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Hoffman 6 ICANN 7 February 11, 2020 9 DNS Resolver Information Self-publication 10 draft-ietf-dnsop-resolver-information-01 12 Abstract 14 This document describes methods for DNS resolvers to self-publish 15 information about themselves, such as whether they perform DNSSEC 16 validation or are available over transports other than what is 17 defined in RFC 1035. The information is returned as a JSON object. 18 The names in this object are defined in an IANA registry that allows 19 for light-weight registration. Applications and operating systems 20 can use the methods defined here to get the information from 21 resolvers in order to make choices about how to send future queries 22 to those resolvers. 24 There is a GitHub repo for this draft where pull requests can be 25 issued: https://github.com/DNSOP/draft-ietf-dnsop-resolver- 26 information However, starting issues on the WG mailing list is 27 preferred. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at https://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on August 14, 2020. 46 Copyright Notice 48 Copyright (c) 2020 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (https://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 64 1.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3 65 2. Retrieving Resolver Information by DNS . . . . . . . . . . . 3 66 3. Retrieving Resolver Information by Well-Known URI . . . . . . 4 67 4. Contents of the Returned I-JSON Object . . . . . . . . . . . 5 68 4.1. The "inventory" name . . . . . . . . . . . . . . . . . . 6 69 4.2. Example . . . . . . . . . . . . . . . . . . . . . . . . . 6 70 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 71 5.1. RESINFO RRtype . . . . . . . . . . . . . . . . . . . . . 6 72 5.2. Registry for DNS Resolver Information . . . . . . . . . . 7 73 5.3. resolver-info Well-known URI . . . . . . . . . . . . . . 7 74 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 75 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 76 7.1. Normative References . . . . . . . . . . . . . . . . . . 8 77 7.2. Informative References . . . . . . . . . . . . . . . . . 8 78 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 9 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 81 1. Introduction 83 Historically, DNS stub resolvers typically communicated with the 84 recursive resolvers in their configuration without needing to know 85 anything about the features of the recursive resolvers. More 86 recently, recursive resolvers have different features that may cause 87 stub resolvers to make choices about which configured resolver from 88 its configuration to use, and also how to communicate with the 89 recursive resolver (such as over different transports). Thus stub 90 resolvers need a way to get information from recursive resolvers 91 about features that might affect the communication. 93 This document specifies methods for stub resolvers to ask recursive 94 resolvers for such information. In short, a new RRtype is defined 95 for stub resolvers to query using the DNS, and a new well-known URI 96 is defined for stub resolvers to query using HTTP over TLS. 98 The response from either method is the same: a JSON object. The JSON 99 object MUST use the I-JSON message format defined in [RFC7493]. Note 100 that [RFC7493] was based on RFC 7159, but RFC 7159 was replaced by 101 [RFC8259]. Requiring the use of I-JSON instead of more general JSON 102 format greatly increases the likelihood of interoperability. 104 The information that a resolver might want to give to a recursive 105 resolver is not defined in this document; instead other documents 106 will follow that will specify that information and the format that it 107 comes in. 109 It is important to note that the protocol defined here is only for 110 recursive resolvers, not for authoritative servers. Authoritative 111 servers MUST NOT answer queries that are defined in this protocol. 112 (It is likely that a later protocol will allow authoritative servers 113 to give information in a method similar to the one described in this 114 document.) 116 1.1. Definitions 118 In the rest of this document, the term "resolver" without 119 qualification means "recursive resolver" as defined in [RFC8499]. 120 Also, the term "stub" is used to mean "stub resolver". 122 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 123 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 124 "OPTIONAL" in this document are to be interpreted as described in BCP 125 14 [RFC2119] [RFC8174] when, and only when, they appear in all 126 capitals, as shown here. 128 2. Retrieving Resolver Information by DNS 130 A stub that wants to use the DNS to get information about a resolver 131 can use the DNS query defined here. The query a stub resolver uses 132 is .{in-addr,ip6}.arpa/IN/RESINFO. The RRtype "RESINFO" 133 is defined in this document, and the IANA assignment is given in 134 Section 5.1. The contents of the Rdata in the response to this query 135 is defined in Section 4. If the resolver understands the RESINFO 136 RRtype, the RRset in the Answer section MUST have exactly one record. 138 In this section, ".{in-addr,ip6}.arpa" is the domain name 139 associated with the reverse lookup of an IP address of the resolver 140 (resolvers can have multiple addresses). For example, if the 141 resolver is at 192.0.2.1, the query would be 1.2.0.192.in- 142 addr.arpa/IN/RESINFO. 144 A resolver that receives a query with the RRtype of RESINFO with a 145 QNAME of .{in-addr,ip6}.arpa acts as if it is delegated, 146 and responds with its own RESINFO data in the Answer section. The 147 resolver can generate this reply with special code to capture queries 148 for these types of addresses; if the resolver can be configured to 149 also be authoritative for some zones, it can use that configuration 150 to actually be authoritative for the addresses on which it responds. 152 A stub that knows a specific type of information it wants MAY ask for 153 that information by prepending a label with the name of the 154 information in its query. For example, if the stub knows that it 155 wants information whose name is "temp-field2", it would send the 156 query temp-field2..{in-addr,ip6}.arpa/IN/RESINFO. As 157 described in Section 4, the JSON object in the response is likely to 158 have name/value pairs in addition to the one requested. 160 Any query for the RESINFO RRtype that is not in .{in- 161 addr,ip6}.arpa/IN or a subdomain of .{in-addr,ip6}.arpa/ 162 IN is meaningless and MUST result in a NODATA or NXDOMAIN response. 163 Resolvers would not need any special code to meet this requirement; 164 they only need code to handle the RESINFO RRtype that is in .{in-addr,ip6}.arpa/IN or a subdomain of .{in- 166 addr,ip6}.arpa/IN. 168 3. Retrieving Resolver Information by Well-Known URI 170 A stub that wants to use HTTPS to get information about a resolver 171 can use the well-known URI defined here. Because this uses HTTPS, 172 the stub has the possibility of authenticating the TLS connection. 173 If the connection cannot be authenticated (such as if the stub only 174 knows the IP address of the resolver and the resolver's certificate 175 does not have the IP address, or the correct IP address), the stub 176 MAY still use the results with the same lack of assuredness as it 177 would have with using a DNS request described in Section 2. 179 The stub MUST use the HTTP GET method. The URI used to get the 180 resolver information is one of: 182 https://IPADDRESSOFRESOLVER/.well-known/resolver-info/ 184 https://DOMAINNAMEOFRESOLVER/.well-known/resolver-info/ 186 This uses the ".well-known" URI mechanism defined in [RFC8615]. The 187 contents of the response to this query is defined in Section 4. 189 A resolver that uses this protocol to publish its information SHOULD, 190 if possible, have a TLS certificate whose subject identifiers are any 191 IP address that the resolver is available on, as well as any domain 192 names that the resolver operator uses for the resolver. At the time 193 that this document is published, getting IP addresses in TLS 194 certificates is possible, but there are only a few widely-trusted CAs 195 that issue such certificates. [I-D.ietf-acme-ip] describes a new 196 protocol that may cause IP address certificates to become more 197 common. 199 In the future, DHCP and/or DCHPv6 and/or RA may have options that 200 allow the configuration to contain the domain name of a resolver. If 201 so, this can be used for matching the domain name in the TLS 202 certificate. 204 4. Contents of the Returned I-JSON Object 206 The JSON object returned by a DNS query or an HTTPS query MUST 207 contain at least one name/value pair: "inventory", described later in 208 this section. The returned object MAY contain any other name/value 209 pairs. 211 The requirement for the inclusion of the "inventory" name/value pair 212 is so that systems retrieving the information over DNS can create 213 specific queries. Using specific queries can reduce the number of 214 round trips in the case where the answers to queries become large. 215 The "inventory" name/value pair MUST be included in the response even 216 if the query was for a single name. 218 If the request was over DNS using a subdomain under .{in- 219 addr,ip6}.arpa, the resolver SHOULD return an object that contains a 220 name/value pair with that name if the resolver has that information. 221 If the resolver does not have information for that name, it MUST NOT 222 return the name in the object. 224 If the request was over HTTPS, the resolver SHOULD return an object 225 with all known name/value pairs for which it has information. 227 All names in the returned object MUST either be defined in the IANA 228 registry or, if for local use only, begin with the substring "temp-". 229 The IANA registry (Section 5.2) will never register names that begin 230 with "temp-". 232 All names MUST consist only of lower-case ASCII characters, digits, 233 and hyphens (that is, Unicode characters U+0061 through 007A, U+0030 234 through U+0039, and U+002D), and MUST be 63 characters or shorter. 235 As defined in Section 5.2, the IANA registry will not register names 236 that begin with "temp-", so these names can be used freely by any 237 implementer. 239 Note that the message returned by the resolver MUST be in I-JSON 240 format. I-JSON requires that the message MUST be encoded in UTF8. 242 This document only defines one element that can returned: 243 "inventory". All other elements will be defined in other documents. 245 4.1. The "inventory" name 247 The "inventory" name lists all of the types of information for which 248 the resolver has data. The value is an array of strings. 250 4.2. Example 252 The I-JSON object that a resolver returns might look like the 253 following: 255 { 256 "temp-field2": 42, 257 "temp-field1": [ "There is", "no \u000B!" ], 258 "inventory": [ "inventory", "temp-field1", "temp-field2" ] 259 } 261 As specified in [RFC7493], the I-JSON object is encoded as UTF8. 262 This example has no un-escaped non-ASCII characters only because they 263 are not currently allowed in Internet Drafts. For example, the 264 exclamation mark in the second name/value pair could instead be the 265 double exclamation mark character, U+203C. 267 [RFC7493] explicitly allows the returned objects to be in any order. 269 5. IANA Considerations 271 5.1. RESINFO RRtype 273 This document defines a new DNS RR type, RESINFO, whose value TBD 274 will be allocated by IANA from the "Resource Record (RR) TYPEs" sub- 275 registry of the "Domain Name System (DNS) Parameters" registry: 277 Type: RESINFO 279 Value: TBD 281 Meaning: Information self-published by a resolver as an I-JSON (RFC 282 7493) object 283 Reference: This document 285 5.2. Registry for DNS Resolver Information 287 IANA will create a new registry titled "DNS Resolver Information" 288 that will contain definitions of the names that can be used with the 289 protocols defined in this document. The registration procedure is by 290 Expert Review and Specification Required, as defined in [RFC8126]. 292 The specification that is required for registration can be either an 293 Internet-Draft or an RFC. The reviewer for this registry is 294 instructed to generally be liberal in what they accept into the 295 registry: as long as the specification that comes with the 296 registration request is reasonably understandable, the registration 297 should be accepted. 299 The registry has the following fields for each element: 301 Name: The name to be used in the JSON object. This name MUST NOT 302 begin with "temp-". This name MUST conform to the definition of 303 "string" in I-JSON [RFC7493] message format. 305 Value type: The type of data to be used in the JSON object. 307 Specification: The name of the specification for the registered 308 element. 310 5.3. resolver-info Well-known URI 312 Before this draft is complete, mail will be sent to wellknown-uri- 313 review@ietf.org in order to be registered in the "Well-Known URIs" 314 registry at IANA. The mail will contain the following: 316 URI suffix: resolver-info 318 Change controller: IETF 320 Specification document(s): This document 322 Status: permanent 324 6. Security Considerations 326 Unless a DNS request for .{in-addr,ip6}.arpa/IN/RESINFO, 327 or a subdomain, as described in Section 2 is sent over DNS-over-TLS 328 (DoT) [RFC7858] or DNS-over-HTTPS (DoH) [RFC8484], or unless the 329 .{in-addr,ip6}.arpa zone is signed with DNSSEC, the 330 response is susceptible to forgery. Stubs and resolvers SHOULD use 331 normal DNS methods for avoiding forgery such as query ID 332 randomization and source port randomization. A stub resolver will 333 know if it is using DoT or DoH, and if it is using DoT it will know 334 if the communication is authenticated (DoH is always authenticated). 336 An application that is using an operating system API to send queries 337 for .{in-addr,ip6}.arpa/IN/RESINFO or a subdomain will 338 only know if query went over authenticated DoT or DoH if the API 339 supports returning that authentication information. Currently, no 340 common APIs support that type of response. 342 7. References 344 7.1. Normative References 346 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 347 Requirement Levels", BCP 14, RFC 2119, 348 DOI 10.17487/RFC2119, March 1997, 349 . 351 [RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493, 352 DOI 10.17487/RFC7493, March 2015, 353 . 355 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 356 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 357 May 2017, . 359 [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data 360 Interchange Format", STD 90, RFC 8259, 361 DOI 10.17487/RFC8259, December 2017, 362 . 364 [RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 365 Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499, 366 January 2019, . 368 7.2. Informative References 370 [I-D.ietf-acme-ip] 371 Shoemaker, R., "ACME IP Identifier Validation Extension", 372 draft-ietf-acme-ip-08 (work in progress), October 2019. 374 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., 375 and P. Hoffman, "Specification for DNS over Transport 376 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 377 2016, . 379 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 380 Writing an IANA Considerations Section in RFCs", BCP 26, 381 RFC 8126, DOI 10.17487/RFC8126, June 2017, 382 . 384 [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS 385 (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, 386 . 388 [RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers 389 (URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019, 390 . 392 Acknowledgments 394 The idea of various types of servers publishing information about 395 themselves has been around for decades. However this idea has not 396 been used in the DNS. This document aims to fix this omission. 398 Erik Kline suggested using ".{in-addr,ip6}.arpa" as the 399 domain name to allow for the possibility of DNSSEC-signed responses. 401 Authors' Addresses 403 Puneet Sood 404 Google 406 Email: puneets@google.com 408 Roy Arends 409 ICANN 411 Email: roy.arends@icann.org 413 Paul Hoffman 414 ICANN 416 Email: paul.hoffman@icann.org