idnits 2.17.1 draft-hunt-dnsop-aname-00.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 : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == The document seems to use 'NOT RECOMMENDED' as an RFC 2119 keyword, but does not include the phrase in its RFC 2119 key words list. -- The document date (April 7, 2017) is 2576 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) == Missing Reference: 'TBD' is mentioned on line 144, but not defined ** Downref: Normative reference to an Unknown state RFC: RFC 1033 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group E. Hunt 3 Internet-Draft ISC 4 Intended status: Standards Track P. van Dijk 5 Expires: October 9, 2017 PowerDNS 6 A. Eden 7 DNSimple 8 April 7, 2017 10 Address-specific DNS Name Redirection (ANAME) 11 draft-hunt-dnsop-aname-00 13 Abstract 15 This document defines the "ANAME" DNS RR type, to provide similar 16 functionality to CNAME, but only redirects type A and AAAA queries. 17 Unlike CNAME, an ANAME can coexist with other record types. The 18 ANAME RR allows zone owners to redirect queries for apex domain names 19 in a standards compliant manner. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on October 9, 2017. 38 Copyright Notice 40 Copyright (c) 2017 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. The ANAME Resource Record . . . . . . . . . . . . . . . . . . 4 58 3. Authoritative Server Behavior . . . . . . . . . . . . . . . . 4 59 3.1. Address records returned with ANAME . . . . . . . . . . . 4 60 3.2. Coexistence with other types . . . . . . . . . . . . . . 6 61 3.3. DNSSEC signing . . . . . . . . . . . . . . . . . . . . . 6 62 4. Recursive Server Behavior . . . . . . . . . . . . . . . . . . 7 63 5. Operational Considerations . . . . . . . . . . . . . . . . . 8 64 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 65 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 66 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 67 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 68 9.1. Normative References . . . . . . . . . . . . . . . . . . 9 69 9.2. Informative References . . . . . . . . . . . . . . . . . 9 70 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 72 1. Introduction 74 Websites hosted by content distribution networks are often served by 75 multiple IP addresses handling different geographic areas. In many 76 cases, an initial query for a domain name returns a CNAME record 77 whose is a name served by the CDN, and which ultimately 78 resolves to a different final answer depending on the client's IP 79 address or subnet, geographic location, or other considerations. 81 It is common practice for websites to publish content at their 82 registered domain name (sometimes referred to as a "bare domain" or 83 "zone apex": for example, "example.com" rather than 84 "www.example.com"). However, [RFC1033] forbids the use of CNAME 85 records at the same node as any other record type. Zone apex nodes 86 always contain SOA and NS RRsets, and frequently contain other types 87 such as DNSKEY, MX, TXT/SPF, etc. Consequently, a CNAME record is 88 not permitted at zone apex nodes. 90 It should be noted that [RFC4034] relaxed this restriction by 91 allowing coexistence of CNAME with RRSIG and NSEC records, but such 92 exceptions are not applicable to other resource records. RRSIG and 93 NSEC exist to prove the integrity of the CNAME record; they are not 94 intended to associate arbitrary data with the domain name. 96 DNAME [RFC6672] is also not a solution, as its function is to 97 redirect all names in the namespace below the DNAME , not the 98 DNAME itself. 100 Redirecting website lookups to an alternate domain name via SRV or 101 URI resource records would be an effective solution, but to date this 102 approach has not been accepted by browser implementations. In 103 addition, it is not possible to use SRV records with wildcard names. 105 As a result of the above, the only widely supported and standards- 106 compliant way to publish content at a zone apex is to to place A and/ 107 or AAAA records at that node. The flexibility afforded by CNAME is 108 not available. 110 This document specifies a new RR type "ANAME", which provides similar 111 functionality to CNAME, but only for address queries (i.e., for type 112 A or AAAA). The ANAME record can be present at any DNS node, and can 113 coexist with most other RR types, enabling it to be present at a zone 114 apex. Authoritative servers configured with ANAME records will 115 answer address queries for the ANAME owner with addresses found at 116 the ANAME's target, and also with the ANAME itself. Recursive 117 resolvers which understand ANAME can re-query for the ANAME target, 118 just as if they had received a CNAME response. Recursive resolvers 119 which do not understand ANAME will ignore the ANAME and consume the 120 provided A/AAAA records directly. 122 [REMOVE BEFORE PUBLICATION: The authors are aware that similar 123 functionality is currently implemented and deployed by various 124 software vendors and service providers, under names such as ALIAS, 125 ANAME, or CNAME-flattening. It is our hope that most, if not all, of 126 these implementations, will adjust to ANAME as described here. This 127 would improve interoperability of authoritative hosters and would 128 give users more choice.] 130 1.1. Terminology 132 "Address type" refers to a DNS RR type that encodes a network 133 address. Currently the set of address types consists of A and AAAA. 135 "Address query" refers to a DNS query for any address type. 137 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 138 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 139 document are to be interpreted as described in [RFC2119]. 141 2. The ANAME Resource Record 143 This document defines the "ANAME" DNS resource record type, with RR 144 TYPE value [TBD]. 146 The ANAME presentation format is identical to that of CNAME 147 [RFC1033]: 149 owner ttl class ANAME target 151 The wire format is also identical to CNAME, except that name 152 compression is not permitted in ANAME RDATA, per [RFC3597]. 154 No more than one ANAME resource record SHALL be present at any DNS 155 node. 157 3. Authoritative Server Behavior 159 When an ANAME record is present at a DNS node and a query is received 160 by an authoritative server for type A or AAAA, the authoritative 161 server returns the ANAME RR in the answer section. 163 Because not all querying resolvers understand ANAME, the 164 authoritative server MUST also return address records, as described 165 below. This is conceptually similar to the synthesized CNAME record 166 included with DNAME responses [RFC6672]. 168 Authoritative servers implementing ANAME MUST be equipped to resolve 169 the ANAME on the querying resolver's behalf, either by 170 sending queries to an external recursive resolver or by implementing 171 recursive resolution logic internally, so that address records can be 172 expanded when the ANAME is in a separate zone from . 174 If a query for the ANAME returns a chaining response (i.e., 175 CNAME, DNAME, or another ANAME), then the authoritative server (or 176 the resolver tasked with resolving the ANAME on its behalf) 177 MUST attempt to follow the chain until it is able to resolve a final 178 address response, or until resolution fails. Intermediate ANAMEs, 179 CNAMEs, and DNAMEs MUST be omitted from the response. 181 3.1. Address records returned with ANAME 183 If the original query is for type A, and an RRset of type A exists at 184 the final ANAME , then that A RRset (with changed to 185 match that of the ANAME RR), MUST be appended to the answer section 186 after the ANAME RRset. If an AAAA RRset is also known to exist at 187 the ANAME , then the AAAA RRset MAY be appended to the 188 additional section (again, with changed to match that of the 189 ANAME RR). 191 Similarly, if the original query was for type AAAA, and an AAAA RRset 192 exists at the final ANAME , then it is appended to the answer 193 section (with changed), and if an A RRset also exists at the 194 final ANAME then it MAY be appended to the additional 195 section. 197 If the original query is for type ANAME, A and AAAA records MAY be 198 returned in the additional section. 200 If the original query is for type ANY and access to ANY query 201 processing is not restricted, then the answer section MUST contain 202 both the ANAME and the A and AAAA RRsets, if present and successfully 203 resolved at the ANAME . 205 How and when an authoritative server resolves the A and AAAA 206 responses from the ANAME (when it is not itself 207 authoritative for ) is unspecified. If the authoritative 208 server is capable of performing recursive resolution, then it MAY 209 resolve the query itself, or it MAY send address queries to an 210 external resolver. It MAY send address queries to the ANAME 211 when loading the zone and cache the responses locally, or it MAY 212 delay resolution of the address records until a query is received for 213 the ANAME . In either case, for performance reasons, it is 214 RECOMMENDED that address records be cached locally by the 215 authoritative server. 217 Address records cached locally MUST have a limited TTL. The initial 218 TTL for locally-cached address records MUST be set to the lesser of 219 the ANAME TTL and the TTL of the address records retrieved from the 220 ANAME . The local TTL MUST count down, just as it would in a 221 conventional resolver cache. Records with an expired TTL MUST NOT be 222 used to answer address queries until refreshed with a new query to 223 the ANAME . 225 If configured to do so, then the authoritative server MAY, when 226 sending queries to the ANAME , include an EDNS CLIENT-SUBNET 227 (ECS) option [RFC7871], either forwarding an ECS option that was sent 228 to it by the querying resolver, or generating a new ECS option from 229 the querying resolver's address. If a response from the ANAME 230 includes an ECS option with a SCOPE PREFIX-LENGTH greater 231 than zero, the response SHOULD be cached with the ECS data and should 232 only be used in response to queries from the same client subnet. 234 3.2. Coexistence with other types 236 If the zone is configured with an A or AAAA RRset at the same DNS 237 node as ANAME, then the ANAME is considered to have been pre-expanded 238 for zone transfer purposes. When a zone is being transferred to a 239 secondary server, if any address record already exists at the same 240 node as an ANAME RR, then the ANAME RR MUST NOT be further expanded 241 by the authoritative server. 243 ANAME MUST NOT coexist with CNAME or any other RR type that restricts 244 the types with which it can itself coexist. 246 Like other types, ANAME MUST NOT exist below a DNAME, but it can 247 coexist at the same node; in fact, the two can be used cooperatively 248 to redirect both the owner name (via ANAME) and everything under it 249 (via DNAME). 251 ANAME can freely coexist at the same owner name with any other RR 252 type. 254 3.3. DNSSEC signing 256 If the zone in which the ANAME resides is DNSSEC-signed, and if the 257 server has access to its private zone-signing key, then the A and 258 AAAA RRsets MUST be signed, either in advance when populating the A/ 259 AAAA answers for the ANAME records, or "on the fly" when responding 260 to a query. 262 If the server does not have access to the private zone-signing key 263 then it MAY return unsigned address records, but this is NOT 264 RECOMMENDED unless every resolver with access to the zone is known to 265 support ANAME (as might be the case in a split-horizon deployment 266 where ANAME records are only served to an internal network with its 267 own resolvers). 269 Validating resolvers which do not yet implement ANAME will not be 270 able to validate the A and AAAA responses included with an ANAME 271 response unless those responses are validly signed by a DNSKEY at the 272 apex of the zone in which the ANAME resides. Passing along the 273 RRSIGs associated with the original A and AAAA RRsets from the ANAME 274 will not be sufficient for DNSSEC validation. 276 Implementers MAY allow address records associated with the ANAME to 277 be populated and signed by the primary server, then sent along with 278 their RRSIGs to secondaries via zone transfer. In this case, the 279 master server MUST respect the TTLs of the address records, MUST 280 refresh the address records by re-resolving the ANAME when 281 their TTLs expire, SHOULD respond to address queries with TTLs that 282 count down as they would when answering from a normal DNS cache, and 283 MUST inform secondary servers via DNS NOTIFY they need to refresh the 284 zone when address records have been updated. A secondary server 285 SHOULD store address records and associated RRSIGs supplied via zone 286 transfer in such a way that their TTLs will count down, as they would 287 in a normal DNS cache, and ultimately trigger a zone refresh query 288 upon reaching zero. When a secondary server is responding to an 289 address query, it SHOULD answer with the reduced TTL, but when 290 responding to a zone transfer request, it MUST answer with the 291 original TTL received from the primary. 293 If this address record expansion and signing during zone transfer is 294 not supported, then every authoritative server providing ANAME 295 responses in a signed zone SHOULD have access to the private zone- 296 signing key for that zone. Deployment of ANAME in signed zones where 297 address records cannot be signed due to lack of access to the private 298 zone-signing key is NOT RECOMMENDED. 300 When ANAME is present in a signed DNS node and address records exist 301 at the ANAME , the type bit map in the NSEC [RFC4034] or 302 NSEC3 [RFC5155] record for that node MUST include bits for A and/or 303 AAAA as well as ANAME. This is for the benefit of validating 304 resolvers not implementing ANAME which may use a signed proof of 305 nonexistence for type A and AAAA to prevent address queries from 306 being resolved. The type bit map SHOULD only include address types 307 which are known to exist at the . 309 4. Recursive Server Behavior 311 When a recursive resolver sends a query of type A or AAAA and 312 receives a response with an ANAME RRset in the answer section, it 313 MUST re-query for the ANAME . This is necessary because, in 314 some cases, the address received will be dependent on network 315 topology and other considerations, and the resolver may find a 316 different answer than the authoritative server did. (This 317 requirement MAY be relaxed if both the ANAME and are 318 validly signed and provably in the same zone.) 320 If resolution fails -- for example, due to the local resolver being 321 nonfunctional or the ANAME zone being unreachable -- then 322 the resolver MAY use the address records that were included in the 323 authoritative response as a fallback. Otherwise, these records MUST 324 NOT be cached or returned. 326 If configured to do so, the resolver MAY include an EDNS CLIENT- 327 SUBNET option [RFC7871] both when sending the initial query to the 328 ANAME and when re-querying for the ANAME . If the 329 response includes a SCOPE PREFIX-LENGTH greater than zero, the 330 response SHOULD be cached with the ECS data and should only be used 331 in response to queries from the same client subnet. 333 5. Operational Considerations 335 When a zone containing ANAME records is transferred to a secondary 336 server, the ANAME records are transferred, but the A or AAAA records 337 retrieved from the ANAME may not be. If the primary server 338 implements ANAME but the secondary server does not, then the two will 339 return different answers for address queries. It is therefore 340 RECOMMENDED that ANAME not be deployed in a zone unless all of the 341 authoritative servers for that zone implement ANAME, or the primary 342 is able to expand the ANAME with the related address RRsets during 343 the zone transfer. 345 6. Security Considerations 347 An authoritative server which implements ANAME resolves address 348 queries on behalf of its clients, either internally or by querying an 349 external resolver. This resolution must be allowed to take place 350 regardless of whether the client would ordinarily have been permitted 351 by local policy to send recursive queries. 353 When a resolver that does not understand ANAME receives a response 354 containing A or AAAA records with rewritten to match that of 355 the ANAME RR, this may bypass security mechanisms based on local 356 policy limiting access to the original ANAME . 358 A validating resolver that does not understand ANAME will not be able 359 to validate A and AAAA records unless they are signed. 361 Both authoritative servers and resolvers that implement ANAME should 362 carefully check for loops and treat them as an error condition. 364 7. IANA Considerations 366 IANA is requested to assign a DNS RR data type value for the ANAME RR 367 type under the "Resource Record (RR) TYPEs" subregistry under the 368 "Domain Name System (DNS) Parameters" registry. 370 8. Acknowledgments 372 Thanks to Mukund Sivaraman, Stephen Morris, Ray Bellis, Mark Andrews, 373 Richard Salts, Job Snijders, and Hakan Lindqvist for discussion and 374 feedback. 376 9. References 378 9.1. Normative References 380 [RFC1033] Lottor, M., "Domain administrators operations guide", 381 RFC 1033, November 1987. 383 [RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record 384 (RR) Types", RFC 3597, September 2003. 386 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 387 Rose, "Resource Records for the DNS Security Extensions", 388 RFC 4034, March 2005. 390 9.2. Informative References 392 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 393 Requirement Levels", BCP 14, RFC 2119, March 1997. 395 [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS 396 Security (DNSSEC) Hashed Authenticated Denial of 397 Existence", RFC 5155, March 2008. 399 [RFC6672] Rose, S. and W. Wijngaards, "DNAME Redirection in the 400 DNS", RFC 6672, June 2012. 402 [RFC7871] Contavalli, C., van der Gaast, W., Lawrence, D., and W. 403 Kumari, "Client Subnet in DNS Queries", RFC 7871, 404 DOI 10.17487/RFC7871, May 2016, 405 . 407 Authors' Addresses 409 Evan Hunt 410 ISC 411 950 Charter St 412 Redwood City, CA 94063 413 USA 415 Email: each@isc.org 417 Peter van Dijk 418 PowerDNS.COM B.V. 419 Den Haag 420 The Netherlands 422 Email: peter.van.dijk@powerdns.com 423 Anthony Eden 424 DNSimple 425 Boston, MA 426 USA 428 Email: anthony.eden@dnsimple.com 429 URI: https://dnsimple.com/