146 DOI 10.17487/RFC8310, March 2018,
2147 <https://www.rfc-editor.org/info/rfc8310>.
214914.2. Informative References
2151 [IANA_Resource_Registry]
2152 IANA, "Resource Record (RR) TYPEs",
2153 <https://www.iana.org/assignments/dns-parameters/>.
2155 [RFC819] Su, Z. and J. Postel, "The Domain Naming Convention for
2156 Internet User Applications", RFC 819,
2157 DOI 10.17487/RFC0819, August 1982,
2158 <https://www.rfc-editor.org/info/rfc819>.
2160 [RFC952] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet
2161 host table specification", RFC 952, DOI 10.17487/RFC0952,
2162 October 1985, <https://www.rfc-editor.org/info/rfc952>.
2164 [RFC1713] Romao, A., "Tools for DNS debugging", FYI 27, RFC 1713,
2165 DOI 10.17487/RFC1713, November 1994,
2166 <https://www.rfc-editor.org/info/rfc1713>.
2168 [RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
2169 DOI 10.17487/RFC1995, August 1996,
2170 <https://www.rfc-editor.org/info/rfc1995>.
2172 [RFC2775] Carpenter, B., "Internet Transparency", RFC 2775,
2173 DOI 10.17487/RFC2775, February 2000,
2174 <https://www.rfc-editor.org/info/rfc2775>.
2176 [RFC3172] Huston, G., Ed., "Management Guidelines & Operational
2177 Requirements for the Address and Routing Parameter Area
2178 Domain ("arpa")", BCP 52, RFC 3172, DOI 10.17487/RFC3172,
2179 September 2001, <https://www.rfc-editor.org/info/rfc3172>.
2186Hoffman, et al. Best Current Practice [Page 39]
2188RFC 8499 DNS Terminology January 2019
2191 [RFC3425] Lawrence, D., "Obsoleting IQUERY", RFC 3425,
2192 DOI 10.17487/RFC3425, November 2002,
2193 <https://www.rfc-editor.org/info/rfc3425>.
2195 [RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and
2196 W. Stevens, "Basic Socket Interface Extensions for IPv6",
2197 RFC 3493, DOI 10.17487/RFC3493, February 2003,
2198 <https://www.rfc-editor.org/info/rfc3493>.
2200 [RFC3757] Kolkman, O., Schlyter, J., and E. Lewis, "Domain Name
2201 System KEY (DNSKEY) Resource Record (RR) Secure Entry
2202 Point (SEP) Flag", RFC 3757, DOI 10.17487/RFC3757, April
2203 2004, <https://www.rfc-editor.org/info/rfc3757>.
2205 [RFC3912] Daigle, L., "WHOIS Protocol Specification", RFC 3912,
2206 DOI 10.17487/RFC3912, September 2004,
2207 <https://www.rfc-editor.org/info/rfc3912>.
2209 [RFC4641] Kolkman, O. and R. Gieben, "DNSSEC Operational Practices",
2210 RFC 4641, DOI 10.17487/RFC4641, September 2006,
2211 <https://www.rfc-editor.org/info/rfc4641>.
2213 [RFC4697] Larson, M. and P. Barber, "Observed DNS Resolution
2214 Misbehavior", BCP 123, RFC 4697, DOI 10.17487/RFC4697,
2215 October 2006, <https://www.rfc-editor.org/info/rfc4697>.
2217 [RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast
2218 Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786,
2219 December 2006, <https://www.rfc-editor.org/info/rfc4786>.
2221 [RFC4956] Arends, R., Kosters, M., and D. Blacka, "DNS Security
2222 (DNSSEC) Opt-In", RFC 4956, DOI 10.17487/RFC4956, July
2223 2007, <https://www.rfc-editor.org/info/rfc4956>.
2225 [RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines",
2226 BCP 152, RFC 5625, DOI 10.17487/RFC5625, August 2009,
2227 <https://www.rfc-editor.org/info/rfc5625>.
2229 [RFC5890] Klensin, J., "Internationalized Domain Names for
2230 Applications (IDNA): Definitions and Document Framework",
2231 RFC 5890, DOI 10.17487/RFC5890, August 2010,
2232 <https://www.rfc-editor.org/info/rfc5890>.
2234 [RFC5891] Klensin, J., "Internationalized Domain Names in
2235 Applications (IDNA): Protocol", RFC 5891,
2236 DOI 10.17487/RFC5891, August 2010,
2237 <https://www.rfc-editor.org/info/rfc5891>.
2242Hoffman, et al. Best Current Practice [Page 40]
2244RFC 8499 DNS Terminology January 2019
2247 [RFC5892] Faltstrom, P., Ed., "The Unicode Code Points and
2248 Internationalized Domain Names for Applications (IDNA)",
2249 RFC 5892, DOI 10.17487/RFC5892, August 2010,
2250 <https://www.rfc-editor.org/info/rfc5892>.
2252 [RFC5893] Alvestrand, H., Ed. and C. Karp, "Right-to-Left Scripts
2253 for Internationalized Domain Names for Applications
2254 (IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010,
2255 <https://www.rfc-editor.org/info/rfc5893>.
2257 [RFC5894] Klensin, J., "Internationalized Domain Names for
2258 Applications (IDNA): Background, Explanation, and
2259 Rationale", RFC 5894, DOI 10.17487/RFC5894, August 2010,
2260 <https://www.rfc-editor.org/info/rfc5894>.
2262 [RFC6055] Thaler, D., Klensin, J., and S. Cheshire, "IAB Thoughts on
2263 Encodings for Internationalized Domain Names", RFC 6055,
2264 DOI 10.17487/RFC6055, February 2011,
2265 <https://www.rfc-editor.org/info/rfc6055>.
2267 [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
2268 DOI 10.17487/RFC6265, April 2011,
2269 <https://www.rfc-editor.org/info/rfc6265>.
2271 [RFC6303] Andrews, M., "Locally Served DNS Zones", BCP 163,
2272 RFC 6303, DOI 10.17487/RFC6303, July 2011,
2273 <https://www.rfc-editor.org/info/rfc6303>.
2275 [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
2276 Cheshire, "Internet Assigned Numbers Authority (IANA)
2277 Procedures for the Management of the Service Name and
2278 Transport Protocol Port Number Registry", BCP 165,
2279 RFC 6335, DOI 10.17487/RFC6335, August 2011,
2280 <https://www.rfc-editor.org/info/rfc6335>.
2282 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in
2283 Internationalization in the IETF", BCP 166, RFC 6365,
2284 DOI 10.17487/RFC6365, September 2011,
2285 <https://www.rfc-editor.org/info/rfc6365>.
2287 [RFC6672] Rose, S. and W. Wijngaards, "DNAME Redirection in the
2288 DNS", RFC 6672, DOI 10.17487/RFC6672, June 2012,
2289 <https://www.rfc-editor.org/info/rfc6672>.
2291 [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
2292 DOI 10.17487/RFC6762, February 2013,
2293 <https://www.rfc-editor.org/info/rfc6762>.
2298Hoffman, et al. Best Current Practice [Page 41]
2300RFC 8499 DNS Terminology January 2019
2303 [RFC7129] Gieben, R. and W. Mekking, "Authenticated Denial of
2304 Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129,
2305 February 2014, <https://www.rfc-editor.org/info/rfc7129>.
2307 [RFC7480] Newton, A., Ellacott, B., and N. Kong, "HTTP Usage in the
2308 Registration Data Access Protocol (RDAP)", RFC 7480,
2309 DOI 10.17487/RFC7480, March 2015,
2310 <https://www.rfc-editor.org/info/rfc7480>.
2312 [RFC7481] Hollenbeck, S. and N. Kong, "Security Services for the
2313 Registration Data Access Protocol (RDAP)", RFC 7481,
2314 DOI 10.17487/RFC7481, March 2015,
2315 <https://www.rfc-editor.org/info/rfc7481>.
2317 [RFC7482] Newton, A. and S. Hollenbeck, "Registration Data Access
2318 Protocol (RDAP) Query Format", RFC 7482,
2319 DOI 10.17487/RFC7482, March 2015,
2320 <https://www.rfc-editor.org/info/rfc7482>.
2322 [RFC7483] Newton, A. and S. Hollenbeck, "JSON Responses for the
2323 Registration Data Access Protocol (RDAP)", RFC 7483,
2324 DOI 10.17487/RFC7483, March 2015,
2325 <https://www.rfc-editor.org/info/rfc7483>.
2327 [RFC7484] Blanchet, M., "Finding the Authoritative Registration Data
2328 (RDAP) Service", RFC 7484, DOI 10.17487/RFC7484, March
2329 2015, <https://www.rfc-editor.org/info/rfc7484>.
2331 [RFC7485] Zhou, L., Kong, N., Shen, S., Sheng, S., and A. Servin,
2332 "Inventory and Analysis of WHOIS Registration Objects",
2333 RFC 7485, DOI 10.17487/RFC7485, March 2015,
2334 <https://www.rfc-editor.org/info/rfc7485>.
2336 [RFC7793] Andrews, M., "Adding 100.64.0.0/10 Prefixes to the IPv4
2337 Locally-Served DNS Zones Registry", BCP 163, RFC 7793,
2338 DOI 10.17487/RFC7793, May 2016,
2339 <https://www.rfc-editor.org/info/rfc7793>.
2341 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
2342 and P. Hoffman, "Specification for DNS over Transport
2343 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2344 2016, <https://www.rfc-editor.org/info/rfc7858>.
2346 [RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
2347 Transport Layer Security (DTLS)", RFC 8094,
2348 DOI 10.17487/RFC8094, February 2017,
2349 <https://www.rfc-editor.org/info/rfc8094>.
2354Hoffman, et al. Best Current Practice [Page 42]
2356RFC 8499 DNS Terminology January 2019
2359 [RFC8109] Koch, P., Larson, M., and P. Hoffman, "Initializing a DNS
2360 Resolver with Priming Queries", BCP 209, RFC 8109,
2361 DOI 10.17487/RFC8109, March 2017,
2362 <https://www.rfc-editor.org/info/rfc8109>.
2364 [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
2365 (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
2366 <https://www.rfc-editor.org/info/rfc8484>.
2368 [RSSAC026] Root Server System Advisory Committee (RSSAC), "RSSAC
2370 <https://www.icann.org/en/system/files/files/
2371 rssac-026-14mar17-en.pdf>.
2410Hoffman, et al. Best Current Practice [Page 43]
2412RFC 8499 DNS Terminology January 2019
2415Appendix A. Definitions Updated by This Document
2417 The following definitions from RFCs are updated by this document:
2419 o Forwarder in [RFC2308]
2421 o QNAME in [RFC2308]
2423 o Secure Entry Point (SEP) in [RFC3757]; note, however, that this
2424 RFC is already obsolete (see [RFC4033], [RFC4034], [RFC4035]).
2426Appendix B. Definitions First Defined in This Document
2428 The following definitions are first defined in this document:
2430 o "Alias" in Section 2
2432 o "Apex" in Section 7
2434 o "arpa" in Section 7
2436 o "Bailiwick" in Section 7
2438 o "Class independent" in Section 5
2440 o "Delegation-centric zone" in Section 7
2442 o "Delegation" in Section 7
2444 o "DNS operator" in Section 9
2446 o "DNSSEC-aware" in Section 10
2448 o "DNSSEC-unaware" in Section 10
2450 o "Forwarding" in Section 6
2452 o "Full resolver" in Section 6
2454 o "Fully-qualified domain name" in Section 2
2456 o "Global DNS" in Section 2
2458 o "Hardware Security Module (HSM)" in Section 10
2460 o "Host name" in Section 2
2462 o "IDN" in Section 2
2466Hoffman, et al. Best Current Practice [Page 44]
2468RFC 8499 DNS Terminology January 2019
2471 o "In-bailiwick" in Section 7
2473 o "Iterative resolution" in Section 6
2475 o "Label" in Section 2
2477 o "Locally served DNS zone" in Section 2
2479 o "Naming system" in Section 2
2481 o "Negative response" in Section 3
2483 o "Non-recursive query" in Section 6
2485 o "Open resolver" in Section 6
2487 o "Out-of-bailiwick" in Section 7
2489 o "Passive DNS" in Section 6
2491 o "Policy-implementing resolver" in Section 6
2493 o "Presentation format" in Section 5
2495 o "Priming" in Section 6
2497 o "Private DNS" in Section 2
2499 o "Recursive resolver" in Section 6
2501 o "Referrals" in Section 4
2503 o "Registrant" in Section 9
2505 o "Registrar" in Section 9
2507 o "Registry" in Section 9
2509 o "Root zone" in Section 7
2511 o "Secure Entry Point (SEP)" in Section 10
2513 o "Signing software" in Section 10
2515 o "Split DNS" in Section 6
2517 o "Stub resolver" in Section 6
2522Hoffman, et al. Best Current Practice [Page 45]
2524RFC 8499 DNS Terminology January 2019
2527 o "Subordinate" in Section 8
2529 o "Superordinate" in Section 8
2531 o "TLD" in Section 2
2533 o "Validating resolver" in Section 10
2535 o "Validation" in Section 10
2537 o "View" in Section 6
2539 o "Zone transfer" in Section 6
2549 Authoritative data 24
2550 Authoritative server 19
2551 Authoritative-only server 19
2552 arpa: Address and Routing Parameter Area Domain 26
2559 Class independent 16
2561 Closest provable encloser 27
2562 Combined signing key (CSK) 33
2566 DNSSEC Policy (DP) 34
2567 DNSSEC Practice Statement (DPS) 34
2568 DNSSEC-aware and DNSSEC-unaware 30
2570 Delegation-centric zone 26
2578Hoffman, et al. Best Current Practice [Page 46]
2580RFC 8499 DNS Terminology January 2019
2586 Empty non-terminals (ENT) 26
2595 Full-service resolver 18
2596 Fully-qualified domain name (FQDN) 8
2603 Hardware security module (HSM) 34
2610 Insecure delegation 31
2612 Internationalized Domain Name 9
2614 Iterative resolution 18
2617 Key signing key (KSK) 33
2622 Locally served DNS zone 8
2634Hoffman, et al. Best Current Practice [Page 47]
2636RFC 8499 DNS Terminology January 2019
2649 Negative response 11
2651 Non-recursive query 18
2665 Policy-implementing resolver 21
2666 Presentation format 14
2670 Privacy-enabling DNS server 22
2684 Recursive resolver 17
2690Hoffman, et al. Best Current Practice [Page 48]
2692RFC 8499 DNS Terminology January 2019
2698 Reverse DNS, reverse lookup 26
2707 Secure Entry Point (SEP) 33
2712 Source of Synthesis 28
2714 Split-horizon DNS 21
2730 Validating resolver 33
2737 Wildcard domain name 27
2746Hoffman, et al. Best Current Practice [Page 49]
2748RFC 8499 DNS Terminology January 2019
2755 Zone signing key (ZSK) 33
2760 The following is the Acknowledgements section of RFC 7719.
2762 The authors gratefully acknowledge all of the authors of DNS-
2763 related RFCs that proceed this one. Comments from Tony Finch,
2764 Stephane Bortzmeyer, Niall O'Reilly, Colm MacCarthaigh, Ray
2765 Bellis, John Kristoff, Robert Edmonds, Paul Wouters, Shumon Huque,
2766 Paul Ebersman, David Lawrence, Matthijs Mekking, Casey Deccio, Bob
2767 Harold, Ed Lewis, John Klensin, David Black, and many others in
2768 the DNSOP Working Group helped shape RFC 7719.
2770 Most of the major changes between RFC 7719 and this document came
2771 from active discussion on the DNSOP WG. Specific people who
2772 contributed material to this document include: Bob Harold, Dick
2773 Franks, Evan Hunt, John Dickinson, Mark Andrews, Martin Hoffmann,
2774 Paul Vixie, Peter Koch, Duane Wessels, Allison Mankin, Giovane Moura,
2775 Roni Even, Dan Romascanu, and Vladmir Cunat.
2782 Email: paul.hoffman@icann.org
2787 Email: ajs@anvilwalrusden.com
2791 Japan Registry Services Co., Ltd.
2792 Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda
2793 Chiyoda-ku, Tokyo 101-0065
2796 Phone: +81 3 5215 8451
2797 Email: fujiwara@jprs.co.jp
2802Hoffman, et al. Best Current Practice [Page 50]