1 Internet Engineering Task Force (IETF) P. Hoffman
2 Request for Comments: 8499 ICANN
3 BCP: 219 A. Sullivan
4 Obsoletes: 7719
5 Updates: 2308 K. Fujiwara
6 Category: Best Current Practice JPRS
7 ISSN: 2070-1721 January 2019
8
9
10 DNS Terminology
11
12 Abstract
13
14 The Domain Name System (DNS) is defined in literally dozens of
15 different RFCs. The terminology used by implementers and developers
16 of DNS protocols, and by operators of DNS systems, has sometimes
17 changed in the decades since the DNS was first defined. This
18 document gives current definitions for many of the terms used in the
19 DNS in a single document.
20
21 This document obsoletes RFC 7719 and updates RFC 2308.
22
23 Status of This Memo
24
25 This memo documents an Internet Best Current Practice.
26
27 This document is a product of the Internet Engineering Task Force
28 (IETF). It represents the consensus of the IETF community. It has
29 received public review and has been approved for publication by the
30 Internet Engineering Steering Group (IESG). Further information on
31 BCPs is available in Section 2 of RFC 7841.
32
33 Information about the current status of this document, any errata,
34 and how to provide feedback on it may be obtained at
35 https://www.rfc-editor.org/info/rfc8499.
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53 RFC 8499 DNS Terminology January 2019
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56 Copyright Notice
57
58 Copyright (c) 2019 IETF Trust and the persons identified as the
59 document authors. All rights reserved.
60
61 This document is subject to BCP 78 and the IETF Trust's Legal
62 Provisions Relating to IETF Documents
63 (https://trustee.ietf.org/license-info) in effect on the date of
64 publication of this document. Please review these documents
65 carefully, as they describe your rights and restrictions with respect
66 to this document. Code Components extracted from this document must
67 include Simplified BSD License text as described in Section 4.e of
68 the Trust Legal Provisions and are provided without warranty as
69 described in the Simplified BSD License.
70
71 Table of Contents
72
73 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
74 2. Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
75 3. DNS Response Codes . . . . . . . . . . . . . . . . . . . . . 10
76 4. DNS Transactions . . . . . . . . . . . . . . . . . . . . . . 11
77 5. Resource Records . . . . . . . . . . . . . . . . . . . . . . 14
78 6. DNS Servers and Clients . . . . . . . . . . . . . . . . . . . 16
79 7. Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
80 8. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . . . 27
81 9. Registration Model . . . . . . . . . . . . . . . . . . . . . 28
82 10. General DNSSEC . . . . . . . . . . . . . . . . . . . . . . . 30
83 11. DNSSEC States . . . . . . . . . . . . . . . . . . . . . . . . 34
84 12. Security Considerations . . . . . . . . . . . . . . . . . . . 36
85 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
86 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
87 14.1. Normative References . . . . . . . . . . . . . . . . . . 36
88 14.2. Informative References . . . . . . . . . . . . . . . . . 39
89 Appendix A. Definitions Updated by This Document . . . . . . . . 44
90 Appendix B. Definitions First Defined in This Document . . . . . 44
91 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
92 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 50
93 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50
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110
111 1. Introduction
112
113 The Domain Name System (DNS) is a simple query-response protocol
114 whose messages in both directions have the same format. (Section 2
115 gives a definition of "public DNS", which is often what people mean
116 when they say "the DNS".) The protocol and message format are
117 defined in [RFC1034] and [RFC1035]. These RFCs defined some terms,
118 and later documents defined others. Some of the terms from [RFC1034]
119 and [RFC1035] have somewhat different meanings now than they did in
120 1987.
121
122 This document contains a collection of a wide variety of DNS-related
123 terms, organized loosely by topic. Some of them have been precisely
124 defined in earlier RFCs, some have been loosely defined in earlier
125 RFCs, and some are not defined in an earlier RFC at all.
126
127 Other organizations sometimes define DNS-related terms their own way.
128 For example, the WHATWG defines "domain" at
129 <https://url.spec.whatwg.org/>. The Root Server System Advisory
130 Committee (RSSAC) has a good lexicon [RSSAC026].
131
132 Most of the definitions listed here represent the consensus
133 definition of the DNS community -- both protocol developers and
134 operators. Some of the definitions differ from earlier RFCs, and
135 those differences are noted. In this document, where the consensus
136 definition is the same as the one in an RFC, that RFC is quoted.
137 Where the consensus definition has changed somewhat, the RFC is
138 mentioned but the new stand-alone definition is given. See
139 Appendix A for a list of the definitions that this document updates.
140
141 It is important to note that, during the development of this
142 document, it became clear that some DNS-related terms are interpreted
143 quite differently by different DNS experts. Further, some terms that
144 are defined in early DNS RFCs now have definitions that are generally
145 agreed to, but that are different from the original definitions.
146 Therefore, this document is a substantial revision to [RFC7719].
147
148 Note that there is no single consistent definition of "the DNS". It
149 can be considered to be some combination of the following: a commonly
150 used naming scheme for objects on the Internet; a distributed
151 database representing the names and certain properties of these
152 objects; an architecture providing distributed maintenance,
153 resilience, and loose coherency for this database; and a simple
154 query-response protocol (as mentioned below) implementing this
155 architecture. Section 2 defines "global DNS" and "private DNS" as a
156 way to deal with these differing definitions.
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165
166 Capitalization in DNS terms is often inconsistent among RFCs and
167 various DNS practitioners. The capitalization used in this document
168 is a best guess at current practices, and is not meant to indicate
169 that other capitalization styles are wrong or archaic. In some
170 cases, multiple styles of capitalization are used for the same term
171 due to quoting from different RFCs.
172
173 Readers should note that the terms in this document are grouped by
174 topic. Someone who is not already familiar with the DNS probably
175 cannot learn about the DNS from scratch by reading this document from
176 front to back. Instead, skipping around may be the only way to get
177 enough context to understand some of the definitions. This document
178 has an index that might be useful for readers who are attempting to
179 learn the DNS by reading this document.
180
181 2. Names
182
183 Naming system: A naming system associates names with data. Naming
184 systems have many significant facets that help differentiate them
185 from each other. Some commonly identified facets include:
186
187 * Composition of names
188
189 * Format of names
190
191 * Administration of names
192
193 * Types of data that can be associated with names
194
195 * Types of metadata for names
196
197 * Protocol for getting data from a name
198
199 * Context for resolving a name
200
201 Note that this list is a small subset of facets that people have
202 identified over time for naming systems, and the IETF has yet to
203 agree on a good set of facets that can be used to compare naming
204 systems. For example, other facets might include "protocol to
205 update data in a name", "privacy of names", and "privacy of data
206 associated with names", but those are not as well defined as the
207 ones listed above. The list here is chosen because it helps
208 describe the DNS and naming systems similar to the DNS.
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220
221 Domain name: An ordered list of one or more labels.
222
223 Note that this is a definition independent of the DNS RFCs
224 ([RFC1034] and [RFC1035]), and the definition here also applies to
225 systems other than the DNS. [RFC1034] defines the "domain name
226 space" using mathematical trees and their nodes in graph theory,
227 and that definition has the same practical result as the
228 definition here. Any path of a directed acyclic graph can be
229 represented by a domain name consisting of the labels of its
230 nodes, ordered by decreasing distance from the root(s) (which is
231 the normal convention within the DNS, including this document). A
232 domain name whose last label identifies a root of the graph is
233 fully qualified; other domain names whose labels form a strict
234 prefix of a fully-qualified domain name are relative to its first
235 omitted node.
236
237 Also note that different IETF and non-IETF documents have used the
238 term "domain name" in many different ways. It is common for
239 earlier documents to use "domain name" to mean "names that match
240 the syntax in [RFC1035]", but possibly with additional rules such
241 as "and are, or will be, resolvable in the global DNS" or "but
242 only using the presentation format".
243
244 Label: An ordered list of zero or more octets that makes up a
245 portion of a domain name. Using graph theory, a label identifies
246 one node in a portion of the graph of all possible domain names.
247
248 Global DNS: Using the short set of facets listed in "Naming system",
249 the global DNS can be defined as follows. Most of the rules here
250 come from [RFC1034] and [RFC1035], although the term "global DNS"
251 has not been defined before now.
252
253 Composition of names: A name in the global DNS has one or more
254 labels. The length of each label is between 0 and 63 octets
255 inclusive. In a fully-qualified domain name, the last label in
256 the ordered list is 0 octets long; it is the only label whose
257 length may be 0 octets, and it is called the "root" or "root
258 label". A domain name in the global DNS has a maximum total
259 length of 255 octets in the wire format; the root represents one
260 octet for this calculation. (Multicast DNS [RFC6762] allows names
261 up to 255 bytes plus a terminating zero byte based on a different
262 interpretation of RFC 1035 and what is included in the 255
263 octets.)
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275
276 Format of names: Names in the global DNS are domain names. There
277 are three formats: wire format, presentation format, and common
278 display.
279
280 The basic wire format for names in the global DNS is a list of
281 labels ordered by decreasing distance from the root, with the
282 root label last. Each label is preceded by a length octet.
283 [RFC1035] also defines a compression scheme that modifies this
284 format.
285
286 The presentation format for names in the global DNS is a list
287 of labels ordered by decreasing distance from the root, encoded
288 as ASCII, with a "." character between each label. In
289 presentation format, a fully-qualified domain name includes the
290 root label and the associated separator dot. For example, in
291 presentation format, a fully-qualified domain name with two
292 non-root labels is always shown as "example.tld." instead of
293 "example.tld". [RFC1035] defines a method for showing octets
294 that do not display in ASCII.
295
296 The common display format is used in applications and free
297 text. It is the same as the presentation format, but showing
298 the root label and the "." before it is optional and is rarely
299 done. For example, in common display format, a fully-qualified
300 domain name with two non-root labels is usually shown as
301 "example.tld" instead of "example.tld.". Names in the common
302 display format are normally written such that the
303 directionality of the writing system presents labels by
304 decreasing distance from the root (so, in both English and the
305 C programming language the root or Top-Level Domain (TLD) label
306 in the ordered list is rightmost; but in Arabic, it may be
307 leftmost, depending on local conventions).
308
309 Administration of names: Administration is specified by delegation
310 (see the definition of "delegation" in Section 7). Policies for
311 administration of the root zone in the global DNS are determined
312 by the names operational community, which convenes itself in the
313 Internet Corporation for Assigned Names and Numbers (ICANN). The
314 names operational community selects the IANA Functions Operator
315 for the global DNS root zone. At the time of writing, that
316 operator is Public Technical Identifiers (PTI). (See
317 <https://pti.icann.org/> for more information about PTI operating
318 the IANA Functions.) The name servers that serve the root zone
319 are provided by independent root operators. Other zones in the
320 global DNS have their own policies for administration.
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330
331 Types of data that can be associated with names: A name can have
332 zero or more resource records associated with it. There are
333 numerous types of resource records with unique data structures
334 defined in many different RFCs and in the IANA registry at
335 [IANA_Resource_Registry].
336
337 Types of metadata for names: Any name that is published in the DNS
338 appears as a set of resource records (see the definition of
339 "RRset" in Section 5). Some names do not, themselves, have data
340 associated with them in the DNS, but they "appear" in the DNS
341 anyway because they form part of a longer name that does have data
342 associated with it (see the definition of "empty non-terminals" in
343 Section 7).
344
345 Protocol for getting data from a name: The protocol described in
346 [RFC1035].
347
348 Context for resolving a name: The global DNS root zone distributed
349 by PTI.
350
351 Private DNS: Names that use the protocol described in [RFC1035] but
352 that do not rely on the global DNS root zone or names that are
353 otherwise not generally available on the Internet but are using
354 the protocol described in [RFC1035]. A system can use both the
355 global DNS and one or more private DNS systems; for example, see
356 "Split DNS" in Section 6.
357
358 Note that domain names that do not appear in the DNS, and that are
359 intended never to be looked up using the DNS protocol, are not
360 part of the global DNS or a private DNS even though they are
361 domain names.
362
363 Multicast DNS (mDNS): "Multicast DNS (mDNS) provides the ability to
364 perform DNS-like operations on the local link in the absence of
365 any conventional Unicast DNS server. In addition, Multicast DNS
366 designates a portion of the DNS namespace to be free for local
367 use, without the need to pay any annual fee, and without the need
368 to set up delegations or otherwise configure a conventional DNS
369 server to answer for those names." (Quoted from [RFC6762],
370 Abstract) Although it uses a compatible wire format, mDNS is,
371 strictly speaking, a different protocol than DNS. Also, where the
372 above quote says "a portion of the DNS namespace", it would be
373 clearer to say "a portion of the domain name space". The names in
374 mDNS are not intended to be looked up in the DNS.
375
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385
386 Locally served DNS zone: A locally served DNS zone is a special case
387 of private DNS. Names are resolved using the DNS protocol in a
388 local context. [RFC6303] defines subdomains of IN-ADDR.ARPA that
389 are locally served zones. Resolution of names through locally
390 served zones may result in ambiguous results. For example, the
391 same name may resolve to different results in different locally
392 served DNS zone contexts. The context for a locally served DNS
393 zone may be explicit, such as those that are listed in [RFC6303]
394 and [RFC7793], or implicit, such as those defined by local DNS
395 administration and not known to the resolution client.
396
397 Fully-Qualified Domain Name (FQDN): This is often just a clear way
398 of saying the same thing as "domain name of a node", as outlined
399 above. However, the term is ambiguous. Strictly speaking, a
400 fully-qualified domain name would include every label, including
401 the zero-length label of the root: such a name would be written
402 "www.example.net." (note the terminating dot). But, because every
403 name eventually shares the common root, names are often written
404 relative to the root (such as "www.example.net") and are still
405 called "fully qualified". This term first appeared in [RFC819].
406 In this document, names are often written relative to the root.
407
408 The need for the term "fully-qualified domain name" comes from the
409 existence of partially qualified domain names, which are names
410 where one or more of the last labels in the ordered list are
411 omitted (for example, a domain name of "www" relative to
412 "example.net" identifies "www.example.net"). Such relative names
413 are understood only by context.
414
415 Host name: This term and its equivalent, "hostname", have been
416 widely used but are not defined in [RFC1034], [RFC1035],
417 [RFC1123], or [RFC2181]. The DNS was originally deployed into the
418 Host Tables environment as outlined in [RFC952], and it is likely
419 that the term followed informally from the definition there. Over
420 time, the definition seems to have shifted. "Host name" is often
421 meant to be a domain name that follows the rules in Section 3.5 of
422 [RFC1034], which is also called the "preferred name syntax". (In
423 that syntax, every character in each label is a letter, a digit,
424 or a hyphen). Note that any label in a domain name can contain
425 any octet value; hostnames are generally considered to be domain
426 names where every label follows the rules in the "preferred name
427 syntax", with the amendment that labels can start with ASCII
428 digits (this amendment comes from Section 2.1 of [RFC1123]).
429
430 People also sometimes use the term "hostname" to refer to just the
431 first label of an FQDN, such as "printer" in
432 "printer.admin.example.com". (Sometimes this is formalized in
433 configuration in operating systems.) In addition, people
434
435
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441 sometimes use this term to describe any name that refers to a
442 machine, and those might include labels that do not conform to the
443 "preferred name syntax".
444
445 Top-Level Domain (TLD): A Top-Level Domain is a zone that is one
446 layer below the root, such as "com" or "jp". There is nothing
447 special, from the point of view of the DNS, about TLDs. Most of
448 them are also delegation-centric zones (defined in Section 7), and
449 there are significant policy issues around their operation. TLDs
450 are often divided into sub-groups such as Country Code Top-Level
451 Domains (ccTLDs), Generic Top-Level Domains (gTLDs), and others;
452 the division is a matter of policy and beyond the scope of this
453 document.
454
455 Internationalized Domain Name (IDN): The Internationalized Domain
456 Names for Applications (IDNA) protocol is the standard mechanism
457 for handling domain names with non-ASCII characters in
458 applications in the DNS. The current standard at the time of this
459 writing, normally called "IDNA2008", is defined in [RFC5890],
460 [RFC5891], [RFC5892], [RFC5893], and [RFC5894]. These documents
461 define many IDN-specific terms such as "LDH label", "A-label", and
462 "U-label". [RFC6365] defines more terms that relate to
463 internationalization (some of which relate to IDNs); [RFC6055] has
464 a much more extensive discussion of IDNs, including some new
465 terminology.
466
467 Subdomain: "A domain is a subdomain of another domain if it is
468 contained within that domain. This relationship can be tested by
469 seeing if the subdomain's name ends with the containing domain's
470 name." (Quoted from [RFC1034], Section 3.1) For example, in the
471 host name "nnn.mmm.example.com", both "mmm.example.com" and
472 "nnn.mmm.example.com" are subdomains of "example.com". Note that
473 the comparisons here are done on whole labels; that is,
474 "ooo.example.com" is not a subdomain of "oo.example.com".
475
476 Alias: The owner of a CNAME resource record, or a subdomain of the
477 owner of a DNAME resource record (DNAME records are defined in
478 [RFC6672]). See also "canonical name".
479
480 Canonical name: A CNAME resource record "identifies its owner name
481 as an alias, and specifies the corresponding canonical name in the
482 RDATA section of the RR." (Quoted from [RFC1034], Section 3.6.2)
483 This usage of the word "canonical" is related to the mathematical
484 concept of "canonical form".
485
486
487
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496 CNAME: "It has been traditional to refer to the [owner] of a CNAME
497 record as 'a CNAME'. This is unfortunate, as 'CNAME' is an
498 abbreviation of 'canonical name', and the [owner] of a CNAME
499 record is most certainly not a canonical name." (Quoted from
500 [RFC2181], Section 10.1.1. The quoted text has been changed from
501 "label" to "owner".)
502
503 3. DNS Response Codes
504
505 Some of the response codes (RCODEs) that are defined in [RFC1035]
506 have acquired their own shorthand names. All of the RCODEs are
507 listed at [IANA_Resource_Registry], although that list uses mixed-
508 case capitalization, while most documents use all caps. Some of the
509 common names for values defined in [RFC1035] are described in this
510 section. This section also includes an additional RCODE and a
511 general definition. The official list of all RCODEs is in the IANA
512 registry.
513
514 NOERROR: This RCODE appears as "No error condition" in Section 4.1.1
515 of [RFC1035].
516
517 FORMERR: This RCODE appears as "Format error - The name server was
518 unable to interpret the query" in Section 4.1.1 of [RFC1035].
519
520 SERVFAIL: This RCODE appears as "Server failure - The name server
521 was unable to process this query due to a problem with the name
522 server" in Section 4.1.1 of [RFC1035].
523
524 NXDOMAIN: This RCODE appears as "Name Error [...] this code
525 signifies that the domain name referenced in the query does not
526 exist." in Section 4.1.1 of [RFC1035]. [RFC2308] established
527 NXDOMAIN as a synonym for Name Error.
528
529 NOTIMP: This RCODE appears as "Not Implemented - The name server
530 does not support the requested kind of query" in Section 4.1.1 of
531 [RFC1035].
532
533 REFUSED: This RCODE appears as "Refused - The name server refuses to
534 perform the specified operation for policy reasons. For example,
535 a name server may not wish to provide the information to the
536 particular requester, or a name server may not wish to perform a
537 particular operation (e.g., zone transfer) for particular data."
538 in Section 4.1.1 of [RFC1035].
539
540 NODATA: "A pseudo RCODE which indicates that the name is valid, for
541 the given class, but [there] are no records of the given type. A
542 NODATA response has to be inferred from the answer." (Quoted from
543 [RFC2308], Section 1) "NODATA is indicated by an answer with the
544
545
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550
551 RCODE set to NOERROR and no relevant answers in the Answer
552 section. The authority section will contain an SOA record, or
553 there will be no NS records there." (Quoted from [RFC2308],
554 Section 2.2) Note that referrals have a similar format to NODATA
555 replies; [RFC2308] explains how to distinguish them.
556
557 The term "NXRRSET" is sometimes used as a synonym for NODATA.
558 However, this is a mistake, given that NXRRSET is a specific error
559 code defined in [RFC2136].
560
561 Negative response: A response that indicates that a particular RRset
562 does not exist or whose RCODE indicates that the nameserver cannot
563 answer. Sections 2 and 7 of [RFC2308] describe the types of
564 negative responses in detail.
565
566 4. DNS Transactions
567
568 The header of a DNS message is its first 12 octets. Many of the
569 fields and flags in the diagrams in Sections 4.1.1 through 4.1.3 of
570 [RFC1035] are referred to by their names in each diagram. For
571 example, the response codes are called "RCODEs", the data for a
572 record is called the "RDATA", and the authoritative answer bit is
573 often called "the AA flag" or "the AA bit".
574
575 Class: A class "identifies a protocol family or instance of a
576 protocol". (Quoted from [RFC1034], Section 3.6) "The DNS tags all
577 data with a class as well as the type, so that we can allow
578 parallel use of different formats for data of type address."
579 (Quoted from [RFC1034], Section 2.2) In practice, the class for
580 nearly every query is "IN" (the Internet). There are some queries
581 for "CH" (the Chaos class), but they are usually for the purposes
582 of information about the server itself rather than for a different
583 type of address.
584
585 QNAME: The most commonly used rough definition is that the QNAME is
586 a field in the Question section of a query. "A standard query
587 specifies a target domain name (QNAME), query type (QTYPE), and
588 query class (QCLASS) and asks for RRs which match." (Quoted from
589 [RFC1034], Section 3.7.1) Strictly speaking, the definition comes
590 from [RFC1035], Section 4.1.2, where the QNAME is defined in
591 respect of the Question section. This definition appears to be
592 applied consistently: the discussion of inverse queries in
593 Section 6.4.1 refers to the "owner name of the query RR and its
594 TTL", because inverse queries populate the Answer section and
595 leave the Question section empty. (Inverse queries are deprecated
596 in [RFC3425]; thus, relevant definitions do not appear in this
597 document.)
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605
606 However, [RFC2308] has an alternate definition that puts the QNAME
607 in the answer (or series of answers) instead of the query. It
608 defines QNAME as "...the name in the query section of an answer,
609 or where this resolves to a CNAME, or CNAME chain, the data field
610 of the last CNAME. The last CNAME in this sense is that which
611 contains a value which does not resolve to another CNAME." This
612 definition has a certain internal logic, because of the way CNAME
613 substitution works and the definition of CNAME. If a name server
614 does not find an RRset that matches a query, but does find the
615 same name in the same class with a CNAME record, then the name
616 server "includes the CNAME record in the response and restarts the
617 query at the domain name specified in the data field of the CNAME
618 record." (Quoted from [RFC1034], Section 3.6.2) This is made
619 explicit in the resolution algorithm outlined in Section 4.3.2 of
620 [RFC1034], which says to "change QNAME to the canonical name in
621 the CNAME RR, and go back to step 1" in the case of a CNAME RR.
622 Since a CNAME record explicitly declares that the owner name is
623 canonically named what is in the RDATA, then there is a way to
624 view the new name (i.e., the name that was in the RDATA of the
625 CNAME RR) as also being the QNAME.
626
627 However, this creates a kind of confusion because the response to
628 a query that results in CNAME processing contains in the echoed
629 Question section one QNAME (the name in the original query) and a
630 second QNAME that is in the data field of the last CNAME. The
631 confusion comes from the iterative/recursive mode of resolution,
632 which finally returns an answer that need not actually have the
633 same owner name as the QNAME contained in the original query.
634
635 To address this potential confusion, it is helpful to distinguish
636 between three meanings:
637
638 * QNAME (original): The name actually sent in the Question
639 section in the original query, which is always echoed in the
640 (final) reply in the Question section when the QR bit is set to
641 1.
642
643 * QNAME (effective): A name actually resolved, which is either
644 the name originally queried or a name received in a CNAME chain
645 response.
646
647 * QNAME (final): The name actually resolved, which is either the
648 name actually queried or else the last name in a CNAME chain
649 response.
650
651 Note that, because the definition in [RFC2308] is actually for a
652 different concept than what was in [RFC1034], it would have been
653 better if [RFC2308] had used a different name for that concept.
654
655
656
657 Hoffman, et al. Best Current Practice [Page 12]
658 RFC 8499 DNS Terminology January 2019
659
660
661 In general use today, QNAME almost always means what is defined
662 above as "QNAME (original)".
663
664 Referrals: A type of response in which a server, signaling that it
665 is not (completely) authoritative for an answer, provides the
666 querying resolver with an alternative place to send its query.
667 Referrals can be partial.
668
669 A referral arises when a server is not performing recursive
670 service while answering a query. It appears in step 3(b) of the
671 algorithm in [RFC1034], Section 4.3.2.
672
673 There are two types of referral response. The first is a downward
674 referral (sometimes described as "delegation response"), where the
675 server is authoritative for some portion of the QNAME. The
676 authority section RRset's RDATA contains the name servers
677 specified at the referred-to zone cut. In normal DNS operation,
678 this kind of response is required in order to find names beneath a
679 delegation. The bare use of "referral" means this kind of
680 referral, and many people believe that this is the only legitimate
681 kind of referral in the DNS.
682
683 The second is an upward referral (sometimes described as "root
684 referral"), where the server is not authoritative for any portion
685 of the QNAME. When this happens, the referred-to zone in the
686 authority section is usually the root zone ("."). In normal DNS
687 operation, this kind of response is not required for resolution or
688 for correctly answering any query. There is no requirement that
689 any server send upward referrals. Some people regard upward
690 referrals as a sign of a misconfiguration or error. Upward
691 referrals always need some sort of qualifier (such as "upward" or
692 "root") and are never identified simply by the word "referral".
693
694 A response that has only a referral contains an empty answer
695 section. It contains the NS RRset for the referred-to zone in the
696 Authority section. It may contain RRs that provide addresses in
697 the additional section. The AA bit is clear.
698
699 In the case where the query matches an alias, and the server is
700 not authoritative for the target of the alias but is authoritative
701 for some name above the target of the alias, the resolution
702 algorithm will produce a response that contains both the
703 authoritative answer for the alias and a referral. Such a partial
704 answer and referral response has data in the Answer section. It
705 has the NS RRset for the referred-to zone in the Authority
706 section. It may contain RRs that provide addresses in the
707
708
709
710
711
712 Hoffman, et al. Best Current Practice [Page 13]
713 RFC 8499 DNS Terminology January 2019
714
715
716 additional section. The AA bit is set, because the first name in
717 the Answer section matches the QNAME and the server is
718 authoritative for that answer (see [RFC1035], Section 4.1.1).
719
720 5. Resource Records
721
722 RR: An acronym for resource record. (See [RFC1034], Section 3.6.)
723
724 RRset: A set of resource records "with the same label, class and
725 type, but with different data" (according to [RFC2181],
726 Section 5). Also written as "RRSet" in some documents. As a
727 clarification, "same label" in this definition means "same owner
728 name". In addition, [RFC2181] states that "the TTLs of all RRs in
729 an RRSet must be the same".
730
731 Note that RRSIG resource records do not match this definition.
732 [RFC4035] says:
733
734 An RRset MAY have multiple RRSIG RRs associated with it. Note
735 that as RRSIG RRs are closely tied to the RRsets whose
736 signatures they contain, RRSIG RRs, unlike all other DNS RR
737 types, do not form RRsets. In particular, the TTL values among
738 RRSIG RRs with a common owner name do not follow the RRset
739 rules described in [RFC2181].
740
741 Master file: "Master files are text files that contain RRs in text
742 form. Since the contents of a zone can be expressed in the form
743 of a list of RRs a master file is most often used to define a
744 zone, though it can be used to list a cache's contents." (Quoted
745 from [RFC1035], Section 5) Master files are sometimes called "zone
746 files".
747
748 Presentation format: The text format used in master files. This
749 format is shown but not formally defined in [RFC1034] or
750 [RFC1035]. The term "presentation format" first appears in
751 [RFC4034].
752
753 EDNS: The extension mechanisms for DNS, defined in [RFC6891].
754 Sometimes called "EDNS0" or "EDNS(0)" to indicate the version
755 number. EDNS allows DNS clients and servers to specify message
756 sizes larger than the original 512 octet limit, to expand the
757 response code space and to carry additional options that affect
758 the handling of a DNS query.
759
760 OPT: A pseudo-RR (sometimes called a "meta-RR") that is used only to
761 contain control information pertaining to the question-and-answer
762 sequence of a specific transaction. (Definition paraphrased from
763 [RFC6891], Section 6.1.1.) It is used by EDNS.
764
765
766
767 Hoffman, et al. Best Current Practice [Page 14]
768 RFC 8499 DNS Terminology January 2019
769
770
771 Owner: "The domain name where the RR is found." (Quoted from
772 [RFC1034], Section 3.6) Often appears in the term "owner name".
773
774 SOA field names: DNS documents, including the definitions here,
775 often refer to the fields in the RDATA of an SOA resource record
776 by field name. "SOA" stands for "start of a zone of authority".
777 Those fields are defined in Section 3.3.13 of [RFC1035]. The
778 names (in the order they appear in the SOA RDATA) are MNAME,
779 RNAME, SERIAL, REFRESH, RETRY, EXPIRE, and MINIMUM. Note that the
780 meaning of the MINIMUM field is updated in Section 4 of [RFC2308];
781 the new definition is that the MINIMUM field is only "the TTL to
782 be used for negative responses". This document tends to use field
783 names instead of terms that describe the fields.
784
785 TTL: The maximum "time to live" of a resource record. "A TTL value
786 is an unsigned number, with a minimum value of 0, and a maximum
787 value of 2147483647. That is, a maximum of 2^31 - 1. When
788 transmitted, this value shall be encoded in the less significant
789 31 bits of the 32 bit TTL field, with the most significant, or
790 sign, bit set to zero." (Quoted from [RFC2181], Section 8) (Note
791 that [RFC1035] erroneously stated that this is a signed integer;
792 that was fixed by [RFC2181].)
793
794 The TTL "specifies the time interval that the resource record may
795 be cached before the source of the information should again be
796 consulted." (Quoted from [RFC1035], Section 3.2.1) Section 4.1.3
797 of the same document states: "the time interval (in seconds) that
798 the resource record may be cached before it should be discarded".
799 Despite being defined for a resource record, the TTL of every
800 resource record in an RRset is required to be the same ([RFC2181],
801 Section 5.2).
802
803 The reason that the TTL is the maximum time to live is that a
804 cache operator might decide to shorten the time to live for
805 operational purposes, such as if there is a policy to disallow TTL
806 values over a certain number. Some servers are known to ignore
807 the TTL on some RRsets (such as when the authoritative data has a
808 very short TTL) even though this is against the advice in RFC
809 1035. An RRset can be flushed from the cache before the end of
810 the TTL interval, at which point, the value of the TTL becomes
811 unknown because the RRset with which it was associated no longer
812 exists.
813
814 There is also the concept of a "default TTL" for a zone, which can
815 be a configuration parameter in the server software. This is
816 often expressed by a default for the entire server, and a default
817 for a zone using the $TTL directive in a zone file. The $TTL
818 directive was added to the master file format by [RFC2308].
819
820
821
822 Hoffman, et al. Best Current Practice [Page 15]
823 RFC 8499 DNS Terminology January 2019
824
825
826 Class independent: A resource record type whose syntax and semantics
827 are the same for every DNS class. A resource record type that is
828 not class independent has different meanings depending on the DNS
829 class of the record, or the meaning is undefined for some class.
830 Most resource record types are defined for class 1 (IN, the
831 Internet), but many are undefined for other classes.
832
833 Address records: Records whose type is A or AAAA. [RFC2181]
834 informally defines these as "(A, AAAA, etc)". Note that new types
835 of address records could be defined in the future.
836
837 6. DNS Servers and Clients
838
839 This section defines the terms used for the systems that act as DNS
840 clients, DNS servers, or both. In past RFCs, DNS servers are
841 sometimes called "name servers", "nameservers", or just "servers".
842 There is no formal definition of "DNS server", but RFCs generally
843 assume that it is an Internet server that listens for queries and
844 sends responses using the DNS protocol defined in [RFC1035] and its
845 successors.
846
847 It is important to note that the terms "DNS server" and "name server"
848 require context in order to understand the services being provided.
849 Both authoritative servers and recursive resolvers are often called
850 "DNS servers" and "name servers" even though they serve different
851 roles (but may be part of the same software package).
852
853 For terminology specific to the public DNS root server system, see
854 [RSSAC026]. That document defines terms such as "root server", "root
855 server operator", and terms that are specific to the way that the
856 root zone of the public DNS is served.
857
858 Resolver: A program "that extract[s] information from name servers
859 in response to client requests." (Quoted from [RFC1034],
860 Section 2.4) A resolver performs queries for a name, type, and
861 class, and receives responses. The logical function is called
862 "resolution". In practice, the term is usually referring to some
863 specific type of resolver (some of which are defined below), and
864 understanding the use of the term depends on understanding the
865 context.
866
867 A related term is "resolve", which is not formally defined in
868 [RFC1034] or [RFC1035]. An imputed definition might be "asking a
869 question that consists of a domain name, class, and type, and
870 receiving some sort of response". Similarly, an imputed
871 definition of "resolution" might be "the response received from
872 resolving".
873
874
875
876
877 Hoffman, et al. Best Current Practice [Page 16]
878 RFC 8499 DNS Terminology January 2019
879
880
881 Stub resolver: A resolver that cannot perform all resolution itself.
882 Stub resolvers generally depend on a recursive resolver to
883 undertake the actual resolution function. Stub resolvers are
884 discussed but never fully defined in Section 5.3.1 of [RFC1034].
885 They are fully defined in Section 6.1.3.1 of [RFC1123].
886
887 Iterative mode: A resolution mode of a server that receives DNS
888 queries and responds with a referral to another server.
889 Section 2.3 of [RFC1034] describes this as "The server refers the
890 client to another server and lets the client pursue the query." A
891 resolver that works in iterative mode is sometimes called an
892 "iterative resolver". See also "iterative resolution" later in
893 this section.
894
895 Recursive mode: A resolution mode of a server that receives DNS
896 queries and either responds to those queries from a local cache or
897 sends queries to other servers in order to get the final answers
898 to the original queries. Section 2.3 of [RFC1034] describes this
899 as "the first server pursues the query for the client at another
900 server". Section 4.3.1 of [RFC1034] says: "in [recursive] mode
901 the name server acts in the role of a resolver and returns either
902 an error or the answer, but never referrals." That same section
903 also says:
904
905 The recursive mode occurs when a query with RD set arrives at a
906 server which is willing to provide recursive service; the
907 client can verify that recursive mode was used by checking that
908 both RA and RD are set in the reply.
909
910 A server operating in recursive mode may be thought of as having a
911 name server side (which is what answers the query) and a resolver
912 side (which performs the resolution function). Systems operating
913 in this mode are commonly called "recursive servers". Sometimes
914 they are called "recursive resolvers". In practice, it is not
915 possible to know in advance whether the server that one is
916 querying will also perform recursion; both terms can be observed
917 in use interchangeably.
918
919 Recursive resolver: A resolver that acts in recursive mode. In
920 general, a recursive resolver is expected to cache the answers it
921 receives (which would make it a full-service resolver), but some
922 recursive resolvers might not cache.
923
924 [RFC4697] tried to differentiate between a recursive resolver and
925 an iterative resolver.
926
927
928
929
930
931
932 Hoffman, et al. Best Current Practice [Page 17]
933 RFC 8499 DNS Terminology January 2019
934
935
936 Recursive query: A query with the Recursion Desired (RD) bit set to
937 1 in the header. (See Section 4.1.1 of [RFC1035].) If recursive
938 service is available and is requested by the RD bit in the query,
939 the server uses its resolver to answer the query. (See
940 Section 4.3.2 of [RFC1034].)
941
942 Non-recursive query: A query with the Recursion Desired (RD) bit set
943 to 0 in the header. A server can answer non-recursive queries
944 using only local information: the response contains either an
945 error, the answer, or a referral to some other server "closer" to
946 the answer. (See Section 4.3.1 of [RFC1034].)
947
948 Iterative resolution: A name server may be presented with a query
949 that can only be answered by some other server. The two general
950 approaches to dealing with this problem are "recursive", in which
951 the first server pursues the query on behalf of the client at
952 another server, and "iterative", in which the server refers the
953 client to another server and lets the client pursue the query
954 there. (See Section 2.3 of [RFC1034].)
955
956 In iterative resolution, the client repeatedly makes non-recursive
957 queries and follows referrals and/or aliases. The iterative
958 resolution algorithm is described in Section 5.3.3 of [RFC1034].
959
960 Full resolver: This term is used in [RFC1035], but it is not defined
961 there. RFC 1123 defines a "full-service resolver" that may or may
962 not be what was intended by "full resolver" in [RFC1035]. This
963 term is not properly defined in any RFC.
964
965 Full-service resolver: Section 6.1.3.1 of [RFC1123] defines this
966 term to mean a resolver that acts in recursive mode with a cache
967 (and meets other requirements).
968
969 Priming: "The act of finding the list of root servers from a
970 configuration that lists some or all of the purported IP addresses
971 of some or all of those root servers." (Quoted from [RFC8109],
972 Section 2) In order to operate in recursive mode, a resolver needs
973 to know the address of at least one root server. Priming is most
974 often done from a configuration setting that contains a list of
975 authoritative servers for the root zone.
976
977 Root hints: "Operators who manage a DNS recursive resolver typically
978 need to configure a 'root hints file'. This file contains the
979 names and IP addresses of the authoritative name servers for the
980 root zone, so the software can bootstrap the DNS resolution
981 process. For many pieces of software, this list comes built into
982 the software." (Quoted from [IANA_RootFiles]) This file is often
983 used in priming.
984
985
986
987 Hoffman, et al. Best Current Practice [Page 18]
988 RFC 8499 DNS Terminology January 2019
989
990
991 Negative caching: "The storage of knowledge that something does not
992 exist, cannot or does not give an answer." (Quoted from
993 [RFC2308], Section 1)
994
995 Authoritative server: "A server that knows the content of a DNS zone
996 from local knowledge, and thus can answer queries about that zone
997 without needing to query other servers." (Quoted from [RFC2182],
998 Section 2) An authoritative server is named in the NS ("name
999 server") record in a zone. It is a system that responds to DNS
1000 queries with information about zones for which it has been
1001 configured to answer with the AA flag in the response header set
1002 to 1. It is a server that has authority over one or more DNS
1003 zones. Note that it is possible for an authoritative server to
1004 respond to a query without the parent zone delegating authority to
1005 that server. Authoritative servers also provide "referrals",
1006 usually to child zones delegated from them; these referrals have
1007 the AA bit set to 0 and come with referral data in the Authority
1008 and (if needed) the Additional sections.
1009
1010 Authoritative-only server: A name server that only serves
1011 authoritative data and ignores requests for recursion. It will
1012 "not normally generate any queries of its own. Instead it answers
1013 non-recursive queries from iterative resolvers looking for
1014 information in zones it serves." (Quoted from [RFC4697],
1015 Section 2.4) In this case, "ignores requests for recursion" means
1016 "responds to requests for recursion with responses indicating that
1017 recursion was not performed".
1018
1019 Zone transfer: The act of a client requesting a copy of a zone and
1020 an authoritative server sending the needed information. (See
1021 Section 7 for a description of zones.) There are two common
1022 standard ways to do zone transfers: the AXFR ("Authoritative
1023 Transfer") mechanism to copy the full zone (described in
1024 [RFC5936], and the IXFR ("Incremental Transfer") mechanism to copy
1025 only parts of the zone that have changed (described in [RFC1995]).
1026 Many systems use non-standard methods for zone transfer outside
1027 the DNS protocol.
1028
1029 Slave server: See "Secondary server".
1030
1031 Secondary server: "An authoritative server which uses zone transfer
1032 to retrieve the zone." (Quoted from [RFC1996], Section 2.1)
1033 Secondary servers are also discussed in [RFC1034]. [RFC2182]
1034 describes secondary servers in more detail. Although early DNS
1035 RFCs such as [RFC1996] referred to this as a "slave", the current
1036 common usage has shifted to calling it a "secondary".
1037
1038 Master server: See "Primary server".
1039
1040
1041
1042 Hoffman, et al. Best Current Practice [Page 19]
1043 RFC 8499 DNS Terminology January 2019
1044
1045
1046 Primary server: "Any authoritative server configured to be the
1047 source of zone transfer for one or more [secondary] servers."
1048 (Quoted from [RFC1996], Section 2.1) Or, more specifically,
1049 [RFC2136] calls it "an authoritative server configured to be the
1050 source of AXFR or IXFR data for one or more [secondary] servers".
1051 Primary servers are also discussed in [RFC1034]. Although early
1052 DNS RFCs such as [RFC1996] referred to this as a "master", the
1053 current common usage has shifted to "primary".
1054
1055 Primary master: "The primary master is named in the zone's SOA MNAME
1056 field and optionally by an NS RR." (Quoted from [RFC1996],
1057 Section 2.1) [RFC2136] defines "primary master" as "Master server
1058 at the root of the AXFR/IXFR dependency graph. The primary master
1059 is named in the zone's SOA MNAME field and optionally by an NS RR.
1060 There is by definition only one primary master server per zone."
1061
1062 The idea of a primary master is only used in [RFC1996] and
1063 [RFC2136]. A modern interpretation of the term "primary master"
1064 is a server that is both authoritative for a zone and that gets
1065 its updates to the zone from configuration (such as a master file)
1066 or from UPDATE transactions.
1067
1068 Stealth server: This is "like a slave server except not listed in an
1069 NS RR for the zone." (Quoted from [RFC1996], Section 2.1)
1070
1071 Hidden master: A stealth server that is a primary server for zone
1072 transfers. "In this arrangement, the master name server that
1073 processes the updates is unavailable to general hosts on the
1074 Internet; it is not listed in the NS RRset." (Quoted from
1075 [RFC6781], Section 3.4.3) An earlier RFC, [RFC4641], said that the
1076 hidden master's name "appears in the SOA RRs MNAME field",
1077 although, in some setups, the name does not appear at all in the
1078 public DNS. A hidden master can also be a secondary server for
1079 the zone itself.
1080
1081 Forwarding: The process of one server sending a DNS query with the
1082 RD bit set to 1 to another server to resolve that query.
1083 Forwarding is a function of a DNS resolver; it is different than
1084 simply blindly relaying queries.
1085
1086 [RFC5625] does not give a specific definition for forwarding, but
1087 describes in detail what features a system that forwards needs to
1088 support. Systems that forward are sometimes called "DNS proxies",
1089 but that term has not yet been defined (even in [RFC5625]).
1090
1091
1092
1093
1094
1095
1096
1097 Hoffman, et al. Best Current Practice [Page 20]
1098 RFC 8499 DNS Terminology January 2019
1099
1100
1101 Forwarder: Section 1 of [RFC2308] describes a forwarder as "a
1102 nameserver used to resolve queries instead of directly using the
1103 authoritative nameserver chain". [RFC2308] further says "The
1104 forwarder typically either has better access to the internet, or
1105 maintains a bigger cache which may be shared amongst many
1106 resolvers." That definition appears to suggest that forwarders
1107 normally only query authoritative servers. In current use,
1108 however, forwarders often stand between stub resolvers and
1109 recursive servers. [RFC2308] is silent on whether a forwarder is
1110 iterative-only or can be a full-service resolver.
1111
1112 Policy-implementing resolver: A resolver acting in recursive mode
1113 that changes some of the answers that it returns based on policy
1114 criteria, such as to prevent access to malware sites or
1115 objectionable content. In general, a stub resolver has no idea
1116 whether upstream resolvers implement such policy or, if they do,
1117 the exact policy about what changes will be made. In some cases,
1118 the user of the stub resolver has selected the policy-implementing
1119 resolver with the explicit intention of using it to implement the
1120 policies. In other cases, policies are imposed without the user
1121 of the stub resolver being informed.
1122
1123 Open resolver: A full-service resolver that accepts and processes
1124 queries from any (or nearly any) client. This is sometimes also
1125 called a "public resolver", although the term "public resolver" is
1126 used more with open resolvers that are meant to be open, as
1127 compared to the vast majority of open resolvers that are probably
1128 misconfigured to be open. Open resolvers are discussed in
1129 [RFC5358].
1130
1131 Split DNS: The terms "split DNS" and "split-horizon DNS" have long
1132 been used in the DNS community without formal definition. In
1133 general, they refer to situations in which DNS servers that are
1134 authoritative for a particular set of domains provide partly or
1135 completely different answers in those domains depending on the
1136 source of the query. The effect of this is that a domain name
1137 that is notionally globally unique nevertheless has different
1138 meanings for different network users. This can sometimes be the
1139 result of a "view" configuration, described below.
1140
1141 Section 3.8 of [RFC2775] gives a related definition that is too
1142 specific to be generally useful.
1143
1144 View: A configuration for a DNS server that allows it to provide
1145 different responses depending on attributes of the query, such as
1146 for "split DNS". Typically, views differ by the source IP address
1147 of a query, but can also be based on the destination IP address,
1148 the type of query (such as AXFR), whether it is recursive, and so
1149
1150
1151
1152 Hoffman, et al. Best Current Practice [Page 21]
1153 RFC 8499 DNS Terminology January 2019
1154
1155
1156 on. Views are often used to provide more names or different
1157 addresses to queries from "inside" a protected network than to
1158 those "outside" that network. Views are not a standardized part
1159 of the DNS, but they are widely implemented in server software.
1160
1161 Passive DNS: A mechanism to collect DNS data by storing DNS
1162 responses from name servers. Some of these systems also collect
1163 the DNS queries associated with the responses, although doing so
1164 raises some privacy concerns. Passive DNS databases can be used
1165 to answer historical questions about DNS zones such as which
1166 values were present at a given time in the past, or when a name
1167 was spotted first. Passive DNS databases allow searching of the
1168 stored records on keys other than just the name and type, such as
1169 "find all names which have A records of a particular value".
1170
1171 Anycast: "The practice of making a particular service address
1172 available in multiple, discrete, autonomous locations, such that
1173 datagrams sent are routed to one of several available locations."
1174 (Quoted from [RFC4786], Section 2) See [RFC4786] for more detail
1175 on Anycast and other terms that are specific to its use.
1176
1177 Instance: "When anycast routing is used to allow more than one
1178 server to have the same IP address, each one of those servers is
1179 commonly referred to as an 'instance'." It goes on to say: "An
1180 instance of a server, such as a root server, is often referred to
1181 as an 'Anycast instance'." (Quoted from [RSSAC026])
1182
1183 Privacy-enabling DNS server: "A DNS server that implements DNS over
1184 TLS [RFC7858] and may optionally implement DNS over DTLS
1185 [RFC8094]." (Quoted from [RFC8310], Section 2) Other types of DNS
1186 servers might also be considered privacy-enabling, such as those
1187 running DNS over HTTPS [RFC8484].
1188
1189 7. Zones
1190
1191 This section defines terms that are used when discussing zones that
1192 are being served or retrieved.
1193
1194 Zone: "Authoritative information is organized into units called
1195 ZONEs, and these zones can be automatically distributed to the
1196 name servers which provide redundant service for the data in a
1197 zone." (Quoted from [RFC1034], Section 2.4)
1198
1199 Child: "The entity on record that has the delegation of the domain
1200 from the Parent." (Quoted from [RFC7344], Section 1.1)
1201
1202
1203
1204
1205
1206
1207 Hoffman, et al. Best Current Practice [Page 22]
1208 RFC 8499 DNS Terminology January 2019
1209
1210
1211 Parent: "The domain in which the Child is registered." (Quoted from
1212 [RFC7344], Section 1.1) Earlier, "parent name server" was defined
1213 in [RFC0882] as "the name server that has authority over the place
1214 in the domain name space that will hold the new domain". (Note
1215 that [RFC0882] was obsoleted by [RFC1034] and [RFC1035].)
1216 [RFC819] also has some description of the relationship between
1217 parents and children.
1218
1219 Origin:
1220
1221 There are two different uses for this term:
1222
1223 (a) "The domain name that appears at the top of a zone (just
1224 below the cut that separates the zone from its parent)... The
1225 name of the zone is the same as the name of the domain at the
1226 zone's origin." (Quoted from [RFC2181], Section 6) These
1227 days, this sense of "origin" and "apex" (defined below) are
1228 often used interchangeably.
1229
1230 (b) The domain name within which a given relative domain name
1231 appears in zone files. Generally seen in the context of
1232 "$ORIGIN", which is a control entry defined in [RFC1035],
1233 Section 5.1, as part of the master file format. For example,
1234 if the $ORIGIN is set to "example.org.", then a master file
1235 line for "www" is in fact an entry for "www.example.org.".
1236
1237 Apex: The point in the tree at an owner of an SOA and corresponding
1238 authoritative NS RRset. This is also called the "zone apex".
1239 [RFC4033] defines it as "the name at the child's side of a zone
1240 cut". The "apex" can usefully be thought of as a data-theoretic
1241 description of a tree structure, and "origin" is the name of the
1242 same concept when it is implemented in zone files. The
1243 distinction is not always maintained in use, however, and one can
1244 find uses that conflict subtly with this definition. [RFC1034]
1245 uses the term "top node of the zone" as a synonym of "apex", but
1246 that term is not widely used. These days, the first sense of
1247 "origin" (above) and "apex" are often used interchangeably.
1248
1249 Zone cut: The delimitation point between two zones where the origin
1250 of one of the zones is the child of the other zone.
1251
1252 "Zones are delimited by 'zone cuts'. Each zone cut separates a
1253 'child' zone (below the cut) from a 'parent' zone (above the
1254 cut)." (Quoted from [RFC2181], Section 6; note that this is
1255 barely an ostensive definition.) Section 4.2 of [RFC1034] uses
1256 "cuts" instead of "zone cut".
1257
1258
1259
1260
1261
1262 Hoffman, et al. Best Current Practice [Page 23]
1263 RFC 8499 DNS Terminology January 2019
1264
1265
1266 Delegation: The process by which a separate zone is created in the
1267 name space beneath the apex of a given domain. Delegation happens
1268 when an NS RRset is added in the parent zone for the child origin.
1269 Delegation inherently happens at a zone cut. The term is also
1270 commonly a noun: the new zone that is created by the act of
1271 delegating.
1272
1273 Authoritative data: "All of the RRs attached to all of the nodes
1274 from the top node of the zone down to leaf nodes or nodes above
1275 cuts around the bottom edge of the zone." (Quoted from [RFC1034],
1276 Section 4.2.1) Note that this definition might inadvertently also
1277 cause any NS records that appear in the zone to be included, even
1278 those that might not truly be authoritative because there are
1279 identical NS RRs below the zone cut. This reveals the ambiguity
1280 in the notion of authoritative data, because the parent-side NS
1281 records authoritatively indicate the delegation, even though they
1282 are not themselves authoritative data.
1283
1284 [RFC4033], Section 2, defines "Authoritative RRset", which is
1285 related to authoritative data but has a more precise definition.
1286
1287 Lame delegation: "A lame delegations exists [sic] when a nameserver
1288 is delegated responsibility for providing nameservice for a zone
1289 (via NS records) but is not performing nameservice for that zone
1290 (usually because it is not set up as a primary or secondary for
1291 the zone)." (Quoted from [RFC1912], Section 2.8) Another
1292 definition is that a lame delegation "...happens when a name
1293 server is listed in the NS records for some domain and in fact it
1294 is not a server for that domain. Queries are thus sent to the
1295 wrong servers, who don't know nothing [sic] (at least not as
1296 expected) about the queried domain. Furthermore, sometimes these
1297 hosts (if they exist!) don't even run name servers." (Quoted from
1298 [RFC1713], Section 2.3)
1299
1300 Glue records: "...[Resource records] which are not part of the
1301 authoritative data [of the zone], and are address RRs for the
1302 [name] servers [in subzones]. These RRs are only necessary if the
1303 name server's name is 'below' the cut, and are only used as part
1304 of a referral response." Without glue "we could be faced with the
1305 situation where the NS RRs tell us that in order to learn a name
1306 server's address, we should contact the server using the address
1307 we wish to learn." (Quoted from [RFC1034], Section 4.2.1)
1308
1309 A later definition is that glue "includes any record in a zone
1310 file that is not properly part of that zone, including nameserver
1311 records of delegated sub-zones (NS records), address records that
1312 accompany those NS records (A, AAAA, etc), and any other stray
1313 data that might appear." (Quoted from [RFC2181], Section 5.4.1)
1314
1315
1316
1317 Hoffman, et al. Best Current Practice [Page 24]
1318 RFC 8499 DNS Terminology January 2019
1319
1320
1321 Although glue is sometimes used today with this wider definition
1322 in mind, the context surrounding the definition in [RFC2181]
1323 suggests it is intended to apply to the use of glue within the
1324 document itself and not necessarily beyond.
1325
1326 Bailiwick: "In-bailiwick" is a modifier to describe a name server
1327 whose name is either a subdomain of or (rarely) the same as the
1328 origin of the zone that contains the delegation to the name
1329 server. In-bailiwick name servers may have glue records in their
1330 parent zone (using the first of the definitions of "glue records"
1331 in the definition above). (The word "bailiwick" means the
1332 district or territory where a bailiff or policeman has
1333 jurisdiction.)
1334
1335 "In-bailiwick" names are divided into two types of names for name
1336 servers: "in-domain" names and "sibling domain" names.
1337
1338 * In-domain: a modifier to describe a name server whose name is
1339 either subordinate to or (rarely) the same as the owner name of
1340 the NS resource records. An in-domain name server name needs
1341 to have glue records or name resolution fails. For example, a
1342 delegation for "child.example.com" may have "in-domain" name
1343 server name "ns.child.example.com".
1344
1345 * Sibling domain: a name server's name that is either subordinate
1346 to or (rarely) the same as the zone origin and not subordinate
1347 to or the same as the owner name of the NS resource records.
1348 Glue records for sibling domains are allowed, but not
1349 necessary. For example, a delegation for "child.example.com"
1350 in "example.com" zone may have "sibling" name server name
1351 "ns.another.example.com".
1352
1353 "Out-of-bailiwick" is the antonym of "in-bailiwick". It is a
1354 modifier to describe a name server whose name is not subordinate
1355 to or the same as the zone origin. Glue records for out-of-
1356 bailiwick name servers are useless. The following table shows
1357 examples of delegation types.
1358
1359 Delegation |Parent|Name Server Name | Type
1360 -----------+------+------------------+-----------------------------
1361 com | . |a.gtld-servers.net|in-bailiwick / sibling domain
1362 net | . |a.gtld-servers.net|in-bailiwick / in-domain
1363 example.org| org |ns.example.org |in-bailiwick / in-domain
1364 example.org| org |ns.ietf.org |in-bailiwick / sibling domain
1365 example.org| org |ns.example.com |out-of-bailiwick
1366 example.jp | jp |ns.example.jp |in-bailiwick / in-domain
1367 example.jp | jp |ns.example.ne.jp |in-bailiwick / sibling domain
1368 example.jp | jp |ns.example.com |out-of-bailiwick
1369
1370
1371
1372 Hoffman, et al. Best Current Practice [Page 25]
1373 RFC 8499 DNS Terminology January 2019
1374
1375
1376 Root zone: The zone of a DNS-based tree whose apex is the zero-
1377 length label. Also sometimes called "the DNS root".
1378
1379 Empty non-terminals (ENT): "Domain names that own no resource
1380 records but have subdomains that do." (Quoted from [RFC4592],
1381 Section 2.2.2) A typical example is in SRV records: in the name
1382 "_sip._tcp.example.com", it is likely that "_tcp.example.com" has
1383 no RRsets, but that "_sip._tcp.example.com" has (at least) an SRV
1384 RRset.
1385
1386 Delegation-centric zone: A zone that consists mostly of delegations
1387 to child zones. This term is used in contrast to a zone that
1388 might have some delegations to child zones but also has many data
1389 resource records for the zone itself and/or for child zones. The
1390 term is used in [RFC4956] and [RFC5155], but it is not defined in
1391 either document.
1392
1393 Occluded name: "The addition of a delegation point via dynamic
1394 update will render all subordinate domain names to be in a limbo,
1395 still part of the zone but not available to the lookup process.
1396 The addition of a DNAME resource record has the same impact. The
1397 subordinate names are said to be 'occluded'." (Quoted from
1398 [RFC5936], Section 3.5)
1399
1400 Fast flux DNS: This "occurs when a domain is [found] in DNS using A
1401 records to multiple IP addresses, each of which has a very short
1402 Time-to-Live (TTL) value associated with it. This means that the
1403 domain resolves to varying IP addresses over a short period of
1404 time." (Quoted from [RFC6561], Section 1.1.5, with a typo
1405 corrected) In addition to having legitimate uses, fast flux DNS
1406 can used to deliver malware. Because the addresses change so
1407 rapidly, it is difficult to ascertain all the hosts. It should be
1408 noted that the technique also works with AAAA records, but such
1409 use is not frequently observed on the Internet as of this writing.
1410
1411 Reverse DNS, reverse lookup: "The process of mapping an address to a
1412 name is generally known as a 'reverse lookup', and the
1413 IN-ADDR.ARPA and IP6.ARPA zones are said to support the 'reverse
1414 DNS'." (Quoted from [RFC5855], Section 1)
1415
1416 Forward lookup: "Hostname-to-address translation". (Quoted from
1417 [RFC3493], Section 6)
1418
1419 arpa: Address and Routing Parameter Area Domain: "The 'arpa' domain
1420 was originally established as part of the initial deployment of
1421 the DNS, to provide a transition mechanism from the Host Tables
1422 that were common in the ARPANET, as well as a home for the IPv4
1423 reverse mapping domain. During 2000, the abbreviation was
1424
1425
1426
1427 Hoffman, et al. Best Current Practice [Page 26]
1428 RFC 8499 DNS Terminology January 2019
1429
1430
1431 redesignated to 'Address and Routing Parameter Area' in the hope
1432 of reducing confusion with the earlier network name." (Quoted
1433 from [RFC3172], Section 2) .arpa is an "infrastructure domain", a
1434 domain whose "role is to support the operating infrastructure of
1435 the Internet". (Quoted from [RFC3172], Section 2) See [RFC3172]
1436 for more history of this name.
1437
1438 Service name: "Service names are the unique key in the Service Name
1439 and Transport Protocol Port Number registry. This unique symbolic
1440 name for a service may also be used for other purposes, such as in
1441 DNS SRV records." (Quoted from [RFC6335], Section 5)
1442
1443 8. Wildcards
1444
1445 Wildcard: [RFC1034] defined "wildcard", but in a way that turned out
1446 to be confusing to implementers. For an extended discussion of
1447 wildcards, including clearer definitions, see [RFC4592]. Special
1448 treatment is given to RRs with owner names starting with the label
1449 "*". "Such RRs are called 'wildcards'. Wildcard RRs can be
1450 thought of as instructions for synthesizing RRs." (Quoted from
1451 [RFC1034], Section 4.3.3)
1452
1453 Asterisk label: "The first octet is the normal label type and length
1454 for a 1-octet-long label, and the second octet is the ASCII
1455 representation [RFC20] for the '*' character. A descriptive name
1456 of a label equaling that value is an 'asterisk label'." (Quoted
1457 from [RFC4592], Section 2.1.1)
1458
1459 Wildcard domain name: "A 'wildcard domain name' is defined by having
1460 its initial (i.e., leftmost or least significant) label, in binary
1461 format: 0000 0001 0010 1010 (binary) = 0x01 0x2a (hexadecimal)".
1462 (Quoted from [RFC4592], Section 2.1.1) The second octet in this
1463 label is the ASCII representation for the "*" character.
1464
1465 Closest encloser: "The longest existing ancestor of a name."
1466 (Quoted from [RFC5155], Section 1.3) An earlier definition is "The
1467 node in the zone's tree of existing domain names that has the most
1468 labels matching the query name (consecutively, counting from the
1469 root label downward). Each match is a 'label match' and the order
1470 of the labels is the same." (Quoted from [RFC4592],
1471 Section 3.3.1)
1472
1473 Closest provable encloser: "The longest ancestor of a name that can
1474 be proven to exist. Note that this is only different from the
1475 closest encloser in an Opt-Out zone." (Quoted from [RFC5155],
1476 Section 1.3) See Section 10 for more on "opt-out".
1477
1478
1479
1480
1481
1482 Hoffman, et al. Best Current Practice [Page 27]
1483 RFC 8499 DNS Terminology January 2019
1484
1485
1486 Next closer name: "The name one label longer than the closest
1487 provable encloser of a name." (Quoted from [RFC5155],
1488 Section 1.3)
1489
1490 Source of Synthesis: "The source of synthesis is defined in the
1491 context of a query process as that wildcard domain name
1492 immediately descending from the closest encloser, provided that
1493 this wildcard domain name exists. 'Immediately descending' means
1494 that the source of synthesis has a name of the form:
1495 <asterisk label>.<closest encloser>."
1496 (Quoted from [RFC4592], Section 3.3.1)
1497
1498 9. Registration Model
1499
1500 Registry: The administrative operation of a zone that allows
1501 registration of names within that zone. People often use this
1502 term to refer only to those organizations that perform
1503 registration in large delegation-centric zones (such as TLDs); but
1504 formally, whoever decides what data goes into a zone is the
1505 registry for that zone. This definition of "registry" is from a
1506 DNS point of view; for some zones, the policies that determine
1507 what can go in the zone are decided by zones that are
1508 superordinate and not the registry operator.
1509
1510 Registrant: An individual or organization on whose behalf a name in
1511 a zone is registered by the registry. In many zones, the registry
1512 and the registrant may be the same entity, but in TLDs they often
1513 are not.
1514
1515 Registrar: A service provider that acts as a go-between for
1516 registrants and registries. Not all registrations require a
1517 registrar, though it is common to have registrars involved in
1518 registrations in TLDs.
1519
1520 EPP: The Extensible Provisioning Protocol (EPP), which is commonly
1521 used for communication of registration information between
1522 registries and registrars. EPP is defined in [RFC5730].
1523
1524 WHOIS: A protocol specified in [RFC3912], often used for querying
1525 registry databases. WHOIS data is frequently used to associate
1526 registration data (such as zone management contacts) with domain
1527 names. The term "WHOIS data" is often used as a synonym for the
1528 registry database, even though that database may be served by
1529 different protocols, particularly RDAP. The WHOIS protocol is
1530 also used with IP address registry data.
1531
1532
1533
1534
1535
1536
1537 Hoffman, et al. Best Current Practice [Page 28]
1538 RFC 8499 DNS Terminology January 2019
1539
1540
1541 RDAP: The Registration Data Access Protocol, defined in [RFC7480],
1542 [RFC7481], [RFC7482], [RFC7483], [RFC7484], and [RFC7485]. The
1543 RDAP protocol and data format are meant as a replacement for
1544 WHOIS.
1545
1546 DNS operator: An entity responsible for running DNS servers. For a
1547 zone's authoritative servers, the registrant may act as their own
1548 DNS operator, their registrar may do it on their behalf, or they
1549 may use a third-party operator. For some zones, the registry
1550 function is performed by the DNS operator plus other entities who
1551 decide about the allowed contents of the zone.
1552
1553 Public suffix: "A domain that is controlled by a public registry."
1554 (Quoted from [RFC6265], Section 5.3) A common definition for this
1555 term is a domain under which subdomains can be registered by third
1556 parties and on which HTTP cookies (which are described in detail
1557 in [RFC6265]) should not be set. There is no indication in a
1558 domain name whether it is a public suffix; that can only be
1559 determined by outside means. In fact, both a domain and a
1560 subdomain of that domain can be public suffixes.
1561
1562 There is nothing inherent in a domain name to indicate whether it
1563 is a public suffix. One resource for identifying public suffixes
1564 is the Public Suffix List (PSL) maintained by Mozilla
1565 (http://publicsuffix.org/).
1566
1567 For example, at the time this document is published, the "com.au"
1568 domain is listed as a public suffix in the PSL. (Note that this
1569 example might change in the future.)
1570
1571 Note that the term "public suffix" is controversial in the DNS
1572 community for many reasons, and it may be significantly changed in
1573 the future. One example of the difficulty of calling a domain a
1574 public suffix is that designation can change over time as the
1575 registration policy for the zone changes, such as was the case
1576 with the "uk" TLD in 2014.
1577
1578 Subordinate and Superordinate: These terms are introduced in
1579 [RFC5731] for use in the registration model, but not defined
1580 there. Instead, they are given in examples. "For example, domain
1581 name 'example.com' has a superordinate relationship to host name
1582 ns1.example.com'... For example, host ns1.example1.com is a
1583 subordinate host of domain example1.com, but it is a not a
1584 subordinate host of domain example2.com." (Quoted from [RFC5731],
1585 Section 1.1) These terms are strictly ways of referring to the
1586 relationship standing of two domains where one is a subdomain of
1587 the other.
1588
1589
1590
1591
1592 Hoffman, et al. Best Current Practice [Page 29]
1593 RFC 8499 DNS Terminology January 2019
1594
1595
1596 10. General DNSSEC
1597
1598 Most DNSSEC terms are defined in [RFC4033], [RFC4034], [RFC4035], and
1599 [RFC5155]. The terms that have caused confusion in the DNS community
1600 are highlighted here.
1601
1602 DNSSEC-aware and DNSSEC-unaware: These two terms, which are used in
1603 some RFCs, have not been formally defined. However, Section 2 of
1604 [RFC4033] defines many types of resolvers and validators,
1605 including "non-validating security-aware stub resolver",
1606 "non-validating stub resolver", "security-aware name server",
1607 "security-aware recursive name server", "security-aware resolver",
1608 "security-aware stub resolver", and "security-oblivious
1609 'anything'". (Note that the term "validating resolver", which is
1610 used in some places in DNSSEC-related documents, is also not
1611 defined in those RFCs, but is defined below.)
1612
1613 Signed zone: "A zone whose RRsets are signed and that contains
1614 properly constructed DNSKEY, Resource Record Signature (RRSIG),
1615 Next Secure (NSEC), and (optionally) DS records." (Quoted from
1616 [RFC4033], Section 2) It has been noted in other contexts that the
1617 zone itself is not really signed, but all the relevant RRsets in
1618 the zone are signed. Nevertheless, if a zone that should be
1619 signed contains any RRsets that are not signed (or opted out),
1620 those RRsets will be treated as bogus, so the whole zone needs to
1621 be handled in some way.
1622
1623 It should also be noted that, since the publication of [RFC6840],
1624 NSEC records are no longer required for signed zones: a signed
1625 zone might include NSEC3 records instead. [RFC7129] provides
1626 additional background commentary and some context for the NSEC and
1627 NSEC3 mechanisms used by DNSSEC to provide authenticated denial-
1628 of-existence responses. NSEC and NSEC3 are described below.
1629
1630 Unsigned zone: Section 2 of [RFC4033] defines this as "a zone that
1631 is not signed". Section 2 of [RFC4035] defines this as a "zone
1632 that does not include these records [properly constructed DNSKEY,
1633 Resource Record Signature (RRSIG), Next Secure (NSEC), and
1634 (optionally) DS records] according to the rules in this
1635 section..." There is an important note at the end of Section 5.2
1636 of [RFC4035] that defines an additional situation in which a zone
1637 is considered unsigned: "If the resolver does not support any of
1638 the algorithms listed in an authenticated DS RRset, then the
1639 resolver will not be able to verify the authentication path to the
1640 child zone. In this case, the resolver SHOULD treat the child
1641 zone as if it were unsigned."
1642
1643
1644
1645
1646
1647 Hoffman, et al. Best Current Practice [Page 30]
1648 RFC 8499 DNS Terminology January 2019
1649
1650
1651 NSEC: "The NSEC record allows a security-aware resolver to
1652 authenticate a negative reply for either name or type
1653 non-existence with the same mechanisms used to authenticate other
1654 DNS replies." (Quoted from [RFC4033], Section 3.2) In short, an
1655 NSEC record provides authenticated denial of existence.
1656
1657 "The NSEC resource record lists two separate things: the next
1658 owner name (in the canonical ordering of the zone) that contains
1659 authoritative data or a delegation point NS RRset, and the set of
1660 RR types present at the NSEC RR's owner name." (Quoted from
1661 Section 4 of RFC 4034)
1662
1663 NSEC3: Like the NSEC record, the NSEC3 record also provides
1664 authenticated denial of existence; however, NSEC3 records mitigate
1665 zone enumeration and support Opt-Out. NSEC3 resource records
1666 require associated NSEC3PARAM resource records. NSEC3 and
1667 NSEC3PARAM resource records are defined in [RFC5155].
1668
1669 Note that [RFC6840] says that [RFC5155] "is now considered part of
1670 the DNS Security Document Family as described by Section 10 of
1671 [RFC4033]". This means that some of the definitions from earlier
1672 RFCs that only talk about NSEC records should probably be
1673 considered to be talking about both NSEC and NSEC3.
1674
1675 Opt-out: "The Opt-Out Flag indicates whether this NSEC3 RR may cover
1676 unsigned delegations." (Quoted from [RFC5155], Section 3.1.2.1)
1677 Opt-out tackles the high costs of securing a delegation to an
1678 insecure zone. When using Opt-Out, names that are an insecure
1679 delegation (and empty non-terminals that are only derived from
1680 insecure delegations) don't require an NSEC3 record or its
1681 corresponding RRSIG records. Opt-Out NSEC3 records are not able
1682 to prove or deny the existence of the insecure delegations.
1683 (Adapted from [RFC7129], Section 5.1)
1684
1685 Insecure delegation: "A signed name containing a delegation (NS
1686 RRset), but lacking a DS RRset, signifying a delegation to an
1687 unsigned subzone." (Quoted from [RFC4956], Section 2)
1688
1689 Zone enumeration: "The practice of discovering the full content of a
1690 zone via successive queries." (Quoted from [RFC5155],
1691 Section 1.3) This is also sometimes called "zone walking". Zone
1692 enumeration is different from zone content guessing where the
1693 guesser uses a large dictionary of possible labels and sends
1694 successive queries for them, or matches the contents of NSEC3
1695 records against such a dictionary.
1696
1697
1698
1699
1700
1701
1702 Hoffman, et al. Best Current Practice [Page 31]
1703 RFC 8499 DNS Terminology January 2019
1704
1705
1706 Validation: Validation, in the context of DNSSEC, refers to one of
1707 the following:
1708
1709 * Checking the validity of DNSSEC signatures,
1710
1711 * Checking the validity of DNS responses, such as those including
1712 authenticated denial of existence, or
1713
1714 * Building an authentication chain from a trust anchor to a DNS
1715 response or individual DNS RRsets in a response
1716
1717 The first two definitions above consider only the validity of
1718 individual DNSSEC components such as the RRSIG validity or NSEC
1719 proof validity. The third definition considers the components of
1720 the entire DNSSEC authentication chain; thus, it requires
1721 "configured knowledge of at least one authenticated DNSKEY or DS
1722 RR" (as described in [RFC4035], Section 5).
1723
1724 [RFC4033], Section 2, says that a "Validating Security-Aware Stub
1725 Resolver... performs signature validation" and uses a trust anchor
1726 "as a starting point for building the authentication chain to a
1727 signed DNS response"; thus, it uses the first and third
1728 definitions above. The process of validating an RRSIG resource
1729 record is described in [RFC4035], Section 5.3.
1730
1731 [RFC5155] refers to validating responses throughout the document,
1732 in the context of hashed authenticated denial of existence; this
1733 uses the second definition above.
1734
1735 The term "authentication" is used interchangeably with
1736 "validation", in the sense of the third definition above.
1737 [RFC4033], Section 2, describes the chain linking trust anchor to
1738 DNS data as the "authentication chain". A response is considered
1739 to be authentic if "all RRsets in the Answer and Authority
1740 sections of the response [are considered] to be authentic" (Quoted
1741 from [RFC4035]) DNS data or responses deemed to be authentic or
1742 validated have a security status of "secure" ([RFC4035],
1743 Section 4.3; [RFC4033], Section 5). "Authenticating both DNS keys
1744 and data is a matter of local policy, which may extend or even
1745 override the [DNSSEC] protocol extensions..." (Quoted from
1746 [RFC4033], Section 3.1)
1747
1748 The term "verification", when used, is usually a synonym for
1749 "validation".
1750
1751
1752
1753
1754
1755
1756
1757 Hoffman, et al. Best Current Practice [Page 32]
1758 RFC 8499 DNS Terminology January 2019
1759
1760
1761 Validating resolver: A security-aware recursive name server,
1762 security-aware resolver, or security-aware stub resolver that is
1763 applying at least one of the definitions of validation (above), as
1764 appropriate to the resolution context. For the same reason that
1765 the generic term "resolver" is sometimes ambiguous and needs to be
1766 evaluated in context (see Section 6), "validating resolver" is a
1767 context-sensitive term.
1768
1769 Key signing key (KSK): DNSSEC keys that "only sign the apex DNSKEY
1770 RRset in a zone." (Quoted from [RFC6781], Section 3.1)
1771
1772 Zone signing key (ZSK): "DNSSEC keys that can be used to sign all
1773 the RRsets in a zone that require signatures, other than the apex
1774 DNSKEY RRset." (Quoted from [RFC6781], Section 3.1) Also note
1775 that a ZSK is sometimes used to sign the apex DNSKEY RRset.
1776
1777 Combined signing key (CSK): "In cases where the differentiation
1778 between the KSK and ZSK is not made, i.e., where keys have the
1779 role of both KSK and ZSK, we talk about a Single-Type Signing
1780 Scheme." (Quoted from [RFC6781], Section 3.1) This is sometimes
1781 called a "combined signing key" or "CSK". It is operational
1782 practice, not protocol, that determines whether a particular key
1783 is a ZSK, a KSK, or a CSK.
1784
1785 Secure Entry Point (SEP): A flag in the DNSKEY RDATA that "can be
1786 used to distinguish between keys that are intended to be used as
1787 the secure entry point into the zone when building chains of
1788 trust, i.e., they are (to be) pointed to by parental DS RRs or
1789 configured as a trust anchor.... Therefore, it is suggested that
1790 the SEP flag be set on keys that are used as KSKs and not on keys
1791 that are used as ZSKs, while in those cases where a distinction
1792 between a KSK and ZSK is not made (i.e., for a Single-Type Signing
1793 Scheme), it is suggested that the SEP flag be set on all keys."
1794 (Quoted from [RFC6781], Section 3.2.3) Note that the SEP flag is
1795 only a hint, and its presence or absence may not be used to
1796 disqualify a given DNSKEY RR from use as a KSK or ZSK during
1797 validation.
1798
1799 The original definition of SEPs was in [RFC3757]. That definition
1800 clearly indicated that the SEP was a key, not just a bit in the
1801 key. The abstract of [RFC3757] says: "With the Delegation Signer
1802 (DS) resource record (RR), the concept of a public key acting as a
1803 secure entry point (SEP) has been introduced. During exchanges of
1804 public keys with the parent there is a need to differentiate SEP
1805 keys from other public keys in the Domain Name System KEY (DNSKEY)
1806 resource record set. A flag bit in the DNSKEY RR is defined to
1807
1808
1809
1810
1811
1812 Hoffman, et al. Best Current Practice [Page 33]
1813 RFC 8499 DNS Terminology January 2019
1814
1815
1816 indicate that DNSKEY is to be used as a SEP." That definition of
1817 the SEP as a key was made obsolete by [RFC4034], and the
1818 definition from [RFC6781] is consistent with [RFC4034].
1819
1820 Trust anchor: "A configured DNSKEY RR or DS RR hash of a DNSKEY RR.
1821 A validating security-aware resolver uses this public key or hash
1822 as a starting point for building the authentication chain to a
1823 signed DNS response. In general, a validating resolver will have
1824 to obtain the initial values of its trust anchors via some secure
1825 or trusted means outside the DNS protocol." (Quoted from
1826 [RFC4033], Section 2)
1827
1828 DNSSEC Policy (DP): A statement that "sets forth the security
1829 requirements and standards to be implemented for a DNSSEC-signed
1830 zone." (Quoted from [RFC6841], Section 2)
1831
1832 DNSSEC Practice Statement (DPS): "A practices disclosure document
1833 that may support and be a supplemental document to the DNSSEC
1834 Policy (if such exists), and it states how the management of a
1835 given zone implements procedures and controls at a high level."
1836 (Quoted from [RFC6841], Section 2)
1837
1838 Hardware security module (HSM): A specialized piece of hardware that
1839 is used to create keys for signatures and to sign messages without
1840 ever disclosing the private key. In DNSSEC, HSMs are often used
1841 to hold the private keys for KSKs and ZSKs and to create the
1842 signatures used in RRSIG records at periodic intervals.
1843
1844 Signing software: Authoritative DNS servers that support DNSSEC
1845 often contain software that facilitates the creation and
1846 maintenance of DNSSEC signatures in zones. There is also stand-
1847 alone software that can be used to sign a zone regardless of
1848 whether the authoritative server itself supports signing.
1849 Sometimes signing software can support particular HSMs as part of
1850 the signing process.
1851
1852 11. DNSSEC States
1853
1854 A validating resolver can determine that a response is in one of four
1855 states: secure, insecure, bogus, or indeterminate. These states are
1856 defined in [RFC4033] and [RFC4035], although the definitions in the
1857 two documents differ a bit. This document makes no effort to
1858 reconcile the definitions in the two documents, and takes no position
1859 as to whether they need to be reconciled.
1860
1861
1862
1863
1864
1865
1866
1867 Hoffman, et al. Best Current Practice [Page 34]
1868 RFC 8499 DNS Terminology January 2019
1869
1870
1871 Section 5 of [RFC4033] says:
1872
1873 A validating resolver can determine the following 4 states:
1874
1875 Secure: The validating resolver has a trust anchor, has a chain
1876 of trust, and is able to verify all the signatures in the
1877 response.
1878
1879 Insecure: The validating resolver has a trust anchor, a chain
1880 of trust, and, at some delegation point, signed proof of the
1881 non-existence of a DS record. This indicates that subsequent
1882 branches in the tree are provably insecure. A validating
1883 resolver may have a local policy to mark parts of the domain
1884 space as insecure.
1885
1886 Bogus: The validating resolver has a trust anchor and a secure
1887 delegation indicating that subsidiary data is signed, but
1888 the response fails to validate for some reason: missing
1889 signatures, expired signatures, signatures with unsupported
1890 algorithms, data missing that the relevant NSEC RR says
1891 should be present, and so forth.
1892
1893 Indeterminate: There is no trust anchor that would indicate that a
1894 specific portion of the tree is secure. This is the default
1895 operation mode.
1896
1897 Section 4.3 of [RFC4035] says:
1898
1899 A security-aware resolver must be able to distinguish between four
1900 cases:
1901
1902 Secure: An RRset for which the resolver is able to build a chain
1903 of signed DNSKEY and DS RRs from a trusted security anchor to
1904 the RRset. In this case, the RRset should be signed and is
1905 subject to signature validation, as described above.
1906
1907 Insecure: An RRset for which the resolver knows that it has no
1908 chain of signed DNSKEY and DS RRs from any trusted starting
1909 point to the RRset. This can occur when the target RRset lies
1910 in an unsigned zone or in a descendent [sic] of an unsigned
1911 zone. In this case, the RRset may or may not be signed, but
1912 the resolver will not be able to verify the signature.
1913
1914 Bogus: An RRset for which the resolver believes that it ought to
1915 be able to establish a chain of trust but for which it is
1916 unable to do so, either due to signatures that for some reason
1917 fail to validate or due to missing data that the relevant
1918 DNSSEC RRs indicate should be present. This case may indicate
1919
1920
1921
1922 Hoffman, et al. Best Current Practice [Page 35]
1923 RFC 8499 DNS Terminology January 2019
1924
1925
1926 an attack but may also indicate a configuration error or some
1927 form of data corruption.
1928
1929 Indeterminate: An RRset for which the resolver is not able to
1930 determine whether the RRset should be signed, as the resolver
1931 is not able to obtain the necessary DNSSEC RRs. This can occur
1932 when the security-aware resolver is not able to contact
1933 security-aware name servers for the relevant zones.
1934
1935 12. Security Considerations
1936
1937 These definitions do not change any security considerations for the
1938 DNS.
1939
1940 13. IANA Considerations
1941
1942 This document has no IANA actions.
1943
1944 14. References
1945
1946 14.1. Normative References
1947
1948 [IANA_RootFiles]
1949 IANA, "Root Files",
1950 <https://www.iana.org/domains/root/files>.
1951
1952 [RFC0882] Mockapetris, P., "Domain names: Concepts and facilities",
1953 RFC 882, DOI 10.17487/RFC0882, November 1983,
1954 <https://www.rfc-editor.org/info/rfc882>.
1955
1956 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
1957 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
1958 <https://www.rfc-editor.org/info/rfc1034>.
1959
1960 [RFC1035] Mockapetris, P., "Domain names - implementation and
1961 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
1962 November 1987, <https://www.rfc-editor.org/info/rfc1035>.
1963
1964 [RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
1965 Application and Support", STD 3, RFC 1123,
1966 DOI 10.17487/RFC1123, October 1989,
1967 <https://www.rfc-editor.org/info/rfc1123>.
1968
1969 [RFC1912] Barr, D., "Common DNS Operational and Configuration
1970 Errors", RFC 1912, DOI 10.17487/RFC1912, February 1996,
1971 <https://www.rfc-editor.org/info/rfc1912>.
1972
1973
1974
1975
1976
1977 Hoffman, et al. Best Current Practice [Page 36]
1978 RFC 8499 DNS Terminology January 2019
1979
1980
1981 [RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
1982 Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
1983 August 1996, <https://www.rfc-editor.org/info/rfc1996>.
1984
1985 [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
1986 "Dynamic Updates in the Domain Name System (DNS UPDATE)",
1987 RFC 2136, DOI 10.17487/RFC2136, April 1997,
1988 <https://www.rfc-editor.org/info/rfc2136>.
1989
1990 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
1991 Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
1992 <https://www.rfc-editor.org/info/rfc2181>.
1993
1994 [RFC2182] Elz, R., Bush, R., Bradner, S., and M. Patton, "Selection
1995 and Operation of Secondary DNS Servers", BCP 16, RFC 2182,
1996 DOI 10.17487/RFC2182, July 1997,
1997 <https://www.rfc-editor.org/info/rfc2182>.
1998
1999 [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
2000 NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,
2001 <https://www.rfc-editor.org/info/rfc2308>.
2002
2003 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and
2004 S. Rose, "DNS Security Introduction and Requirements",
2005 RFC 4033, DOI 10.17487/RFC4033, March 2005,
2006 <https://www.rfc-editor.org/info/rfc4033>.
2007
2008 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and
2009 S. Rose, "Resource Records for the DNS Security
2010 Extensions", RFC 4034, DOI 10.17487/RFC4034, March 2005,
2011 <https://www.rfc-editor.org/info/rfc4034>.
2012
2013 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and
2014 S. Rose, "Protocol Modifications for the DNS Security
2015 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
2016 <https://www.rfc-editor.org/info/rfc4035>.
2017
2018 [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name
2019 System", RFC 4592, DOI 10.17487/RFC4592, July 2006,
2020 <https://www.rfc-editor.org/info/rfc4592>.
2021
2022 [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
2023 Security (DNSSEC) Hashed Authenticated Denial of
2024 Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,
2025 <https://www.rfc-editor.org/info/rfc5155>.
2026
2027
2028
2029
2030
2031
2032 Hoffman, et al. Best Current Practice [Page 37]
2033 RFC 8499 DNS Terminology January 2019
2034
2035
2036 [RFC5358] Damas, J. and F. Neves, "Preventing Use of Recursive
2037 Nameservers in Reflector Attacks", BCP 140, RFC 5358,
2038 DOI 10.17487/RFC5358, October 2008,
2039 <https://www.rfc-editor.org/info/rfc5358>.
2040
2041 [RFC5730] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
2042 STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,
2043 <https://www.rfc-editor.org/info/rfc5730>.
2044
2045 [RFC5731] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
2046 Domain Name Mapping", STD 69, RFC 5731,
2047 DOI 10.17487/RFC5731, August 2009,
2048 <https://www.rfc-editor.org/info/rfc5731>.
2049
2050 [RFC5855] Abley, J. and T. Manderson, "Nameservers for IPv4 and IPv6
2051 Reverse Zones", BCP 155, RFC 5855, DOI 10.17487/RFC5855,
2052 May 2010, <https://www.rfc-editor.org/info/rfc5855>.
2053
2054 [RFC5936] Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
2055 (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,
2056 <https://www.rfc-editor.org/info/rfc5936>.
2057
2058 [RFC6561] Livingood, J., Mody, N., and M. O'Reirdan,
2059 "Recommendations for the Remediation of Bots in ISP
2060 Networks", RFC 6561, DOI 10.17487/RFC6561, March 2012,
2061 <https://www.rfc-editor.org/info/rfc6561>.
2062
2063 [RFC6781] Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
2064 Operational Practices, Version 2", RFC 6781,
2065 DOI 10.17487/RFC6781, December 2012,
2066 <https://www.rfc-editor.org/info/rfc6781>.
2067
2068 [RFC6840] Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and
2069 Implementation Notes for DNS Security (DNSSEC)", RFC 6840,
2070 DOI 10.17487/RFC6840, February 2013,
2071 <https://www.rfc-editor.org/info/rfc6840>.
2072
2073 [RFC6841] Ljunggren, F., Eklund Lowinder, AM., and T. Okubo, "A
2074 Framework for DNSSEC Policies and DNSSEC Practice
2075 Statements", RFC 6841, DOI 10.17487/RFC6841, January 2013,
2076 <https://www.rfc-editor.org/info/rfc6841>.
2077
2078 [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
2079 for DNS (EDNS(0))", STD 75, RFC 6891,
2080 DOI 10.17487/RFC6891, April 2013,
2081 <https://www.rfc-editor.org/info/rfc6891>.
2082
2083
2084
2085
2086
2087 Hoffman, et al. Best Current Practice [Page 38]
2088 RFC 8499 DNS Terminology January 2019
2089
2090
2091 [RFC7344] Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
2092 DNSSEC Delegation Trust Maintenance", RFC 7344,
2093 DOI 10.17487/RFC7344, September 2014,
2094 <https://www.rfc-editor.org/info/rfc7344>.
2095
2096 [RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
2097 Terminology", RFC 7719, DOI 10.17487/RFC7719, December
2098 2015, <https://www.rfc-editor.org/info/rfc7719>.
2099
2100 [RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
2101 for DNS over TLS and DNS over DTLS", RFC 8310,
2102 DOI 10.17487/RFC8310, March 2018,
2103 <https://www.rfc-editor.org/info/rfc8310>.
2104
2105 14.2. Informative References
2106
2107 [IANA_Resource_Registry]
2108 IANA, "Resource Record (RR) TYPEs",
2109 <https://www.iana.org/assignments/dns-parameters/>.
2110
2111 [RFC819] Su, Z. and J. Postel, "The Domain Naming Convention for
2112 Internet User Applications", RFC 819,
2113 DOI 10.17487/RFC0819, August 1982,
2114 <https://www.rfc-editor.org/info/rfc819>.
2115
2116 [RFC952] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet
2117 host table specification", RFC 952, DOI 10.17487/RFC0952,
2118 October 1985, <https://www.rfc-editor.org/info/rfc952>.
2119
2120 [RFC1713] Romao, A., "Tools for DNS debugging", FYI 27, RFC 1713,
2121 DOI 10.17487/RFC1713, November 1994,
2122 <https://www.rfc-editor.org/info/rfc1713>.
2123
2124 [RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
2125 DOI 10.17487/RFC1995, August 1996,
2126 <https://www.rfc-editor.org/info/rfc1995>.
2127
2128 [RFC2775] Carpenter, B., "Internet Transparency", RFC 2775,
2129 DOI 10.17487/RFC2775, February 2000,
2130 <https://www.rfc-editor.org/info/rfc2775>.
2131
2132 [RFC3172] Huston, G., Ed., "Management Guidelines & Operational
2133 Requirements for the Address and Routing Parameter Area
2134 Domain ("arpa")", BCP 52, RFC 3172, DOI 10.17487/RFC3172,
2135 September 2001, <https://www.rfc-editor.org/info/rfc3172>.
2136
2137
2138
2139
2140
2141
2142 Hoffman, et al. Best Current Practice [Page 39]
2143 RFC 8499 DNS Terminology January 2019
2144
2145
2146 [RFC3425] Lawrence, D., "Obsoleting IQUERY", RFC 3425,
2147 DOI 10.17487/RFC3425, November 2002,
2148 <https://www.rfc-editor.org/info/rfc3425>.
2149
2150 [RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and
2151 W. Stevens, "Basic Socket Interface Extensions for IPv6",
2152 RFC 3493, DOI 10.17487/RFC3493, February 2003,
2153 <https://www.rfc-editor.org/info/rfc3493>.
2154
2155 [RFC3757] Kolkman, O., Schlyter, J., and E. Lewis, "Domain Name
2156 System KEY (DNSKEY) Resource Record (RR) Secure Entry
2157 Point (SEP) Flag", RFC 3757, DOI 10.17487/RFC3757, April
2158 2004, <https://www.rfc-editor.org/info/rfc3757>.
2159
2160 [RFC3912] Daigle, L., "WHOIS Protocol Specification", RFC 3912,
2161 DOI 10.17487/RFC3912, September 2004,
2162 <https://www.rfc-editor.org/info/rfc3912>.
2163
2164 [RFC4641] Kolkman, O. and R. Gieben, "DNSSEC Operational Practices",
2165 RFC 4641, DOI 10.17487/RFC4641, September 2006,
2166 <https://www.rfc-editor.org/info/rfc4641>.
2167
2168 [RFC4697] Larson, M. and P. Barber, "Observed DNS Resolution
2169 Misbehavior", BCP 123, RFC 4697, DOI 10.17487/RFC4697,
2170 October 2006, <https://www.rfc-editor.org/info/rfc4697>.
2171
2172 [RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast
2173 Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786,
2174 December 2006, <https://www.rfc-editor.org/info/rfc4786>.
2175
2176 [RFC4956] Arends, R., Kosters, M., and D. Blacka, "DNS Security
2177 (DNSSEC) Opt-In", RFC 4956, DOI 10.17487/RFC4956, July
2178 2007, <https://www.rfc-editor.org/info/rfc4956>.
2179
2180 [RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines",
2181 BCP 152, RFC 5625, DOI 10.17487/RFC5625, August 2009,
2182 <https://www.rfc-editor.org/info/rfc5625>.
2183
2184 [RFC5890] Klensin, J., "Internationalized Domain Names for
2185 Applications (IDNA): Definitions and Document Framework",
2186 RFC 5890, DOI 10.17487/RFC5890, August 2010,
2187 <https://www.rfc-editor.org/info/rfc5890>.
2188
2189 [RFC5891] Klensin, J., "Internationalized Domain Names in
2190 Applications (IDNA): Protocol", RFC 5891,
2191 DOI 10.17487/RFC5891, August 2010,
2192 <https://www.rfc-editor.org/info/rfc5891>.
2193
2194
2195
2196
2197 Hoffman, et al. Best Current Practice [Page 40]
2198 RFC 8499 DNS Terminology January 2019
2199
2200
2201 [RFC5892] Faltstrom, P., Ed., "The Unicode Code Points and
2202 Internationalized Domain Names for Applications (IDNA)",
2203 RFC 5892, DOI 10.17487/RFC5892, August 2010,
2204 <https://www.rfc-editor.org/info/rfc5892>.
2205
2206 [RFC5893] Alvestrand, H., Ed. and C. Karp, "Right-to-Left Scripts
2207 for Internationalized Domain Names for Applications
2208 (IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010,
2209 <https://www.rfc-editor.org/info/rfc5893>.
2210
2211 [RFC5894] Klensin, J., "Internationalized Domain Names for
2212 Applications (IDNA): Background, Explanation, and
2213 Rationale", RFC 5894, DOI 10.17487/RFC5894, August 2010,
2214 <https://www.rfc-editor.org/info/rfc5894>.
2215
2216 [RFC6055] Thaler, D., Klensin, J., and S. Cheshire, "IAB Thoughts on
2217 Encodings for Internationalized Domain Names", RFC 6055,
2218 DOI 10.17487/RFC6055, February 2011,
2219 <https://www.rfc-editor.org/info/rfc6055>.
2220
2221 [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
2222 DOI 10.17487/RFC6265, April 2011,
2223 <https://www.rfc-editor.org/info/rfc6265>.
2224
2225 [RFC6303] Andrews, M., "Locally Served DNS Zones", BCP 163,
2226 RFC 6303, DOI 10.17487/RFC6303, July 2011,
2227 <https://www.rfc-editor.org/info/rfc6303>.
2228
2229 [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
2230 Cheshire, "Internet Assigned Numbers Authority (IANA)
2231 Procedures for the Management of the Service Name and
2232 Transport Protocol Port Number Registry", BCP 165,
2233 RFC 6335, DOI 10.17487/RFC6335, August 2011,
2234 <https://www.rfc-editor.org/info/rfc6335>.
2235
2236 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in
2237 Internationalization in the IETF", BCP 166, RFC 6365,
2238 DOI 10.17487/RFC6365, September 2011,
2239 <https://www.rfc-editor.org/info/rfc6365>.
2240
2241 [RFC6672] Rose, S. and W. Wijngaards, "DNAME Redirection in the
2242 DNS", RFC 6672, DOI 10.17487/RFC6672, June 2012,
2243 <https://www.rfc-editor.org/info/rfc6672>.
2244
2245 [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
2246 DOI 10.17487/RFC6762, February 2013,
2247 <https://www.rfc-editor.org/info/rfc6762>.
2248
2249
2250
2251
2252 Hoffman, et al. Best Current Practice [Page 41]
2253 RFC 8499 DNS Terminology January 2019
2254
2255
2256 [RFC7129] Gieben, R. and W. Mekking, "Authenticated Denial of
2257 Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129,
2258 February 2014, <https://www.rfc-editor.org/info/rfc7129>.
2259
2260 [RFC7480] Newton, A., Ellacott, B., and N. Kong, "HTTP Usage in the
2261 Registration Data Access Protocol (RDAP)", RFC 7480,
2262 DOI 10.17487/RFC7480, March 2015,
2263 <https://www.rfc-editor.org/info/rfc7480>.
2264
2265 [RFC7481] Hollenbeck, S. and N. Kong, "Security Services for the
2266 Registration Data Access Protocol (RDAP)", RFC 7481,
2267 DOI 10.17487/RFC7481, March 2015,
2268 <https://www.rfc-editor.org/info/rfc7481>.
2269
2270 [RFC7482] Newton, A. and S. Hollenbeck, "Registration Data Access
2271 Protocol (RDAP) Query Format", RFC 7482,
2272 DOI 10.17487/RFC7482, March 2015,
2273 <https://www.rfc-editor.org/info/rfc7482>.
2274
2275 [RFC7483] Newton, A. and S. Hollenbeck, "JSON Responses for the
2276 Registration Data Access Protocol (RDAP)", RFC 7483,
2277 DOI 10.17487/RFC7483, March 2015,
2278 <https://www.rfc-editor.org/info/rfc7483>.
2279
2280 [RFC7484] Blanchet, M., "Finding the Authoritative Registration Data
2281 (RDAP) Service", RFC 7484, DOI 10.17487/RFC7484, March
2282 2015, <https://www.rfc-editor.org/info/rfc7484>.
2283
2284 [RFC7485] Zhou, L., Kong, N., Shen, S., Sheng, S., and A. Servin,
2285 "Inventory and Analysis of WHOIS Registration Objects",
2286 RFC 7485, DOI 10.17487/RFC7485, March 2015,
2287 <https://www.rfc-editor.org/info/rfc7485>.
2288
2289 [RFC7793] Andrews, M., "Adding 100.64.0.0/10 Prefixes to the IPv4
2290 Locally-Served DNS Zones Registry", BCP 163, RFC 7793,
2291 DOI 10.17487/RFC7793, May 2016,
2292 <https://www.rfc-editor.org/info/rfc7793>.
2293
2294 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
2295 and P. Hoffman, "Specification for DNS over Transport
2296 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2297 2016, <https://www.rfc-editor.org/info/rfc7858>.
2298
2299 [RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
2300 Transport Layer Security (DTLS)", RFC 8094,
2301 DOI 10.17487/RFC8094, February 2017,
2302 <https://www.rfc-editor.org/info/rfc8094>.
2303
2304
2305
2306
2307 Hoffman, et al. Best Current Practice [Page 42]
2308 RFC 8499 DNS Terminology January 2019
2309
2310
2311 [RFC8109] Koch, P., Larson, M., and P. Hoffman, "Initializing a DNS
2312 Resolver with Priming Queries", BCP 209, RFC 8109,
2313 DOI 10.17487/RFC8109, March 2017,
2314 <https://www.rfc-editor.org/info/rfc8109>.
2315
2316 [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
2317 (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
2318 <https://www.rfc-editor.org/info/rfc8484>.
2319
2320 [RSSAC026] Root Server System Advisory Committee (RSSAC), "RSSAC
2321 Lexicon", 2017,
2322 <https://www.icann.org/en/system/files/files/
2323 rssac-026-14mar17-en.pdf>.
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362 Hoffman, et al. Best Current Practice [Page 43]
2363 RFC 8499 DNS Terminology January 2019
2364
2365
2366 Appendix A. Definitions Updated by This Document
2367
2368 The following definitions from RFCs are updated by this document:
2369
2370 o Forwarder in [RFC2308]
2371
2372 o QNAME in [RFC2308]
2373
2374 o Secure Entry Point (SEP) in [RFC3757]; note, however, that this
2375 RFC is already obsolete (see [RFC4033], [RFC4034], [RFC4035]).
2376
2377 Appendix B. Definitions First Defined in This Document
2378
2379 The following definitions are first defined in this document:
2380
2381 o "Alias" in Section 2
2382
2383 o "Apex" in Section 7
2384
2385 o "arpa" in Section 7
2386
2387 o "Bailiwick" in Section 7
2388
2389 o "Class independent" in Section 5
2390
2391 o "Delegation-centric zone" in Section 7
2392
2393 o "Delegation" in Section 7
2394
2395 o "DNS operator" in Section 9
2396
2397 o "DNSSEC-aware" in Section 10
2398
2399 o "DNSSEC-unaware" in Section 10
2400
2401 o "Forwarding" in Section 6
2402
2403 o "Full resolver" in Section 6
2404
2405 o "Fully-qualified domain name" in Section 2
2406
2407 o "Global DNS" in Section 2
2408
2409 o "Hardware Security Module (HSM)" in Section 10
2410
2411 o "Host name" in Section 2
2412
2413 o "IDN" in Section 2
2414
2415
2416
2417 Hoffman, et al. Best Current Practice [Page 44]
2418 RFC 8499 DNS Terminology January 2019
2419
2420
2421 o "In-bailiwick" in Section 7
2422
2423 o "Iterative resolution" in Section 6
2424
2425 o "Label" in Section 2
2426
2427 o "Locally served DNS zone" in Section 2
2428
2429 o "Naming system" in Section 2
2430
2431 o "Negative response" in Section 3
2432
2433 o "Non-recursive query" in Section 6
2434
2435 o "Open resolver" in Section 6
2436
2437 o "Out-of-bailiwick" in Section 7
2438
2439 o "Passive DNS" in Section 6
2440
2441 o "Policy-implementing resolver" in Section 6
2442
2443 o "Presentation format" in Section 5
2444
2445 o "Priming" in Section 6
2446
2447 o "Private DNS" in Section 2
2448
2449 o "Recursive resolver" in Section 6
2450
2451 o "Referrals" in Section 4
2452
2453 o "Registrant" in Section 9
2454
2455 o "Registrar" in Section 9
2456
2457 o "Registry" in Section 9
2458
2459 o "Root zone" in Section 7
2460
2461 o "Secure Entry Point (SEP)" in Section 10
2462
2463 o "Signing software" in Section 10
2464
2465 o "Split DNS" in Section 6
2466
2467 o "Stub resolver" in Section 6
2468
2469
2470
2471
2472 Hoffman, et al. Best Current Practice [Page 45]
2473 RFC 8499 DNS Terminology January 2019
2474
2475
2476 o "Subordinate" in Section 8
2477
2478 o "Superordinate" in Section 8
2479
2480 o "TLD" in Section 2
2481
2482 o "Validating resolver" in Section 10
2483
2484 o "Validation" in Section 10
2485
2486 o "View" in Section 6
2487
2488 o "Zone transfer" in Section 6
2489
2490 Index
2491
2492 A
2493 Address records 16
2494 Alias 9
2495 Anycast 22
2496 Apex 23
2497 Asterisk label 27
2498 Authoritative data 24
2499 Authoritative server 19
2500 Authoritative-only server 19
2501 arpa: Address and Routing Parameter Area Domain 26
2502
2503 C
2504 CNAME 10
2505 Canonical name 9
2506 Child 22
2507 Class 11
2508 Class independent 16
2509 Closest encloser 27
2510 Closest provable encloser 27
2511 Combined signing key (CSK) 33
2512
2513 D
2514 DNS operator 29
2515 DNSSEC Policy (DP) 34
2516 DNSSEC Practice Statement (DPS) 34
2517 DNSSEC-aware and DNSSEC-unaware 30
2518 Delegation 24
2519 Delegation-centric zone 26
2520 Domain name 5
2521
2522
2523
2524
2525
2526
2527 Hoffman, et al. Best Current Practice [Page 46]
2528 RFC 8499 DNS Terminology January 2019
2529
2530
2531 E
2532 EDNS 14
2533 EPP 28
2534 Empty non-terminals (ENT) 26
2535
2536 F
2537 FORMERR 10
2538 Fast flux DNS 26
2539 Forward lookup 26
2540 Forwarder 21
2541 Forwarding 20
2542 Full resolver 18
2543 Full-service resolver 18
2544 Fully-qualified domain name (FQDN) 8
2545
2546 G
2547 Global DNS 5
2548 Glue records 24
2549
2550 H
2551 Hardware security module (HSM) 34
2552 Hidden master 20
2553 Host name 8
2554
2555 I
2556 IDN 9
2557 In-bailiwick 25
2558 Insecure delegation 31
2559 Instance 22
2560 Internationalized Domain Name 9
2561 Iterative mode 17
2562 Iterative resolution 18
2563
2564 K
2565 Key signing key (KSK) 33
2566
2567 L
2568 Label 5
2569 Lame delegation 24
2570 Locally served DNS zone 8
2571
2572 M
2573 Master file 14
2574 Master server 19
2575 Multicast DNS 7
2576 mDNS 7
2577
2578
2579
2580
2581
2582 Hoffman, et al. Best Current Practice [Page 47]
2583 RFC 8499 DNS Terminology January 2019
2584
2585
2586 N
2587 NODATA 10
2588 NOERROR 10
2589 NOTIMP 10
2590 NS 19
2591 NSEC 31
2592 NSEC3 31
2593 NXDOMAIN 10
2594 Naming system 4
2595 Negative caching 19
2596 Negative response 11
2597 Next closer name 28
2598 Non-recursive query 18
2599
2600 O
2601 OPT 14
2602 Occluded name 26
2603 Open resolver 21
2604 Opt-out 31
2605 Origin 23
2606 Out-of-bailiwick 25
2607 Owner 15
2608
2609 P
2610 Parent 23
2611 Passive DNS 22
2612 Policy-implementing resolver 21
2613 Presentation format 14
2614 Primary master 20
2615 Primary server 20
2616 Priming 18
2617 Privacy-enabling DNS server 22
2618 Private DNS 7
2619 Public suffix 29
2620
2621 Q
2622 QNAME 11
2623
2624 R
2625 RDAP 29
2626 REFUSED 10
2627 RR 14
2628 RRset 14
2629 Recursive mode 17
2630 Recursive query 18
2631 Recursive resolver 17
2632 Referrals 13
2633 Registrant 28
2634
2635
2636
2637 Hoffman, et al. Best Current Practice [Page 48]
2638 RFC 8499 DNS Terminology January 2019
2639
2640
2641 Registrar 28
2642 Registry 28
2643 Resolver 16
2644 Reverse DNS, reverse lookup 26
2645 Root hints 18
2646 Root zone 26
2647
2648 S
2649 SERVFAIL 10
2650 SOA 14
2651 SOA field names 14
2652 Secondary server 19
2653 Secure Entry Point (SEP) 33
2654 Service name 27
2655 Signed zone 30
2656 Signing software 34
2657 Slave server 19
2658 Source of Synthesis 28
2659 Split DNS 21
2660 Split-horizon DNS 21
2661 Stealth server 20
2662 Stub resolver 17
2663 Subdomain 9
2664 Subordinate 29
2665 Superordinate 29
2666
2667 T
2668 TLD 9
2669 TTL 15
2670 Trust anchor 34
2671
2672 U
2673 Unsigned zone 30
2674
2675 V
2676 Validating resolver 33
2677 Validation 32
2678 View 21
2679
2680 W
2681 WHOIS 28
2682 Wildcard 27
2683 Wildcard domain name 27
2684
2685
2686
2687
2688
2689
2690
2691
2692 Hoffman, et al. Best Current Practice [Page 49]
2693 RFC 8499 DNS Terminology January 2019
2694
2695
2696 Z
2697 Zone 22
2698 Zone cut 23
2699 Zone enumeration 31
2700 Zone signing key (ZSK) 33
2701 Zone transfer 19
2702
2703 Acknowledgements
2704
2705 The following is the Acknowledgements section of RFC 7719.
2706
2707 The authors gratefully acknowledge all of the authors of DNS-
2708 related RFCs that proceed this one. Comments from Tony Finch,
2709 Stephane Bortzmeyer, Niall O'Reilly, Colm MacCarthaigh, Ray
2710 Bellis, John Kristoff, Robert Edmonds, Paul Wouters, Shumon Huque,
2711 Paul Ebersman, David Lawrence, Matthijs Mekking, Casey Deccio, Bob
2712 Harold, Ed Lewis, John Klensin, David Black, and many others in
2713 the DNSOP Working Group helped shape RFC 7719.
2714
2715 Most of the major changes between RFC 7719 and this document came
2716 from active discussion on the DNSOP WG. Specific people who
2717 contributed material to this document include: Bob Harold, Dick
2718 Franks, Evan Hunt, John Dickinson, Mark Andrews, Martin Hoffmann,
2719 Paul Vixie, Peter Koch, Duane Wessels, Allison Mankin, Giovane Moura,
2720 Roni Even, Dan Romascanu, and Vladmir Cunat.
2721
2722 Authors' Addresses
2723
2724 Paul Hoffman
2725 ICANN
2726
2727 Email: paul.hoffman@icann.org
2728
2729
2730 Andrew Sullivan
2731
2732 Email: ajs@anvilwalrusden.com
2733
2734
2735 Kazunori Fujiwara
2736 Japan Registry Services Co., Ltd.
2737 Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda
2738 Chiyoda-ku, Tokyo 101-0065
2739 Japan
2740
2741 Phone: +81 3 5215 8451
2742 Email: fujiwara@jprs.co.jp
2743
2744
2745
2746
2747 Hoffman, et al. Best Current Practice [Page 50]
2748
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