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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group P. Hoffman 3 Internet-Draft ICANN 4 Obsoletes: 7719 (if approved) A. Sullivan 5 Updates: 2308 (if approved) Oracle 6 Intended status: Best Current Practice K. Fujiwara 7 Expires: September 6, 2018 JPRS 8 March 5, 2018 10 DNS Terminology 11 draft-ietf-dnsop-terminology-bis-09 13 Abstract 15 The DNS is defined in literally dozens of different RFCs. The 16 terminology used by implementers and developers of DNS protocols, and 17 by operators of DNS systems, has sometimes changed in the decades 18 since the DNS was first defined. This document gives current 19 definitions for many of the terms used in the DNS in a single 20 document. 22 This document will be the successor to RFC 7719, and thus will 23 obsolete RFC 7719. It will also update RFC 2308. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on September 6, 2018. 42 Copyright Notice 44 Copyright (c) 2018 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (https://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 2. Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 61 3. DNS Response Codes . . . . . . . . . . . . . . . . . . . . . 8 62 4. DNS Transactions . . . . . . . . . . . . . . . . . . . . . . 9 63 5. Resource Records . . . . . . . . . . . . . . . . . . . . . . 12 64 6. DNS Servers and Clients . . . . . . . . . . . . . . . . . . . 14 65 7. Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 66 8. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . . . 24 67 9. Registration Model . . . . . . . . . . . . . . . . . . . . . 25 68 10. General DNSSEC . . . . . . . . . . . . . . . . . . . . . . . 27 69 11. DNSSEC States . . . . . . . . . . . . . . . . . . . . . . . . 31 70 12. Security Considerations . . . . . . . . . . . . . . . . . . . 33 71 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33 72 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 33 73 14.1. Normative References . . . . . . . . . . . . . . . . . . 33 74 14.2. Informative References . . . . . . . . . . . . . . . . . 36 75 Appendix A. Definitions Updated by this Document . . . . . . . . 40 76 Appendix B. Definitions First Defined in this Document . . . . . 40 77 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 78 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 45 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46 81 1. Introduction 83 The Domain Name System (DNS) is a simple query-response protocol 84 whose messages in both directions have the same format. (Section 2 85 gives a definition of "public DNS", which is often what people mean 86 when they say "the DNS".) The protocol and message format are 87 defined in [RFC1034] and [RFC1035]. These RFCs defined some terms, 88 but later documents defined others. Some of the terms from [RFC1034] 89 and [RFC1035] now have somewhat different meanings than they did in 90 1987. 92 This document collects a wide variety of DNS-related terms. Some of 93 them have been precisely defined in earlier RFCs, some have been 94 loosely defined in earlier RFCs, and some are not defined in any 95 earlier RFC at all. 97 Most of the definitions here are the consensus definition of the DNS 98 community -- both protocol developers and operators. Some of the 99 definitions differ from earlier RFCs, and those differences are 100 noted. In this document, where the consensus definition is the same 101 as the one in an RFC, that RFC is quoted. Where the consensus 102 definition has changed somewhat, the RFC is mentioned but the new 103 stand-alone definition is given. See Appendix A for a list of the 104 definitions that this document updates. 106 It is important to note that, during the development of this 107 document, it became clear that some DNS-related terms are interpreted 108 quite differently by different DNS experts. Further, some terms that 109 are defined in early DNS RFCs now have definitions that are generally 110 agreed to, but that are different from the original definitions. 111 Therefore, this document is a substantial revision to [RFC7719]. 113 The terms are organized loosely by topic. Some definitions are for 114 new terms for things that are commonly talked about in the DNS 115 community but that never had terms defined for them. 117 Other organizations sometimes define DNS-related terms their own way. 118 For example, the W3C defines "domain" at 119 https://specs.webplatform.org/url/webspecs/develop/. The Root Server 120 System Advisory Committee (RSSAC) has a good lexicon [RSSAC026]. 122 Note that there is no single consistent definition of "the DNS". It 123 can be considered to be some combination of the following: a commonly 124 used naming scheme for objects on the Internet; a distributed 125 database representing the names and certain properties of these 126 objects; an architecture providing distributed maintenance, 127 resilience, and loose coherency for this database; and a simple 128 query-response protocol (as mentioned below) implementing this 129 architecture. Section 2 defines "global DNS" and "private DNS" as a 130 way to deal with these differing definitions. 132 Capitalization in DNS terms is often inconsistent among RFCs and 133 various DNS practitioners. The capitalization used in this document 134 is a best guess at current practices, and is not meant to indicate 135 that other capitalization styles are wrong or archaic. In some 136 cases, multiple styles of capitalization are used for the same term 137 due to quoting from different RFCs. 139 2. Names 141 Naming system: A naming system associates names with data. Naming 142 systems have many significant facets that help differentiate them. 143 Some commonly-identified facets include: 145 * Composition of names 147 * Format of names 149 * Administration of names 151 * Types of data that can be associated with names 153 * Types of metadata for names 155 * Protocol for getting data from a name 157 * Context for resolving a name 159 Note that this list is a small subset of facets that people have 160 identified over time for naming systems, and the IETF has yet to 161 agree on a good set of facets that can be used to compare naming 162 systems. For example, other facets might include "protocol to 163 update data in a name", "privacy of names", and "privacy of data 164 associated with names", but those are not as well-defined as the 165 ones listed above. The list here is chosen because it helps 166 describe the DNS and naming systems similar to the DNS. 168 Domain name: An ordered list of one or more labels. 170 Note that this is a definition independent of the DNS RFCs, and 171 the definition here also applies to systems other than the DNS. 172 [RFC1034] defines the "domain name space" using mathematical trees 173 and their nodes in graph theory, and this definition has the same 174 practical result as the definition here. Using graph theory, a 175 domain name is a list of labels identifying a portion along one 176 edge of a directed acyclic graph. A domain name can be relative 177 to parts of the tree, or it can be fully qualified (in which case, 178 it begins at the common root of the graph). 180 Also note that different IETF and non-IETF documents have used the 181 term "domain name" in many different ways. It is common for 182 earlier documents to use "domain name" to mean "names that match 183 the syntax in [RFC1035]", but possibly with additional rules such 184 as "and are, or will be, resolvable in the global DNS" or "but 185 only using the presentation format". 187 Label: An ordered list of zero or more octets and which makes up a 188 portion of a domain name. Using graph theory, a label identifies 189 one node in a portion of the graph of all possible domain names. 191 Global DNS: Using the short set of facets listed in "Naming system", 192 the global DNS can be defined as follows. Most of the rules here 193 come from [RFC1034] and [RFC1035], although the term "global DNS" 194 has not been defined before now. 196 Composition of names -- A name in the global DNS has one or more 197 labels. The length of each label is between 0 and 63 octets 198 inclusive. In a fully-qualified domain name, the first label in 199 the ordered list is 0 octets long; it is the only label whose 200 length may be 0 octets, and it is called the "root" or "root 201 label". A domain name in the global DNS has a maximum total 202 length of 255 octets in the wire format; the root represents one 203 octet for this calculation. 205 Format of names -- Names in the global DNS are domain names. 206 There are three formats: wire format, presentation format, and 207 common display. 209 The basic wire format for names in the global DNS is a list of 210 labels ordered by decreasing distance from the root, with the root 211 label last. Each label is preceded by a length octet. [RFC1035] 212 also defines a compression scheme that modifies this format. 214 The presentation format for names in the global DNS is a list of 215 labels ordered by decreasing distance from the root, encoded as 216 ASCII, with a "." character between each label. In presentation 217 format, a fully-qualified domain name includes the root label and 218 the associated separator dot. For example, in presentation 219 format, a fully-qualified domain name with two non-root labels is 220 always shown as "example.tld." instead of "example.tld". 221 [RFC1035] defines a method for showing octets that do not display 222 in ASCII. 224 The common display format is used in applications and free text. 225 It is the same as the presentation format, but showing the root 226 label and the "." before it is optional and is rarely done. For 227 example, in common display format, a fully-qualified domain name 228 with two non-root labels is usually shown as "example.tld" instead 229 of "example.tld.". Names in the common display format are 230 normally written such that the directionality of the writing 231 system presents labels by decreasing distance from the root (so, 232 in both English and C the first label in the ordered list is 233 right-most; but in Arabic it may be left-most, depending on local 234 conventions). 236 Administration of names -- Administration is specified by 237 delegation (see the definition of "delegation" in Section 7). 238 Policies for administration of the root zone in the global DNS are 239 determined by the names operational community, which convenes 240 itself in the Internet Corporation for Assigned Names and Numbers 241 (ICANN). The names operational community selects the IANA 242 Functions Operator for the global DNS root zone. At the time this 243 document is published, that operator is Public Technical 244 Identifiers (PTI). The name servers that serve the root zone are 245 provided by independent root operators. Other zones in the global 246 DNS have their own policies for administration. 248 Types of data that can be associated with names -- A name can have 249 zero or more resource records associated with it. There are 250 numerous types of resource records with unique data structures 251 defined in many different RFCs and in the IANA registry at 252 [IANA_Resource_Registry]. 254 Types of metadata for names -- Any name that is published in the 255 DNS appears as a set of resource records (see the definition of 256 "RRset" in Section 5). Some names do not themselves have data 257 associated with them in the DNS, but "appear" in the DNS anyway 258 because they form part of a longer name that does have data 259 associated with it (see the defintion of "empty non-terminals" in 260 Section 7). 262 Protocol for getting data from a name -- The protocol described in 263 [RFC1035]. 265 Context for resolving a name -- The global DNS root zone 266 distributed by PTI. 268 Private DNS: Names that use the protocol described in [RFC1035] but 269 that do not rely on the global DNS root zone, or names that are 270 otherwise not generally available on the Internet but are using 271 the protocol described in [RFC1035]. A system can use both the 272 global DNS and one or more private DNS systems; for example, see 273 "Split DNS" in Section 6. 275 Note that domain names that do not appear in the DNS, and that are 276 intended never to be looked up using the DNS protocol, are not 277 part of the global DNS or a private DNS even though they are 278 domain names. 280 Locally served DNS zone: A locally served DNS zone is a special case 281 of private DNS. Names are resolved using the DNS protocol in a 282 local context. [RFC6303] defines subdomains of IN-ADDR.ARPA that 283 are locally served zones. Resolution of names through locally 284 served zones may result in ambiguous results. For example, the 285 same name may resolve to different results in different locally 286 served DNS zone contexts. The context through which a locally 287 served zone may be explicit, for example, as defined in [RFC6303], 288 or implicit, as defined by local DNS administration and not known 289 to the resolution client. 291 Fully qualified domain name (FQDN): This is often just a clear way 292 of saying the same thing as "domain name of a node", as outlined 293 above. However, the term is ambiguous. Strictly speaking, a 294 fully qualified domain name would include every label, including 295 the zero-length label of the root: such a name would be written 296 "www.example.net." (note the terminating dot). But because every 297 name eventually shares the common root, names are often written 298 relative to the root (such as "www.example.net") and are still 299 called "fully qualified". This term first appeared in [RFC0819]. 300 In this document, names are often written relative to the root. 302 The need for the term "fully qualified domain name" comes from the 303 existence of partially qualified domain names, which are names 304 where one or more of the earliest labels in the ordered list are 305 omitted (for example, a name of "www" derived from 306 "www.example.net"). Such relative names are understood only by 307 context. 309 Host name: This term and its equivalent, "hostname", have been 310 widely used but are not defined in [RFC1034], [RFC1035], 311 [RFC1123], or [RFC2181]. The DNS was originally deployed into the 312 Host Tables environment as outlined in [RFC0952], and it is likely 313 that the term followed informally from the definition there. Over 314 time, the definition seems to have shifted. "Host name" is often 315 meant to be a domain name that follows the rules in Section 3.5 of 316 [RFC1034], the "preferred name syntax". Note that any label in a 317 domain name can contain any octet value; hostnames are generally 318 considered to be domain names where every label follows the rules 319 in the "preferred name syntax", with the amendment that labels can 320 start with ASCII digits (this amendment comes from Section 2.1 of 321 [RFC1123]). 323 People also sometimes use the term hostname to refer to just the 324 first label of an FQDN, such as "printer" in 325 "printer.admin.example.com". (Sometimes this is formalized in 326 configuration in operating systems.) In addition, people 327 sometimes use this term to describe any name that refers to a 328 machine, and those might include labels that do not conform to the 329 "preferred name syntax". 331 TLD: A Top-Level Domain, meaning a zone that is one layer below the 332 root, such as "com" or "jp". There is nothing special, from the 333 point of view of the DNS, about TLDs. Most of them are also 334 delegation-centric zones (defined in Section 7, and there are 335 significant policy issues around their operation. TLDs are often 336 divided into sub-groups such as Country Code Top-Level Domains 337 (ccTLDs), Generic Top-Level Domains (gTLDs), and others; the 338 division is a matter of policy, and beyond the scope of this 339 document. 341 IDN: The common abbreviation for "Internationalized Domain Name". 342 The IDNA protocol is the standard mechanism for handling domain 343 names with non-ASCII characters in applications in the DNS. The 344 current standard, normally called "IDNA2008", is defined in 345 [RFC5890], [RFC5891], [RFC5892], [RFC5893], and [RFC5894]. These 346 documents define many IDN-specific terms such as "LDH label", 347 "A-label", and "U-label". [RFC6365] defines more terms that 348 relate to internationalization (some of which relate to IDNs), and 349 [RFC6055] has a much more extensive discussion of IDNs, including 350 some new terminology. 352 Subdomain: "A domain is a subdomain of another domain if it is 353 contained within that domain. This relationship can be tested by 354 seeing if the subdomain's name ends with the containing domain's 355 name." (Quoted from [RFC1034], Section 3.1). For example, in the 356 host name "nnn.mmm.example.com", both "mmm.example.com" and 357 "nnn.mmm.example.com" are subdomains of "example.com". 359 Alias: The owner of a CNAME resource record, or a subdomain of the 360 owner of a DNAME resource record. See also "canonical name". 362 Canonical name: A CNAME resource record "identifies its owner name 363 as an alias, and specifies the corresponding canonical name in the 364 RDATA section of the RR." (Quoted from [RFC1034], Section 3.6.2) 365 This usage of the word "canonical" is related to the mathematical 366 concept of "canonical form". 368 CNAME: "It is traditional to refer to the owner of a CNAME record as 369 'a CNAME'. This is unfortunate, as 'CNAME' is an abbreviation of 370 'canonical name', and the owner of a CNAME record is an alias, not 371 a canonical name." (Quoted from [RFC2181], Section 10.1.1) 373 3. DNS Response Codes 375 Some of response codes that are defined in [RFC1035] have acquired 376 their own shorthand names. All of the RCODEs are listed at 377 [IANA_Resource_Registry], although that site uses mixed-case 378 capitalization, while most documents use all-caps. Some of the 379 common names are described here, but the official list is in the IANA 380 registry. 382 NOERROR: "No error condition" (Quoted from [RFC1035], 383 Section 4.1.1.) 385 FORMERR: "Format error - The name server was unable to interpret the 386 query." (Quoted from [RFC1035], Section 4.1.1.) 388 SERVFAIL: "Server failure - The name server was unable to process 389 this query due to a problem with the name server." (Quoted from 390 [RFC1035], Section 4.1.1.) 392 NXDOMAIN: "Name Error - Meaningful only for responses from an 393 authoritative name server, this code signifies that the domain 394 name referenced in the query does not exist." (Quoted from 395 [RFC1035], Section 4.1.1.) 397 NOTIMP: "Not Implemented - The name server does not support the 398 requested kind of query." (Quoted from [RFC1035], Section 4.1.1.) 400 REFUSED: "Refused - The name server refuses to perform the specified 401 operation for policy reasons. For example, a name server may not 402 wish to provide the information to the particular requester, or a 403 name server may not wish to perform a particular operation (e.g., 404 zone transfer) for particular data." (Quoted from [RFC1035], 405 Section 4.1.1.) 407 NODATA: "A pseudo RCODE which indicates that the name is valid for 408 the given class, but there are no records of the given type. A 409 NODATA response has to be inferred from the answer." (Quoted from 410 [RFC2308], Section 1.) "NODATA is indicated by an answer with the 411 RCODE set to NOERROR and no relevant answers in the answer 412 section. The authority section will contain an SOA record, or 413 there will be no NS records there." (Quoted from [RFC2308], 414 Section 2.2.) Note that referrals have a similar format to NODATA 415 replies; [RFC2308] explains how to distinguish them. 417 The term "NXRRSET" is sometimes used as a synonym for NODATA. 418 However, this is a mistake, given that NXRRSET is a specific error 419 code defined in [RFC2136]. 421 Negative response: A response that indicates that a particular RRset 422 does not exist, or whose RCODE indicates the nameserver cannot 423 answer. Sections 2 and 7 of [RFC2308] describe the types of 424 negative responses in detail. 426 4. DNS Transactions 428 The header of a DNS message is its first 12 octets. Many of the 429 fields and flags in the header diagram in Sections 4.1.1 through 430 4.1.3 of [RFC1035] are referred to by their names in that diagram. 431 For example, the response codes are called "RCODEs", the data for a 432 record is called the "RDATA", and the authoritative answer bit is 433 often called "the AA flag" or "the AA bit". 435 QNAME: The most commonly-used rough definition is that the QNAME is 436 a field in the Question section of a query. "A standard query 437 specifies a target domain name (QNAME), query type (QTYPE), and 438 query class (QCLASS) and asks for RRs which match." (Quoted from 439 [RFC1034], Section 3.7.1.). Strictly speaking, the definition 440 comes from [RFC1035], Section 4.1.2, where the QNAME is defined in 441 respect of the Question Section. This definition appears to be 442 applied consistently: the discussion of inverse queries in section 443 6.4 refers to the "owner name of the query RR and its TTL", 444 because inverse queries populate the Answer Section and leave the 445 Question Section empty. (Inverse queries are deprecated in 446 [RFC3425], and so relevant definitions do not appear in this 447 document.) 449 [RFC2308], however, has an alternate definition that puts the 450 QNAME in the answer (or series of answers) instead of the query. 451 It defines QNAME as: "...the name in the query section of an 452 answer, or where this resolves to a CNAME, or CNAME chain, the 453 data field of the last CNAME. The last CNAME in this sense is 454 that which contains a value which does not resolve to another 455 CNAME." This definition has a certain internal logic, because of 456 the way CNAME substitution works and the definition of CNAME. If 457 a name server does not find an RRset that matches a query, but it 458 finds the same name in the same class with a CNAME record, then 459 the name server "includes the CNAME record in the response and 460 restarts the query at the domain name specified in the data field 461 of the CNAME record." ([RFC1034] Section 3.6.2). This is made 462 explicit in the resolution algorithm outlined in Section 4.3.2 of 463 [RFC1034], which says to "change QNAME to the canonical name in 464 the CNAME RR, and go back to step 1" in the case of a CNAME RR. 465 Since a CNAME record explicitly declares that the owner name is 466 canonically named what is in the RDATA, then there is a way to 467 view the new name (i.e. the name that was in the RDATA of the 468 CNAME RR) as also being the QNAME. 470 This creates a kind of confusion, however, because the answer to a 471 query that results in CNAME processing contains in the echoed 472 Question Section one QNAME (the name in the original query), and a 473 second QNAME that is in the data field of the last CNAME. The 474 confusion comes from the iterative/recursive mode of resolution, 475 which finally returns an answer that need not actually have the 476 same owner name as the QNAME contained in the original query. 478 To address this potential confusion, it is helpful to distinguish 479 between three meanings: 481 * QNAME (original): The name actually sent in the Question 482 Section in the orignal query, which is always echoed in the 483 (final) reply in the Question Section when the QR bit is set to 484 1. 486 * QNAME (effective): A name actually resolved, which is either 487 the name originally queried, or a name received in a CNAME 488 chain response. 490 * QNAME (final): The name actually resolved, which is either the 491 name actually queried or else the last name in a CNAME chain 492 response. 494 Note that, because the definition in [RFC2308] is actually for a 495 different concept than what was in [RFC1034], it would have be 496 better if [RFC2308] had used a different name for that concept. 497 In general use today, QNAME almost always means what is defined 498 above as "QNAME (original)". 500 Referrals: A type of response in which a server, signalling that it 501 is not (completely) authoritative for an answer, provides the 502 querying resolver with an alternative place to send its query. 503 Referrals can be partial. 505 A referral arises when a server is not performing recursive 506 service while answering a query. It appears in step 3(b) of the 507 algorithm in [RFC1034], Section 4.3.2. 509 There are two types of referral response. The first is a downward 510 referral (sometimes described as "delegation response"), where the 511 server is authoritative for some portion of the QNAME. The 512 authority section RRset's RDATA contains the name servers 513 specified at the referred-to zone cut. In normal DNS operation, 514 this kind of response is required in order to find names beneath a 515 delegation. The bare use of "referral" means this kind of 516 referral, and many people believe that this is the only legitimate 517 kind of referral in the DNS. 519 The second is an upward referral (sometimes described as "root 520 referral"), where the server is not authoritative for any portion 521 of the QNAME. When this happens, the referred-to zone in the 522 authority section is usually the root zone (.). In normal DNS 523 operation, this kind of response is not required for resolution or 524 for correctly answering any query. There is no requirement that 525 any server send upward referrals. Some people regard upward 526 referrals as a sign of a misconfiguration or error. Upward 527 referrals always need some sort of qualifier (such as "upward" or 528 "root"), and are never identified by the bare word "referral". 530 A response that has only a referral contains an empty answer 531 section. It contains the NS RRset for the referred-to zone in the 532 authority section. It may contain RRs that provide addresses in 533 the additional section. The AA bit is clear. 535 In the case where the query matches an alias, and the server is 536 not authoritative for the target of the alias but it is 537 authoritative for some name above the target of the alias, the 538 resolution algorithm will produce a response that contains both 539 the authoritative answer for the alias, and also a referral. Such 540 a partial answer and referral response has data in the answer 541 section. It has the NS RRset for the referred-to zone in the 542 authority section. It may contain RRs that provide addresses in 543 the additional section. The AA bit is set, because the first name 544 in the answer section matches the QNAME and the server is 545 authoritative for that answer (see [RFC1035], Section 4.1.1). 547 5. Resource Records 549 RR: An acronym for resource record. ([RFC1034], Section 3.6.) 551 RRset: A set of resource records with the same label, class and 552 type, but with different data. (Definition from [RFC2181]) Also 553 spelled RRSet in some documents. As a clarification, "same label" 554 in this definition means "same owner name". In addition, 555 [RFC2181] states that "the TTLs of all RRs in an RRSet must be the 556 same". (This definition is definitely not the same as "the 557 response one gets to a query for QTYPE=ANY", which is an 558 unfortunate misunderstanding.) 560 Master file: "Master files are text files that contain RRs in text 561 form. Since the contents of a zone can be expressed in the form 562 of a list of RRs a master file is most often used to define a 563 zone, though it can be used to list a cache's contents." 564 ([RFC1035], Section 5.) Master files are sometimes called "zone 565 files". 567 Presentation format: The text format used in master files. This 568 format is shown but not formally defined in [RFC1034] and 569 [RFC1035]. The term "presentation format" first appears in 570 [RFC4034]. 572 EDNS: The extension mechanisms for DNS, defined in [RFC6891]. 573 Sometimes called "EDNS0" or "EDNS(0)" to indicate the version 574 number. EDNS allows DNS clients and servers to specify message 575 sizes larger than the original 512 octet limit, to expand the 576 response code space, and potentially to carry additional options 577 that affect the handling of a DNS query. 579 OPT: A pseudo-RR (sometimes called a "meta-RR") that is used only to 580 contain control information pertaining to the question-and-answer 581 sequence of a specific transaction. (Definition from [RFC6891], 582 Section 6.1.1) It is used by EDNS. 584 Owner: The domain name where a RR is found ([RFC1034], Section 3.6). 585 Often appears in the term "owner name". 587 SOA field names: DNS documents, including the definitions here, 588 often refer to the fields in the RDATA of an SOA resource record 589 by field name. Those fields are defined in Section 3.3.13 of 590 [RFC1035]. The names (in the order they appear in the SOA RDATA) 591 are MNAME, RNAME, SERIAL, REFRESH, RETRY, EXPIRE, and MINIMUM. 592 Note that the meaning of MINIMUM field is updated in Section 4 of 593 [RFC2308]; the new definition is that the MINIMUM field is only 594 "the TTL to be used for negative responses". This document tends 595 to use field names instead of terms that describe the fields. 597 TTL: The maximum "time to live" of a resource record. "A TTL value 598 is an unsigned number, with a minimum value of 0, and a maximum 599 value of 2147483647. That is, a maximum of 2^31 - 1. When 600 transmitted, the TTL is encoded in the less significant 31 bits of 601 the 32 bit TTL field, with the most significant, or sign, bit set 602 to zero." (Quoted from [RFC2181], Section 8) (Note that [RFC1035] 603 erroneously stated that this is a signed integer; that was fixed 604 by [RFC2181].) 606 The TTL "specifies the time interval that the resource record may 607 be cached before the source of the information should again be 608 consulted". (Quoted from [RFC1035], Section 3.2.1) Also: "the 609 time interval (in seconds) that the resource record may be cached 610 before it should be discarded". (Quoted from [RFC1035], 611 Section 4.1.3). Despite being defined for a resource record, the 612 TTL of every resource record in an RRset is required to be the 613 same ([RFC2181], Section 5.2). 615 The reason that the TTL is the maximum time to live is that a 616 cache operator might decide to shorten the time to live for 617 operational purposes, such as if there is a policy to disallow TTL 618 values over a certain number. Some servers are known to ignore 619 the TTL on some RRsets (such as when the authoritative data has a 620 very short TTL) even though this is against the advice in RFC 621 1035. An RRset can be flushed from the cache before the end of 622 the TTL interval, at which point the value of the TTL becomes 623 unknown because the RRset with which it was associated no longer 624 exists. 626 There is also the concept of a "default TTL" for a zone, which can 627 be a configuration parameter in the server software. This is 628 often expressed by a default for the entire server, and a default 629 for a zone using the $TTL directive in a zone file. The $TTL 630 directive was added to the master file format by [RFC2308]. 632 Class independent: A resource record type whose syntax and semantics 633 are the same for every DNS class. A resource record type that is 634 not class independent has different meanings depending on the DNS 635 class of the record, or the meaning is undefined for classes other 636 than IN (class 1, the Internet). 638 Address records: Records whose type is A or AAAA. [RFC2181] 639 informally defines these as "(A, AAAA, etc)". Note that new types 640 of address records could be defined in the future. 642 6. DNS Servers and Clients 644 This section defines the terms used for the systems that act as DNS 645 clients, DNS servers, or both. In the RFCs, DNS servers are 646 sometimes called "name servers", "nameservers", or just "servers". 647 There is no formal definition of DNS server, but the RFCs generally 648 assume that it is an Internet server that listens for queries and 649 sends responses using the DNS protocol defined in [RFC1035] and its 650 successors. 652 For terminology specific to the public DNS root server system, see 653 [RSSAC026]. That document defines terms such as "root server", "root 654 server operator", and terms that are specific to the way that the 655 root zone of the public DNS is served. 657 Resolver: A program "that extract[s] information from name servers 658 in response to client requests." (Quoted from [RFC1034], 659 Section 2.4) "The resolver is located on the same machine as the 660 program that requests the resolver's services, but it may need to 661 consult name servers on other hosts." (Quoted from [RFC1034], 662 Section 5.1) A resolver performs queries for a name, type, and 663 class, and receives answers. The logical function is called 664 "resolution". In practice, the term is usually referring to some 665 specific type of resolver (some of which are defined below), and 666 understanding the use of the term depends on understanding the 667 context. 669 A related term is "resolve", which is not formally defined in 670 [RFC1034] or [RFC1035]. An imputed definition might be "asking a 671 question that consists of a domain name, class, and type, and 672 receiving some sort of answer". Similarly, an imputed definition 673 of "resolution" might be "the answer received from resolving". 675 Stub resolver: A resolver that cannot perform all resolution itself. 676 Stub resolvers generally depend on a recursive resolver to 677 undertake the actual resolution function. Stub resolvers are 678 discussed but never fully defined in Section 5.3.1 of [RFC1034]. 679 They are fully defined in Section 6.1.3.1 of [RFC1123]. 681 Iterative mode: A resolution mode of a server that receives DNS 682 queries and responds with a referral to another server. 683 Section 2.3 of [RFC1034] describes this as "The server refers the 684 client to another server and lets the client pursue the query". A 685 resolver that works in iterative mode is sometimes called an 686 "iterative resolver". See also "iterative resolution" later in 687 this section. 689 Recursive mode: A resolution mode of a server that receives DNS 690 queries and either responds to those queries from a local cache or 691 sends queries to other servers in order to get the final answers 692 to the original queries. Section 2.3 of [RFC1034] describes this 693 as "The first server pursues the query for the client at another 694 server". A server operating in recursive mode may be thought of 695 as having a name server side (which is what answers the query) and 696 a resolver side (which performs the resolution function). Systems 697 operating in this mode are commonly called "recursive servers". 698 Sometimes they are called "recursive resolvers". While strictly 699 the difference between these is that one of them sends queries to 700 another recursive server and the other does not, in practice it is 701 not possible to know in advance whether the server that one is 702 querying will also perform recursion; both terms can be observed 703 in use interchangeably. 705 Full resolver: This term is used in [RFC1035], but it is not defined 706 there. RFC 1123 defines a "full-service resolver" that may or may 707 not be what was intended by "full resolver" in [RFC1035]. This 708 term is not properly defined in any RFC. 710 Full-service resolver: Section 6.1.3.1 of [RFC1123] defines this 711 term to mean a resolver that acts in recursive mode with a cache 712 (and meets other requirements). 714 Recursive resolver: A resolver that acts in recursive mode. In 715 general, a recursive resolver is expected to cache the answers it 716 receives (which would make it a full-service resolver), but some 717 recursive resolvers might not cache. 719 Recursive query: A query with the Recursion Desired (RD) bit set to 720 1 in the header.(See Section 4.1.1 of [RFC1035].) If recursive 721 service is available and is requested by the RD bit in the query, 722 the server uses its resolver to answer the query. (See 723 Section 4.3.2 of [RFC1035].) 725 Non-recursive query: A query with the Recursion Desired (RD) bit set 726 to 0 in the header. A server can answer non-recursive queries 727 using only local information: the response contains either an 728 error, the answer, or a referral to some other server "closer" to 729 the answer. (See Section 4.3.1 of [RFC1035].) 731 Iterative query: Synonym for non-recursive query that happens to be 732 a query in a series of recursive queries, but that is itself not a 733 recursive query. This term is used in a number of RFCs though 734 never explicitly defined. 736 Iterative resolution: A name server may be presented with a query 737 that can only be answered by some other server. The two general 738 approaches to dealing with this problem are "recursive", in which 739 the first server pursues the query for the client at another 740 server, and "iterative", in which the server refers the client to 741 another server and lets the client pursue the query there. (See 742 Section 2.3 of [RFC1034].) 744 In iterative resolution, the client repeatedly makes non-recursive 745 queries and follows referrals and/or aliases. The iterative 746 resolution algorithm is described in Section 5.3.3 of [RFC1034]. 748 Priming: "The act of finding the list of root servers from a 749 configuration that lists some or all of the purported IP addresses 750 of some or all of those root servers." (Quoted from [RFC8109], 751 Section 2.) In order to operate in recursive mode, a resolver 752 needs to know the address of at least one root server. Priming is 753 most often done from a configuration setting that contains a list 754 of authoritative servers for the root zone. 756 Root hints: "Operators who manage a DNS recursive resolver typically 757 need to configure a 'root hints file'. This file contains the 758 names and IP addresses of the authoritative name servers for the 759 root zone, so the software can bootstrap the DNS resolution 760 process. For many pieces of software, this list comes built into 761 the software." (Quoted from [IANA_RootFiles]) This file is often 762 used in priming. 764 Negative caching: "The storage of knowledge that something does not 765 exist, cannot give an answer, or does not give an answer." 766 (Quoted from [RFC2308], Section 1) 768 Authoritative server: "A server that knows the content of a DNS zone 769 from local knowledge, and thus can answer queries about that zone 770 without needing to query other servers." (Quoted from [RFC2182], 771 Section 2.) It is a system that responds to DNS queries with 772 information about zones for which it has been configured to answer 773 with the AA flag in the response header set to 1. It is a server 774 that has authority over one or more DNS zones. Note that it is 775 possible for an authoritative server to respond to a query without 776 the parent zone delegating authority to that server. 777 Authoritative servers also provide "referrals", usually to child 778 zones delegated from them; these referrals have the AA bit set to 779 0 and come with referral data in the Authority and (if needed) the 780 Additional sections. 782 Authoritative-only server: A name server that only serves 783 authoritative data and ignores requests for recursion. It will 784 "not normally generate any queries of its own. Instead, it 785 answers non-recursive queries from iterative resolvers looking for 786 information in zones it serves." (Quoted from [RFC4697], 787 Section 2.4) 789 Zone transfer: The act of a client requesting a copy of a zone and 790 an authoritative server sending the needed information. (See 791 Section 7 for a description of zones.) There are two common 792 standard ways to do zone transfers: the AXFR ("Authoritative 793 Transfer") mechanism to copy the full zone (described in 794 [RFC5936], and the IXFR ("Incremental Transfer") mechanism to copy 795 only parts of the zone that have changed (described in [RFC1995]). 796 Many systems use non-standard methods for zone transfer outside 797 the DNS protocol. 799 Secondary server: "An authoritative server which uses zone transfer 800 to retrieve the zone" (Quoted from [RFC1996], Section 2.1). 801 Secondary servers are also discussed in [RFC1034]. [RFC2182] 802 describes secondary servers in more detail. Although early DNS 803 RFCs such as [RFC1996] referred to this as a "slave", the current 804 common usage has shifted to calling it a "secondary". 806 Slave server: See secondary server. 808 Primary server: "Any authoritative server configured to be the 809 source of zone transfer for one or more [secondary] servers" 810 (Quoted from [RFC1996], Section 2.1) or, more specifically, "an 811 authoritative server configured to be the source of AXFR or IXFR 812 data for one or more [secondary] servers" (Quoted from [RFC2136]). 813 Primary servers are also discussed in [RFC1034]. Although early 814 DNS RFCs such as [RFC1996] referred to this as a "master", the 815 current common usage has shifted to "primary". 817 Master server: See primary server. 819 Primary master: "The primary master is named in the zone's SOA MNAME 820 field and optionally by an NS RR". (Quoted from [RFC1996], 821 Section 2.1). [RFC2136] defines "primary master" as "Master 822 server at the root of the AXFR/IXFR dependency graph. The primary 823 master is named in the zone's SOA MNAME field and optionally by an 824 NS RR. There is by definition only one primary master server per 825 zone." The idea of a primary master is only used by [RFC2136], 826 and is considered archaic in other parts of the DNS. 828 The idea of a primary master is only used in [RFC1996] and 829 [RFC2136]. A modern interpretation of the term "primary master" 830 is a server that is both authoritative for a zone and that gets 831 its updates to the zone from configuration (such as a master file) 832 or from UPDATE transactions. 834 Stealth server: This is "like a slave server except not listed in an 835 NS RR for the zone." (Quoted from [RFC1996], Section 2.1) 837 Hidden master: A stealth server that is a primary server for zone 838 transfers. "In this arrangement, the master name server that 839 processes the updates is unavailable to general hosts on the 840 Internet; it is not listed in the NS RRset." (Quoted from 841 [RFC6781], Section 3.4.3). An earlier RFC, [RFC4641], said that 842 the hidden master's name "appears in the SOA RRs MNAME field", 843 although in some setups, the name does not appear at all in the 844 public DNS. A hidden master can also be a secondary server 845 itself. 847 Forwarding: The process of one server sending a DNS query with the 848 RD bit set to 1 to another server to resolve that query. 849 Forwarding is a function of a DNS resolver; it is different than 850 simply blindly relaying queries. 852 [RFC5625] does not give a specific definition for forwarding, but 853 describes in detail what features a system that forwards needs to 854 support. Systems that forward are sometimes called "DNS proxies", 855 but that term has not yet been defined (even in [RFC5625]). 857 Forwarder: Section 1 of [RFC2308] describes a forwarder as "a 858 nameserver used to resolve queries instead of directly using the 859 authoritative nameserver chain". [RFC2308] further says "The 860 forwarder typically either has better access to the internet, or 861 maintains a bigger cache which may be shared amongst many 862 resolvers." That definition appears to suggest that forwarders 863 normally only query authoritative servers. In current use, 864 however, forwarders often stand between stub resolvers and 865 recursive servers. [RFC2308] is silent on whether a forwarder is 866 iterative-only or can be a full-service resolver. 868 Policy-implementing resolver: A resolver acting in recursive mode 869 that changes some of the answers that it returns based on policy 870 criteria, such as to prevent access to malware sites or 871 objectionable content. In general, a stub resolver has no idea 872 whether upstream resolvers implement such policy or, if they do, 873 the exact policy about what changes will be made. In some cases, 874 the user of the stub resolver has selected the policy-implementing 875 resolver with the explicit intention of using it to implement the 876 policies. In other cases, policies are imposed without the user 877 of the stub resolver being informed. 879 Open resolver: A full-service resolver that accepts and processes 880 queries from any (or nearly any) stub resolver. This is sometimes 881 also called a "public resolver", although the term "public 882 resolver" is used more with open resolvers that are meant to be 883 open, as compared to the vast majority of open resolvers that are 884 probably misconfigured to be open. Open resolvers are discussed 885 in [RFC5358] 887 View: A configuration for a DNS server that allows it to provide 888 different answers depending on attributes of the query. 889 Typically, views differ by the source IP address of a query, but 890 can also be based on the destination IP address, the type of query 891 (such as AXFR), whether it is recursive, and so on. Views are 892 often used to provide more names or different addresses to queries 893 from "inside" a protected network than to those "outside" that 894 network. Views are not a standardized part of the DNS, but they 895 are widely implemented in server software. 897 Passive DNS: A mechanism to collect DNS data by storing DNS 898 responses from name servers. Some of these systems also collect 899 the DNS queries associated with the responses, although doing so 900 raises some privacy concerns. Passive DNS databases can be used 901 to answer historical questions about DNS zones such as which 902 values were present at a given time in the past, or when a name 903 was spotted first. Passive DNS databases allow searching of the 904 stored records on keys other than just the name and type, such as 905 "find all names which have A records of a particular value". 907 Anycast: "The practice of making a particular service address 908 available in multiple, discrete, autonomous locations, such that 909 datagrams sent are routed to one of several available locations." 910 (Quoted from [RFC4786], Section 2) 912 Instance: "When anycast routing is used to allow more than one 913 server to have the same IP address, each one of those servers is 914 commonly referred to as an 'instance'." "An instance of a server, 915 such as a root server, is often referred to as an 'Anycast 916 instance'." (Quoted from [RSSAC026]) 918 Split DNS: "Where a corporate network serves up partly or completely 919 different DNS inside and outside its firewall. There are many 920 possible variants on this; the basic point is that the 921 correspondence between a given FQDN (fully qualified domain name) 922 and a given IPv4 address is no longer universal and stable over 923 long periods." (Quoted from [RFC2775], Section 3.8) 925 7. Zones 927 This section defines terms that are used when discussing zones that 928 are being served or retrieved. 930 Zone: "Authoritative information is organized into units called 931 'zones', and these zones can be automatically distributed to the 932 name servers which provide redundant service for the data in a 933 zone." (Quoted from [RFC1034], Section 2.4) 935 Child: "The entity on record that has the delegation of the domain 936 from the Parent." (Quoted from [RFC7344], Section 1.1) 938 Parent: "The domain in which the Child is registered." (Quoted from 939 [RFC7344], Section 1.1) Earlier, "parent name server" was defined 940 in [RFC0882] as "the name server that has authority over the place 941 in the domain name space that will hold the new domain". (Note 942 that [RFC0882] was obsoleted by [RFC1034] and [RFC1035].) 943 [RFC0819] also has some description of the relationship between 944 parents and children. 946 Origin: 948 (a) "The domain name that appears at the top of a zone (just below 949 the cut that separates the zone from its parent). The name of the 950 zone is the same as the name of the domain at the zone's origin." 951 (Quoted from [RFC2181], Section 6.) These days, this sense of 952 "origin" and "apex" (defined below) are often used 953 interchangeably. 955 (b) The domain name within which a given relative domain name 956 appears in zone files. Generally seen in the context of 957 "$ORIGIN", which is a control entry defined in [RFC1035], 958 Section 5.1, as part of the master file format. For example, if 959 the $ORIGIN is set to "example.org.", then a master file line for 960 "www" is in fact an entry for "www.example.org.". 962 Apex: The point in the tree at an owner of an SOA and corresponding 963 authoritative NS RRset. This is also called the "zone apex". 964 [RFC4033] defines it as "the name at the child's side of a zone 965 cut". The "apex" can usefully be thought of as a data-theoretic 966 description of a tree structure, and "origin" is the name of the 967 same concept when it is implemented in zone files. The 968 distinction is not always maintained in use, however, and one can 969 find uses that conflict subtly with this definition. [RFC1034] 970 uses the term "top node of the zone" as a synonym of "apex", but 971 that term is not widely used. These days, the first sense of 972 "origin" (above) and "apex" are often used interchangeably. 974 Zone cut: The delimitation point between two zones where the origin 975 of one of the zones is the child of the other zone. 977 "Zones are delimited by 'zone cuts'. Each zone cut separates a 978 'child' zone (below the cut) from a 'parent' zone (above the cut). 979 (Quoted from [RFC2181], Section 6; note that this is barely an 980 ostensive definition.) Section 4.2 of [RFC1034] uses "cuts" as 981 'zone cut'." 983 Delegation: The process by which a separate zone is created in the 984 name space beneath the apex of a given domain. Delegation happens 985 when an NS RRset is added in the parent zone for the child origin. 986 Delegation inherently happens at a zone cut. The term is also 987 commonly a noun: the new zone that is created by the act of 988 delegating. 990 Authoritative data: "All of the RRs attached to all of the nodes 991 from the top node of the zone down to leaf nodes or nodes above 992 cuts around the bottom edge of the zone." (Quoted from [RFC1034], 993 Section 4.2.1) It is noted that this definition might 994 inadvertently also include any NS records that appear in the zone, 995 even those that might not truly be authoritative because there are 996 identical NS RRs below the zone cut. This reveals the ambiguity 997 in the notion of authoritative data, because the parent-side NS 998 records authoritatively indicate the delegation, even though they 999 are not themselves authoritative data. 1001 Lame delegation: "A lame delegations exists when a nameserver is 1002 delegated responsibility for providing nameservice for a zone (via 1003 NS records) but is not performing nameservice for that zone 1004 (usually because it is not set up as a primary or secondary for 1005 the zone)." (Definition from [RFC1912], Section 2.8) 1007 Glue records: "[Resource records] which are not part of the 1008 authoritative data [of the zone], and are address resource records 1009 for the [name servers in subzones]. These RRs are only necessary 1010 if the name server's name is 'below' the cut, and are only used as 1011 part of a referral response." Without glue "we could be faced 1012 with the situation where the NS RRs tell us that in order to learn 1013 a name server's address, we should contact the server using the 1014 address we wish to learn." (Definition from [RFC1034], 1015 Section 4.2.1) 1017 A later definition is that glue "includes any record in a zone 1018 file that is not properly part of that zone, including nameserver 1019 records of delegated sub-zones (NS records), address records that 1020 accompany those NS records (A, AAAA, etc), and any other stray 1021 data that might appear" ([RFC2181], Section 5.4.1). Although glue 1022 is sometimes used today with this wider definition in mind, the 1023 context surrounding the [RFC2181] definition suggests it is 1024 intended to apply to the use of glue within the document itself 1025 and not necessarily beyond. 1027 Bailiwick: "In-bailiwick" is an adjective to describe a name server 1028 whose name is either subordinate to or (rarely) the same as the 1029 origin of the zone that contains the delegation to the name 1030 server. In-bailiwick name servers may have glue records in their 1031 parent zone (using the first of the definitions of "glue records" 1032 in the definition above). (The term "bailiwick" means the 1033 district or territory where a bailiff or policeman has 1034 jusrisdiction.) 1036 "In-bailiwick" names are divided into two type of name server 1037 names: "in-domain" names and "sibling domain" names. 1039 * In-domain: an adjective to describe a name server whose name is 1040 either subordinate to or (rarely) the same as the owner name of 1041 the NS resource records. An in-domain name server name MUST 1042 have glue records or name resolution fails. For example, a 1043 delegation for "child.example.com" may have "in-domain" name 1044 server name "ns.child.example.com". 1046 * Sibling domain: a name server's name that is either subordinate 1047 to or (rarely) the same as the zone origin and not subordinate 1048 to or the same as the owner name of the NS resource records. 1049 Glue records for sibling domains are allowed, but not 1050 necessary. For example, a delegation for "child.example.com" 1051 in "example.com" zone may have "sibling" name server name 1052 "ns.another.example.com". 1054 "Out-of-bailiwick" is the antonym of in-bailiwick. An adjective 1055 to describe a name server whose name is not subordinate to or the 1056 same as the zone origin. Glue records for out-of-bailiwick name 1057 servers are useless. Following table shows examples of delegation 1058 types. 1060 Delegation |Parent|Name Server Name | Type 1061 -----------+------+------------------+----------------------------- 1062 com | . |a.gtld-servers.net|in-bailiwick / sibling domain 1063 net | . |a.gtld-servers.net|in-bailiwick / in-domain 1064 example.org| org |ns.example.org |in-bailiwick / in-domain 1065 example.org| org |ns.ietf.org |in-bailiwick / sibling domain 1066 example.org| org |ns.example.com |out-of-bailiwick 1067 example.jp | jp |ns.example.jp |in-bailiwick / in-domain 1068 example.jp | jp |ns.example.ne.jp |in-bailiwick / sibling domain 1069 example.jp | jp |ns.example.com |out-of-bailiwick 1071 Root zone: The zone of a DNS-based tree whose apex is the zero- 1072 length label. Also sometimes called "the DNS root". 1074 Empty non-terminals (ENT): "Domain names that own no resource 1075 records but have subdomains that do." (Quoted from [RFC4592], 1076 Section 2.2.2.) A typical example is in SRV records: in the name 1077 "_sip._tcp.example.com", it is likely that "_tcp.example.com" has 1078 no RRsets, but that "_sip._tcp.example.com" has (at least) an SRV 1079 RRset. 1081 Delegation-centric zone: A zone that consists mostly of delegations 1082 to child zones. This term is used in contrast to a zone that 1083 might have some delegations to child zones, but also has many data 1084 resource records for the zone itself and/or for child zones. The 1085 term is used in [RFC4956] and [RFC5155], but is not defined there. 1087 Occluded name: "The addition of a delegation point via dynamic 1088 update will render all subordinate domain names to be in a limbo, 1089 still part of the zone, but not available to the lookup process. 1090 The addition of a DNAME resource record has the same impact. The 1091 subordinate names are said to be 'occluded'." (Quoted from 1092 [RFC5936], Section 3.5) 1094 Fast flux DNS: This "occurs when a domain is found in DNS using A 1095 records to multiple IP addresses, each of which has a very short 1096 Time-to-Live (TTL) value associated with it. This means that the 1097 domain resolves to varying IP addresses over a short period of 1098 time." (Quoted from [RFC6561], Section 1.1.5, with typo 1099 corrected) It is often used to deliver malware. Because the 1100 addresses change so rapidly, it is difficult to ascertain all the 1101 hosts. It should be noted that the technique also works with AAAA 1102 records, but such use is not frequently observed on the Internet 1103 as of this writing. 1105 Reverse DNS, reverse lookup: "The process of mapping an address to a 1106 name is generally known as a 'reverse lookup', and the IN- 1107 ADDR.ARPA and IP6.ARPA zones are said to support the 'reverse 1108 DNS'." (Quoted from [RFC5855], Section 1) 1110 Forward lookup: "Hostname-to-address translation". (Quoted from 1111 [RFC2133], Section 6) 1113 arpa: Address and Routing Parameter Area Domain: "The 'arpa' domain 1114 was originally established as part of the initial deployment of 1115 the DNS, to provide a transition mechanism from the Host Tables 1116 that were common in the ARPANET, as well as a home for the IPv4 1117 reverse mapping domain. During 2000, the abbreviation was 1118 redesignated to 'Address and Routing Parameter Area' in the hope 1119 of reducing confusion with the earlier network name." (Quoted 1120 from [RFC3172], Section 2.) .arpa is an "infrastructure domain", a 1121 domain whose "role is to support the operating infrastructure of 1122 the Internet". (Quoted from [RFC3172], Section 2.) 1124 Service name: "Service names are the unique key in the Service Name 1125 and Transport Protocol Port Number registry. This unique symbolic 1126 name for a service may also be used for other purposes, such as in 1127 DNS SRV records." (Quoted from [RFC6335], Section 5.) 1129 8. Wildcards 1131 Wildcard: [RFC1034] defined "wildcard", but in a way that turned out 1132 to be confusing to implementers. For an extended discussion of 1133 wildcards, including clearer definitions, see [RFC4592]. Special 1134 treatment is given to RRs with owner names starting with the label 1135 "*". "Such RRs are called 'wildcards'. Wildcard RRs can be 1136 thought of as instructions for synthesizing RRs." (Quoted from 1137 [RFC1034], Section 4.3.3) 1139 Asterisk label: "The first octet is the normal label type and length 1140 for a 1-octet-long label, and the second octet is the ASCII 1141 representation for the '*' character. A descriptive name of a 1142 label equaling that value is an 'asterisk label'." (Quoted from 1143 [RFC4592], Section 2.1.1) 1145 Wildcard domain name: "A 'wildcard domain name' is defined by having 1146 its initial (i.e., leftmost or least significant) label be 1147 asterisk label." (Quoted from [RFC4592], Section 2.1.1) 1149 Closest encloser: "The longest existing ancestor of a name." 1150 (Quoted from [RFC5155], Section 1.3) An earlier definition is "The 1151 node in the zone's tree of existing domain names that has the most 1152 labels matching the query name (consecutively, counting from the 1153 root label downward). Each match is a 'label match' and the order 1154 of the labels is the same." (Quoted from [RFC4592], 1155 Section 3.3.1) 1157 Closest provable encloser: "The longest ancestor of a name that can 1158 be proven to exist. Note that this is only different from the 1159 closest encloser in an Opt-Out zone." (Quoted from [RFC5155], 1160 Section 1.3) 1162 Next closer name: "The name one label longer than the closest 1163 provable encloser of a name." (Quoted from [RFC5155], 1164 Section 1.3) 1166 Source of Synthesis: "The source of synthesis is defined in the 1167 context of a query process as that wildcard domain name 1168 immediately descending from the closest encloser, provided that 1169 this wildcard domain name exists. 'Immediately descending' means 1170 that the source of synthesis has a name of the form: .." (Quoted from [RFC4592], 1172 Section 3.3.1) 1174 9. Registration Model 1176 Registry: The administrative operation of a zone that allows 1177 registration of names within that zone. People often use this 1178 term to refer only to those organizations that perform 1179 registration in large delegation-centric zones (such as TLDs); but 1180 formally, whoever decides what data goes into a zone is the 1181 registry for that zone. This definition of "registry" is from a 1182 DNS point of view; for some zones, the policies that determine 1183 what can go in the zone are decided by superior zones and not the 1184 registry operator. 1186 Registrant: An individual or organization on whose behalf a name in 1187 a zone is registered by the registry. In many zones, the registry 1188 and the registrant may be the same entity, but in TLDs they often 1189 are not. 1191 Registrar: A service provider that acts as a go-between for 1192 registrants and registries. Not all registrations require a 1193 registrar, though it is common to have registrars involved in 1194 registrations in TLDs. 1196 EPP: The Extensible Provisioning Protocol (EPP), which is commonly 1197 used for communication of registration information between 1198 registries and registrars. EPP is defined in [RFC5730]. 1200 WHOIS: A protocol specified in [RFC3912], often used for querying 1201 registry databases. WHOIS data is frequently used to associate 1202 registration data (such as zone management contacts) with domain 1203 names. The term "WHOIS data" is often used as a synonym for the 1204 registry database, even though that database may be served by 1205 different protocols, particularly RDAP. The WHOIS protocol is 1206 also used with IP address registry data. 1208 RDAP: The Registration Data Access Protocol, defined in [RFC7480], 1209 [RFC7481], [RFC7482], [RFC7483], [RFC7484], and [RFC7485]. The 1210 RDAP protocol and data format are meant as a replacement for 1211 WHOIS. 1213 DNS operator: An entity responsible for running DNS servers. For a 1214 zone's authoritative servers, the registrant may act as their own 1215 DNS operator, or their registrar may do it on their behalf, or 1216 they may use a third-party operator. For some zones, the registry 1217 function is performed by the DNS operator plus other entities who 1218 decide about the allowed contents of the zone. 1220 Public suffix: "A domain that is controlled by a public registry." 1221 (Quoted from [RFC6265], Section 5.3) A common definition for this 1222 term is a domain under which subdomains can be registered, and on 1223 which HTTP cookies (which are described in detail in [RFC6265]) 1224 should not be set. There is no indication in a domain name 1225 whether it is a public suffix; that can only be determined by 1226 outside means. In fact, both a domain and a subdomain of that 1227 domain can be public suffixes. 1229 There is nothing inherent in a domain name to indicate whether it 1230 is a public suffix. One resource for identifying public suffixes 1231 is the Public Suffix List (PSL) maintained by Mozilla 1232 (http://publicsuffix.org/). 1234 For example, at the time this document is published, the "com.au" 1235 domain is listed as a public suffix in the PSL. (Note that this 1236 example might change in the future.) 1238 Note that the term "public suffix" is controversial in the DNS 1239 community for many reasons, and may be significantly changed in 1240 the future. One example of the difficulty of calling a domain a 1241 public suffix is that designation can change over time as the 1242 registration policy for the zone changes, such as was the case 1243 with the "uk" TLD in 2014. 1245 Subordinate and Superordinate: These terms are introduced in 1246 [RFC3731] for use in the registration model, but not defined 1247 there. Instead, they are given in examples. "For example, domain 1248 name 'example.com' has a superordinate relationship to host name 1249 ns1.example.com'." "For example, host ns1.example1.com is a 1250 subordinate host of domain example1.com, but it is a not a 1251 subordinate host of domain example2.com." (Quoted from [RFC3731], 1252 Section 1.1.) These terms are strictly ways of referring to the 1253 relationship standing of two domains where one is a subdomain of 1254 the other. 1256 10. General DNSSEC 1258 Most DNSSEC terms are defined in [RFC4033], [RFC4034], [RFC4035], and 1259 [RFC5155]. The terms that have caused confusion in the DNS community 1260 are highlighted here. 1262 DNSSEC-aware and DNSSEC-unaware: These two terms, which are used in 1263 some RFCs, have not been formally defined. However, Section 2 of 1264 [RFC4033] defines many types of resolvers and validators, 1265 including "non-validating security-aware stub resolver", "non- 1266 validating stub resolver", "security-aware name server", 1267 "security-aware recursive name server", "security-aware resolver", 1268 "security-aware stub resolver", and "security-oblivious 1269 'anything'". (Note that the term "validating resolver", which is 1270 used in some places in DNSSEC-related documents, is also not 1271 defined in those RFCs, but is defined below.) 1273 Signed zone: "A zone whose RRsets are signed and that contains 1274 properly constructed DNSKEY, Resource Record Signature (RRSIG), 1275 Next Secure (NSEC), and (optionally) DS records." (Quoted from 1276 [RFC4033], Section 2.) It has been noted in other contexts that 1277 the zone itself is not really signed, but all the relevant RRsets 1278 in the zone are signed. Nevertheless, if a zone that should be 1279 signed contains any RRsets that are not signed (or opted out), 1280 those RRsets will be treated as bogus, so the whole zone needs to 1281 be handled in some way. 1283 It should also be noted that, since the publication of [RFC6840], 1284 NSEC records are no longer required for signed zones: a signed 1285 zone might include NSEC3 records instead. [RFC7129] provides 1286 additional background commentary and some context for the NSEC and 1287 NSEC3 mechanisms used by DNSSEC to provide authenticated denial- 1288 of-existence responses. NSEC and NSEC3 are described below. 1290 Unsigned zone: Section 2 of [RFC4033] defines this as "a zone that 1291 is not signed". Section 2 of [RFC4035] defines this as "A zone 1292 that does not include these records [properly constructed DNSKEY, 1293 Resource Record Signature (RRSIG), Next Secure (NSEC), and 1294 (optionally) DS records] according to the rules in this section". 1295 There is an important note at the end of Section 5.2 of [RFC4035] 1296 that defines an additional situation in which a zone is considered 1297 unsigned: "If the resolver does not support any of the algorithms 1298 listed in an authenticated DS RRset, then the resolver will not be 1299 able to verify the authentication path to the child zone. In this 1300 case, the resolver SHOULD treat the child zone as if it were 1301 unsigned." 1303 NSEC: "The NSEC record allows a security-aware resolver to 1304 authenticate a negative reply for either name or type non- 1305 existence with the same mechanisms used to authenticate other DNS 1306 replies." (Quoted from [RFC4033], Section 3.2.) In short, an 1307 NSEC record provides authenticated denial of existence. 1309 "The NSEC resource record lists two separate things: the next 1310 owner name (in the canonical ordering of the zone) that contains 1311 authoritative data or a delegation point NS RRset, and the set of 1312 RR types present at the NSEC RR's owner name." (Quoted from 1313 Section 4 of RFC 4034) 1315 NSEC3: Like the NSEC record, the NSEC3 record also provides 1316 authenticated denial of existence; however, NSEC3 records mitigate 1317 against zone enumeration and support Opt-Out. NSEC resource 1318 records require associated NSEC3PARAM resource records. NSEC3 and 1319 NSEC3PARAM resource records are defined in [RFC5155]. 1321 Note that [RFC6840] says that [RFC5155] "is now considered part of 1322 the DNS Security Document Family as described by Section 10 of 1323 [RFC4033]". This means that some of the definitions from earlier 1324 RFCs that only talk about NSEC records should probably be 1325 considered to be talking about both NSEC and NSEC3. 1327 Opt-out: "The Opt-Out Flag indicates whether this NSEC3 RR may cover 1328 unsigned delegations." (Quoted from [RFC5155], Section 3.1.2.1.) 1329 Opt-out tackles the high costs of securing a delegation to an 1330 insecure zone. When using Opt-Out, names that are an insecure 1331 delegation (and empty non-terminals that are only derived from 1332 insecure delegations) don't require an NSEC3 record or its 1333 corresponding RRSIG records. Opt-Out NSEC3 records are not able 1334 to prove or deny the existence of the insecure delegations. 1335 (Adapted from [RFC7129], Section 5.1) 1337 Insecure delegation: "A signed name containing a delegation (NS 1338 RRset), but lacking a DS RRset, signifying a delegation to an 1339 unsigned subzone." (Quoted from [RFC4956], Section 2.) 1341 Zone enumeration: "The practice of discovering the full content of a 1342 zone via successive queries." (Quoted from [RFC5155], 1343 Section 1.3.) This is also sometimes called "zone walking". Zone 1344 enumeration is different from zone content guessing where the 1345 guesser uses a large dictionary of possible labels and sends 1346 successive queries for them, or matches the contents of NSEC3 1347 records against such a dictionary. 1349 Validation: Validation, in the context of DNSSEC, refers to one of 1350 the following: 1352 * Checking the validity of DNSSEC signatures 1354 * Checking the validity of DNS responses, such as those including 1355 authenticated denial of existence 1357 * Building an authentication chain from a trust anchor to a DNS 1358 response or individual DNS RRsets in a response 1360 The first two definitions above consider only the validity of 1361 individual DNSSEC components such as the RRSIG validity or NSEC 1362 proof validity. The third definition considers the components of 1363 the entire DNSSEC authentication chain, and thus requires 1364 "configured knowledge of at least one authenticated DNSKEY or DS 1365 RR" (as described in [RFC4035], Section 5). 1367 [RFC4033], Section 2, says that a "Validating Security-Aware Stub 1368 Resolver... performs signature validation" and uses a trust anchor 1369 "as a starting point for building the authentication chain to a 1370 signed DNS response", and thus uses the first and third 1371 definitions above. The process of validating an RRSIG resource 1372 record is described in [RFC4035], Section 5.3. 1374 [RFC5155] refers to validating responses throughout the document, 1375 in the context of hashed authenticated denial of existence; this 1376 uses the second definition above. 1378 The term "authentication" is used interchangeably with 1379 "validation", in the sense of the third definition above. 1380 [RFC4033], Section 2, describes the chain linking trust anchor to 1381 DNS data as the "authentication chain". A response is considered 1382 to be authentic if "all RRsets in the Answer and Authority 1383 sections of the response [are considered] to be authentic" 1384 ([RFC4035]). DNS data or responses deemed to be authentic or 1385 validated have a security status of "secure" ([RFC4035], 1386 Section 4.3; [RFC4033], Section 5). "Authenticating both DNS keys 1387 and data is a matter of local policy, which may extend or even 1388 override the [DNSSEC] protocol extensions" ([RFC4033], 1389 Section 3.1). 1391 The term "verification", when used, is usually synonym for 1392 "validation". 1394 Validating resolver: A security-aware recursive name server, 1395 security-aware resolver, or security-aware stub resolver that is 1396 applying at least one of the definitions of validation (above), as 1397 appropriate to the resolution context. For the same reason that 1398 the generic term "resolver" is sometimes ambiguous and needs to be 1399 evaluated in context (see Section 6), "validating resolver" is a 1400 context-sensitive term. 1402 Key signing key (KSK): DNSSEC keys that "only sign the apex DNSKEY 1403 RRset in a zone."(Quoted from [RFC6781], Section 3.1) 1405 Zone signing key (ZSK): "DNSSEC keys that can be used to sign all 1406 the RRsets in a zone that require signatures, other than the apex 1407 DNSKEY RRset." (Quoted from [RFC6781], Section 3.1) Also note 1408 that a ZSK is sometimes used to sign the apex DNSKEY RRset. 1410 Combined signing key (CSK): "In cases where the differentiation 1411 between the KSK and ZSK is not made, i.e., where keys have the 1412 role of both KSK and ZSK, we talk about a Single-Type Signing 1413 Scheme." (Quoted from [RFC6781], Section 3.1) This is sometimes 1414 called a "combined signing key" or CSK. It is operational 1415 practice, not protocol, that determines whether a particular key 1416 is a ZSK, a KSK, or a CSK. 1418 Secure Entry Point (SEP): A flag in the DNSKEY RDATA that "can be 1419 used to distinguish between keys that are intended to be used as 1420 the secure entry point into the zone when building chains of 1421 trust, i.e., they are (to be) pointed to by parental DS RRs or 1422 configured as a trust anchor. Therefore, it is suggested that the 1423 SEP flag be set on keys that are used as KSKs and not on keys that 1424 are used as ZSKs, while in those cases where a distinction between 1425 a KSK and ZSK is not made (i.e., for a Single-Type Signing 1426 Scheme), it is suggested that the SEP flag be set on all keys." 1427 (Quoted from [RFC6781], Section 3.2.3.) Note that the SEP flag is 1428 only a hint, and its presence or absence may not be used to 1429 disqualify a given DNSKEY RR from use as a KSK or ZSK during 1430 validation. 1432 The original defintion of SEPs was in [RFC3757]. That definition 1433 clearly indicated that the SEP was a key, not just a bit in the 1434 key. The abstract of [RFC3757] says: "With the Delegation Signer 1435 (DS) resource record (RR), the concept of a public key acting as a 1436 secure entry point (SEP) has been introduced. During exchanges of 1437 public keys with the parent there is a need to differentiate SEP 1438 keys from other public keys in the Domain Name System KEY (DNSKEY) 1439 resource record set. A flag bit in the DNSKEY RR is defined to 1440 indicate that DNSKEY is to be used as a SEP." That definition of 1441 the SEP as a key was made obsolete by [RFC4034], and the 1442 definition from [RFC6781] is consistent with [RFC4034]. 1444 Trust anchor: "A configured DNSKEY RR or DS RR hash of a DNSKEY RR. 1445 A validating security-aware resolver uses this public key or hash 1446 as a starting point for building the authentication chain to a 1447 signed DNS response." (Quoted from [RFC4033], Section 2) 1449 DNSSEC Policy (DP): A statement that "sets forth the security 1450 requirements and standards to be implemented for a DNSSEC-signed 1451 zone." (Quoted from [RFC6841], Section 2) 1453 DNSSEC Practice Statement (DPS): "A practices disclosure document 1454 that may support and be a supplemental document to the DNSSEC 1455 Policy (if such exists), and it states how the management of a 1456 given zone implements procedures and controls at a high level." 1457 (Quoted from [RFC6841], Section 2) 1459 Hardware security module (HSM): A specialized piece of hardware that 1460 is used to create keys for signatures and to sign messages. In 1461 DNSSEC, HSMs are often used to hold the private keys for KSKs and 1462 ZSKs and to create the signatures used in RRSIG records at 1463 periodic intervals. 1465 Signing software: Authoritative DNS servers that support DNSSEC 1466 often contain software that facilitates the creation and 1467 maintenance of DNSSEC signatures in zones. There is also stand- 1468 alone software that can be used to sign a zone regardless of 1469 whether the authoritative server itself supports signing. 1470 Sometimes signing software can support particular HSMs as part of 1471 the signing process. 1473 11. DNSSEC States 1475 A validating resolver can determine that a response is in one of four 1476 states: secure, insecure, bogus, or indeterminate. These states are 1477 defined in [RFC4033] and [RFC4035], although the two definitions 1478 differ a bit. This document makes no effort to reconcile the two 1479 definitions, and takes no position as to whether they need to be 1480 reconciled. 1482 Section 5 of [RFC4033] says: 1484 A validating resolver can determine the following 4 states: 1486 Secure: The validating resolver has a trust anchor, has a chain 1487 of trust, and is able to verify all the signatures in the 1488 response. 1490 Insecure: The validating resolver has a trust anchor, a chain 1491 of trust, and, at some delegation point, signed proof of the 1492 non-existence of a DS record. This indicates that subsequent 1493 branches in the tree are provably insecure. A validating 1494 resolver may have a local policy to mark parts of the domain 1495 space as insecure. 1497 Bogus: The validating resolver has a trust anchor and a secure 1498 delegation indicating that subsidiary data is signed, but 1499 the response fails to validate for some reason: missing 1500 signatures, expired signatures, signatures with unsupported 1501 algorithms, data missing that the relevant NSEC RR says 1502 should be present, and so forth. 1504 Indeterminate: There is no trust anchor that would indicate that a 1505 specific portion of the tree is secure. This is the default 1506 operation mode. 1508 Section 4.3 of [RFC4035] says: 1510 A security-aware resolver must be able to distinguish between four 1511 cases: 1513 Secure: An RRset for which the resolver is able to build a chain 1514 of signed DNSKEY and DS RRs from a trusted security anchor to 1515 the RRset. In this case, the RRset should be signed and is 1516 subject to signature validation, as described above. 1518 Insecure: An RRset for which the resolver knows that it has no 1519 chain of signed DNSKEY and DS RRs from any trusted starting 1520 point to the RRset. This can occur when the target RRset lies 1521 in an unsigned zone or in a descendent [sic] of an unsigned 1522 zone. In this case, the RRset may or may not be signed, but 1523 the resolver will not be able to verify the signature. 1525 Bogus: An RRset for which the resolver believes that it ought to 1526 be able to establish a chain of trust but for which it is 1527 unable to do so, either due to signatures that for some reason 1528 fail to validate or due to missing data that the relevant 1529 DNSSEC RRs indicate should be present. This case may indicate 1530 an attack but may also indicate a configuration error or some 1531 form of data corruption. 1533 Indeterminate: An RRset for which the resolver is not able to 1534 determine whether the RRset should be signed, as the resolver 1535 is not able to obtain the necessary DNSSEC RRs. This can occur 1536 when the security-aware resolver is not able to contact 1537 security-aware name servers for the relevant zones. 1539 12. Security Considerations 1541 These definitions do not change any security considerations for the 1542 DNS. 1544 13. IANA Considerations 1546 None. 1548 14. References 1550 14.1. Normative References 1552 [IANA_RootFiles] 1553 Internet Assigned Numbers Authority, "IANA Root Files", 1554 2016, . 1556 [RFC0882] Mockapetris, P., "Domain names: Concepts and facilities", 1557 RFC 882, DOI 10.17487/RFC0882, November 1983, 1558 . 1560 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 1561 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 1562 . 1564 [RFC1035] Mockapetris, P., "Domain names - implementation and 1565 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 1566 November 1987, . 1568 [RFC1123] Braden, R., Ed., "Requirements for Internet Hosts - 1569 Application and Support", STD 3, RFC 1123, 1570 DOI 10.17487/RFC1123, October 1989, 1571 . 1573 [RFC1912] Barr, D., "Common DNS Operational and Configuration 1574 Errors", RFC 1912, DOI 10.17487/RFC1912, February 1996, 1575 . 1577 [RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone 1578 Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996, 1579 August 1996, . 1581 [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, 1582 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 1583 RFC 2136, DOI 10.17487/RFC2136, April 1997, 1584 . 1586 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 1587 Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997, 1588 . 1590 [RFC2182] Elz, R., Bush, R., Bradner, S., and M. Patton, "Selection 1591 and Operation of Secondary DNS Servers", BCP 16, RFC 2182, 1592 DOI 10.17487/RFC2182, July 1997, 1593 . 1595 [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS 1596 NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998, 1597 . 1599 [RFC3731] Hollenbeck, S., "Extensible Provisioning Protocol (EPP) 1600 Domain Name Mapping", RFC 3731, DOI 10.17487/RFC3731, 1601 March 2004, . 1603 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 1604 Rose, "DNS Security Introduction and Requirements", 1605 RFC 4033, DOI 10.17487/RFC4033, March 2005, 1606 . 1608 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 1609 Rose, "Resource Records for the DNS Security Extensions", 1610 RFC 4034, DOI 10.17487/RFC4034, March 2005, 1611 . 1613 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 1614 Rose, "Protocol Modifications for the DNS Security 1615 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 1616 . 1618 [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name 1619 System", RFC 4592, DOI 10.17487/RFC4592, July 2006, 1620 . 1622 [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS 1623 Security (DNSSEC) Hashed Authenticated Denial of 1624 Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008, 1625 . 1627 [RFC5358] Damas, J. and F. Neves, "Preventing Use of Recursive 1628 Nameservers in Reflector Attacks", BCP 140, RFC 5358, 1629 DOI 10.17487/RFC5358, October 2008, 1630 . 1632 [RFC5730] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)", 1633 STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009, 1634 . 1636 [RFC5855] Abley, J. and T. Manderson, "Nameservers for IPv4 and IPv6 1637 Reverse Zones", BCP 155, RFC 5855, DOI 10.17487/RFC5855, 1638 May 2010, . 1640 [RFC5936] Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol 1641 (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010, 1642 . 1644 [RFC6561] Livingood, J., Mody, N., and M. O'Reirdan, 1645 "Recommendations for the Remediation of Bots in ISP 1646 Networks", RFC 6561, DOI 10.17487/RFC6561, March 2012, 1647 . 1649 [RFC6781] Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC 1650 Operational Practices, Version 2", RFC 6781, 1651 DOI 10.17487/RFC6781, December 2012, 1652 . 1654 [RFC6840] Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and 1655 Implementation Notes for DNS Security (DNSSEC)", RFC 6840, 1656 DOI 10.17487/RFC6840, February 2013, 1657 . 1659 [RFC6841] Ljunggren, F., Eklund Lowinder, AM., and T. Okubo, "A 1660 Framework for DNSSEC Policies and DNSSEC Practice 1661 Statements", RFC 6841, DOI 10.17487/RFC6841, January 2013, 1662 . 1664 [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms 1665 for DNS (EDNS(0))", STD 75, RFC 6891, 1666 DOI 10.17487/RFC6891, April 2013, 1667 . 1669 [RFC7344] Kumari, W., Gudmundsson, O., and G. Barwood, "Automating 1670 DNSSEC Delegation Trust Maintenance", RFC 7344, 1671 DOI 10.17487/RFC7344, September 2014, 1672 . 1674 [RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 1675 Terminology", RFC 7719, DOI 10.17487/RFC7719, December 1676 2015, . 1678 14.2. Informative References 1680 [IANA_Resource_Registry] 1681 Internet Assigned Numbers Authority, "Resource Record (RR) 1682 TYPEs", 2017, 1683 . 1685 [RFC0819] Su, Z. and J. Postel, "The Domain Naming Convention for 1686 Internet User Applications", RFC 819, 1687 DOI 10.17487/RFC0819, August 1982, 1688 . 1690 [RFC0952] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet 1691 host table specification", RFC 952, DOI 10.17487/RFC0952, 1692 October 1985, . 1694 [RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995, 1695 DOI 10.17487/RFC1995, August 1996, 1696 . 1698 [RFC2133] Gilligan, R., Thomson, S., Bound, J., and W. Stevens, 1699 "Basic Socket Interface Extensions for IPv6", RFC 2133, 1700 DOI 10.17487/RFC2133, April 1997, 1701 . 1703 [RFC2775] Carpenter, B., "Internet Transparency", RFC 2775, 1704 DOI 10.17487/RFC2775, February 2000, 1705 . 1707 [RFC3172] Huston, G., Ed., "Management Guidelines & Operational 1708 Requirements for the Address and Routing Parameter Area 1709 Domain ("arpa")", BCP 52, RFC 3172, DOI 10.17487/RFC3172, 1710 September 2001, . 1712 [RFC3425] Lawrence, D., "Obsoleting IQUERY", RFC 3425, 1713 DOI 10.17487/RFC3425, November 2002, 1714 . 1716 [RFC3757] Kolkman, O., Schlyter, J., and E. Lewis, "Domain Name 1717 System KEY (DNSKEY) Resource Record (RR) Secure Entry 1718 Point (SEP) Flag", RFC 3757, DOI 10.17487/RFC3757, April 1719 2004, . 1721 [RFC3912] Daigle, L., "WHOIS Protocol Specification", RFC 3912, 1722 DOI 10.17487/RFC3912, September 2004, 1723 . 1725 [RFC4641] Kolkman, O. and R. Gieben, "DNSSEC Operational Practices", 1726 RFC 4641, DOI 10.17487/RFC4641, September 2006, 1727 . 1729 [RFC4697] Larson, M. and P. Barber, "Observed DNS Resolution 1730 Misbehavior", BCP 123, RFC 4697, DOI 10.17487/RFC4697, 1731 October 2006, . 1733 [RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast 1734 Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786, 1735 December 2006, . 1737 [RFC4956] Arends, R., Kosters, M., and D. Blacka, "DNS Security 1738 (DNSSEC) Opt-In", RFC 4956, DOI 10.17487/RFC4956, July 1739 2007, . 1741 [RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines", 1742 BCP 152, RFC 5625, DOI 10.17487/RFC5625, August 2009, 1743 . 1745 [RFC5890] Klensin, J., "Internationalized Domain Names for 1746 Applications (IDNA): Definitions and Document Framework", 1747 RFC 5890, DOI 10.17487/RFC5890, August 2010, 1748 . 1750 [RFC5891] Klensin, J., "Internationalized Domain Names in 1751 Applications (IDNA): Protocol", RFC 5891, 1752 DOI 10.17487/RFC5891, August 2010, 1753 . 1755 [RFC5892] Faltstrom, P., Ed., "The Unicode Code Points and 1756 Internationalized Domain Names for Applications (IDNA)", 1757 RFC 5892, DOI 10.17487/RFC5892, August 2010, 1758 . 1760 [RFC5893] Alvestrand, H., Ed. and C. Karp, "Right-to-Left Scripts 1761 for Internationalized Domain Names for Applications 1762 (IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010, 1763 . 1765 [RFC5894] Klensin, J., "Internationalized Domain Names for 1766 Applications (IDNA): Background, Explanation, and 1767 Rationale", RFC 5894, DOI 10.17487/RFC5894, August 2010, 1768 . 1770 [RFC6055] Thaler, D., Klensin, J., and S. Cheshire, "IAB Thoughts on 1771 Encodings for Internationalized Domain Names", RFC 6055, 1772 DOI 10.17487/RFC6055, February 2011, 1773 . 1775 [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, 1776 DOI 10.17487/RFC6265, April 2011, 1777 . 1779 [RFC6303] Andrews, M., "Locally Served DNS Zones", BCP 163, 1780 RFC 6303, DOI 10.17487/RFC6303, July 2011, 1781 . 1783 [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. 1784 Cheshire, "Internet Assigned Numbers Authority (IANA) 1785 Procedures for the Management of the Service Name and 1786 Transport Protocol Port Number Registry", BCP 165, 1787 RFC 6335, DOI 10.17487/RFC6335, August 2011, 1788 . 1790 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in 1791 Internationalization in the IETF", BCP 166, RFC 6365, 1792 DOI 10.17487/RFC6365, September 2011, 1793 . 1795 [RFC7129] Gieben, R. and W. Mekking, "Authenticated Denial of 1796 Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129, 1797 February 2014, . 1799 [RFC7480] Newton, A., Ellacott, B., and N. Kong, "HTTP Usage in the 1800 Registration Data Access Protocol (RDAP)", RFC 7480, 1801 DOI 10.17487/RFC7480, March 2015, 1802 . 1804 [RFC7481] Hollenbeck, S. and N. Kong, "Security Services for the 1805 Registration Data Access Protocol (RDAP)", RFC 7481, 1806 DOI 10.17487/RFC7481, March 2015, 1807 . 1809 [RFC7482] Newton, A. and S. Hollenbeck, "Registration Data Access 1810 Protocol (RDAP) Query Format", RFC 7482, 1811 DOI 10.17487/RFC7482, March 2015, 1812 . 1814 [RFC7483] Newton, A. and S. Hollenbeck, "JSON Responses for the 1815 Registration Data Access Protocol (RDAP)", RFC 7483, 1816 DOI 10.17487/RFC7483, March 2015, 1817 . 1819 [RFC7484] Blanchet, M., "Finding the Authoritative Registration Data 1820 (RDAP) Service", RFC 7484, DOI 10.17487/RFC7484, March 1821 2015, . 1823 [RFC7485] Zhou, L., Kong, N., Shen, S., Sheng, S., and A. Servin, 1824 "Inventory and Analysis of WHOIS Registration Objects", 1825 RFC 7485, DOI 10.17487/RFC7485, March 2015, 1826 . 1828 [RFC8109] Koch, P., Larson, M., and P. Hoffman, "Initializing a DNS 1829 Resolver with Priming Queries", BCP 209, RFC 8109, 1830 DOI 10.17487/RFC8109, March 2017, 1831 . 1833 [RSSAC026] 1834 Root Server System Advisory Committee (RSSAC), "RSSAC 1835 Lexicon", 2017, 1836 . 1839 Appendix A. Definitions Updated by this Document 1841 The following definitions from RFCs are updated by this document: 1843 o Forwarder in [RFC2308] 1845 o Secure Entry Point (SEP) in [RFC3757]; note, however, that this 1846 RFC is already obsolete 1848 Appendix B. Definitions First Defined in this Document 1850 The following definitions are first defined in this document: 1852 o "Alias" in Section 2 1854 o "Apex" in Section 7 1856 o "arpa" in Section 7 1858 o "Class independent" in Section 5 1860 o "Delegation-centric zone" in Section 7 1862 o "Delegation" in Section 7 1864 o "DNS operator" in Section 9 1866 o "DNSSEC-aware" in Section 10 1868 o "DNSSEC-unaware" in Section 10 1870 o "Forwarding" in Section 6 1872 o "Full resolver" in Section 6 1874 o "Fully qualified domain name" in Section 2 1876 o "Global DNS" in Section 2 1878 o "Hardware Security Module (HSM)" in Section 10 1880 o "Host name" in Section 2 1882 o "IDN" in Section 2 1884 o "In-bailiwick" in Section 7 1886 o "Label" in Section 2 1887 o "Locally served DNS zone" in Section 2 1889 o "Naming system" in Section 2 1891 o "Negative response" in Section 3 1893 o "Open resolver" in Section 6 1895 o "Out-of-bailiwick" in Section 7 1897 o "Passive DNS" in Section 6 1899 o "Policy-implementing resolver" in Section 6 1901 o "Presentation format" in Section 5 1903 o "Priming" in Section 6 1905 o "Private DNS" in Section 2 1907 o "Recursive resolver" in Section 6 1909 o "Referrals" in Section 4 1911 o "Registrant" in Section 9 1913 o "Registrar" in Section 9 1915 o "Registry" in Section 9 1917 o "Root zone" in Section 7 1919 o "Secure Entry Point (SEP)" in Section 10 1921 o "Signing software" in Section 10 1923 o "Stub resolver" in Section 6 1925 o "TLD" in Section 2 1927 o "Validating resolver" in Section 10 1929 o "Validation" in Section 10 1931 o "View" in Section 6 1933 o "Zone transfer" in Section 6 1935 Index 1937 A 1938 Address records 14 1939 Alias 8 1940 Anycast 19 1941 Apex 21 1942 Asterisk label 24 1943 Authoritative data 21 1944 Authoritative server 16 1945 Authoritative-only server 17 1946 arpa: Address and Routing Parameter Area Domain 24 1948 C 1949 CNAME 8 1950 Canonical name 8 1951 Child 20 1952 Class independent 14 1953 Closest encloser 24 1954 Closest provable encloser 25 1955 Combined signing key (CSK) 30 1957 D 1958 DNS operator 26 1959 DNSSEC Policy (DP) 31 1960 DNSSEC Practice Statement (DPS) 31 1961 DNSSEC-aware and DNSSEC-unaware 27 1962 Delegation 21 1963 Delegation-centric zone 23 1964 Domain name 4 1966 E 1967 EDNS 12 1968 EPP 25 1969 Empty non-terminals (ENT) 23 1971 F 1972 FORMERR 9 1973 Fast flux DNS 23 1974 Forward lookup 24 1975 Forwarder 18 1976 Forwarding 18 1977 Full resolver 15 1978 Full-service resolver 15 1979 Fully qualified domain name (FQDN) 7 1981 G 1982 Global DNS 4 1983 Glue records 21 1985 H 1986 Hardware security module (HSM) 31 1987 Hidden master 18 1988 Host name 7 1990 I 1991 IDN 8 1992 In-bailiwick 22 1993 Insecure delegation 28 1994 Instance 19 1995 Iterative mode 15 1996 Iterative query 16 1997 Iterative resolution 16 1999 K 2000 Key signing key (KSK) 30 2002 L 2003 Label 4 2004 Lame delegation 21 2005 Locally served DNS zone 6 2007 M 2008 Master file 12 2009 Master server 17 2011 N 2012 NODATA 9 2013 NOERROR 8 2014 NOTIMP 9 2015 NSEC 28 2016 NSEC3 28 2017 NXDOMAIN 9 2018 Naming system 3 2019 Negative caching 16 2020 Negative response 9 2021 Next closer name 25 2022 Non-recursive query 16 2024 O 2025 OPT 13 2026 Occluded name 23 2027 Open resolver 19 2028 Opt-out 28 2029 Origin 20 2030 Out-of-bailiwick 22 2031 Owner 13 2033 P 2034 Parent 20 2035 Passive DNS 19 2036 Policy-implementing resolver 19 2037 Presentation format 12 2038 Primary master 18 2039 Primary server 17 2040 Priming 16 2041 Private DNS 6 2042 Public suffix 26 2044 Q 2045 QNAME 10 2047 R 2048 RDAP 26 2049 REFUSED 9 2050 RR 12 2051 RRset 12 2052 Recursive mode 15 2053 Recursive query 15 2054 Recursive resolver 15 2055 Referrals 11 2056 Registrant 25 2057 Registrar 25 2058 Registry 25 2059 Resolver 14 2060 Reverse DNS, reverse lookup 24 2061 Root hints 16 2062 Root zone 23 2064 S 2065 SERVFAIL 9 2066 SOA field names 13 2067 Secondary server 17 2068 Secure Entry Point (SEP) 30 2069 Service name 24 2070 Signed zone 27 2071 Signing software 31 2072 Slave server 17 2073 Source of Synthesis 25 2074 Split DNS 20 2075 Stealth server 18 2076 Stub resolver 15 2077 Subdomain 8 2078 Subordinate 26 2079 Superordinate 26 2081 T 2082 TLD 7 2083 TTL 13 2084 Trust anchor 31 2086 U 2087 Unsigned zone 27 2089 V 2090 Validating resolver 30 2091 Validation 29 2092 View 19 2094 W 2095 WHOIS 26 2096 Wildcard 24 2097 Wildcard domain name 24 2099 Z 2100 Zone 20 2101 Zone cut 21 2102 Zone enumeration 28 2103 Zone signing key (ZSK) 30 2104 Zone transfer 17 2106 Acknowledgements 2108 The following is the Acknowledgements for RFC 7719. Additional 2109 acknowledgements may be added as this draft is worked on. 2111 The authors gratefully acknowledge all of the authors of DNS-related 2112 RFCs that proceed this one. Comments from Tony Finch, Stephane 2113 Bortzmeyer, Niall O'Reilly, Colm MacCarthaigh, Ray Bellis, John 2114 Kristoff, Robert Edmonds, Paul Wouters, Shumon Huque, Paul Ebersman, 2115 David Lawrence, Matthijs Mekking, Casey Deccio, Bob Harold, Ed Lewis, 2116 John Klensin, David Black, and many others in the DNSOP Working Group 2117 helped shape RFC 7719. 2119 Additional people contributed to this document, including: Bob 2120 Harold, Dick Franks, Evan Hunt, John Dickinson, Mark Andrews, Martin 2121 Hoffmann, Paul Vixie, Peter Koch, [[ MORE NAMES WILL APPEAR HERE AS 2122 FOLKS CONTRIBUTE]]. 2124 Authors' Addresses 2126 Paul Hoffman 2127 ICANN 2129 Email: paul.hoffman@icann.org 2131 Andrew Sullivan 2132 Oracle 2133 100 Milverton Drive 2134 Mississauga, ON L5R 4H1 2135 Canada 2137 Email: andrew.s.sullivan@oracle.com 2139 Kazunori Fujiwara 2140 Japan Registry Services Co., Ltd. 2141 Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda 2142 Chiyoda-ku, Tokyo 101-0065 2143 Japan 2145 Phone: +81 3 5215 8451 2146 Email: fujiwara@jprs.co.jp