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If it is intended as a requirements expression, it should be rewritten using one of the combinations defined in RFC 2119; otherwise it should not be all-uppercase. -- The document date (8 February 2022) is 102 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Obsolete informational reference (is this intentional?): RFC 2845 (Obsoleted by RFC 8945) Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DNSOP M. Andrews 3 Internet-Draft ISC 4 Updates: 1034 (if approved) S. Huque 5 Intended status: Standards Track Salesforce 6 Expires: 12 August 2022 P. Wouters 7 Aiven 8 D. Wessels 9 Verisign 10 8 February 2022 12 DNS Referral Glue Requirements 13 draft-ietf-dnsop-glue-is-not-optional-04 15 Abstract 17 The DNS uses referral glue records to allow iterative clients to find 18 the addresses of nameservers that are contained within a delegated 19 zone. Authoritative Servers are expected to return all available 20 referral glue records in a referral response. If message size 21 constraints prevent the inclusion of all in-domain referral glue 22 records, the server MUST set the TC flag to inform the client that 23 the response is incomplete, and that the client SHOULD use another 24 transport to retrieve the full response. This document updates RFC 25 1034 to clarify correct server behavior. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at https://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on 12 August 2022. 44 Copyright Notice 46 Copyright (c) 2022 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 51 license-info) in effect on the date of publication of this document. 52 Please review these documents carefully, as they describe your rights 53 and restrictions with respect to this document. Code Components 54 extracted from this document must include Revised BSD License text as 55 described in Section 4.e of the Trust Legal Provisions and are 56 provided without warranty as described in the Revised BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 61 1.1. Reserved Words . . . . . . . . . . . . . . . . . . . . . 3 62 2. Types of Referral Glue . . . . . . . . . . . . . . . . . . . 3 63 2.1. In-Domain Referral Glue . . . . . . . . . . . . . . . . . 3 64 2.2. Sibling Referral Glue . . . . . . . . . . . . . . . . . . 4 65 2.3. Cyclic Sibling Referral Glue . . . . . . . . . . . . . . 5 66 2.4. Missing Referral Glue . . . . . . . . . . . . . . . . . . 5 67 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 6 68 3.1. In-Domain Referral Glue . . . . . . . . . . . . . . . . . 6 69 3.2. Sibling Referral Glue . . . . . . . . . . . . . . . . . . 7 70 3.3. Updates to RFC 1034 . . . . . . . . . . . . . . . . . . . 7 71 4. Security Considerations . . . . . . . . . . . . . . . . . . . 7 72 5. Operational Considerations . . . . . . . . . . . . . . . . . 8 73 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 74 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 75 8. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 76 9. Normative References . . . . . . . . . . . . . . . . . . . . 9 77 10. Informative References . . . . . . . . . . . . . . . . . . . 9 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 80 1. Introduction 82 The Domain Name System (DNS) [RFC1034], [RFC1035] uses referral glue 83 records to allow iterative clients to find the addresses of 84 nameservers that are contained within a delegated zone. Referral 85 glue records are added to the parent zone as part of the delegation 86 process and returned in referral responses, otherwise a resolver 87 following the referral has no way of finding these addresses. 88 Authoritative servers are expected to return all available in-domain 89 referral glue records in a referral response. If message size 90 constraints prevent the inclusion of all in-domain glue records over 91 the chosen transport, the server MUST set the TC (Truncated) flag to 92 inform the client that the response is incomplete, and that the 93 client SHOULD use another transport retrieve the full response. This 94 document clarifies that expectation. 96 DNS responses sometimes contain optional data in the additional 97 section. In-domain referral glue records, however, are not optional. 98 Several other protocol extensions, when used, are also not optional. 99 This includes TSIG [RFC2845], OPT [RFC6891], and SIG(0) [RFC2931]. 101 At the time of this writing, referral glue is the only type of glue 102 defined for the DNS. Referral glue records are always addresses (A 103 or AAAA records) of a delegation's authoritative name servers. New 104 work underway in the IETF may lead to definitions for other types of 105 glue data, with requirements that differ from referral glue. This 106 document only describes requirements for referral glue. Unless 107 stated otherwise, "glue" in the remainder of this document always 108 means "referral glue." 110 Note that this document only clarifies requirements of name server 111 software implementations. It does not place any requirements on data 112 placed in DNS zones or registries. 114 1.1. Reserved Words 116 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 117 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 118 document are to be interpreted as described in [RFC2119]. 120 2. Types of Referral Glue 122 This section describes different types of glue that may be found in 123 DNS referral responses. Note that the type of glue depends on the 124 QNAME. A particular record can be in-domain glue for one response 125 and sibling glue for another. 127 2.1. In-Domain Referral Glue 129 The following is a simple example of glue records present in the 130 delegating zone "test" for the child zone "foo.test". The 131 nameservers for foo.test (ns1.foo.test and ns2.foo.test) are both 132 below the delegation point. They are configured as glue records in 133 the "test" zone: 135 foo.test. 86400 IN NS ns1.foo.test. 136 foo.test. 86400 IN NS ns2.foo.test. 137 ns1.foo.test. 86400 IN A 192.0.2.1 138 ns2.foo.test. 86400 IN AAAA 2001:db8::2:2 140 A referral response from "test" for "foo.test" with in-domain glue 141 looks like this: 143 ;; QUESTION SECTION: 144 ;www.foo.test. IN A 146 ;; AUTHORITY SECTION: 147 foo.test. 86400 IN NS ns1.foo.test. 148 foo.test. 86400 IN NS ns2.foo.test. 150 ;; ADDITIONAL SECTION: 151 ns1.foo.test. 86400 IN A 192.0.2.1 152 ns2.foo.test. 86400 IN AAAA 2001:db8::2:2 154 2.2. Sibling Referral Glue 156 Sibling glue are glue records that are not contained in the delegated 157 zone itself, but in another zone delegated from the same parent. In 158 many cases, these are not strictly required for resolution, since the 159 resolver can make follow-on queries to the other zone to resolve the 160 nameserver addresses after following the referral to the sibling 161 zone. However, most nameserver implementations today provide them as 162 an optimization to obviate the need for extra traffic from iterative 163 resolvers. 165 Here the delegating zone "test" contains two delegations for the 166 child zones "bar.test" and "foo.test": 168 bar.test. 86400 IN NS ns1.bar.test. 169 bar.test. 86400 IN NS ns2.bar.test. 170 ns1.bar.test. 86400 IN A 192.0.2.1 171 ns2.bar.test. 86400 IN AAAA 2001:db8::2:2 173 foo.test. 86400 IN NS ns1.bar.test. 174 foo.test. 86400 IN NS ns2.bar.test. 176 A referral response from "test" for "foo.test" with sibling glue 177 looks like this: 179 ;; QUESTION SECTION: 180 ;www.foo.test. IN A 182 ;; AUTHORITY SECTION: 183 foo.test. 86400 IN NS ns1.bar.test. 184 foo.test. 86400 IN NS ns2.bar.test. 186 ;; ADDITIONAL SECTION: 187 ns1.bar.test. 86400 IN A 192.0.2.1 188 ns2.bar.test. 86400 IN AAAA 2001:db8::2:2 190 2.3. Cyclic Sibling Referral Glue 192 The use of sibling glue can introduce cyclic dependencies. This 193 happens when one domain specifies name servers from a sibling domain, 194 and vice versa. This type of cyclic dependency can only be broken 195 when the delegating name server includes the sibling glue in a 196 referral response. 198 Here the delegating zone "test" contains two delegations for the 199 child zones "bar.test" and "foo.test", and each use name servers 200 under the other: 202 bar.test. 86400 IN NS ns1.foo.test. 203 bar.test. 86400 IN NS ns2.foo.test. 204 ns1.bar.test. 86400 IN A 192.0.2.1 205 ns2.bar.test. 86400 IN AAAA 2001:db8::2:2 207 foo.test. 86400 IN NS ns1.bar.test. 208 foo.test. 86400 IN NS ns2.bar.test. 209 ns1.foo.test. 86400 IN A 192.0.2.3 210 ns2.foo.test. 86400 IN AAAA 2001:db8::2:4 212 A referral response from "test" for "bar.test" with sibling glue 213 looks like this: 215 ;; QUESTION SECTION: 216 ;www.bar.test. IN A 218 ;; AUTHORITY SECTION: 219 bar.test. 86400 IN NS ns1.foo.test. 220 bar.test. 86400 IN NS ns2.foo.test. 222 ;; ADDITIONAL SECTION: 223 ns1.foo.test. 86400 IN A 192.0.2.3 224 ns2.foo.test. 86400 IN AAAA 2001:db8::2:4 226 In late 2021 the authors analyzed zone file data available from 227 ICANN's Centralized Zone Data Service [CZDS] and found 222 out of 228 approximately 209,000,000 total delegations that had only sibling NS 229 RRs in a cyclic dependency as above. 231 2.4. Missing Referral Glue 233 An example of missing glue is included here, even though it can not 234 be considered as a type of glue. While not common, real examples of 235 responses that lack required glue, and with TC=0, have been shown to 236 occur and cause resolution failures. 238 The example below is based on a response observed in June 2020. The 239 names have been altered to fall under documentation domains. It 240 shows a case where none of the glue records present in the zone fit 241 into the available space of the UDP response, and the TC flag was not 242 set. While this example shows a referral with DNSSEC records 243 [RFC4033], [RFC4034], [RFC4035], this behavior has been seen with 244 plain DNS responses as well. Some records have been truncated for 245 display purposes. Note that at the time of this writing, the servers 246 originally responsible for this example have been updated and now 247 correctly set the TC flag. 249 % dig +norec +dnssec +bufsize=512 +ignore @ns.example.net \ 250 rh202ns2.355.foo.example 252 ; <<>> DiG 9.15.4 <<>> +norec +dnssec +bufsize +ignore \ 253 @ns.example.net rh202ns2.355.foo.example 254 ; (2 servers found) 255 ;; global options: +cmd 256 ;; Got answer: 257 ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 8798 258 ;; flags: qr; QUERY: 1, ANSWER: 0, AUTHORITY: 9, ADDITIONAL: 1 260 ;; OPT PSEUDOSECTION: 261 ; EDNS: version: 0, flags: do; udp: 4096 262 ;; QUESTION SECTION: 263 ;rh202ns2.355.foo.example. IN A 265 ;; AUTHORITY SECTION: 266 foo.example. 86400 IN NS rh120ns2.368.foo.example. 267 foo.example. 86400 IN NS rh202ns2.355.foo.example. 268 foo.example. 86400 IN NS rh120ns1.368.foo.example. 269 foo.example. 86400 IN NS rh202ns1.355.foo.example. 270 foo.example. 3600 IN DS 51937 8 1 ... 271 foo.example. 3600 IN DS 635 8 2 ... 272 foo.example. 3600 IN DS 51937 8 2 ... 273 foo.example. 3600 IN DS 635 8 1 ... 274 foo.example. 3600 IN RRSIG DS 8 2 3600 ... 276 3. Requirements 278 This section describes updated requirements for including glue in 279 referral responses. 281 3.1. In-Domain Referral Glue 283 This document clarifies that when a name server generates a referral 284 response, it MUST include all available in-domain glue records in the 285 additional section, or MUST set TC=1 if constrained by message size. 287 At the time of writing, most iterative clients send initial queries 288 over UDP and retry over TCP upon receiving a response with the TC 289 flag set. UDP responses are generally limited to between 1232 and 290 4096 bytes, due to values commonly used for the EDNS0 UDP Message 291 Size field [RFC6891], [FLAGDAY2020]. TCP responses are limited to 292 65,536 bytes. 294 3.2. Sibling Referral Glue 296 This document clarifies that when a name server generates a referral 297 response, it SHOULD include all available glue records in the 298 additional section. If after adding all in-domain glue records, not 299 all sibling glue records fit due to message size constraints, the 300 name server is NOT REQUIRED to set TC=1. 302 Note that users may experience resolution failures for domains with 303 only sibling glue when a name servers chooses to omit them in a 304 referral response. As described in Section 2.3, such domains are 305 rare. 307 3.3. Updates to RFC 1034 309 Replace 311 "Copy the NS RRs for the subzone into the authority section of the 312 reply. Put whatever addresses are available into the additional 313 section, using glue RRs if the addresses are not available from 314 authoritative data or the cache. Go to step 4." 316 with 318 "Copy the NS RRs for the subzone into the authority section of the 319 reply. Put whatever NS addresses are available into the additional 320 section, using glue RRs if the addresses are not available from 321 authoritative data or the cache. If all in-domain glue RRs do not 322 fit, set TC=1 in the header. Go to step 4." 324 4. Security Considerations 326 This document clarifies correct DNS server behavior and does not 327 introduce any changes or new security considerations. 329 5. Operational Considerations 331 At the time of this writing, the behavior of most DNS server 332 implementations is to set the TC flag only if none of the available 333 glue records fit in a response over UDP transport. The updated 334 requirements in this document might lead to an increase in the 335 fraction of UDP responses with the TC flag set, and consequently an 336 increase in the number of queries to over TCP transport. 338 6. IANA Considerations 340 There are no actions for IANA. 342 7. Acknowledgements 344 The authors wish to thank Joe Abley, Brian Dickson, Geoff Huston, 345 Jared Mauch, George Michaelson, Benno Overeinder, John R Levine, 346 Shinta Sato, Puneet Sood, Ralf Weber, Tim Wicinski, Suzanne Woolf, 347 and other members of the DNSOP working group for their input. 349 8. Changes 351 RFC Editor: Please remove this section before publication. 353 This section lists substantial changes to the document as it is being 354 worked on. 356 From -01 to -02: 358 * Clarified that "servers" means "authoritative servers". 360 * Clarified that "available glue" means "all available glue". 362 * Updated examples and placed before RFC 1034 update. 364 From -02 to -03: 366 * Clarified scope to focus only on name server responses, and not 367 zone/registry data. 369 * Reorganized with section 2 as Types of Glue and section 3 as 370 Requirements. 372 * Removed any discussion of promoted / orphan glue. 374 * Use appropriate documentation addresses and domain names. 376 * Added Sibling Cyclic Glue example. 378 From -03 to -04: 380 * Use "referral glue" on the assumption that other types of glue may 381 be defined in the future. 383 * Added Operational Considerations section. 385 * Note many current implementations set TC=1 only when no glue RRs 386 fit. New requirements may lead to more truncation and TCP. 388 * Sibling glue can be optional. Only require TC=1 when all in- 389 domain glue RRs don't fit. 391 * Avoid talking about requirements for UDP/TCP specifically, and 392 talk more generically about message size constraints regardless of 393 transport. 395 9. Normative References 397 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 398 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 399 . 401 [RFC1035] Mockapetris, P., "Domain names - implementation and 402 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 403 November 1987, . 405 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 406 Requirement Levels", BCP 14, RFC 2119, 407 DOI 10.17487/RFC2119, March 1997, 408 . 410 10. Informative References 412 [CZDS] ICANN, "Centralized Zone Data Service", January 2022, 413 . 415 [FLAGDAY2020] 416 Various DNS software and service providers, "DNS Flag Day 417 2020", October 2020, . 419 [RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B. 420 Wellington, "Secret Key Transaction Authentication for DNS 421 (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000, 422 . 424 [RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures 425 ( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September 426 2000, . 428 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 429 Rose, "DNS Security Introduction and Requirements", 430 RFC 4033, DOI 10.17487/RFC4033, March 2005, 431 . 433 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 434 Rose, "Resource Records for the DNS Security Extensions", 435 RFC 4034, DOI 10.17487/RFC4034, March 2005, 436 . 438 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 439 Rose, "Protocol Modifications for the DNS Security 440 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 441 . 443 [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms 444 for DNS (EDNS(0))", STD 75, RFC 6891, 445 DOI 10.17487/RFC6891, April 2013, 446 . 448 Authors' Addresses 450 M. Andrews 451 ISC 453 Email: marka@isc.org 455 Shumon Huque 456 Salesforce 458 Email: shuque@gmail.com 460 Paul Wouters 461 Aiven 463 Email: paul.wouters@aiven.io 465 Duane Wessels 466 Verisign 468 Email: dwessels@verisign.com