idnits 2.17.1 draft-ietf-dnsop-terminology-bis-08.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == There are 1 instance of lines with non-RFC2606-compliant FQDNs in the document. ** The document seems to lack a both a reference to RFC 2119 and the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords. RFC 2119 keyword, line 985: '...s. An in-domain name server name MUST...' RFC 2119 keyword, line 1217: '...se, the resolver SHOULD treat the chil...' -- The draft header indicates that this document obsoletes RFC7719, but the abstract doesn't seem to directly say this. It does mention RFC7719 though, so this could be OK. -- The draft header indicates that this document updates RFC2308, but the abstract doesn't seem to directly say this. It does mention RFC2308 though, so this could be OK. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year (Using the creation date from RFC2308, updated by this document, for RFC5378 checks: 1997-01-17) -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (November 27, 2017) is 2341 days in the past. Is this intentional? Checking references for intended status: Best Current Practice ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'DNSSEC' is mentioned on line 1305, but not defined ** Obsolete normative reference: RFC 882 (Obsoleted by RFC 1034, RFC 1035) ** Obsolete normative reference: RFC 3731 (Obsoleted by RFC 4931) ** Downref: Normative reference to an Informational RFC: RFC 6561 ** Downref: Normative reference to an Informational RFC: RFC 6781 ** Downref: Normative reference to an Informational RFC: RFC 6841 ** Obsolete normative reference: RFC 7719 (Obsoleted by RFC 8499) -- Obsolete informational reference (is this intentional?): RFC 2133 (Obsoleted by RFC 2553) -- Obsolete informational reference (is this intentional?): RFC 3757 (Obsoleted by RFC 4033, RFC 4034, RFC 4035) -- Obsolete informational reference (is this intentional?): RFC 4641 (Obsoleted by RFC 6781) -- Obsolete informational reference (is this intentional?): RFC 7482 (Obsoleted by RFC 9082) -- Obsolete informational reference (is this intentional?): RFC 7483 (Obsoleted by RFC 9083) -- Obsolete informational reference (is this intentional?): RFC 7484 (Obsoleted by RFC 9224) Summary: 7 errors (**), 0 flaws (~~), 3 warnings (==), 10 comments (--). 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: May 31, 2018 JPRS 8 November 27, 2017 10 DNS Terminology 11 draft-ietf-dnsop-terminology-bis-08 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 http://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 May 31, 2018. 42 Copyright Notice 44 Copyright (c) 2017 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 (http://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 Header and Response Codes . . . . . . . . . . . . . . . . 9 62 4. Resource Records . . . . . . . . . . . . . . . . . . . . . . 12 63 5. DNS Servers and Clients . . . . . . . . . . . . . . . . . . . 13 64 6. Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 65 7. Registration Model . . . . . . . . . . . . . . . . . . . . . 24 66 8. General DNSSEC . . . . . . . . . . . . . . . . . . . . . . . 25 67 9. DNSSEC States . . . . . . . . . . . . . . . . . . . . . . . . 30 68 10. Security Considerations . . . . . . . . . . . . . . . . . . . 31 69 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 70 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 71 12.1. Normative References . . . . . . . . . . . . . . . . . . 31 72 12.2. Informative References . . . . . . . . . . . . . . . . . 34 73 Appendix A. Definitions Updated by this Document . . . . . . . . 37 74 Appendix B. Definitions First Defined in this Document . . . . . 38 75 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 76 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 43 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43 79 1. Introduction 81 The Domain Name System (DNS) is a simple query-response protocol 82 whose messages in both directions have the same format. (See 83 Section 2 for a fuller definition.) The protocol and message format 84 are defined in [RFC1034] and [RFC1035]. These RFCs defined some 85 terms, but later documents defined others. Some of the terms from 86 [RFC1034] and [RFC1035] now have somewhat different meanings than 87 they did in 1987. 89 This document collects a wide variety of DNS-related terms. Some of 90 them have been precisely defined in earlier RFCs, some have been 91 loosely defined in earlier RFCs, and some are not defined in any 92 earlier RFC at all. 94 Most of the definitions here are the consensus definition of the DNS 95 community -- both protocol developers and operators. Some of the 96 definitions differ from earlier RFCs, and those differences are 97 noted. In this document, where the consensus definition is the same 98 as the one in an RFC, that RFC is quoted. Where the consensus 99 definition has changed somewhat, the RFC is mentioned but the new 100 stand-alone definition is given. See Appendix A for a list of the 101 definitions that this document updates. 103 It is important to note that, during the development of this 104 document, it became clear that some DNS-related terms are interpreted 105 quite differently by different DNS experts. Further, some terms that 106 are defined in early DNS RFCs now have definitions that are generally 107 agreed to, but that are different from the original definitions. 108 Therefore, this document is a substantial revision to [RFC7719]. 110 The terms are organized loosely by topic. Some definitions are for 111 new terms for things that are commonly talked about in the DNS 112 community but that never had terms defined for them. 114 Other organizations sometimes define DNS-related terms their own way. 115 For example, the W3C defines "domain" at 116 https://specs.webplatform.org/url/webspecs/develop/. The Root Server 117 System Advisory Committee (RSSAC) has a good lexicon [RSSAC026]. 119 Note that there is no single consistent definition of "the DNS". It 120 can be considered to be some combination of the following: a commonly 121 used naming scheme for objects on the Internet; a distributed 122 database representing the names and certain properties of these 123 objects; an architecture providing distributed maintenance, 124 resilience, and loose coherency for this database; and a simple 125 query-response protocol (as mentioned below) implementing this 126 architecture. Section 2 defines "global DNS" and "private DNS" as a 127 way to deal with these differing definitions. 129 Capitalization in DNS terms is often inconsistent among RFCs and 130 various DNS practitioners. The capitalization used in this document 131 is a best guess at current practices, and is not meant to indicate 132 that other capitalization styles are wrong or archaic. In some 133 cases, multiple styles of capitalization are used for the same term 134 due to quoting from different RFCs. 136 2. Names 138 Naming system: A naming system associates names with data. Naming 139 systems have many significant facets that help differentiate them. 140 Some commonly-identified facets include: 142 * Composition of names 144 * Format of names 145 * Administration of names 147 * Types of data that can be associated with names 149 * Types of metadata for names 151 * Protocol for getting data from a name 153 * Context for resolving a name 155 Note that this list is a small subset of facets that people have 156 identified over time for naming systems, and the IETF has yet to 157 agree on a good set of facets that can be used to compare naming 158 systems. For example, other facets might include "protocol to 159 update data in a name", "privacy of names", and "privacy of data 160 associated with names", but those are not as well-defined as the 161 ones listed above. The list here is chosen because it helps 162 describe the DNS and naming systems similar to the DNS. 164 Domain name: An ordered list of one or more labels. 166 Note that this is a definition independent of the DNS RFCs, and 167 the definition here also applies to systems other than the DNS. 168 [RFC1034] defines the "domain name space" using mathematical trees 169 and their nodes in graph theory, and the definition in [RFC1034] 170 has the same practical result as the definition here. Using graph 171 theory, a domain name is a list of labels identifying a portion 172 along one edge of a directed acyclic graph. A domain name can be 173 relative to other parts of the tree, or it can be fully qualified 174 (in which case, it begins at the common root of the graph). 176 Also note that different IETF and non-IETF documents have used the 177 term "domain name" in many different ways. It is common for 178 earlier documents to use "domain name" to mean "names that match 179 the syntax in [RFC1035]", but possibly with additional rules such 180 as "and are, or will be, resolvable in the global DNS" or "but 181 only using the presentation format". 183 Label: An ordered list of zero or more octets and which makes up a 184 portion of a domain name. Using graph theory, a label identifies 185 one node in a portion of the graph of all possible domain names. 187 Global DNS: Using the short set of facets listed in "Naming system", 188 the global DNS can be defined as follows. Most of the rules here 189 come from [RFC1034] and [RFC1035], although the term "global DNS" 190 has not been defined before now. 192 Composition of names -- A name in the global DNS has one or more 193 labels. The length of each label is between 0 and 63 octets 194 inclusive. In a fully-qualified domain name, the first label in 195 the ordered list is 0 octets long; it is the only label whose 196 length may be 0 octets, and it is called the "root" or "root 197 label". A domain name in the global DNS has a maximum total 198 length of 255 octets in the wire format; the root represents one 199 octet for this calculation. 201 Format of names -- Names in the global DNS are domain names. 202 There are three formats: wire format, presentation format, and 203 common display. 205 The basic wire format for names in the global DNS is a list of 206 labels ordered by decreasing distance from the root, with the root 207 label last. Each label is preceded by a length octet. [RFC1035] 208 also defines a compression scheme that modifies this format. 210 The presentation format for names in the global DNS is a list of 211 labels ordered by decreasing distance from the root, encoded as 212 ASCII, with a "." character between each label. In presentation 213 format, a fully-qualified domain name includes the root label and 214 the associated separator dot. For example, in presentation 215 format, a fully-qualified domain name with two non-root labels is 216 always shown as "example.tld." instead of "example.tld". 217 [RFC1035] defines a method for showing octets that do not display 218 in ASCII. 220 The common display format is used in applications and free text. 221 It is the same as the presentation format, but showing the root 222 label and the "." before it is optional and is rarely done. For 223 example, in common display format, a fully-qualified domain name 224 with two non-root labels is usually shown as "example.tld" instead 225 of "example.tld.". Names in the common display format are 226 normally written such that the directionality of the writing 227 system presents labels by decreasing distance from the root (so, 228 in both English and C the first label in the ordered list is 229 right-most; but in Arabic it may be left-most, depending on local 230 conventions). 232 Administration of names -- Administration is specified by 233 delegation (see the definition of to "delegation" in Section 6). 234 Policies for administration of the root zone in the global DNS are 235 determined by the names operational community, which convenes 236 itself in the Internet Corporation for Assigned Names and Numbers 237 (ICANN). The names operational community selects the IANA 238 Functions Operator for the global DNS root zone. At the time this 239 document is published, that operator is Public Technical 240 Identifiers (PTI). The name servers that serve the root zone are 241 provided by independent root operators. Other zones in the global 242 DNS have their own policies for administration. 244 Types of data that can be associated with names -- A name can have 245 zero or more resource records associated with it. There are 246 numerous types of resource records with unique data structures 247 defined in many different RFCs and in the IANA registry at 248 [IANA_Resource_Registry]. 250 Types of metadata for names -- Any name that is published in the 251 DNS appears as a set of resource records (see the definition of 252 "RRset" in Section 4). Some names do not themselves have data 253 associated with them in the DNS, but "appear" in the DNS anyway 254 because they form part of a longer name that does have data 255 associated with it (see the defintion of "empty non-terminals" in 256 Section 6). 258 Protocol for getting data from a name -- The protocol described in 259 [RFC1035]. 261 Context for resolving a name -- The global DNS root zone 262 distributed by PTI. 264 Private DNS: Names that use the protocol described in [RFC1035] but 265 that do not rely on the global DNS root zone, or names that are 266 otherwise not generally available on the Internet but are using 267 the protocol described in [RFC1035]. A system can use both the 268 global DNS and one or more private DNS systems; for example, see 269 "Split DNS" in Section 7. 271 Note that domain names that do not appear in the DNS, and that are 272 intended never to be looked up using the DNS protocol, are not 273 part of the global DNS or a private DNS even though they are 274 domain names. 276 Locally served DNS zone: A locally served DNS zone is a special case 277 of private DNS. Names are resolved using the DNS protocol in a 278 local context. [RFC6303] defines subdomains of IN-ADDR.ARPA that 279 are locally served zones. Resolution of names through locally 280 served zones may result in ambiguous results. For example, the 281 same name may resolve to different results in different locally 282 served DNS zone contexts. The context through which a locally 283 served zone may be explicit, for example, as defined in [RFC6303], 284 or implicit, as defined by local DNS administration and not known 285 to the resolution client. 287 Fully qualified domain name (FQDN): This is often just a clear way 288 of saying the same thing as "domain name of a node", as outlined 289 above. However, the term is ambiguous. Strictly speaking, a 290 fully qualified domain name would include every label, including 291 the zero-length label of the root: such a name would be written 292 "www.example.net." (note the terminating dot). But because every 293 name eventually shares the common root, names are often written 294 relative to the root (such as "www.example.net") and are still 295 called "fully qualified". This term first appeared in [RFC0819]. 296 In this document, names are often written relative to the root. 298 The need for the term "fully qualified domain name" comes from the 299 existence of partially qualified domain names, which are names 300 where one or more of the earliest labels in the ordered list are 301 omitted (for example, "www"). Such relative names are understood 302 only by context. 304 Host name: This term and its equivalent, "hostname", have been 305 widely used but are not defined in [RFC1034], [RFC1035], 306 [RFC1123], or [RFC2181]. The DNS was originally deployed into the 307 Host Tables environment as outlined in [RFC0952], and it is likely 308 that the term followed informally from the definition there. Over 309 time, the definition seems to have shifted. "Host name" is often 310 meant to be a domain name that follows the rules in Section 3.5 of 311 [RFC1034], the "preferred name syntax". Note that any label in a 312 domain name can contain any octet value; hostnames are generally 313 considered to be domain names where every label follows the rules 314 in the "preferred name syntax", with the amendment that labels can 315 start with ASCII digits (this amendment comes from Section 2.1 of 316 [RFC1123]). 318 People also sometimes use the term hostname to refer to just the 319 first label of an FQDN, such as "printer" in 320 "printer.admin.example.com". (Sometimes this is formalized in 321 configuration in operating systems.) In addition, people 322 sometimes use this term to describe any name that refers to a 323 machine, and those might include labels that do not conform to the 324 "preferred name syntax". 326 TLD: A Top-Level Domain, meaning a zone that is one layer below the 327 root, such as "com" or "jp". There is nothing special, from the 328 point of view of the DNS, about TLDs. Most of them are also 329 delegation-centric zones, and there are significant policy issues 330 around their operation. TLDs are often divided into sub-groups 331 such as Country Code Top-Level Domains (ccTLDs), Generic Top-Level 332 Domains (gTLDs), and others; the division is a matter of policy, 333 and beyond the scope of this document. 335 IDN: The common abbreviation for "Internationalized Domain Name". 336 The IDNA protocol is the standard mechanism for handling domain 337 names with non-ASCII characters in applications in the DNS. The 338 current standard, normally called "IDNA2008", is defined in 339 [RFC5890], [RFC5891], [RFC5892], [RFC5893], and [RFC5894]. These 340 documents define many IDN-specific terms such as "LDH label", 341 "A-label", and "U-label". [RFC6365] defines more terms that 342 relate to internationalization (some of which relate to IDNs), and 343 [RFC6055] has a much more extensive discussion of IDNs, including 344 some new terminology. 346 Subdomain: "A domain is a subdomain of another domain if it is 347 contained within that domain. This relationship can be tested by 348 seeing if the subdomain's name ends with the containing domain's 349 name." (Quoted from [RFC1034], Section 3.1). For example, in the 350 host name "nnn.mmm.example.com", both "mmm.example.com" and 351 "nnn.mmm.example.com" are subdomains of "example.com". 353 Alias: The owner of a CNAME resource record, or a subdomain of the 354 owner of a DNAME resource record. See also "canonical name". 356 Canonical name: A CNAME resource record "identifies its owner name 357 as an alias, and specifies the corresponding canonical name in the 358 RDATA section of the RR." (Quoted from [RFC1034], Section 3.6.2) 359 This usage of the word "canonical" is related to the mathematical 360 concept of "canonical form". 362 CNAME: "It is traditional to refer to the owner of a CNAME record as 363 'a CNAME'. This is unfortunate, as 'CNAME' is an abbreviation of 364 'canonical name', and the owner of a CNAME record is an alias, not 365 a canonical name." (Quoted from [RFC2181], Section 10.1.1) 367 Public suffix: "A domain that is controlled by a public registry." 368 (Quoted from [RFC6265], Section 5.3) A common definition for this 369 term is a domain under which subdomains can be registered, and on 370 which HTTP cookies ([RFC6265]) should not be set. There is no 371 indication in a domain name whether it is a public suffix; that 372 can only be determined by outside means. In fact, both a domain 373 and a subdomain of that domain can be public suffixes. 375 There is nothing inherent in a domain name to indicate whether it 376 is a public suffix. One resource for identifying public suffixes 377 is the Public Suffix List (PSL) maintained by Mozilla 378 (http://publicsuffix.org/). 380 For example, at the time this document is published, the "com.au" 381 domain is listed as a public suffix in the PSL. (Note that this 382 example might change in the future.) 383 Note that the term "public suffix" is controversial in the DNS 384 community for many reasons, and may be significantly changed in 385 the future. One example of the difficulty of calling a domain a 386 public suffix is that designation can change over time as the 387 registration policy for the zone changes, such as was the case 388 with the "uk" TLD in 2014. 390 3. DNS Header and Response Codes 392 The header of a DNS message is its first 12 octets. Many of the 393 fields and flags in the header diagram in Sections 4.1.1 through 394 4.1.3 of [RFC1035] are referred to by their names in that diagram. 395 For example, the response codes are called "RCODEs", the data for a 396 record is called the "RDATA", and the authoritative answer bit is 397 often called "the AA flag" or "the AA bit". 399 QNAME The most commonly-used rough definition is that the QNAME is a 400 field in the Question section of a query. "A standard query 401 specifies a target domain name (QNAME), query type (QTYPE), and 402 query class (QCLASS) and asks for RRs which match." (Quoted from 403 [RFC1034], Section 3.7.1.). Strictly speaking, the definition 404 comes from [RFC1035], Section 4.1.2, where the QNAME is defined in 405 respect of the Question Section. This definition appears to be 406 applied consistently: the discussion of inverse queries in section 407 6.4 refers to the "owner name of the query RR and its TTL", 408 because inverse queries populate the Answer Section and leave the 409 Question Section empty. (Inverse queries are deprecated in 410 [RFC3425], and so relevant definitions do not appear in this 411 document.) 413 [RFC2308], however, has an alternate definition that puts the 414 QNAME in the answer (or series of answers) instead of the query. 415 It defines QNAME as: "...the name in the query section of an 416 answer, or where this resolves to a CNAME, or CNAME chain, the 417 data field of the last CNAME. The last CNAME in this sense is 418 that which contains a value which does not resolve to another 419 CNAME." This definition has a certain internal logic, because of 420 the way CNAME substitution works and the definition of CNAME. If 421 a name server does not find an RRset that matches a query, but it 422 finds the same name in the same class with a CNAME record, then 423 the name server "includes the CNAME record in the response and 424 restarts the query at the domain name specified in the data field 425 of the CNAME record." ([RFC1034] Section 3.6.2). This is made 426 explicit in the resolution algorithm outlined in Section 4.3.2 of 427 [RFC1034], which says to "change QNAME to the canonical name in 428 the CNAME RR, and go back to step 1" in the case of a CNAME RR. 429 Since a CNAME record explicitly declares that the owner name is 430 canonically named what is in the RDATA, then there is a way to 431 view the new name (i.e. the name that was in the RDATA of the 432 CNAME RR) as also being the QNAME. 434 This creates a kind of confusion, however, because the answer to a 435 query that results in CNAME processing contains in the echoed 436 Question Section one QNAME (the name in the original query), and a 437 second QNAME that is in the data field of the last CNAME. The 438 confusion comes from the iterative/recursive mode of resolution, 439 which finally returns an answer that need not actually have the 440 same owner name as the QNAME contained in the original query. 442 To address this potential confusion, it is helpful to distinguish 443 between three meanings: 445 * QNAME (original): The name actually sent in the Question 446 Section in the orignal query, which is always echoed in the 447 (final) reply in the Question Section when the QR bit is set to 448 1. 450 * QNAME (effective): A name actually resolved, which is either 451 the name originally queried, or a name received in a CNAME 452 chain response. 454 * QNAME (final): The name actually resolved, which is either the 455 name actually queried or else the last name in a CNAME chain 456 response. 458 Some of response codes that are defined in [RFC1035] have acquired 459 their own shorthand names. All of the RCODEs are listed at 460 http://www.iana.org/assignments/dns-parameters, although that site 461 uses mixed-case capitalization, while most documents use all-caps. 462 Some of the names are described here, but the official list is in the 463 IANA registry. 465 NOERROR: "No error condition" (Quoted from [RFC1035], 466 Section 4.1.1.) 468 FORMERR: "Format error - The name server was unable to interpret the 469 query." (Quoted from [RFC1035], Section 4.1.1.) 471 SERVFAIL: "Server failure - The name server was unable to process 472 this query due to a problem with the name server." (Quoted from 473 [RFC1035], Section 4.1.1.) 475 NXDOMAIN: "Name Error - Meaningful only for responses from an 476 authoritative name server, this code signifies that the domain 477 name referenced in the query does not exist." (Quoted from 478 [RFC1035], Section 4.1.1.) 480 NOTIMP: "Not Implemented - The name server does not support the 481 requested kind of query." (Quoted from [RFC1035], Section 4.1.1.) 483 REFUSED: "Refused - The name server refuses to perform the specified 484 operation for policy reasons. For example, a name server may not 485 wish to provide the information to the particular requester, or a 486 name server may not wish to perform a particular operation (e.g., 487 zone transfer) for particular data." (Quoted from [RFC1035], 488 Section 4.1.1.) 490 NODATA: "A pseudo RCODE which indicates that the name is valid for 491 the given class, but there are no records of the given type. A 492 NODATA response has to be inferred from the answer." (Quoted from 493 [RFC2308], Section 1.) "NODATA is indicated by an answer with the 494 RCODE set to NOERROR and no relevant answers in the answer 495 section. The authority section will contain an SOA record, or 496 there will be no NS records there." (Quoted from [RFC2308], 497 Section 2.2.) Note that referrals have a similar format to NODATA 498 replies; [RFC2308] explains how to distinguish them. 500 The term "NXRRSET" is sometimes used as a synonym for NODATA. 501 However, this is a mistake, given that NXRRSET is a specific error 502 code defined in [RFC2136]. 504 Negative response: A response that indicates that a particular RRset 505 does not exist, or whose RCODE indicates the nameserver cannot 506 answer. Sections 2 and 7 of [RFC2308] describe the types of 507 negative responses in detail. 509 Referrals: \[\[ This text is being modified in the WG and a changed 510 definition will appear in a future draft. \]\] 512 Data from the authority section of a non-authoritative answer. 513 [RFC1035] Section 2.1 defines "authoritative" data. However, 514 referrals at zone cuts (defined in Section 6) are not 515 authoritative. Referrals may be zone cut NS resource records and 516 their glue records. NS records on the parent side of a zone cut 517 are an authoritative delegation, but are normally not treated as 518 authoritative data. In general, a referral is a way for a server 519 to send an answer saying that the server does not know the answer, 520 but knows where the query should be directed in order to get an 521 answer. Historically, many authoritative servers answered with a 522 referral to the root zone when queried for a name for which they 523 were not authoritative, but this practice has declined. 525 4. Resource Records 527 RR: An acronym for resource record. ([RFC1034], Section 3.6.) 529 RRset: A set of resource records with the same label, class and 530 type, but with different data. (Definition from [RFC2181]) Also 531 spelled RRSet in some documents. As a clarification, "same label" 532 in this definition means "same owner name". In addition, 533 [RFC2181] states that "the TTLs of all RRs in an RRSet must be the 534 same". (This definition is definitely not the same as "the 535 response one gets to a query for QTYPE=ANY", which is an 536 unfortunate misunderstanding.) 538 Master file: "Master files are text files that contain RRs in text 539 form. Since the contents of a zone can be expressed in the form 540 of a list of RRs a master file is most often used to define a 541 zone, though it can be used to list a cache's contents." 542 ([RFC1035], Section 5.) 544 Presentation format: The text format used in master files. This 545 format is shown but not formally defined in [RFC1034] and 546 [RFC1035]. The term "presentation format" first appears in 547 [RFC4034]. 549 EDNS: The extension mechanisms for DNS, defined in [RFC6891]. 550 Sometimes called "EDNS0" or "EDNS(0)" to indicate the version 551 number. EDNS allows DNS clients and servers to specify message 552 sizes larger than the original 512 octet limit, to expand the 553 response code space, and potentially to carry additional options 554 that affect the handling of a DNS query. 556 OPT: A pseudo-RR (sometimes called a "meta-RR") that is used only to 557 contain control information pertaining to the question-and-answer 558 sequence of a specific transaction. (Definition from [RFC6891], 559 Section 6.1.1) It is used by EDNS. 561 Owner: The domain name where a RR is found ([RFC1034], Section 3.6). 562 Often appears in the term "owner name". 564 SOA field names: DNS documents, including the definitions here, 565 often refer to the fields in the RDATA of an SOA resource record 566 by field name. Those fields are defined in Section 3.3.13 of 567 [RFC1035]. The names (in the order they appear in the SOA RDATA) 568 are MNAME, RNAME, SERIAL, REFRESH, RETRY, EXPIRE, and MINIMUM. 569 Note that the meaning of MINIMUM field is updated in Section 4 of 570 [RFC2308]; the new definition is that the MINIMUM field is only 571 "the TTL to be used for negative responses". This document tends 572 to use field names instead of terms that describe the fields. 574 TTL: The maximum "time to live" of a resource record. "A TTL value 575 is an unsigned number, with a minimum value of 0, and a maximum 576 value of 2147483647. That is, a maximum of 2^31 - 1. When 577 transmitted, the TTL is encoded in the less significant 31 bits of 578 the 32 bit TTL field, with the most significant, or sign, bit set 579 to zero." (Quoted from [RFC2181], Section 8) (Note that [RFC1035] 580 erroneously stated that this is a signed integer; that was fixed 581 by [RFC2181].) 583 The TTL "specifies the time interval that the resource record may 584 be cached before the source of the information should again be 585 consulted". (Quoted from [RFC1035], Section 3.2.1) Also: "the 586 time interval (in seconds) that the resource record may be cached 587 before it should be discarded". (Quoted from [RFC1035], 588 Section 4.1.3). Despite being defined for a resource record, the 589 TTL of every resource record in an RRset is required to be the 590 same ([RFC2181], Section 5.2). 592 The reason that the TTL is the maximum time to live is that a 593 cache operator might decide to shorten the time to live for 594 operational purposes, such as if there is a policy to disallow TTL 595 values over a certain number. Also, if a value is flushed from 596 the cache when its value is still positive, the value effectively 597 becomes zero. Some servers are known to ignore the TTL on some 598 RRsets (such as when the authoritative data has a very short TTL) 599 even though this is against the advice in RFC 1035. 601 There is also the concept of a "default TTL" for a zone, which can 602 be a configuration parameter in the server software. This is 603 often expressed by a default for the entire server, and a default 604 for a zone using the $TTL directive in a zone file. The $TTL 605 directive was added to the master file format by [RFC2308]. 607 Class independent: A resource record type whose syntax and semantics 608 are the same for every DNS class. A resource record type that is 609 not class independent has different meanings depending on the DNS 610 class of the record, or the meaning is undefined for classes other 611 than IN (class 1, the Internet). 613 5. DNS Servers and Clients 615 This section defines the terms used for the systems that act as DNS 616 clients, DNS servers, or both. In the RFCs, DNS servers are 617 sometimes called "name servers", "nameservers", or just "servers". 618 There is no formal definition of DNS server, but the RFCs generally 619 assume that it is an Internet server that listens for queries and 620 sends responses using the DNS protocol defined in [RFC1035] and its 621 successors. 623 For terminology specific to the public DNS root server system, see 624 [RSSAC026]. That document defines terms such as "root server", "root 625 server operator", and terms that are specific to the way that the 626 root zone of the public DNS is served. 628 Resolver: A program "that extract[s] information from name servers 629 in response to client requests." (Quoted from [RFC1034], 630 Section 2.4) "The resolver is located on the same machine as the 631 program that requests the resolver's services, but it may need to 632 consult name servers on other hosts." (Quoted from [RFC1034], 633 Section 5.1) A resolver performs queries for a name, type, and 634 class, and receives answers. The logical function is called 635 "resolution". In practice, the term is usually referring to some 636 specific type of resolver (some of which are defined below), and 637 understanding the use of the term depends on understanding the 638 context. 640 A related term is "resolve", which is not formally defined in 641 [RFC1034] or [RFC1035]. An imputed definition might be "asking a 642 question that consists of a domain name, class, and type, and 643 receiving some sort of answer". Similarly, an imputed definition 644 of "resolution" might be "the answer received from resolving". 646 Stub resolver: A resolver that cannot perform all resolution itself. 647 Stub resolvers generally depend on a recursive resolver to 648 undertake the actual resolution function. Stub resolvers are 649 discussed but never fully defined in Section 5.3.1 of [RFC1034]. 650 They are fully defined in Section 6.1.3.1 of [RFC1123]. 652 Iterative mode: A resolution mode of a server that receives DNS 653 queries and responds with a referral to another server. 654 Section 2.3 of [RFC1034] describes this as "The server refers the 655 client to another server and lets the client pursue the query". A 656 resolver that works in iterative mode is sometimes called an 657 "iterative resolver". 659 Recursive mode: A resolution mode of a server that receives DNS 660 queries and either responds to those queries from a local cache or 661 sends queries to other servers in order to get the final answers 662 to the original queries. Section 2.3 of [RFC1034] describes this 663 as "The first server pursues the query for the client at another 664 server". A server operating in recursive mode may be thought of 665 as having a name server side (which is what answers the query) and 666 a resolver side (which performs the resolution function). Systems 667 operating in this mode are commonly called "recursive servers". 668 Sometimes they are called "recursive resolvers". While strictly 669 the difference between these is that one of them sends queries to 670 another recursive server and the other does not, in practice it is 671 not possible to know in advance whether the server that one is 672 querying will also perform recursion; both terms can be observed 673 in use interchangeably. 675 Full resolver: This term is used in [RFC1035], but it is not defined 676 there. RFC 1123 defines a "full-service resolver" that may or may 677 not be what was intended by "full resolver" in [RFC1035]. This 678 term is not properly defined in any RFC. 680 Full-service resolver: Section 6.1.3.1 of [RFC1123] defines this 681 term to mean a resolver that acts in recursive mode with a cache 682 (and meets other requirements). 684 Recursive resolver: A resolver that acts in recursive mode. In 685 general, a recursive resolver is expected to cache the answers it 686 receives (which would make it a full-service resolver), but some 687 recursive resolvers might not cache. 689 Recursive query: A query with the Recursion Desired (RD) bit set to 690 1 in the header.(See Section 4.1.1 of [RFC1035].) If recursive 691 service is available and is requested by the RD bit in the query, 692 the server uses its resolver to answer the query. (See 693 Section 4.3.2 of [RFC1035].) 695 Non-recursive query: A query with the Recursion Desired (RD) bit set 696 to 0 in the header. A server can answer non-recursive queries 697 using only local information: the response contains either an 698 error, the answer, or a referral to some other server "closer" to 699 the answer. (See Section 4.3.1 of [RFC1035].) 701 Iterative query: Synonym for non-recursive query that happens to be 702 a query in a series of recursive queries, but that is itself not a 703 recursive query. This term is used in a number of RFCs though 704 never explicitly defined. 706 Iterative resolution: A name server may be presented with a query 707 that can only be answered by some other server. The two general 708 approaches to dealing with this problem are "recursive", in which 709 the first server pursues the query for the client at another 710 server, and "iterative", in which the server refers the client to 711 another server and lets the client pursue the query there. (See 712 Section 2.3 of [RFC1034].) 714 In iterative resolution, the client repeatedly makes non-recursive 715 queries and follows referrals and/or aliases. The iterative 716 resolution algorithm is described in Section 5.3.3 of [RFC1034]. 718 Priming: "The act of finding the list of root servers from a 719 configuration that lists some or all of the purported IP addresses 720 of some or all of those root servers." (Quoted from [RFC8109], 721 Section 2.) Priming is most often done from a configuration 722 setting that contains a list of authoritative servers for the root 723 zone. 725 Root hints: "Operators who manage a DNS recursive resolver typically 726 need to configure a 'root hints file'. This file contains the 727 names and IP addresses of the authoritative name servers for the 728 root zone, so the software can bootstrap the DNS resolution 729 process. For many pieces of software, this list comes built into 730 the software." (Quoted from [IANA_RootFiles]) 732 Negative caching: "The storage of knowledge that something does not 733 exist, cannot give an answer, or does not give an answer." 734 (Quoted from [RFC2308], Section 1) 736 Authoritative server: "A server that knows the content of a DNS zone 737 from local knowledge, and thus can answer queries about that zone 738 without needing to query other servers." (Quoted from [RFC2182], 739 Section 2.) It is a system that responds to DNS queries with 740 information about zones for which it has been configured to answer 741 with the AA flag in the response header set to 1. It is a server 742 that has authority over one or more DNS zones. Note that it is 743 possible for an authoritative server to respond to a query without 744 the parent zone delegating authority to that server. 745 Authoritative servers also provide "referrals", usually to child 746 zones delegated from them; these referrals have the AA bit set to 747 0 and come with referral data in the Authority and (if needed) the 748 Additional sections. 750 Authoritative-only server: A name server that only serves 751 authoritative data and ignores requests for recursion. It will 752 "not normally generate any queries of its own. Instead, it 753 answers non-recursive queries from iterative resolvers looking for 754 information in zones it serves." (Quoted from [RFC4697], 755 Section 2.4) 757 Zone transfer: The act of a client requesting a copy of a zone and 758 an authoritative server sending the needed information. (See 759 Section 6 for a description of zones.) There are two common 760 standard ways to do zone transfers: the AXFR ("Authoritative 761 Transfer") mechanism to copy the full zone (described in 762 [RFC5936], and the IXFR ("Incremental Transfer") mechanism to copy 763 only parts of the zone that have changed (described in [RFC1995]). 764 Many systems use non-standard methods for zone transfer outside 765 the DNS protocol. 767 Secondary server: "An authoritative server which uses zone transfer 768 to retrieve the zone" (Quoted from [RFC1996], Section 2.1). 769 [RFC2182] describes secondary servers in detail. Although early 770 DNS RFCs such as [RFC1996] referred to this as a "slave", the 771 current common usage has shifted to calling it a "secondary". 772 Secondary servers are also discussed in [RFC1034]. 774 Slave server: See secondary server. 776 Primary server: "Any authoritative server configured to be the 777 source of zone transfer for one or more [secondary] servers" 778 (Quoted from [RFC1996], Section 2.1) or, more specifically, "an 779 authoritative server configured to be the source of AXFR or IXFR 780 data for one or more [secondary] servers" (Quoted from [RFC2136]). 781 Although early DNS RFCs such as [RFC1996] referred to this as a 782 "master", the current common usage has shifted to "primary". 783 Primary servers are also discussed in [RFC1034]. 785 Master server: See primary server. 787 Primary master: \[\[ There is active discussion in the WG of this 788 term. It will be resolved in a future version of the draft. \]\] 790 "The primary master is named in the zone's SOA MNAME field and 791 optionally by an NS RR". (Quoted from [RFC1996], Section 2.1). 792 [RFC2136] defines "primary master" as "Master server at the root 793 of the AXFR/IXFR dependency graph. The primary master is named in 794 the zone's SOA MNAME field and optionally by an NS RR. There is 795 by definition only one primary master server per zone." The idea 796 of a primary master is only used by [RFC2136], and is considered 797 archaic in other parts of the DNS. 799 Stealth server: This is "like a slave server except not listed in an 800 NS RR for the zone." (Quoted from [RFC1996], Section 2.1) 802 Hidden master: A stealth server that is a primary server for zone 803 transfers. "In this arrangement, the master name server that 804 processes the updates is unavailable to general hosts on the 805 Internet; it is not listed in the NS RRset." (Quoted from 806 [RFC6781], Section 3.4.3). An earlier RFC, [RFC4641], said that 807 the hidden master's name "appears in the SOA RRs MNAME field", 808 although in some setups, the name does not appear at all in the 809 public DNS. A hidden master can also be a secondary server 810 itself. 812 Forwarding: The process of one server sending a DNS query with the 813 RD bit set to 1 to another server to resolve that query. 815 Forwarding is a function of a DNS resolver; it is different than 816 simply blindly relaying queries. 818 [RFC5625] does not give a specific definition for forwarding, but 819 describes in detail what features a system that forwards need to 820 support. Systems that forward are sometimes called "DNS proxies", 821 but that term has not yet been defined (even in [RFC5625]). 823 Forwarder: Section 1 of [RFC2308] describes a forwarder as "a 824 nameserver used to resolve queries instead of directly using the 825 authoritative nameserver chain". [RFC2308] further says "The 826 forwarder typically either has better access to the internet, or 827 maintains a bigger cache which may be shared amongst many 828 resolvers." That definition appears to suggest that forwarders 829 normally only query authoritative servers. In current use, 830 however, forwarders often stand between stub resolvers and 831 recursive servers. [RFC2308] is silent on whether a forwarder is 832 iterative-only or can be a full-service resolver. 834 Policy-implementing resolver: A resolver acting in recursive mode 835 that changes some of the answers that it returns based on policy 836 criteria, such as to prevent access to malware sites or 837 objectionable content. In general, a stub resolver has no idea 838 whether upstream resolvers implement such policy or, if they do, 839 the exact policy about what changes will be made. In some cases, 840 the user of the stub resolver has selected the policy-implementing 841 resolver with the explicit intention of using it to implement the 842 policies. In other cases, policies are imposed without the user 843 of the stub resolver being informed. 845 Open resolver: A full-service resolver that accepts and processes 846 queries from any (or nearly any) stub resolver. This is sometimes 847 also called a "public resolver", although the term "public 848 resolver" is used more with open resolvers that are meant to be 849 open, as compared to the vast majority of open resolvers that are 850 probably misconfigured to be open. Open resolvers are discussed 851 in [RFC5358] 853 View: A configuration for a DNS server that allows it to provide 854 different answers depending on attributes of the query. 855 Typically, views differ by the source IP address of a query, but 856 can also be based on the destination IP address, the type of query 857 (such as AXFR), whether it is recursive, and so on. Views are 858 often used to provide more names or different addresses to queries 859 from "inside" a protected network than to those "outside" that 860 network. Views are not a standardized part of the DNS, but they 861 are widely implemented in server software. 863 Passive DNS: A mechanism to collect DNS data by storing DNS 864 transactions from name servers. Some of these systems also 865 collect the DNS queries associated with the responses. Passive 866 DNS databases can be used to answer historical questions about DNS 867 zones such as which answers were witnessed at what times in the 868 past. Passive DNS databases allow searching of the stored records 869 on keys other than just the name and type, such as "find all names 870 which have A records of a particular value". 872 Anycast: "The practice of making a particular service address 873 available in multiple, discrete, autonomous locations, such that 874 datagrams sent are routed to one of several available locations." 875 (Quoted from [RFC4786], Section 2) 877 Instance: "When anycast routing is used to allow more than one 878 server to have the same IP address, each one of those servers is 879 commonly referred to as an 'instance'." "An instance of a server, 880 such as a root server, is often referred to as an 'Anycast 881 instance'." (Quoted from [RSSAC026]) 883 Split DNS: "Where a corporate network serves up partly or completely 884 different DNS inside and outside its firewall. There are many 885 possible variants on this; the basic point is that the 886 correspondence between a given FQDN (fully qualified domain name) 887 and a given IPv4 address is no longer universal and stable over 888 long periods." (Quoted from [RFC2775], Section 3.8) 890 6. Zones 892 This section defines terms that are used when discussing zones that 893 are being served or retrieved. 895 Zone: "Authoritative information is organized into units called 896 'zones', and these zones can be automatically distributed to the 897 name servers which provide redundant service for the data in a 898 zone." (Quoted from [RFC1034], Section 2.4) 900 Child: "The entity on record that has the delegation of the domain 901 from the Parent." (Quoted from [RFC7344], Section 1.1) 903 Parent: "The domain in which the Child is registered." (Quoted from 904 [RFC7344], Section 1.1) Earlier, "parent name server" was defined 905 in [RFC0882] as "the name server that has authority over the place 906 in the domain name space that will hold the new domain". (Note 907 that [RFC0882] was obsoleted by [RFC1034] and [RFC1035].) 908 [RFC0819] also has some description of the relationship between 909 parents and children. 911 Origin: 913 (a) "The domain name that appears at the top of a zone (just below 914 the cut that separates the zone from its parent). The name of the 915 zone is the same as the name of the domain at the zone's origin." 916 (Quoted from [RFC2181], Section 6.) These days, this sense of 917 "origin" and "apex" (defined below) are often used 918 interchangeably. 920 (b) The domain name within which a given relative domain name 921 appears in zone files. Generally seen in the context of 922 "$ORIGIN", which is a control entry defined in [RFC1035], 923 Section 5.1, as part of the master file format. For example, if 924 the $ORIGIN is set to "example.org.", then a master file line for 925 "www" is in fact an entry for "www.example.org.". 927 Apex: The point in the tree at an owner of an SOA and corresponding 928 authoritative NS RRset. This is also called the "zone apex". 929 [RFC4033] defines it as "the name at the child's side of a zone 930 cut". The "apex" can usefully be thought of as a data-theoretic 931 description of a tree structure, and "origin" is the name of the 932 same concept when it is implemented in zone files. The 933 distinction is not always maintained in use, however, and one can 934 find uses that conflict subtly with this definition. [RFC1034] 935 uses the term "top node of the zone" as a synonym of "apex", but 936 that term is not widely used. These days, the first sense of 937 "origin" (above) and "apex" are often used interchangeably. 939 Zone cut: The delimitation point between two zones where the origin 940 of one of the zones is the child of the other zone. 942 "Zones are delimited by 'zone cuts'. Each zone cut separates a 943 'child' zone (below the cut) from a 'parent' zone (above the cut). 944 (Quoted from [RFC2181], Section 6; note that this is barely an 945 ostensive definition.) Section 4.2 of [RFC1034] uses "cuts" as 946 'zone cut'." 948 Delegation: The process by which a separate zone is created in the 949 name space beneath the apex of a given domain. Delegation happens 950 when an NS RRset is added in the parent zone for the child origin. 951 Delegation inherently happens at a zone cut. The term is also 952 commonly a noun: the new zone that is created by the act of 953 delegating. 955 Glue records: "[Resource records] which are not part of the 956 authoritative data [of the zone], and are address resource records 957 for the [name servers in subzones]. These RRs are only necessary 958 if the name server's name is 'below' the cut, and are only used as 959 part of a referral response." Without glue "we could be faced 960 with the situation where the NS RRs tell us that in order to learn 961 a name server's address, we should contact the server using the 962 address we wish to learn." (Definition from [RFC1034], 963 Section 4.2.1) 965 A later definition is that glue "includes any record in a zone 966 file that is not properly part of that zone, including nameserver 967 records of delegated sub-zones (NS records), address records that 968 accompany those NS records (A, AAAA, etc), and any other stray 969 data that might appear" ([RFC2181], Section 5.4.1). Although glue 970 is sometimes used today with this wider definition in mind, the 971 context surrounding the [RFC2181] definition suggests it is 972 intended to apply to the use of glue within the document itself 973 and not necessarily beyond. 975 In-bailiwick: An adjective to describe a name server whose name is 976 either subordinate to or (rarely) the same as the zone origin. 977 In-bailiwick name servers may have glue records in their parent 978 zone (using the first of the definitions of "glue records" in the 979 definition above). "In-bailiwick" names are divided into two type 980 of name server names: "in-domain" names and "sibling domain" 981 names: 983 * In-domain -- an adjective to describe a name server whose name 984 is either subordinate to or (rarely) the same as the owner name 985 of the NS resource records. An in-domain name server name MUST 986 have glue records or name resolution fails. For example, a 987 delegation for "child.example.com" may have "in-domain" name 988 server name "ns.child.example.com". 990 * Sibling domain: -- a name server's name that is either 991 subordinate to or (rarely) the same as the zone origin and not 992 subordinate to or the same as the owner name of the NS resource 993 records. Glue records for sibling domains are allowed, but not 994 necessary. For example, a delegation for "child.example.com" 995 in "example.com" zone may have "sibling" name server name 996 "ns.another.example.com". 998 Out-of-bailiwick: The antonym of in-bailiwick. An adjective to 999 describe a name server whose name is not subordinate to or the 1000 same as the zone origin. Glue records for out-of-bailiwick name 1001 servers are useless. 1003 Authoritative data: "All of the RRs attached to all of the nodes 1004 from the top node of the zone down to leaf nodes or nodes above 1005 cuts around the bottom edge of the zone." (Quoted from [RFC1034], 1006 Section 4.2.1) It is noted that this definition might 1007 inadvertently also include any NS records that appear in the zone, 1008 even those that might not truly be authoritative because there are 1009 identical NS RRs below the zone cut. This reveals the ambiguity 1010 in the notion of authoritative data, because the parent-side NS 1011 records authoritatively indicate the delegation, even though they 1012 are not themselves authoritative data. 1014 Root zone: The zone of a DNS-based tree whose apex is the zero- 1015 length label. Also sometimes called "the DNS root". 1017 Empty non-terminals (ENT): "Domain names that own no resource 1018 records but have subdomains that do." (Quoted from [RFC4592], 1019 Section 2.2.2.) A typical example is in SRV records: in the name 1020 "_sip._tcp.example.com", it is likely that "_tcp.example.com" has 1021 no RRsets, but that "_sip._tcp.example.com" has (at least) an SRV 1022 RRset. 1024 Delegation-centric zone: A zone that consists mostly of delegations 1025 to child zones. This term is used in contrast to a zone that 1026 might have some delegations to child zones, but also has many data 1027 resource records for the zone itself and/or for child zones. The 1028 term is used in [RFC4956] and [RFC5155], but is not defined there. 1030 Wildcard: [RFC1034] defined "wildcard", but in a way that turned out 1031 to be confusing to implementers. Special treatment is given to 1032 RRs with owner names starting with the label "*". "Such RRs are 1033 called 'wildcards'. Wildcard RRs can be thought of as 1034 instructions for synthesizing RRs." (Quoted from [RFC1034], 1035 Section 4.3.3) For an extended discussion of wildcards, including 1036 clearer definitions, see [RFC4592]. 1038 Asterisk label: "The first octet is the normal label type and length 1039 for a 1-octet-long label, and the second octet is the ASCII 1040 representation for the '*' character. A descriptive name of a 1041 label equaling that value is an 'asterisk label'." (Quoted from 1042 [RFC4592], Section 2.1.1) 1044 Wildcard domain name: "A 'wildcard domain name' is defined by having 1045 its initial (i.e., leftmost or least significant) label be 1046 asterisk label." (Quoted from [RFC4592], Section 2.1.1) 1048 Closest encloser: "The longest existing ancestor of a name." 1049 (Quoted from [RFC5155], Section 1.3) An earlier definition is "The 1050 node in the zone's tree of existing domain names that has the most 1051 labels matching the query name (consecutively, counting from the 1052 root label downward). Each match is a 'label match' and the order 1053 of the labels is the same." (Quoted from [RFC4592], 1054 Section 3.3.1) 1056 Closest provable encloser: "The longest ancestor of a name that can 1057 be proven to exist. Note that this is only different from the 1058 closest encloser in an Opt-Out zone." (Quoted from [RFC5155], 1059 Section 1.3) 1061 Next closer name: "The name one label longer than the closest 1062 provable encloser of a name." (Quoted from [RFC5155], 1063 Section 1.3) 1065 Source of Synthesis: "The source of synthesis is defined in the 1066 context of a query process as that wildcard domain name 1067 immediately descending from the closest encloser, provided that 1068 this wildcard domain name exists. 'Immediately descending' means 1069 that the source of synthesis has a name of the form: .." (Quoted from [RFC4592], 1071 Section 3.3.1) 1073 Occluded name: "The addition of a delegation point via dynamic 1074 update will render all subordinate domain names to be in a limbo, 1075 still part of the zone, but not available to the lookup process. 1076 The addition of a DNAME resource record has the same impact. The 1077 subordinate names are said to be 'occluded'." (Quoted from 1078 [RFC5936], Section 3.5) 1080 Fast flux DNS: This "occurs when a domain is found in DNS using A 1081 records to multiple IP addresses, each of which has a very short 1082 Time-to-Live (TTL) value associated with it. This means that the 1083 domain resolves to varying IP addresses over a short period of 1084 time." (Quoted from [RFC6561], Section 1.1.5, with typo 1085 corrected) It is often used to deliver malware. Because the 1086 addresses change so rapidly, it is difficult to ascertain all the 1087 hosts. It should be noted that the technique also works with AAAA 1088 records, but such use is not frequently observed on the Internet 1089 as of this writing. 1091 Reverse DNS, reverse lookup: "The process of mapping an address to a 1092 name is generally known as a 'reverse lookup', and the IN- 1093 ADDR.ARPA and IP6.ARPA zones are said to support the 'reverse 1094 DNS'." (Quoted from [RFC5855], Section 1) 1096 Forward lookup: "Hostname-to-address translation". (Quoted from 1097 [RFC2133], Section 6) 1099 arpa: Address and Routing Parameter Area Domain: "The 'arpa' domain 1100 was originally established as part of the initial deployment of 1101 the DNS, to provide a transition mechanism from the Host Tables 1102 that were common in the ARPANET, as well as a home for the IPv4 1103 reverse mapping domain. During 2000, the abbreviation was 1104 redesignated to 'Address and Routing Parameter Area' in the hope 1105 of reducing confusion with the earlier network name." (Quoted 1106 from [RFC3172], Section 2.) 1108 Infrastructure domain: A domain whose "role is to support the 1109 operating infrastructure of the Internet". (Quoted from 1110 [RFC3172], Section 2.) 1112 Service name: "Service names are the unique key in the Service Name 1113 and Transport Protocol Port Number registry. This unique symbolic 1114 name for a service may also be used for other purposes, such as in 1115 DNS SRV records." (Quoted from [RFC6335], Section 5.) 1117 7. Registration Model 1119 Registry: The administrative operation of a zone that allows 1120 registration of names within that zone. People often use this 1121 term to refer only to those organizations that perform 1122 registration in large delegation-centric zones (such as TLDs); but 1123 formally, whoever decides what data goes into a zone is the 1124 registry for that zone. This definition of "registry" is from a 1125 DNS point of view; for some zones, the policies that determine 1126 what can go in the zone are decided by superior zones and not the 1127 registry operator. 1129 Registrant: An individual or organization on whose behalf a name in 1130 a zone is registered by the registry. In many zones, the registry 1131 and the registrant may be the same entity, but in TLDs they often 1132 are not. 1134 Registrar: A service provider that acts as a go-between for 1135 registrants and registries. Not all registrations require a 1136 registrar, though it is common to have registrars involved in 1137 registrations in TLDs. 1139 EPP: The Extensible Provisioning Protocol (EPP), which is commonly 1140 used for communication of registration information between 1141 registries and registrars. EPP is defined in [RFC5730]. 1143 WHOIS: A protocol specified in [RFC3912], often used for querying 1144 registry databases. WHOIS data is frequently used to associate 1145 registration data (such as zone management contacts) with domain 1146 names. The term "WHOIS data" is often used as a synonym for the 1147 registry database, even though that database may be served by 1148 different protocols, particularly RDAP. The WHOIS protocol is 1149 also used with IP address registry data. 1151 RDAP: The Registration Data Access Protocol, defined in [RFC7480], 1152 [RFC7481], [RFC7482], [RFC7483], [RFC7484], and [RFC7485]. The 1153 RDAP protocol and data format are meant as a replacement for 1154 WHOIS. 1156 DNS operator: An entity responsible for running DNS servers. For a 1157 zone's authoritative servers, the registrant may act as their own 1158 DNS operator, or their registrar may do it on their behalf, or 1159 they may use a third-party operator. For some zones, the registry 1160 function is performed by the DNS operator plus other entities who 1161 decide about the allowed contents of the zone. 1163 Subordinate and Superordinate: These terms are introduced in 1164 [RFC3731] but not defined there. Instead, they are given in 1165 examples. "For example, domain name 'example.com' has a 1166 superordinate relationship to host name ns1.example.com'." "For 1167 example, host ns1.example1.com is a subordinate host of domain 1168 example1.com, but it is a not a subordinate host of domain 1169 example2.com." (Quoted from [RFC3731], Section 1.1.) These terms 1170 are strictly ways of referring to the relationship standing of two 1171 domains where one is a subdomain of the other. 1173 8. General DNSSEC 1175 Most DNSSEC terms are defined in [RFC4033], [RFC4034], [RFC4035], and 1176 [RFC5155]. The terms that have caused confusion in the DNS community 1177 are highlighted here. 1179 DNSSEC-aware and DNSSEC-unaware: These two terms, which are used in 1180 some RFCs, have not been formally defined. However, Section 2 of 1181 [RFC4033] defines many types of resolvers and validators, 1182 including "non-validating security-aware stub resolver", "non- 1183 validating stub resolver", "security-aware name server", 1184 "security-aware recursive name server", "security-aware resolver", 1185 "security-aware stub resolver", and "security-oblivious 1186 'anything'". (Note that the term "validating resolver", which is 1187 used in some places in DNSSEC-related documents, is also not 1188 defined in those RFCs, but is defined below.) 1190 Signed zone: "A zone whose RRsets are signed and that contains 1191 properly constructed DNSKEY, Resource Record Signature (RRSIG), 1192 Next Secure (NSEC), and (optionally) DS records." (Quoted from 1193 [RFC4033], Section 2.) It has been noted in other contexts that 1194 the zone itself is not really signed, but all the relevant RRsets 1195 in the zone are signed. Nevertheless, if a zone that should be 1196 signed contains any RRsets that are not signed (or opted out), 1197 those RRsets will be treated as bogus, so the whole zone needs to 1198 be handled in some way. 1200 It should also be noted that, since the publication of [RFC6840], 1201 NSEC records are no longer required for signed zones: a signed 1202 zone might include NSEC3 records instead. [RFC7129] provides 1203 additional background commentary and some context for the NSEC and 1204 NSEC3 mechanisms used by DNSSEC to provide authenticated denial- 1205 of-existence responses. NSEC and NSEC3 are described below. 1207 Unsigned zone: Section 2 of [RFC4033] defines this as "a zone that 1208 is not signed". Section 2 of [RFC4035] defines this as "A zone 1209 that does not include these records [properly constructed DNSKEY, 1210 Resource Record Signature (RRSIG), Next Secure (NSEC), and 1211 (optionally) DS records] according to the rules in this section". 1212 There is an important note at the end of Section 5.2 of [RFC4035] 1213 that defines an additional situation in which a zone is considered 1214 unsigned: "If the resolver does not support any of the algorithms 1215 listed in an authenticated DS RRset, then the resolver will not be 1216 able to verify the authentication path to the child zone. In this 1217 case, the resolver SHOULD treat the child zone as if it were 1218 unsigned." 1220 NSEC: "The NSEC record allows a security-aware resolver to 1221 authenticate a negative reply for either name or type non- 1222 existence with the same mechanisms used to authenticate other DNS 1223 replies." (Quoted from [RFC4033], Section 3.2.) In short, an 1224 NSEC record provides authenticated denial of existence. 1226 "The NSEC resource record lists two separate things: the next 1227 owner name (in the canonical ordering of the zone) that contains 1228 authoritative data or a delegation point NS RRset, and the set of 1229 RR types present at the NSEC RR's owner name." (Quoted from 1230 Section 4 of RFC 4034) 1232 NSEC3: Like the NSEC record, the NSEC3 record also provides 1233 authenticated denial of existence; however, NSEC3 records mitigate 1234 against zone enumeration and support Opt-Out. NSEC resource 1235 records require associated NSEC3PARAM resource records. NSEC3 and 1236 NSEC3PARAM resource records are defined in [RFC5155]. 1238 Note that [RFC6840] says that [RFC5155] "is now considered part of 1239 the DNS Security Document Family as described by Section 10 of 1240 [RFC4033]". This means that some of the definitions from earlier 1241 RFCs that only talk about NSEC records should probably be 1242 considered to be talking about both NSEC and NSEC3. 1244 Opt-out: "The Opt-Out Flag indicates whether this NSEC3 RR may cover 1245 unsigned delegations." (Quoted from [RFC5155], Section 3.1.2.1.) 1246 Opt-out tackles the high costs of securing a delegation to an 1247 insecure zone. When using Opt-Out, names that are an insecure 1248 delegation (and empty non-terminals that are only derived from 1249 insecure delegations) don't require an NSEC3 record or its 1250 corresponding RRSIG records. Opt-Out NSEC3 records are not able 1251 to prove or deny the existence of the insecure delegations. 1252 (Adapted from [RFC7129], Section 5.1) 1254 Insecure delegation: "A signed name containing a delegation (NS 1255 RRset), but lacking a DS RRset, signifying a delegation to an 1256 unsigned subzone." (Quoted from [RFC4956], Section 2.) 1258 Zone enumeration: "The practice of discovering the full content of a 1259 zone via successive queries." (Quoted from [RFC5155], 1260 Section 1.3.) This is also sometimes called "zone walking". Zone 1261 enumeration is different from zone content guessing where the 1262 guesser uses a large dictionary of possible labels and sends 1263 successive queries for them, or matches the contents of NSEC3 1264 records against such a dictionary. 1266 Validation: Validation, in the context of DNSSEC, refers to the 1267 following: 1269 * Checking the validity of DNSSEC signatures 1271 * Checking the validity of DNS responses, such as those including 1272 authenticated denial of existence 1274 * Building an authentication chain from a trust anchor to a DNS 1275 response or individual DNS RRsets in a response 1277 The first two definitions above consider only the validity of 1278 individual DNSSEC components such as the RRSIG validity or NSEC 1279 proof validity. The third definition considers the components of 1280 the entire DNSSEC authentication chain, and thus requires 1281 "configured knowledge of at least one authenticated DNSKEY or DS 1282 RR" (as described in [RFC4035], Section 5). 1284 [RFC4033], Section 2, says that a "Validating Security-Aware Stub 1285 Resolver... performs signature validation" and uses a trust anchor 1286 "as a starting point for building the authentication chain to a 1287 signed DNS response", and thus uses the first and third 1288 definitions above. The process of validating an RRSIG resource 1289 record is described in [RFC4035], Section 5.3. 1291 [RFC5155] refers to validating responses throughout the document, 1292 in the context of hashed authenticated denial of existence; this 1293 uses the second definition above. 1295 The term "authentication" is used interchangeably with 1296 "validation", in the sense of the third definition above. 1297 [RFC4033], Section 2, describes the chain linking trust anchor to 1298 DNS data as the "authentication chain". A response is considered 1299 to be authentic if "all RRsets in the Answer and Authority 1300 sections of the response [are considered] to be authentic" 1301 ([RFC4035]). DNS data or responses deemed to be authentic or 1302 validated have a security status of "secure" ([RFC4035], 1303 Section 4.3; [RFC4033], Section 5). "Authenticating both DNS keys 1304 and data is a matter of local policy, which may extend or even 1305 override the [DNSSEC] protocol extensions" ([RFC4033], 1306 Section 3.1). 1308 The term "verification", when used, is usually synonym for 1309 "validation". 1311 Validating resolver: A security-aware recursive name server, 1312 security-aware resolver, or security-aware stub resolver that is 1313 applying at least one of the definitions of validation (above), as 1314 appropriate to the resolution context. For the same reason that 1315 the generic term "resolver" is sometimes ambiguous and needs to be 1316 evaluated in context (see Section 5), "validating resolver" is a 1317 context-sensitive term. 1319 Key signing key (KSK): DNSSEC keys that "only sign the apex DNSKEY 1320 RRset in a zone."(Quoted from [RFC6781], Section 3.1) 1322 Zone signing key (ZSK): "DNSSEC keys that can be used to sign all 1323 the RRsets in a zone that require signatures, other than the apex 1324 DNSKEY RRset." (Quoted from [RFC6781], Section 3.1) Note that the 1325 roles KSK and ZSK are not mutually exclusive: a single key can be 1326 both KSK and ZSK at the same time. Also note that a ZSK is 1327 sometimes used to sign the apex DNSKEY RRset. 1329 Combined signing key (CSK): "In cases where the differentiation 1330 between the KSK and ZSK is not made, i.e., where keys have the 1331 role of both KSK and ZSK, we talk about a Single-Type Signing 1332 Scheme." (Quoted from [RFC6781], Section 3.1) This is sometimes 1333 called a "combined signing key" or CSK. It is operational 1334 practice, not protocol, that determines whether a particular key 1335 is a ZSK, a KSK, or a CSK. 1337 Secure Entry Point (SEP): A flag in the DNSKEY RDATA that "can be 1338 used to distinguish between keys that are intended to be used as 1339 the secure entry point into the zone when building chains of 1340 trust, i.e., they are (to be) pointed to by parental DS RRs or 1341 configured as a trust anchor. Therefore, it is suggested that the 1342 SEP flag be set on keys that are used as KSKs and not on keys that 1343 are used as ZSKs, while in those cases where a distinction between 1344 a KSK and ZSK is not made (i.e., for a Single-Type Signing 1345 Scheme), it is suggested that the SEP flag be set on all keys." 1346 (Quoted from [RFC6781], Section 3.2.3.) Note that the SEP flag is 1347 only a hint, and its presence or absence may not be used to 1348 disqualify a given DNSKEY RR from use as a KSK or ZSK during 1349 validation. 1351 The original defintion of SEPs was in [RFC3757]. That definition 1352 clearly indicated that the SEP was a key, not just a bit in the 1353 key. The abstract of [RFC3757] says: "With the Delegation Signer 1354 (DS) resource record (RR), the concept of a public key acting as a 1355 secure entry point (SEP) has been introduced. During exchanges of 1356 public keys with the parent there is a need to differentiate SEP 1357 keys from other public keys in the Domain Name System KEY (DNSKEY) 1358 resource record set. A flag bit in the DNSKEY RR is defined to 1359 indicate that DNSKEY is to be used as a SEP." That definition of 1360 the SEP as a key was made obsolete by [RFC4034], and the 1361 definition from [RFC6781] is consistent with [RFC4034]. 1363 Trust anchor: "A configured DNSKEY RR or DS RR hash of a DNSKEY RR. 1364 A validating security-aware resolver uses this public key or hash 1365 as a starting point for building the authentication chain to a 1366 signed DNS response." (Quoted from [RFC4033], Section 2) 1368 DNSSEC Policy (DP): A statement that "sets forth the security 1369 requirements and standards to be implemented for a DNSSEC-signed 1370 zone." (Quoted from [RFC6841], Section 2) 1372 DNSSEC Practice Statement (DPS): "A practices disclosure document 1373 that may support and be a supplemental document to the DNSSEC 1374 Policy (if such exists), and it states how the management of a 1375 given zone implements procedures and controls at a high level." 1376 (Quoted from [RFC6841], Section 2) 1378 Hardware security module (HSM): A specialized piece of hardware that 1379 is used to create keys for signatures and to sign messages. In 1380 DNSSEC, HSMs are often used to hold the private keys for KSKs and 1381 ZSKs and to create the RRSIG records at periodic intervals. 1383 Signing software: Authoritative DNS servers that supports DNSSEC 1384 often contains software that facilitates the creation and 1385 maintenance of DNSSEC signatures in zones. There is also stand- 1386 alone software that can be used to sign a zone regardless of 1387 whether the authoritative server itself supports signing. 1388 Sometimes signing software can support particular HSMs as part of 1389 the signing process. 1391 9. DNSSEC States 1393 A validating resolver can determine that a response is in one of four 1394 states: secure, insecure, bogus, or indeterminate. These states are 1395 defined in [RFC4033] and [RFC4035], although the two definitions 1396 differ a bit. This document makes no effort to reconcile the two 1397 definitions, and takes no position as to whether they need to be 1398 reconciled. 1400 Section 5 of [RFC4033] says: 1402 A validating resolver can determine the following 4 states: 1404 Secure: The validating resolver has a trust anchor, has a chain 1405 of trust, and is able to verify all the signatures in the 1406 response. 1408 Insecure: The validating resolver has a trust anchor, a chain 1409 of trust, and, at some delegation point, signed proof of the 1410 non-existence of a DS record. This indicates that subsequent 1411 branches in the tree are provably insecure. A validating 1412 resolver may have a local policy to mark parts of the domain 1413 space as insecure. 1415 Bogus: The validating resolver has a trust anchor and a secure 1416 delegation indicating that subsidiary data is signed, but 1417 the response fails to validate for some reason: missing 1418 signatures, expired signatures, signatures with unsupported 1419 algorithms, data missing that the relevant NSEC RR says 1420 should be present, and so forth. 1422 Indeterminate: There is no trust anchor that would indicate that a 1423 specific portion of the tree is secure. This is the default 1424 operation mode. 1426 Section 4.3 of [RFC4035] says: 1428 A security-aware resolver must be able to distinguish between four 1429 cases: 1431 Secure: An RRset for which the resolver is able to build a chain 1432 of signed DNSKEY and DS RRs from a trusted security anchor to 1433 the RRset. In this case, the RRset should be signed and is 1434 subject to signature validation, as described above. 1436 Insecure: An RRset for which the resolver knows that it has no 1437 chain of signed DNSKEY and DS RRs from any trusted starting 1438 point to the RRset. This can occur when the target RRset lies 1439 in an unsigned zone or in a descendent [sic] of an unsigned 1440 zone. In this case, the RRset may or may not be signed, but 1441 the resolver will not be able to verify the signature. 1443 Bogus: An RRset for which the resolver believes that it ought to 1444 be able to establish a chain of trust but for which it is 1445 unable to do so, either due to signatures that for some reason 1446 fail to validate or due to missing data that the relevant 1447 DNSSEC RRs indicate should be present. This case may indicate 1448 an attack but may also indicate a configuration error or some 1449 form of data corruption. 1451 Indeterminate: An RRset for which the resolver is not able to 1452 determine whether the RRset should be signed, as the resolver 1453 is not able to obtain the necessary DNSSEC RRs. This can occur 1454 when the security-aware resolver is not able to contact 1455 security-aware name servers for the relevant zones. 1457 10. Security Considerations 1459 These definitions do not change any security considerations for the 1460 DNS. 1462 11. IANA Considerations 1464 None. 1466 12. References 1468 12.1. Normative References 1470 [IANA_RootFiles] 1471 Internet Assigned Numbers Authority, "IANA Root Files", 1472 2016, . 1474 [RFC0882] Mockapetris, P., "Domain names: Concepts and facilities", 1475 RFC 882, DOI 10.17487/RFC0882, November 1983, 1476 . 1478 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 1479 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 1480 . 1482 [RFC1035] Mockapetris, P., "Domain names - implementation and 1483 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 1484 November 1987, . 1486 [RFC1123] Braden, R., Ed., "Requirements for Internet Hosts - 1487 Application and Support", STD 3, RFC 1123, 1488 DOI 10.17487/RFC1123, October 1989, . 1491 [RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone 1492 Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996, 1493 August 1996, . 1495 [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, 1496 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 1497 RFC 2136, DOI 10.17487/RFC2136, April 1997, 1498 . 1500 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 1501 Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997, 1502 . 1504 [RFC2182] Elz, R., Bush, R., Bradner, S., and M. Patton, "Selection 1505 and Operation of Secondary DNS Servers", BCP 16, RFC 2182, 1506 DOI 10.17487/RFC2182, July 1997, . 1509 [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS 1510 NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998, 1511 . 1513 [RFC3731] Hollenbeck, S., "Extensible Provisioning Protocol (EPP) 1514 Domain Name Mapping", RFC 3731, DOI 10.17487/RFC3731, 1515 March 2004, . 1517 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 1518 Rose, "DNS Security Introduction and Requirements", 1519 RFC 4033, DOI 10.17487/RFC4033, March 2005, 1520 . 1522 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 1523 Rose, "Resource Records for the DNS Security Extensions", 1524 RFC 4034, DOI 10.17487/RFC4034, March 2005, 1525 . 1527 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 1528 Rose, "Protocol Modifications for the DNS Security 1529 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 1530 . 1532 [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name 1533 System", RFC 4592, DOI 10.17487/RFC4592, July 2006, 1534 . 1536 [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS 1537 Security (DNSSEC) Hashed Authenticated Denial of 1538 Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008, 1539 . 1541 [RFC5358] Damas, J. and F. Neves, "Preventing Use of Recursive 1542 Nameservers in Reflector Attacks", BCP 140, RFC 5358, 1543 DOI 10.17487/RFC5358, October 2008, . 1546 [RFC5730] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)", 1547 STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009, 1548 . 1550 [RFC5855] Abley, J. and T. Manderson, "Nameservers for IPv4 and IPv6 1551 Reverse Zones", BCP 155, RFC 5855, DOI 10.17487/RFC5855, 1552 May 2010, . 1554 [RFC5936] Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol 1555 (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010, 1556 . 1558 [RFC6561] Livingood, J., Mody, N., and M. O'Reirdan, 1559 "Recommendations for the Remediation of Bots in ISP 1560 Networks", RFC 6561, DOI 10.17487/RFC6561, March 2012, 1561 . 1563 [RFC6781] Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC 1564 Operational Practices, Version 2", RFC 6781, 1565 DOI 10.17487/RFC6781, December 2012, . 1568 [RFC6840] Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and 1569 Implementation Notes for DNS Security (DNSSEC)", RFC 6840, 1570 DOI 10.17487/RFC6840, February 2013, . 1573 [RFC6841] Ljunggren, F., Eklund Lowinder, AM., and T. Okubo, "A 1574 Framework for DNSSEC Policies and DNSSEC Practice 1575 Statements", RFC 6841, DOI 10.17487/RFC6841, January 2013, 1576 . 1578 [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms 1579 for DNS (EDNS(0))", STD 75, RFC 6891, 1580 DOI 10.17487/RFC6891, April 2013, . 1583 [RFC7344] Kumari, W., Gudmundsson, O., and G. Barwood, "Automating 1584 DNSSEC Delegation Trust Maintenance", RFC 7344, 1585 DOI 10.17487/RFC7344, September 2014, . 1588 [RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 1589 Terminology", RFC 7719, DOI 10.17487/RFC7719, December 1590 2015, . 1592 12.2. Informative References 1594 [IANA_Resource_Registry] 1595 Internet Assigned Numbers Authority, "Resource Record (RR) 1596 TYPEs", 2017, 1597 . 1599 [RFC0819] Su, Z. and J. Postel, "The Domain Naming Convention for 1600 Internet User Applications", RFC 819, 1601 DOI 10.17487/RFC0819, August 1982, . 1604 [RFC0952] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet 1605 host table specification", RFC 952, DOI 10.17487/RFC0952, 1606 October 1985, . 1608 [RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995, 1609 DOI 10.17487/RFC1995, August 1996, . 1612 [RFC2133] Gilligan, R., Thomson, S., Bound, J., and W. Stevens, 1613 "Basic Socket Interface Extensions for IPv6", RFC 2133, 1614 DOI 10.17487/RFC2133, April 1997, . 1617 [RFC2775] Carpenter, B., "Internet Transparency", RFC 2775, 1618 DOI 10.17487/RFC2775, February 2000, . 1621 [RFC3172] Huston, G., Ed., "Management Guidelines & Operational 1622 Requirements for the Address and Routing Parameter Area 1623 Domain ("arpa")", BCP 52, RFC 3172, DOI 10.17487/RFC3172, 1624 September 2001, . 1626 [RFC3425] Lawrence, D., "Obsoleting IQUERY", RFC 3425, 1627 DOI 10.17487/RFC3425, November 2002, . 1630 [RFC3757] Kolkman, O., Schlyter, J., and E. Lewis, "Domain Name 1631 System KEY (DNSKEY) Resource Record (RR) Secure Entry 1632 Point (SEP) Flag", RFC 3757, DOI 10.17487/RFC3757, April 1633 2004, . 1635 [RFC3912] Daigle, L., "WHOIS Protocol Specification", RFC 3912, 1636 DOI 10.17487/RFC3912, September 2004, . 1639 [RFC4641] Kolkman, O. and R. Gieben, "DNSSEC Operational Practices", 1640 RFC 4641, DOI 10.17487/RFC4641, September 2006, 1641 . 1643 [RFC4697] Larson, M. and P. Barber, "Observed DNS Resolution 1644 Misbehavior", BCP 123, RFC 4697, DOI 10.17487/RFC4697, 1645 October 2006, . 1647 [RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast 1648 Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786, 1649 December 2006, . 1651 [RFC4956] Arends, R., Kosters, M., and D. Blacka, "DNS Security 1652 (DNSSEC) Opt-In", RFC 4956, DOI 10.17487/RFC4956, July 1653 2007, . 1655 [RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines", 1656 BCP 152, RFC 5625, DOI 10.17487/RFC5625, August 2009, 1657 . 1659 [RFC5890] Klensin, J., "Internationalized Domain Names for 1660 Applications (IDNA): Definitions and Document Framework", 1661 RFC 5890, DOI 10.17487/RFC5890, August 2010, 1662 . 1664 [RFC5891] Klensin, J., "Internationalized Domain Names in 1665 Applications (IDNA): Protocol", RFC 5891, 1666 DOI 10.17487/RFC5891, August 2010, . 1669 [RFC5892] Faltstrom, P., Ed., "The Unicode Code Points and 1670 Internationalized Domain Names for Applications (IDNA)", 1671 RFC 5892, DOI 10.17487/RFC5892, August 2010, 1672 . 1674 [RFC5893] Alvestrand, H., Ed. and C. Karp, "Right-to-Left Scripts 1675 for Internationalized Domain Names for Applications 1676 (IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010, 1677 . 1679 [RFC5894] Klensin, J., "Internationalized Domain Names for 1680 Applications (IDNA): Background, Explanation, and 1681 Rationale", RFC 5894, DOI 10.17487/RFC5894, August 2010, 1682 . 1684 [RFC6055] Thaler, D., Klensin, J., and S. Cheshire, "IAB Thoughts on 1685 Encodings for Internationalized Domain Names", RFC 6055, 1686 DOI 10.17487/RFC6055, February 2011, . 1689 [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, 1690 DOI 10.17487/RFC6265, April 2011, . 1693 [RFC6303] Andrews, M., "Locally Served DNS Zones", BCP 163, 1694 RFC 6303, DOI 10.17487/RFC6303, July 2011, 1695 . 1697 [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. 1698 Cheshire, "Internet Assigned Numbers Authority (IANA) 1699 Procedures for the Management of the Service Name and 1700 Transport Protocol Port Number Registry", BCP 165, 1701 RFC 6335, DOI 10.17487/RFC6335, August 2011, 1702 . 1704 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in 1705 Internationalization in the IETF", BCP 166, RFC 6365, 1706 DOI 10.17487/RFC6365, September 2011, . 1709 [RFC7129] Gieben, R. and W. Mekking, "Authenticated Denial of 1710 Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129, 1711 February 2014, . 1713 [RFC7480] Newton, A., Ellacott, B., and N. Kong, "HTTP Usage in the 1714 Registration Data Access Protocol (RDAP)", RFC 7480, 1715 DOI 10.17487/RFC7480, March 2015, . 1718 [RFC7481] Hollenbeck, S. and N. Kong, "Security Services for the 1719 Registration Data Access Protocol (RDAP)", RFC 7481, 1720 DOI 10.17487/RFC7481, March 2015, . 1723 [RFC7482] Newton, A. and S. Hollenbeck, "Registration Data Access 1724 Protocol (RDAP) Query Format", RFC 7482, 1725 DOI 10.17487/RFC7482, March 2015, . 1728 [RFC7483] Newton, A. and S. Hollenbeck, "JSON Responses for the 1729 Registration Data Access Protocol (RDAP)", RFC 7483, 1730 DOI 10.17487/RFC7483, March 2015, . 1733 [RFC7484] Blanchet, M., "Finding the Authoritative Registration Data 1734 (RDAP) Service", RFC 7484, DOI 10.17487/RFC7484, March 1735 2015, . 1737 [RFC7485] Zhou, L., Kong, N., Shen, S., Sheng, S., and A. Servin, 1738 "Inventory and Analysis of WHOIS Registration Objects", 1739 RFC 7485, DOI 10.17487/RFC7485, March 2015, 1740 . 1742 [RFC8109] Koch, P., Larson, M., and P. Hoffman, "Initializing a DNS 1743 Resolver with Priming Queries", BCP 209, RFC 8109, 1744 DOI 10.17487/RFC8109, March 2017, . 1747 [RSSAC026] 1748 Root Server System Advisory Committee (RSSAC), "RSSAC 1749 Lexicon", 2017, 1750 . 1753 Appendix A. Definitions Updated by this Document 1755 The following definitions from RFCs are updated by this document: 1757 o Forwarder in [RFC2308] 1759 o Secure Entry Point (SEP) in [RFC3757]; note, however, that this 1760 RFC is already obsolete 1762 Appendix B. Definitions First Defined in this Document 1764 The following definitions are first defined in this document: 1766 o "Alias" in Section 2 1768 o "Apex" in Section 6 1770 o "arpa" in Section 6 1772 o "Class independent" in Section 4 1774 o "Delegation-centric zone" in Section 6 1776 o "Delegation" in Section 6 1778 o "DNS operator" in Section 7 1780 o "DNSSEC-aware" in Section 8 1782 o "DNSSEC-unaware" in Section 8 1784 o "Forwarding" in Section 5 1786 o "Full resolver" in Section 5 1788 o "Fully qualified domain name" in Section 2 1790 o "Global DNS" in Section 2 1792 o "Hardware Security Module (HSM)" in Section 8 1794 o "Host name" in Section 2 1796 o "IDN" in Section 2 1798 o "In-bailiwick" in Section 6 1800 o "Label" in Section 2 1802 o "Locally served DNS zone" in Section 2 1804 o "Naming system" in Section 2 1806 o "Negative response" in Section 3 1808 o "Open resolver" in Section 5 1809 o "Out-of-bailiwick" in Section 6 1811 o "Passive DNS" in Section 5 1813 o "Policy-implementing resolver" in Section 5 1815 o "Presentation format" in Section 4 1817 o "Priming" in Section 5 1819 o "Private DNS" in Section 2 1821 o "Recursive resolver" in Section 5 1823 o "Referrals" in Section 3 1825 o "Registrant" in Section 7 1827 o "Registrar" in Section 7 1829 o "Registry" in Section 7 1831 o "Root zone" in Section 6 1833 o "Secure Entry Point (SEP)" in Section 8 1835 o "Signing software" in Section 8 1837 o "Stub resolver" in Section 5 1839 o "TLD" in Section 2 1841 o "Validating resolver" in Section 8 1843 o "Validation" in Section 8 1845 o "View" in Section 5 1847 o "Zone transfer" in Section 5 1849 Index 1851 A 1852 Alias 8 1853 Anycast 19 1854 Apex 20 1855 Asterisk label 22 1856 Authoritative data 21 1857 Authoritative server 16 1858 Authoritative-only server 16 1859 arpa: Address and Routing Parameter Area Domain 23 1861 C 1862 CNAME 8 1863 Canonical name 8 1864 Child 19 1865 Class independent 13 1866 Closest encloser 22 1867 Closest provable encloser 23 1868 Combined signing key (CSK) 28 1870 D 1871 DNS operator 25 1872 DNSSEC Policy (DP) 29 1873 DNSSEC Practice Statement (DPS) 29 1874 DNSSEC-aware and DNSSEC-unaware 25 1875 Delegation 20 1876 Delegation-centric zone 22 1877 Domain name 4 1879 E 1880 EDNS 12 1881 EPP 24 1882 Empty non-terminals (ENT) 22 1884 F 1885 FORMERR 10 1886 Fast flux DNS 23 1887 Forward lookup 23 1888 Forwarder 18 1889 Forwarding 17 1890 Full resolver 15 1891 Full-service resolver 15 1892 Fully qualified domain name (FQDN) 7 1894 G 1895 Global DNS 4 1896 Glue records 20 1898 H 1899 Hardware security module (HSM) 29 1900 Hidden master 17 1901 Host name 7 1903 I 1904 IDN 8 1905 In-bailiwick 21 1906 Infrastructure domain 24 1907 Insecure delegation 27 1908 Instance 19 1909 Iterative mode 14 1910 Iterative query 15 1911 Iterative resolution 15 1913 K 1914 Key signing key (KSK) 28 1916 L 1917 Label 4 1918 Locally served DNS zone 6 1920 M 1921 Master file 12 1922 Master server 17 1924 N 1925 NODATA 11 1926 NOERROR 10 1927 NOTIMP 11 1928 NSEC 26 1929 NSEC3 26 1930 NXDOMAIN 10 1931 Naming system 3 1932 Negative caching 16 1933 Negative response 11 1934 Next closer name 23 1935 Non-recursive query 15 1937 O 1938 OPT 12 1939 Occluded name 23 1940 Open resolver 18 1941 Opt-out 26 1942 Origin 20 1943 Out-of-bailiwick 21 1944 Owner 12 1946 P 1947 Parent 19 1948 Passive DNS 19 1949 Policy-implementing resolver 18 1950 Presentation format 12 1951 Primary master 17 1952 Primary server 17 1953 Priming 16 1954 Private DNS 6 1955 Public suffix 8 1957 R 1958 RDAP 25 1959 REFUSED 11 1960 RR 12 1961 RRset 12 1962 Recursive mode 14 1963 Recursive query 15 1964 Recursive resolver 15 1965 Referrals 11 1966 Registrant 24 1967 Registrar 24 1968 Registry 24 1969 Resolver 14 1970 Reverse DNS, reverse lookup 23 1971 Root hints 16 1972 Root zone 22 1974 S 1975 SERVFAIL 10 1976 SOA field names 12 1977 Secondary server 17 1978 Secure Entry Point (SEP) 28 1979 Service name 24 1980 Signed zone 25 1981 Signing software 29 1982 Slave server 17 1983 Source of Synthesis 23 1984 Split DNS 19 1985 Stealth server 17 1986 Stub resolver 14 1987 Subdomain 8 1988 Subordinate 25 1989 Superordinate 25 1991 T 1992 TLD 7 1993 TTL 13 1994 Trust anchor 29 1996 U 1997 Unsigned zone 26 1999 V 2000 Validating resolver 28 2001 Validation 27 2002 View 18 2004 W 2005 WHOIS 24 2006 Wildcard 22 2007 Wildcard domain name 22 2009 Z 2010 Zone 19 2011 Zone cut 20 2012 Zone enumeration 27 2013 Zone signing key (ZSK) 28 2014 Zone transfer 16 2016 Acknowledgements 2018 The following is the Acknowledgements for RFC 7719. Additional 2019 acknowledgements may be added as this draft is worked on. 2021 The authors gratefully acknowledge all of the authors of DNS-related 2022 RFCs that proceed this one. Comments from Tony Finch, Stephane 2023 Bortzmeyer, Niall O'Reilly, Colm MacCarthaigh, Ray Bellis, John 2024 Kristoff, Robert Edmonds, Paul Wouters, Shumon Huque, Paul Ebersman, 2025 David Lawrence, Matthijs Mekking, Casey Deccio, Bob Harold, Ed Lewis, 2026 John Klensin, David Black, and many others in the DNSOP Working Group 2027 helped shape RFC 7719. 2029 Additional people contributed to this document, including: John 2030 Dickinson, Bob Harold, Peter Koch, [[ MORE NAMES WILL APPEAR HERE AS 2031 FOLKS CONTRIBUTE]]. 2033 Authors' Addresses 2035 Paul Hoffman 2036 ICANN 2038 Email: paul.hoffman@icann.org 2040 Andrew Sullivan 2041 Oracle 2042 100 Milverton Drive 2043 Mississauga, ON L5R 4H1 2044 Canada 2046 Email: andrew.s.sullivan@oracle.com 2047 Kazunori Fujiwara 2048 Japan Registry Services Co., Ltd. 2049 Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda 2050 Chiyoda-ku, Tokyo 101-0065 2051 Japan 2053 Phone: +81 3 5215 8451 2054 Email: fujiwara@jprs.co.jp