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'DNS-TERMINOLOGY') == Outdated reference: draft-ietf-dnsop-cookies has been published as RFC 7873 ** Obsolete normative reference: RFC 6824 (Obsoleted by RFC 8684) ** Obsolete normative reference: RFC 6982 (Obsoleted by RFC 7942) ** Downref: Normative reference to an Informational RFC: RFC 7646 == Outdated reference: draft-ietf-dnsop-edns-tcp-keepalive has been published as RFC 7828 Summary: 4 errors (**), 0 flaws (~~), 6 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 dnsop P. Wouters 3 Internet-Draft Red Hat 4 Intended status: Standards Track November 17, 2015 5 Expires: May 20, 2016 7 Chain Query requests in DNS 8 draft-ietf-dnsop-edns-chain-query-05 10 Abstract 12 This document defines an EDNS0 extension that can be used by a 13 security-aware validating Resolver configured to use a Forwarder to 14 send a single query, requesting a complete validation path along with 15 the regular query answer. The reduction in queries lowers the 16 latency and reduces the need to send multiple queries at once. This 17 extension mandates the use of source IP verified transport such as 18 TCP or UDP with EDNS-COOKIE so it cannot be abused in amplification 19 attacks. 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 May 20, 2016. 38 Copyright Notice 40 Copyright (c) 2015 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. Requirements Notation . . . . . . . . . . . . . . . . . . 3 57 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 4. Option Format . . . . . . . . . . . . . . . . . . . . . . . . 5 60 5. Protocol Description . . . . . . . . . . . . . . . . . . . . 5 61 5.1. Discovery of Support . . . . . . . . . . . . . . . . . . 5 62 5.2. Generate a Query . . . . . . . . . . . . . . . . . . . . 6 63 5.3. Send the Option . . . . . . . . . . . . . . . . . . . . . 6 64 5.4. Generate a Response . . . . . . . . . . . . . . . . . . . 6 65 6. Protocol Considerations . . . . . . . . . . . . . . . . . . . 7 66 6.1. DNSSEC Considerations . . . . . . . . . . . . . . . . . . 7 67 6.2. NS record Considerations . . . . . . . . . . . . . . . . 8 68 6.3. TCP Session Management . . . . . . . . . . . . . . . . . 8 69 6.4. Negative Trust Anchors . . . . . . . . . . . . . . . . . 8 70 6.5. Non-Clean Paths . . . . . . . . . . . . . . . . . . . . . 9 71 6.6. Anycast Considerations . . . . . . . . . . . . . . . . . 9 72 7. Implementation Status . . . . . . . . . . . . . . . . . . . . 9 73 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 74 8.1. Amplification Attacks . . . . . . . . . . . . . . . . . . 10 75 9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 10 76 9.1. Simple Query for example.com . . . . . . . . . . . . . . 10 77 9.2. Out-of-path Query for example.com . . . . . . . . . . . . 12 78 9.3. Non-existent data . . . . . . . . . . . . . . . . . . . . 13 79 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 80 10.1. EDNS0 option code for CHAIN . . . . . . . . . . . . . . 14 81 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 82 12. Normative References . . . . . . . . . . . . . . . . . . . . 14 83 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16 85 1. Introduction 87 Traditionally, a DNS client operates in stub-mode. For each DNS 88 question the DNS client needs to resolve, it sends a single query to 89 an upstream Recursive Resolver to obtain a single DNS answer. When 90 DNSSEC [RFC4033] is deployed on such DNS clients, validation requires 91 that the client obtains all the intermediate information from the DNS 92 root down to the queried-for hostname so it can perform DNSSEC 93 validation on the complete chain of trust. 95 Currently, applications send out many UDP requests concurrently. 96 This requires more resources on the DNS client with respect to state 97 (cpu, memory, battery) and bandwidth. There is also no guarantee 98 that the initial set of UDP questions will result in all the records 99 required for DNSSEC validation. More round trips could be required 100 depending on the resulting DNS answers. This especially affects 101 high-latency links. 103 This document specifies an EDNS0 extension that allows a validating 104 Resolver running as a Forwarder to open a TCP connection to another 105 Resolver and request a DNS chain answer using one DNS query/answer 106 pair. This reduces the number of round trips to two. If combined 107 with long lived TCP or [TCP-KEEPALIVE] there is only one round trip. 108 While the upstream Resolver still needs to perform all the individual 109 queries required for the complete answer, it usually has a much 110 bigger cache and does not experience significant slowdown from last- 111 mile latency. 113 This EDNS0 extension allows the Forwarder to indicate which part of 114 the DNS hierarchy it already contains in its cache. This reduces the 115 amount of data required to be transferred and reduces the work the 116 upstream Recursive Resolver has to perform. 118 This EDNS0 extension is only intended to be sent by Forwarders to 119 Recursive Resolvers. It can (and should) be ignored by Authoritative 120 Servers. 122 1.1. Requirements Notation 124 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 125 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 126 document are to be interpreted as described in [RFC2119]. 128 2. Terminology 130 The DNS terminology used in this document is that of 131 [DNS-TERMINOLOGY]. Additionally, the following terms are used: 133 Recursive Resolver: A nameserver that is responsible for resolving 134 domain names for clients by following the domain's delegation 135 chain, starting at the root. Recursive Resolvers frequently use 136 caches to be able to respond to client queries quickly. Described 137 in [RFC1035] chapter 7. 139 Validating Resolver: A recursive nameserver that also performs 140 DNSSEC [RFC4033] validation. Also known as "security-aware 141 resolver". 143 3. Overview 144 When DNSSEC is deployed on a host, it can no longer delegate all DNS 145 work to the upstream Recursive Resolver. Obtaining just the DNS 146 answer itself is not enough to validate that answer using DNSSEC. 147 For DNSSEC validation, the DNS client requires a locally running 148 validating Resolver so it can confirm DNSSEC validation of all 149 intermediary DNS answers. It can configure itself as a Forwarder if 150 it obtains the IP addresses of one or more Recursive Resolvers that 151 are available, or as a stand-alone Recursive Resolver if no 152 functional Recursive Resolvers were obtained. Generating the 153 required queries for validation adds a significant delay in answering 154 the DNS question of the locally running application. The application 155 must wait while the Resolver validates all intermediate answers. 156 Each round-trip adds to the total time waiting on DNS resolution with 157 validation to complete. This makes DNSSEC resolving impractical for 158 devices on networks with a high latency. 160 This document defines the CHAIN option that allows the Resolver to 161 request all intermediate DNS data it requires to resolve and validate 162 a particular DNS answer in a single round-trip. The Resolver could 163 be part of the application or a Recursive Resolver running on the 164 host. 166 Servers answering with CHAIN data should ensure that the transport is 167 TCP or source IP address verified UDP. See Section 8. This avoids 168 abuse in DNS amplification attacks. 170 Applications that support CHAIN internally can perform validation 171 without requiring the host the run a Recursive Resolver. This is 172 particularly useful for virtual servers in a cloud or container based 173 deployment where it is undesirable to run a Recursive Resolver per 174 virtual machine. 176 The format of this option is described in Section 4. 178 As described in Section 5.4, a Recursive Resolver could use this 179 EDNS0 option to include additional data required by the Resolver in 180 the Authority Section of the DNS answer packet when using a source IP 181 verified transport. The Answer Section remains unchanged from a 182 traditional DNS answer and contains the answer and related DNSSEC 183 entries. 185 An empty CHAIN EDNS0 option MAY be sent over any transport as a 186 discovery method. A DNS server receiving such an empty CHAIN option 187 SHOULD add an empty CHAIN option in its answer to indicate that it 188 supports CHAIN for source IP address verified transports. 190 The mechanisms provided by CHAIN raise various security related 191 concerns, related to the additional work, bandwidth, amplification 192 attacks as well as privacy issues with the cache. These concerns are 193 described in Section 8. 195 4. Option Format 197 This draft uses an EDNS0 [RFC6891] option to include client IP 198 information in DNS messages. The option is structured as follows: 200 1 2 3 201 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 202 +-------------------------------+-------------------------------+ 203 ! OPTION-CODE ! OPTION-LENGTH ! 204 +-------------------------------+-------------------------------+ 205 ~ Closest Trust Point (FQDN) ~ 206 +---------------------------------------------------------------+ 208 o OPTION-CODE, 2 octets, for CHAIN is 13. 210 o OPTION-LENGTH, 2 octets, contains the length of the payload 211 (everything after Option-length) in octets. 213 o Closest Trust Point, a variable length Fully Qualified Domain Name 214 ("FQDN") in DNS wire format of the requested start point of the 215 chain. This entry is the 'lowest' known entry in the DNS chain 216 known by the recursive server seeking a CHAIN answer for which it 217 has a validated DS and DNSKEY record. The end point of the chain 218 is obtained from the DNS Query Section itself. No DNS name 219 compression is allowed for this value. 221 5. Protocol Description 223 5.1. Discovery of Support 225 A Forwarder may include a zero-length CHAIN option in a regular query 226 over any transport to discover the DNS server capability for CHAIN. 227 Recursive Resolvers that support and are willing to accept CHAIN 228 queries over source IP verified transport respond to a zero-length 229 CHAIN received by including a zero-length CHAIN option in the answer. 230 If not already using a source IP verified transport, the Forwarder 231 MAY then switch to a source IP verified transport and start sending 232 queries with the CHAIN option to request a CHAIN response from the 233 Recursive Resolver. Examples of source IP verification are the 3-way 234 TCP handshake and UDP with [EDNS-COOKIE]. 236 5.2. Generate a Query 238 In this option value, the Forwarder sets the Closest Trust Point in 239 the chain - furthest from the root - that it already has a DNSSEC 240 validated (secure or not) answer for in its cache. The upstream 241 Recursive Resolver does not need to include any part of the chain 242 from the root down to this option's FQDN. A complete example is 243 described in Section 9.1. 245 The CHAIN option should generally be sent by system Forwarders and 246 Resolvers within an application that also perform DNSSEC validation. 248 5.3. Send the Option 250 When CHAIN is available, the downstream Recursive Resolver can adjust 251 its query strategy based on the desired queries and its cache 252 contents. 254 A Forwarder can request the CHAIN option with every outgoing DNS 255 query. However, it is RECOMMENDED that Forwarders remember which 256 upstream Recursive Resolvers did not return the option (and 257 additional data) with their response. The Forwarder SHOULD fallback 258 to regular DNS for subsequent queries to those Recursive Resolvers. 259 It MAY switch to another Recursive Resolver that does support the 260 CHAIN option or try again later to see if the server has become less 261 loaded and is now willing to answer with Query Chains. 263 5.4. Generate a Response 265 When a query containing a non-zero CHAIN option is received from a 266 Forwarder, the upstream Recursive Resolver supporting CHAIN MAY 267 respond by confirming that it is returning a CHAIN. To do so, it 268 MUST set the CHAIN option to the lowest Trust Point sent as part of 269 the chain, with its corresponding OPTION-LENGTH. It extends the 270 Authority Section in the DNS answer packet with the DNS RRsets 271 required for validating the answer. The DNS RRsets added start with 272 the first chain element below the received Closest Trust Point up to 273 and including the NS and DS RRsets that represent the zone cut 274 (authoritative servers) of the QNAME. The added RRsets MAY be added 275 in matching hierarchical order but a DNS client MUST NOT depend on 276 the order of the added RRsets for validation. The actual DNS answer 277 to the question in the Query Section is placed in the DNS Answer 278 Section identical to the traditional DNS answer. All required DNSSEC 279 related records must be added to their appropriate sections. This 280 includes records required for proof of non-existence of regular and/ 281 or wildcard records, such as NSEC or NSEC3 records. 283 Recursive Resolvers that have not implemented or enabled support for 284 the CHAIN option, or are otherwise unwilling to perform the 285 additional work for a Chain Query due to work load, may safely ignore 286 the option in the incoming queries. Such a server MUST NOT include 287 an CHAIN option when sending DNS answer replies back, thus indicating 288 it is not able or willing to support Chain Queries at this time. 290 Requests with wrongly formatted options (i.e. bogus FQDN) MUST be 291 rejected and a FORMERR response must be returned to the sender, as 292 described by [RFC6891]. 294 Requests resulting in chains that the receiving resolver is unwilling 295 to serve can be rejected by answering the query as a regular DNS 296 reply but with an empty CHAIN payload. Replying with an empty CHAIN 297 can be used for chains that would be too big or chains that would 298 reveal too much information considered private. 300 At any time, a Recursive Resolver that has determined that it is 301 running low on resources can refuse CHAIN queries by replying with a 302 regular DNS reply with an empty CHAIN payload. 304 If a CHAIN answer would be bigger than the Recursive Resolver is 305 willing to serve, it SHOULD send a partial chain starting with the 306 data closest to the top of the chain. The client MAY re-send the 307 query with an updated Closest Trust Point until it has received the 308 full chain. The CHAIN response will contain the lowest Closest Trust 309 Point that was included in the CHAIN answer. 311 If the DNS request results in an CNAME or DNAME for the Answer 312 Section, the Recursive Resolver MUST return these records in the 313 Answer Section similar to regular DNS processing. The CNAME or DNAME 314 target MAY be placed in the Additional Section only if all supporting 315 records for DNSSEC validation of the CNAME or DNAME target are also 316 added to the Authority Section. 318 The response from a Recursive Resolver to a Resolver MUST NOT contain 319 the CHAIN option if none was present in the Resolver's original 320 request. 322 A DNS query that contains the CHAIN option MUST also have the DNSSEC 323 OK ("OK") bit set. If this bit is not set, or if the Checking 324 Disabled ("CD") bit is set, the CHAIN option received MUST be 325 ignored. 327 6. Protocol Considerations 329 6.1. DNSSEC Considerations 330 The presence or absence of an OPT resource record containing an CHAIN 331 option in a DNS query does not change the usage of those resource 332 records and mechanisms used to provide data origin authentication and 333 data integrity to the DNS, as described in [RFC4033], [RFC4034] and 334 [RFC4035]. 336 6.2. NS record Considerations 338 CHAIN responses SHOULD include the NS RRset from the zone itself 339 including the RRSIG records required for validation. It MUST NOT 340 include the NS RRset from parent zone, as this RRset is not signed. 341 If the size of the answer is an important factor, the NS RRset MAY be 342 omited. 344 When a DNSSEC chain is supplied via CHAIN, the Forwarder is no longer 345 required to use the NS RRset, as it can construct the validation path 346 via the DNSKEY and DS RRsets without using the NS RRset. However, 347 the Forwarder might be forced to switch from Forwarder mode to 348 Recursive Resolver mode due to a network topology change. In 349 Recursive Resolver mode, the NS RRsets are needed to find and query 350 Authoritative Servers directly. It is RECOMMENDED that the DNS 351 Forwarder populate its cache with this information to avoid requiring 352 future queries to obtain any missing NS records. Therefore, CHAIN 353 responses MUST include the NS RRset from the child zone, including 354 the RRSIG records required for validation. 356 6.3. TCP Session Management 358 It is RECOMMENDED that TCP sessions not immediately be closed after 359 the DNS answer to the first query is received. It is recommended to 360 use [TCP-KEEPALIVE]. 362 Both DNS clients and servers are subject to resource constraints 363 which will limit the extent to which Chain Queries can be executed. 364 Effective limits for the number of active sessions that can be 365 maintained on individual clients and servers should be established, 366 either as configuration options or by interrogation of process limits 367 imposed by the operating system. 369 In the event that there is greater demand for Chain Queries than can 370 be accommodated, DNS servers may stop advertising the CHAIN option in 371 successive DNS messages. This allows, for example, clients with 372 other candidate servers to query to establish new sessions with 373 different servers in expectation that those servers might still allow 374 Chain Queries. 376 6.4. Negative Trust Anchors 377 If a CHAIN answer would intersect with a Negative Trust Anchor 378 [RFC7646], a partian CHAIN up to the node above the Negative Trust 379 Anchor should be returned. 381 6.5. Non-Clean Paths 383 Many paths between DNS clients and Recursive Resolvers suffer from 384 poor hygiene, limiting the free flow of DNS messages that include 385 particular EDNS0 options, or messages that exceed a particular size. 386 A fallback strategy similar to that described in [RFC6891] section 387 6.2.2 SHOULD be employed to avoid persistent interference due to non- 388 clean paths. 390 6.6. Anycast Considerations 392 Recursive Resolvers of various types are commonly deployed using 393 anycast [RFC4786]. 395 Successive DNS transactions between a client and server using UDP 396 transport may involve responses generated by different anycast nodes, 397 and the use of anycast in the implementation of a DNS server is 398 effectively undetectable by the client. The CHAIN option SHOULD NOT 399 be included in responses using UDP transport from servers provisioned 400 using anycast unless all anycast server nodes are capable of 401 processing the CHAIN option. 403 Changes in network topology between clients and anycast servers may 404 cause disruption to TCP sessions making use of CHAIN more often than 405 with TCP sessions that omit it, since the TCP sessions are expected 406 to be longer-lived. Anycast servers MAY make use of TCP multipath 407 [RFC6824] to anchor the server side of the TCP connection to an 408 unambiguously-unicast address in order to avoid disruption due to 409 topology changes. 411 7. Implementation Status 413 This section records the status of known implementations of the 414 protocol defined by this specification at the time of posting of this 415 Internet-Draft, and is based on a proposal described in [RFC6982]. 416 The description of implementations in this section is intended to 417 assist the IETF in its decision processes in progressing drafts to 418 RFCs. Please note that the listing of any individual implementation 419 here does not imply endorsement by the IETF. Furthermore, no effort 420 has been spent to verify the information presented here that was 421 supplied by IETF contributors. This is not intended as, and must not 422 be construed to be, a catalog of available implementations or their 423 features. Readers are advised to note that other implementations may 424 exist. 426 According to [RFC6982], "this will allow reviewers and working groups 427 to assign due consideration to documents that have the benefit of 428 running code, which may serve as evidence of valuable experimentation 429 and feedback that have made the implemented protocols more mature. 430 It is up to the individual working groups to use this information as 431 they see fit". 433 [While there is some interest, no work has started yet] 435 8. Security Considerations 437 8.1. Amplification Attacks 439 Chain Queries can potentially send very large DNS answers. Attackers 440 could abuse this using spoofed source IP addresses to inflict large 441 Distributed Denial of Service attacks using query-chains as an 442 amplification vector in their attack. While TCP is not vulnerable 443 for this type of abuse, the UDP protocol is vulnerable to this. 445 A Recursive Resolver MUST NOT return CHAIN answers to clients over 446 UDP without source IP address verification. An example of UDP based 447 source IP address verification is [EDNS-COOKIE]. A Recursive 448 Resolver refusing a CHAIN option MUST respond with a zero-length 449 CHAIN option to indicate support for CHAIN queries when a proper 450 transport is used. It MUST NOT send an RCODE of REFUSED. 452 9. Examples 454 9.1. Simple Query for example.com 456 o A web browser on a client machine asks the Forwarder running on 457 localhost to resolve the A record of "www.example.com." by sending 458 a regular DNS UDP query on port 53 to 127.0.0.1. 460 o The Resolver on the client machine checks its cache, and notices 461 it already has a DNSSEC validated entry of "com." in its cache. 462 This includes the DNSKEY RRset with its RRSIG records. In other 463 words, according to its cache, ".com" is DNSSEC validated as 464 "secure" and can be used to continue a DNSSEC validated chain. 466 o The Resolver on the client opens a TCP connection to its upstream 467 Recursive Resolver on port 53. It adds the CHAIN option as 468 follows: 470 * Option-code, set to 13 472 * Option-length, set to 0x00 0x04 473 * Closest Trust Point set to "com." 475 o The upstream Recursive Resolver receives a DNS query over TCP with 476 the CHAIN Closest Trust Point set to "com.". After accepting the 477 query it starts constructing a DNS reply packet. 479 o The upstream Recursive Resolver performs all the regular work to 480 ensure it has all the answers to the query for the A record of 481 "www.example.com.". It does so without using the CHAIN option - 482 unless it is also configured as a Forwarder. The answer to the 483 original DNS question could be the actual A record, the DNSSEC 484 proof of non-existence, or an insecure NXDOMAIN response. 486 o The upstream Recursive Resolver adds the CHAIN option to the DNS 487 response as follows: 489 * Option-code, set to 13 491 * Option-length, set to 0x00 0x04 493 * The Closest Trust Point is set to "com.". 495 o The upstream Recursive Resolver constructs the DNS Authority 496 Section and fills it (in any order) with: 498 * The DS RRset for "example.com." and its corresponding RRSIGs 499 (made by the "com." DNSKEY(s)) 501 * The DNSKEY RRset for "example.com." and its corresponding 502 RRSIGs (made by the "example.com" DNSKEY(s)) 504 * The authoritative NS RRset for "example.com." and its 505 corresponding RRSIGs (from the child zone) 507 If the answer does not exist, and the zone uses DNSSEC, it also 508 adds the proof of non-existence, such as NSEC or NSEC3 records, to 509 the Authority Section. 511 o The upstream Recursive Resolver constructs the DNS Answer 512 Section and fills it with: 514 * The A record of "www.example.com." and its corresponding RRSIGs 516 If the answer does not exist (NODATA or NXDOMAIN), the Answer 517 Section remains empty. For the NXDOMAIN case, the RCode of the 518 DNS answer packet is set to NXDOMAIN. Otherwise it remains 519 NOERROR. 521 o The upstream Recursive Resolver returns the DNS answer over the 522 existing TCP connection. When all data is sent, it SHOULD keep 523 the TCP connection open to allow for additional incoming DNS 524 queries - provided it has enough resources to do so. 526 o The Resolver on the client receives the DNS answer. It processes 527 the Authority Section and the Answer Section and places the 528 information in its local cache. It ensures that no data is 529 accepted into the cache without having proper DNSSEC validation. 530 It MAY do so by looping over the entries in the Authority and 531 Answer Sections. When an entry is validated for its cache, it is 532 removed from the processing list. If an entry cannot be validated 533 it is left in the process list. When the end of the list is 534 reached, the list is processed again until either all entries are 535 placed in the cache, or the remaining items cannot be placed in 536 the cache due to lack of validation. Those entries are then 537 discarded. 539 o If the cache contains a valid answer to the application's query, 540 this answer is returned to the application via a regular DNS 541 answer packet. This packet MUST NOT contain an CHAIN option. If 542 no valid answer can be returned, normal error processing is done. 543 For example, an NXDOMAIN or an empty Answer Section could be 544 returned depending on the error condition. 546 9.2. Out-of-path Query for example.com 548 A Recursive Resolver receives a query for the A record for 549 example.com. It includes the CHAIN option with the following 550 parameters: 552 o Option-code, set to 13 554 o Option-length, set to 0x00 0x0D 556 o The Closest Trust Point set to 'unrelated.ca.' 558 As there is no chain that leads from "unrelated.ca." to 559 "example.com", the Resolving Nameserver answers with an empty CHAIN 560 specified using: 562 o Option-code, set to 13 564 o Option-length, set to 0x00 0x00 566 o The Closest Trust Point is omitted (zero length) 567 Note that the regular answer is still present just as it would be for 568 a query that did not specify the CHAIN option. 570 9.3. Non-existent data 572 A Recursive Resolver receives a query for the A record for 573 "ipv6.toronto.redhat.ca". It includes the CHAIN option with the 574 following parameters: 576 o Option-code, set to 13 578 o Option-length, set to 0x00 0x03 580 o The Closest Trust Point set to 'ca.' 582 Using regular UDP queries towards Authoritative Nameservers, it 583 locates the NS RRset for "toronto.redhat.ca.". When querying for the 584 A record it receives a reply with RCODE "NoError" and an empty Answer 585 Section. The Authority Section contains NSEC3 and RRSIG records 586 proving there is no A RRtype for the QNAME "ipv6.toronto.redhat.ca". 588 The Recursive Resolver constructs a DNS reply with the following 589 CHAIN option parameters: 591 o Option-code, set to 13 593 o Option-length, set to 0x00 0x00 595 o The Closest Trust Point is ommited (zero length) 597 The RCODE is set to "NoError". The Authority Section is filled in 598 with: 600 o The DS RRset for "redhat.ca." plus RRSIGs 602 o The DNSKEY RRset for "redhat.ca." plus RRSIGs 604 o The NS RRset for "redhat.ca." plus RRSIGs (eg ns[01].redhat.ca) 606 o The A RRset for "ns0.redhat.ca." and "ns1.redhat.ca." plus RRSIGs 608 o The DS RRset for "toronto.redhat.ca." plus RRSIGs 610 o The NS RRset for "toronto.redhat.ca." plus RRSIGs (eg 611 ns[01].toronto.redhat.ca) 613 o The DNSKEY RRset for "toronto.redhat.ca." plus RRSIGs 614 o The A RRset and/or AAAA RRset for "ns0.toronto.redhat.ca." and 615 "ns1.toronto.redhat.ca." plus RRSIGs 617 o The NSEC record for "ipv6.toronto.redhat.ca." (proves what RRTYPEs 618 do exist, does not include A) 620 o The NSEC record for "toronto.redhat.ca." (proves no wildcard 621 exists) 623 The Answer Section is empty. The RCode is set to NOERROR. 625 10. IANA Considerations 627 10.1. EDNS0 option code for CHAIN 629 IANA has assigned option code 13 in the "DNS EDNS0 Option Codes 630 (OPT)" registry to CHAIN. 632 11. Acknowledgements 634 Andrew Sullivan pointed out that we do not need any new data formats 635 to support DNS chains. Olafur Gudmundsson ensured the RRsets are 636 returned in the proper Sections. Thanks to Tim Wicinski for his 637 thorough review. 639 12. Normative References 641 [DNS-TERMINOLOGY] 642 Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 643 Terminology", draft-ietf-dnsop-dns-terminology-05 (work in 644 progress), September 2015. 646 [EDNS-COOKIE] 647 Eastlake, Donald., "Domain Name System (DNS) Cookies", 648 draft-ietf-dnsop-cookies (work in progress), November 649 2015. 651 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 652 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 653 . 655 [RFC1035] Mockapetris, P., "Domain names - implementation and 656 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 657 November 1987, . 659 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 660 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 661 RFC2119, March 1997, 662 . 664 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 665 Rose, "DNS Security Introduction and Requirements", RFC 666 4033, DOI 10.17487/RFC4033, March 2005, 667 . 669 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 670 Rose, "Resource Records for the DNS Security Extensions", 671 RFC 4034, DOI 10.17487/RFC4034, March 2005, 672 . 674 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 675 Rose, "Protocol Modifications for the DNS Security 676 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 677 . 679 [RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast 680 Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786, 681 December 2006, . 683 [RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure, 684 "TCP Extensions for Multipath Operation with Multiple 685 Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013, 686 . 688 [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms 689 for DNS (EDNS(0))", STD 75, RFC 6891, DOI 10.17487/ 690 RFC6891, April 2013, 691 . 693 [RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running 694 Code: The Implementation Status Section", RFC 6982, DOI 695 10.17487/RFC6982, July 2013, 696 . 698 [RFC7646] Ebersman, P., Kumari, W., Griffiths, C., Livingood, J., 699 and R. Weber, "Definition and Use of DNSSEC Negative Trust 700 Anchors", RFC 7646, DOI 10.17487/RFC7646, September 2015, 701 . 703 [TCP-KEEPALIVE] 704 Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The 705 edns-tcp-keepalive EDNS0 Option", draft-ietf-dnsop-edns- 706 tcp-keepalive-04 (work in progress), October 2015. 708 Author's Address 710 Paul Wouters 711 Red Hat 713 Email: pwouters@redhat.com