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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 January 18, 2016 5 Expires: July 21, 2016 7 Chain Query requests in DNS 8 draft-ietf-dnsop-edns-chain-query-06 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 potentially 16 lowers the latency and reduces the need to send multiple queries at 17 once. This extension mandates the use of source IP verified 18 transport such as TCP or UDP with EDNS-COOKIE so it cannot be abused 19 in amplification 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 July 21, 2016. 38 Copyright Notice 40 Copyright (c) 2016 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 . . . . . . . . . . . . . . . . . . . . 5 63 5.3. Send the Option . . . . . . . . . . . . . . . . . . . . . 6 64 5.4. Generate a Response . . . . . . . . . . . . . . . . . . . 6 65 6. Protocol Considerations . . . . . . . . . . . . . . . . . . . 7 66 6.1. DNSSEC Considerations . . . . . . . . . . . . . . . . . . 8 67 6.2. NS record Considerations . . . . . . . . . . . . . . . . 8 68 6.3. Session Management . . . . . . . . . . . . . . . . . . . 8 69 6.4. Negative Trust Anchors . . . . . . . . . . . . . . . . . 9 70 6.5. Anycast Considerations . . . . . . . . . . . . . . . . . 9 71 7. Implementation Status . . . . . . . . . . . . . . . . . . . . 9 72 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 73 8.1. Amplification Attacks . . . . . . . . . . . . . . . . . . 10 74 9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 10 75 9.1. Simple Query for example.com . . . . . . . . . . . . . . 10 76 9.2. Out-of-path Query for example.com . . . . . . . . . . . . 12 77 9.3. Non-existent data . . . . . . . . . . . . . . . . . . . . 13 78 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 79 10.1. EDNS0 option code for CHAIN . . . . . . . . . . . . . . 14 80 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 81 12. Normative References . . . . . . . . . . . . . . . . . . . . 14 82 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16 84 1. Introduction 86 Traditionally, a DNS client operates in stub-mode. For each DNS 87 question the DNS client needs to resolve, it sends a single query to 88 an upstream Recursive Resolver to obtain a single DNS answer. When 89 DNSSEC [RFC4033] is deployed on such DNS clients, validation requires 90 that the client obtains all the intermediate information from the DNS 91 root down to the queried-for hostname so it can perform DNSSEC 92 validation on the complete chain of trust. 94 Currently, applications send out many UDP requests concurrently. 95 This requires more resources on the DNS client with respect to state 96 (cpu, memory, battery) and bandwidth. There is also no guarantee 97 that the initial set of UDP questions will result in all the records 98 required for DNSSEC validation. More round trips could be required 99 depending on the resulting DNS answers. This especially affects 100 high-latency links. 102 This document specifies an EDNS0 extension that allows a validating 103 Resolver running as a Forwarder to open a TCP connection to another 104 Resolver and request a DNS chain answer using one DNS query/answer 105 pair. This reduces the number of round trips to two. If combined 106 with long lived TCP or [TCP-KEEPALIVE] there is only one round trip. 107 While the upstream Resolver still needs to perform all the individual 108 queries required for the complete answer, it usually has a much 109 bigger cache and does not experience significant slowdown from last- 110 mile latency. 112 This EDNS0 extension allows the Forwarder to indicate which part of 113 the DNS hierarchy it already contains in its cache. This reduces the 114 amount of data required to be transferred and reduces the work the 115 upstream Recursive Resolver has to perform. 117 This EDNS0 extension is only intended to be sent by Forwarders to 118 Recursive Resolvers. It MUST be ignored by Authoritative Servers. 120 1.1. Requirements Notation 122 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 123 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 124 document are to be interpreted as described in [RFC2119]. 126 2. Terminology 128 The DNS terminology used in this document is that of [RFC7719]. 129 Additionally, the following terms are used: 131 Recursive Resolver: A nameserver that is responsible for resolving 132 domain names for clients by following the domain's delegation 133 chain, starting at the root. Recursive Resolvers frequently use 134 caches to be able to respond to client queries quickly. Described 135 in [RFC1035] chapter 7. 137 Validating Resolver: A recursive nameserver that also performs 138 DNSSEC [RFC4033] validation. Also known as "security-aware 139 resolver". 141 3. Overview 143 When DNSSEC is deployed on a host, it can no longer delegate all DNS 144 work to the upstream Recursive Resolver. Obtaining just the DNS 145 answer itself is not enough to validate that answer using DNSSEC. 146 For DNSSEC validation, the DNS client requires a locally running 147 validating Resolver so it can confirm DNSSEC validation of all 148 intermediary DNS answers. It can configure itself as a Forwarder if 149 it obtains the IP addresses of one or more Recursive Resolvers that 150 are available, or as a stand-alone Recursive Resolver if no 151 functional Recursive Resolvers were obtained. Generating the 152 required queries for validation adds a significant delay in answering 153 the DNS question of the locally running application. The application 154 must wait while the Resolver validates all intermediate answers. 155 Each round-trip adds to the total time waiting on DNS resolution with 156 validation to complete. This makes DNSSEC resolving impractical for 157 devices on networks with a high latency. 159 This document defines the CHAIN option that allows the Resolver to 160 request all intermediate DNS data it requires to resolve and validate 161 a particular DNS answer in a single round-trip. The Resolver could 162 be part of the application or a Recursive Resolver running on the 163 host. 165 Servers answering with CHAIN data should ensure that the transport is 166 TCP or source IP address verified UDP. See Section 8. This avoids 167 abuse in DNS amplification attacks. 169 Applications that support CHAIN internally can perform validation 170 without requiring the host the run a Recursive Resolver. This is 171 particularly useful for virtual servers in a cloud or container based 172 deployment where it is undesirable to run a Recursive Resolver per 173 virtual machine. 175 The format of this option is described in Section 4. 177 As described in Section 5.4, a Recursive Resolver could use this 178 EDNS0 option to include additional data required by the Resolver in 179 the Authority Section of the DNS answer packet when using a source IP 180 verified transport. The Answer Section remains unchanged from a 181 traditional DNS answer and contains the answer and related DNSSEC 182 entries. 184 An empty CHAIN EDNS0 option MAY be sent over any transport as a 185 discovery method. A DNS server receiving such an empty CHAIN option 186 SHOULD add an empty CHAIN option in its answer to indicate that it 187 supports CHAIN for source IP address verified transports. 189 The mechanisms provided by CHAIN raise various security related 190 concerns, related to the additional work, bandwidth, amplification 191 attacks as well as privacy issues with the cache. These concerns are 192 described in Section 8. 194 4. Option Format 196 This draft uses an EDNS0 [RFC6891] option to include client IP 197 information in DNS messages. The option is structured as follows: 199 1 2 3 200 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 1 201 +-------------------------------+-------------------------------+ 202 ! OPTION-CODE ! OPTION-LENGTH ! 203 +-------------------------------+-------------------------------+ 204 ~ Closest Trust Point (FQDN) ~ 205 +---------------------------------------------------------------+ 207 o OPTION-CODE, 2 octets, for CHAIN is 13. 209 o OPTION-LENGTH, 2 octets, contains the length of the payload 210 (everything after Option-length) in octets. 212 o Closest Trust Point, a variable length Fully Qualified Domain Name 213 ("FQDN") in DNS wire format of the requested start point of the 214 chain. This entry is the 'lowest' known entry in the DNS chain 215 known by the recursive server seeking a CHAIN answer for which it 216 has a validated DS and DNSKEY record. The end point of the chain 217 is obtained from the DNS Query Section itself. No DNS name 218 compression is allowed for this value. 220 5. Protocol Description 222 5.1. Discovery of Support 224 A Forwarder may include a zero-length CHAIN option in a regular query 225 over any transport to discover the DNS server capability for CHAIN. 226 Recursive Resolvers that support and are willing to accept CHAIN 227 queries over source IP verified transport respond to a zero-length 228 CHAIN received by including a zero-length CHAIN option in the answer. 229 If not already using a source IP verified transport, the Forwarder 230 MAY then switch to a source IP verified transport and start sending 231 queries with the CHAIN option to request a CHAIN response from the 232 Recursive Resolver. Examples of source IP verification are the 3-way 233 TCP handshake and UDP with [EDNS-COOKIE]. 235 5.2. Generate a Query 237 In this option value, the Forwarder sets the Closest Trust Point in 238 the chain - furthest from the root - that it already has a DNSSEC 239 validated (secure or not) answer for in its cache. The upstream 240 Recursive Resolver does not need to include any part of the chain 241 from the root down to this option's FQDN. A complete example is 242 described in Section 9.1. 244 The CHAIN option should generally be sent by system Forwarders and 245 Resolvers within an application that also perform DNSSEC validation. 247 5.3. Send the Option 249 When CHAIN is available, the downstream Recursive Resolver can adjust 250 its query strategy based on the desired queries and its cache 251 contents. 253 A Forwarder can request the CHAIN option with every outgoing DNS 254 query. However, it is RECOMMENDED that Forwarders remember which 255 upstream Recursive Resolvers did not return the option (and 256 additional data) with their response. The Forwarder SHOULD fallback 257 to regular DNS for subsequent queries to those Recursive Resolvers. 258 It MAY switch to another Recursive Resolver that does support the 259 CHAIN option or try again later to see if the server has become less 260 loaded and is now willing to answer with Query Chains. A fallback 261 strategy similar to that described in [RFC6891] section 6.2.2 SHOULD 262 be employed to avoid persistent interference due to non-clean paths. 264 5.4. Generate a Response 266 When a query containing a non-zero CHAIN option is received from a 267 Forwarder, the upstream Recursive Resolver supporting CHAIN MAY 268 respond by confirming that it is returning a CHAIN. To do so, it 269 MUST set the CHAIN option to the lowest Trust Point sent as part of 270 the chain, with its corresponding OPTION-LENGTH. It extends the 271 Authority Section in the DNS answer packet with the DNS RRsets 272 required for validating the answer. The DNS RRsets added start with 273 the first chain element below the received Closest Trust Point up to 274 and including the NS and DS RRsets that represent the zone cut 275 (authoritative servers) of the QNAME. The added RRsets MAY be added 276 in matching hierarchical order but a DNS client MUST NOT depend on 277 the order of the added RRsets for validation. The actual DNS answer 278 to the question in the Query Section is placed in the DNS Answer 279 Section identical to the traditional DNS answer. All required DNSSEC 280 related records must be added to their appropriate sections. This 281 includes records required for proof of non-existence of regular and/ 282 or wildcard records, such as NSEC or NSEC3 records. 284 Recursive Resolvers that have not implemented or enabled support for 285 the CHAIN option, or are otherwise unwilling to perform the 286 additional work for a Chain Query due to work load, may safely ignore 287 the option in the incoming queries. Such a server MUST NOT include 288 an CHAIN option when sending DNS answer replies back, thus indicating 289 it is not able or willing to support Chain Queries at this time. 291 Requests with wrongly formatted options (i.e. bogus FQDN) MUST be 292 rejected and a FORMERR response must be returned to the sender, as 293 described by [RFC6891]. 295 Requests resulting in chains that the receiving resolver is unwilling 296 to serve can be rejected by answering the query as a regular DNS 297 reply but with an empty CHAIN payload. Replying with an empty CHAIN 298 can be used for chains that would be too big or chains that would 299 reveal too much information considered private. 301 At any time, a Recursive Resolver that has determined that it is 302 running low on resources can refuse CHAIN queries by replying with a 303 regular DNS reply with an empty CHAIN payload. 305 If a CHAIN answer would be bigger than the Recursive Resolver is 306 willing to serve, it SHOULD send a partial chain starting with the 307 data closest to the top of the chain. The client MAY re-send the 308 query with an updated Closest Trust Point until it has received the 309 full chain. The CHAIN response will contain the lowest Closest Trust 310 Point that was included in the CHAIN answer. 312 If the DNS request results in an CNAME or DNAME for the Answer 313 Section, the Recursive Resolver MUST return these records in the 314 Answer Section similar to regular DNS processing. The CNAME or DNAME 315 target MAY be placed in the Additional Section only if all supporting 316 records for DNSSEC validation of the CNAME or DNAME target are also 317 added to the Authority Section. 319 The response from a Recursive Resolver to a Resolver MUST NOT contain 320 the CHAIN option if none was present in the Resolver's original 321 request. 323 A DNS query that contains the CHAIN option MUST also have the DNSSEC 324 OK ("OK") bit set. If this bit is not set, or if the Checking 325 Disabled ("CD") bit is set, the CHAIN option received MUST be 326 ignored. 328 6. Protocol Considerations 329 6.1. DNSSEC Considerations 331 The presence or absence of an OPT resource record containing an CHAIN 332 option in a DNS query does not change the usage of those resource 333 records and mechanisms used to provide data origin authentication and 334 data integrity to the DNS, as described in [RFC4033], [RFC4034] and 335 [RFC4035]. 337 6.2. NS record Considerations 339 CHAIN responses SHOULD include the NS RRset from the zone itself 340 including the RRSIG records required for validation. It MUST NOT 341 include the NS RRset from parent zone, as this RRset is not signed. 342 If the size of the answer is an important factor, the NS RRset MAY be 343 omited. 345 When a DNSSEC chain is supplied via CHAIN, the Forwarder is no longer 346 required to use the NS RRset, as it can construct the validation path 347 via the DNSKEY and DS RRsets without using the NS RRset. However, 348 the Forwarder might be forced to switch from Forwarder mode to 349 Recursive Resolver mode due to a network topology change. In 350 Recursive Resolver mode, the NS RRsets are needed to find and query 351 Authoritative Servers directly. It is RECOMMENDED that the DNS 352 Forwarder populate its cache with this information to avoid requiring 353 future queries to obtain any missing NS records. Therefore, CHAIN 354 responses MUST include the NS RRset from the child zone, including 355 the RRSIG records required for validation. 357 6.3. Session Management 359 It is RECOMMENDED that TCP sessions not immediately be closed after 360 the DNS answer to the first query is received. It is recommended to 361 use [TCP-KEEPALIVE]. 363 Both DNS clients and servers are subject to resource constraints 364 which will limit the extent to which Chain Queries can be executed. 365 Effective limits for the number of active sessions that can be 366 maintained on individual clients and servers should be established, 367 either as configuration options or by interrogation of process limits 368 imposed by the operating system. 370 In the event that there is greater demand for Chain Queries than can 371 be accommodated, DNS servers may stop advertising the CHAIN option in 372 successive DNS messages. This allows, for example, clients with 373 other candidate servers to query to establish new sessions with 374 different servers in expectation that those servers might still allow 375 Chain Queries. 377 6.4. Negative Trust Anchors 379 If a CHAIN answer would intersect with a Negative Trust Anchor 380 [RFC7646], a partial CHAIN up to the node above the Negative Trust 381 Anchor should be returned. 383 6.5. Anycast Considerations 385 Recursive Resolvers of various types are commonly deployed using 386 anycast [RFC4786]. 388 Successive DNS transactions between a client and server using UDP 389 transport may involve responses generated by different anycast nodes, 390 and the use of anycast in the implementation of a DNS server is 391 effectively undetectable by the client. The CHAIN option SHOULD NOT 392 be included in responses using UDP transport from servers provisioned 393 using anycast unless all anycast server nodes are capable of 394 processing the CHAIN option. 396 Since DNS queries using CHAIN may result in longer TCP sessions, 397 network topology changes may disrupt them more frequently. Anycast 398 servers MAY make use of TCP multipath [RFC6824] to anchor the server 399 side of the TCP connection to an unambiguously-unicast address in 400 order to avoid disruption due to topology changes. 402 7. Implementation Status 404 [RFC Editor Note: Please remove this entire seciton prior to 405 publication as an RFC.] 407 This section records the status of known implementations of the 408 protocol defined by this specification at the time of posting of this 409 Internet-Draft, and is based on a proposal described in [RFC6982]. 410 The description of implementations in this section is intended to 411 assist the IETF in its decision processes in progressing drafts to 412 RFCs. Please note that the listing of any individual implementation 413 here does not imply endorsement by the IETF. Furthermore, no effort 414 has been spent to verify the information presented here that was 415 supplied by IETF contributors. This is not intended as, and must not 416 be construed to be, a catalog of available implementations or their 417 features. Readers are advised to note that other implementations may 418 exist. 420 According to [RFC6982], "this will allow reviewers and working groups 421 to assign due consideration to documents that have the benefit of 422 running code, which may serve as evidence of valuable experimentation 423 and feedback that have made the implemented protocols more mature. 424 It is up to the individual working groups to use this information as 425 they see fit". 427 [While there is some interest, no work has started yet] 429 8. Security Considerations 431 8.1. Amplification Attacks 433 Chain Queries can potentially send very large DNS answers. Attackers 434 could abuse this using spoofed source IP addresses to inflict large 435 Distributed Denial of Service attacks using query-chains as an 436 amplification vector in their attack. While TCP is not vulnerable 437 for this type of abuse, the UDP protocol is vulnerable to this. 439 A Recursive Resolver MUST NOT return CHAIN answers to clients over 440 UDP without source IP address verification. An example of UDP based 441 source IP address verification is [EDNS-COOKIE]. A Recursive 442 Resolver refusing a CHAIN option MUST respond with a zero-length 443 CHAIN option to indicate support for CHAIN queries when a proper 444 transport is used. It MUST NOT send an RCODE of REFUSED. 446 9. Examples 448 9.1. Simple Query for example.com 450 o A web browser on a client machine asks the Forwarder running on 451 localhost to resolve the A record of "www.example.com." by sending 452 a regular DNS UDP query on port 53 to 127.0.0.1. 454 o The Resolver on the client machine checks its cache, and notices 455 it already has a DNSSEC validated entry of "com." in its cache. 456 This includes the DNSKEY RRset with its RRSIG records. In other 457 words, according to its cache, ".com" is DNSSEC validated as 458 "secure" and can be used to continue a DNSSEC validated chain. 460 o The Resolver on the client opens a TCP connection to its upstream 461 Recursive Resolver on port 53. It adds the CHAIN option as 462 follows: 464 * Option-code, set to 13 466 * Option-length, set to 5 467 * Closest Trust Point set to "com." (0x03 0x63 0x6f 0x6d 0x00) 469 o The upstream Recursive Resolver receives a DNS query over TCP with 470 the CHAIN Closest Trust Point set to "com.". After accepting the 471 query it starts constructing a DNS reply packet. 473 o The upstream Recursive Resolver performs all the regular work to 474 ensure it has all the answers to the query for the A record of 475 "www.example.com.". It does so without using the CHAIN option - 476 unless it is also configured as a Forwarder. The answer to the 477 original DNS question could be the actual A record, the DNSSEC 478 proof of non-existence, or an insecure NXDOMAIN response. 480 o The upstream Recursive Resolver adds the CHAIN option to the DNS 481 response as follows: 483 * Option-code, set to 13 485 * Option-length, set to 5 487 * The Closest Trust Point is set to "com." (0x03 0x63 0x6f 0x6d 488 0x00) 490 o The upstream Recursive Resolver constructs the DNS Authority 491 Section and fills it (in any order) with: 493 * The DS RRset for "example.com." and its corresponding RRSIGs 494 (made by the "com." DNSKEY(s)) 496 * The DNSKEY RRset for "example.com." and its corresponding 497 RRSIGs (made by the "example.com" DNSKEY(s)) 499 * The authoritative NS RRset for "example.com." and its 500 corresponding RRSIGs (from the child zone) 502 If the answer does not exist, and the zone uses DNSSEC, it also 503 adds the proof of non-existence, such as NSEC or NSEC3 records, to 504 the Authority Section. 506 o The upstream Recursive Resolver constructs the DNS Answer 507 Section and fills it with: 509 * The A record of "www.example.com." and its corresponding RRSIGs 511 If the answer does not exist (NODATA or NXDOMAIN), the Answer 512 Section remains empty. For the NXDOMAIN case, the RCode of the 513 DNS answer packet is set to NXDOMAIN. Otherwise it remains 514 NOERROR. 516 o The upstream Recursive Resolver returns the DNS answer over the 517 existing TCP connection. When all data is sent, it SHOULD keep 518 the TCP connection open to allow for additional incoming DNS 519 queries - provided it has enough resources to do so. 521 o The Resolver on the client receives the DNS answer. It processes 522 the Authority Section and the Answer Section and places the 523 information in its local cache. It ensures that no data is 524 accepted into the cache without having proper DNSSEC validation. 525 It MAY do so by looping over the entries in the Authority and 526 Answer Sections. When an entry is validated for its cache, it is 527 removed from the processing list. If an entry cannot be validated 528 it is left in the process list. When the end of the list is 529 reached, the list is processed again until either all entries are 530 placed in the cache, or the remaining items cannot be placed in 531 the cache due to lack of validation. Those entries are then 532 discarded. 534 o If the cache contains a valid answer to the application's query, 535 this answer is returned to the application via a regular DNS 536 answer packet. This packet MUST NOT contain an CHAIN option. If 537 no valid answer can be returned, normal error processing is done. 538 For example, an NXDOMAIN or an empty Answer Section could be 539 returned depending on the error condition. 541 9.2. Out-of-path Query for example.com 543 A Recursive Resolver receives a query for the A record for 544 example.com. It includes the CHAIN option with the following 545 parameters: 547 o Option-code, set to 13 549 o Option-length, set to 14 551 o The Closest Trust Point set to 'unrelated.ca.' (0x09 0x75 0x6e 552 0x72 0x65 0x6c 0x61 0x74 0x65 0x64 0x03 0x63 0x61 0x00) 554 As there is no chain that leads from "unrelated.ca." to 555 "example.com", the Resolving Nameserver answers with an empty CHAIN 556 specified using: 558 o Option-code, set to 13 560 o Option-length, set to 0x00 0x00 562 o The Closest Trust Point is omitted (zero length) 563 Note that the regular answer is still present just as it would be for 564 a query that did not specify the CHAIN option. 566 9.3. Non-existent data 568 A Recursive Resolver receives a query for the A record for 569 "ipv6.toronto.redhat.ca". It includes the CHAIN option with the 570 following parameters: 572 o Option-code, set to 13 574 o Option-length, set to 0x00 0x03 576 o The Closest Trust Point set to 'ca.' 578 Using regular UDP queries towards Authoritative Nameservers, it 579 locates the NS RRset for "toronto.redhat.ca.". When querying for the 580 A record it receives a reply with RCODE "NoError" and an empty Answer 581 Section. The Authority Section contains NSEC3 and RRSIG records 582 proving there is no A RRtype for the QNAME "ipv6.toronto.redhat.ca". 584 The Recursive Resolver constructs a DNS reply with the following 585 CHAIN option parameters: 587 o Option-code, set to 13 589 o Option-length, set to 0x00 0x00 591 o The Closest Trust Point is ommited (zero length) 593 The RCODE is set to "NoError". The Authority Section is filled in 594 with: 596 o The DS RRset for "redhat.ca." plus RRSIGs 598 o The DNSKEY RRset for "redhat.ca." plus RRSIGs 600 o The NS RRset for "redhat.ca." plus RRSIGs (eg ns[01].redhat.ca) 602 o The A RRset for "ns0.redhat.ca." and "ns1.redhat.ca." plus RRSIGs 604 o The DS RRset for "toronto.redhat.ca." plus RRSIGs 606 o The NS RRset for "toronto.redhat.ca." plus RRSIGs (eg 607 ns[01].toronto.redhat.ca) 609 o The DNSKEY RRset for "toronto.redhat.ca." plus RRSIGs 610 o The A RRset and/or AAAA RRset for "ns0.toronto.redhat.ca." and 611 "ns1.toronto.redhat.ca." plus RRSIGs 613 o The NSEC record for "ipv6.toronto.redhat.ca." (proves what RRTYPEs 614 do exist, does not include A) 616 o The NSEC record for "toronto.redhat.ca." (proves no wildcard 617 exists) 619 The Answer Section is empty. The RCode is set to NOERROR. 621 10. IANA Considerations 623 10.1. EDNS0 option code for CHAIN 625 IANA has assigned option code 13 in the "DNS EDNS0 Option Codes 626 (OPT)" registry to CHAIN. 628 11. Acknowledgements 630 Andrew Sullivan pointed out that we do not need any new data formats 631 to support DNS chains. Olafur Gudmundsson ensured the RRsets are 632 returned in the proper Sections. Thanks to Tim Wicinski for his 633 thorough review. 635 12. Normative References 637 [EDNS-COOKIE] 638 Eastlake, Donald., "Domain Name System (DNS) Cookies", 639 draft-ietf-dnsop-cookies (work in progress), December 640 2015. 642 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 643 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 644 . 646 [RFC1035] Mockapetris, P., "Domain names - implementation and 647 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 648 November 1987, . 650 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 651 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 652 RFC2119, March 1997, 653 . 655 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 656 Rose, "DNS Security Introduction and Requirements", RFC 657 4033, DOI 10.17487/RFC4033, March 2005, 658 . 660 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 661 Rose, "Resource Records for the DNS Security Extensions", 662 RFC 4034, DOI 10.17487/RFC4034, March 2005, 663 . 665 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 666 Rose, "Protocol Modifications for the DNS Security 667 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 668 . 670 [RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast 671 Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786, 672 December 2006, . 674 [RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure, 675 "TCP Extensions for Multipath Operation with Multiple 676 Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013, 677 . 679 [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms 680 for DNS (EDNS(0))", STD 75, RFC 6891, DOI 10.17487/ 681 RFC6891, April 2013, 682 . 684 [RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running 685 Code: The Implementation Status Section", RFC 6982, DOI 686 10.17487/RFC6982, July 2013, 687 . 689 [RFC7646] Ebersman, P., Kumari, W., Griffiths, C., Livingood, J., 690 and R. Weber, "Definition and Use of DNSSEC Negative Trust 691 Anchors", RFC 7646, DOI 10.17487/RFC7646, September 2015, 692 . 694 [RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 695 Terminology", RFC 7719, DOI 10.17487/RFC7719, December 696 2015, . 698 [TCP-KEEPALIVE] 699 Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The 700 edns-tcp-keepalive EDNS0 Option", draft-ietf-dnsop-edns- 701 tcp-keepalive-05 (work in progress), January 2016. 703 Author's Address 705 Paul Wouters 706 Red Hat 708 Email: pwouters@redhat.com