idnits 2.17.1 draft-ietf-dnssd-push-01.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 == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: A client MUST not send a SUBSCRIBE message that duplicates the name, type and class of an existing active subscription. For the purpose of this matching, the established DNS case-insensitivity for US-ASCII letters applies (e.g., "foo.com" and "Foo.com" are the same). If a server receives such a duplicate SUBSCRIBE message this is an error and the server MUST immediately close the TCP connection. == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: A client MUST not send an UNSUBSCRIBE message that does not exactly match the name, type and class of an existing active subscription. If a server receives such an UNSUBSCRIBE message this is an error and the server MUST immediately close the TCP connection. -- The document date (October 19, 2015) is 3112 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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-28) exists of draft-ietf-tls-tls13-10 ** Obsolete normative reference: RFC 793 (Obsoleted by RFC 9293) ** Obsolete normative reference: RFC 5246 (Obsoleted by RFC 8446) ** Obsolete normative reference: RFC 5966 (Obsoleted by RFC 7766) ** Obsolete normative reference: RFC 6195 (Obsoleted by RFC 6895) == Outdated reference: A later version (-10) exists of draft-ietf-dnssd-hybrid-00 == Outdated reference: A later version (-06) exists of draft-sekar-dns-llq-01 -- Obsolete informational reference (is this intentional?): RFC 5077 (Obsoleted by RFC 8446) -- Obsolete informational reference (is this intentional?): RFC 7525 (Obsoleted by RFC 9325) Summary: 4 errors (**), 0 flaws (~~), 6 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force T. Pusateri 3 Internet-Draft Seeking affiliation 4 Intended status: Standards Track S. Cheshire 5 Expires: April 21, 2016 Apple Inc. 6 October 19, 2015 8 DNS Push Notifications 9 draft-ietf-dnssd-push-01 11 Abstract 13 The Domain Name System (DNS) was designed to efficiently return 14 matching records for queries for data that is relatively static. 15 When those records change frequently, DNS is still efficient at 16 returning the updated results when polled. But there exists no 17 mechanism for a client to be asynchronously notified when these 18 changes occur. This document defines a mechanism for a client to be 19 notified of such changes to DNS records, called DNS Push 20 Notifications. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on April 21, 2016. 39 Copyright Notice 41 Copyright (c) 2015 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 58 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 4. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 4 61 5. State Considerations . . . . . . . . . . . . . . . . . . . . 5 62 6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 6 63 6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 6 64 6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 8 65 6.3. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 10 66 6.4. DNS Push Notification Update Messages . . . . . . . . . . 11 67 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 68 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 69 9. Security Considerations . . . . . . . . . . . . . . . . . . . 14 70 9.1. Security Services . . . . . . . . . . . . . . . . . . . . 14 71 9.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 14 72 9.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 15 73 9.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 15 74 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 75 10.1. Normative References . . . . . . . . . . . . . . . . . . 15 76 10.2. Informative References . . . . . . . . . . . . . . . . . 16 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 79 1. Introduction 81 DNS records may be updated using DNS Update [RFC2136]. Other 82 mechanisms such as a Hybrid Proxy [I-D.ietf-dnssd-hybrid] can also 83 generate changes to a DNS zone. This document specifies a protocol 84 for Unicast DNS clients to subscribe to receive asynchronous 85 notifications of changes to RRSets of interest. It is immediately 86 relevant in the case of DNS Service Discovery [RFC6763] but is not 87 limited to that use case and provides a general DNS mechanism for DNS 88 record change notifications. Familiarity with the DNS protocol and 89 DNS packet formats is assumed [RFC1034] [RFC1035] [RFC6195]. 91 1.1. Requirements Language 93 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 94 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 95 document are to be interpreted as described in "Key words for use in 96 RFCs to Indicate Requirement Levels" [RFC2119]. 98 2. Motivation 100 As the domain name system continues to adapt to new uses and changes 101 in deployment, polling has the potential to burden DNS servers at 102 many levels throughout the network. Other network protocols have 103 successfully deployed a publish/subscribe model to state changes 104 following the Observer design pattern. XMPP Publish-Subscribe 105 [XEP-0060] and Atom [RFC4287] are examples. While DNS servers are 106 generally highly tuned and capable of a high rate of query/response 107 traffic, adding a publish/subscribe model for tracking changes to DNS 108 records can result in more timely notification of changes with 109 reduced CPU usage and lower network traffic. 111 Multicast DNS [RFC6762] implementations always listen on a well known 112 link-local IP multicast group, and new services and updates are sent 113 for all group members to receive. Therefore, Multicast DNS already 114 has asynchronous change notification capability. However, when DNS 115 Service Discovery [RFC6763] is used across a wide area network using 116 Unicast DNS (possibly facilitated via a Hybrid Proxy 117 [I-D.ietf-dnssd-hybrid]) it would be beneficial to have an equivalent 118 capability for Unicast DNS, to allow clients to learn about DNS 119 record changes in a timely manner without polling. 121 DNS Long-Lived Queries (LLQ) [I-D.sekar-dns-llq] is an existing 122 deployed solution to provide asynchronous change notifications. Even 123 though it can be used over TCP, LLQ is defined primarily as a UDP- 124 based protocol, and as such it defines its own equivalents of 125 existing TCP features like the three-way handshake. This document 126 builds on experience gained with the LLQ protocol, with an improved 127 design that uses long-lived TCP connections instead of UDP (and 128 therefore doesn't need to duplicate existing TCP functionality), and 129 adopts the syntax and semantics of DNS Update messages [RFC2136] 130 instead of inventing a new vocabulary of messages to communicate DNS 131 zone changes. 133 3. Overview 135 The existing DNS Update protocol [RFC2136] provides a mechanism for 136 clients to add or delete individual resource records (RRs) or entire 137 resource record sets (RRSets) on the zone's server. Adopting this 138 existing syntax and semantics for DNS Push Notifications allows for 139 messages going in the other direction, from server to client, to 140 communicate changes to a zone. The client first must subscribe for 141 Push Notifications by connecting to the server and sending DNS 142 message(s) indicating the RRSet(s) of interest. When the client 143 loses interest in updates to these records, it unsubscribes. The DNS 144 Push Notification server for a zone is any server capable of 145 generating the correct change notifications for a name. It may be a 146 master, slave, or stealth name server [RFC1996]. 148 DNS Push Notification clients are NOT required to implement DNS 149 Update Prerequisite processing. Prerequisites are used to perform 150 tentative atomic test-and-set type operations on the server, and that 151 concept has no application when it comes to an authoritative server 152 telling a client of changes to DNS records. 154 4. Transport 156 Implementations of DNS Update [RFC2136] MAY use either User Datagram 157 Protocol (UDP) [RFC0768] or Transmission Control Protocol (TCP) 158 [RFC0793] as the transport protocol, in keeping with the historical 159 precedent that DNS queries must first be sent over UDP [RFC1123]. 160 This requirement to use UDP has subsequently been relaxed [RFC5966]. 161 DNS Push Notification is defined only for TCP. DNS Push Notification 162 clients MUST use TCP. 164 Either end of the TCP connection can terminate all of the 165 subscriptions on that connection by simply closing the connection 166 abruptly with a TCP RST. (An individual subscription is terminated 167 by sending an UNSUBSCRIBE message for that specific subscription.) 169 If a client closes the connection, it is signaling that it is no 170 longer interested in receiving updates to any of the records it has 171 subscribed. It is informing the server that the server may release 172 all state information it has been keeping with regards to this 173 client. This may occur because the client computer has been 174 disconnected from the network, has gone to sleep, or the application 175 requiring the records has terminated. 177 If a server closes the connection, it is informing the client that it 178 can no longer provide updates for the subscribed records. This may 179 occur because the server application software or operating system is 180 restarting, the application terminated unexpectedly, the server is 181 undergoing maintenance procedures, or the server is overloaded and 182 can no longer provide the information to all the clients that wish to 183 receive it. The client can try to re-subscribe at a later time or 184 connect to another server supporting DNS Push Notifications for the 185 zone. 187 Connection setup over TCP ensures return reachability and alleviates 188 concerns of state overload at the server through anonymous 189 subscriptions. All subscribers are guaranteed to be reachable by the 190 server by virtue of the TCP three-way handshake. Because TCP SYN 191 flooding attacks are possible with any protocol over TCP, 192 implementers are encouraged to use industry best practices to guard 193 against such attacks [IPJ.9-4-TCPSYN]. 195 Transport Layer Security (TLS) [RFC5246] is well understood and 196 deployed across many protocols running over TCP. It is designed to 197 prevent eavesdropping, tampering, or message forgery. TLS is 198 REQUIRED for every connection between a client subscriber and server 199 in this protocol specification. Additional security measures such as 200 client authentication during TLS negotiation MAY also be employed to 201 increase the trust relationship between client and server. 202 Additional authentication of the SRV target using DNSSEC verification 203 and DANE TLSA records [RFC7673] is strongly encouraged. See below in 204 Section 9.2 for details. 206 5. State Considerations 208 Each DNS Push Notification server is capable and handling some finite 209 number of Push Notification subscriptions. This number will vary 210 from server to server and is based on physical machine 211 characteristics, network bandwidth, and operating system resource 212 allocation. After a client establishes a connection to a DNS server, 213 each record subscription is individually accepted or rejected. 214 Servers may employ various techniques to limit subscriptions to a 215 manageable level. Correspondingly, the client is free to establish 216 simultaneous connections to alternate DNS servers that support DNS 217 Push Notifications for the zone and distribute record subscriptions 218 at its discretion. In this way, both clients and servers can react 219 to resource constraints. Token bucket rate limiting schemes are also 220 effective in providing fairness by a server across numerous client 221 requests. 223 6. Protocol Operation 225 A DNS Push Notification exchange begins with the client discovering 226 the appropriate server, and connecting to it. The client may then 227 add and remove Push Notification subscriptions over this connection. 228 In accordance with the current set of active subscriptions the server 229 sends relevant asynchronous Push Notifications to the client. The 230 exchange terminates when either end closes the TCP connection with a 231 TCP RST. 233 6.1. Discovery 235 The first step in DNS Push Notification subscription is to discover 236 an appropriate DNS server that supports DNS Push Notifications for 237 the desired zone. The client MUST also determine which TCP port on 238 the server is listening for connections, which need not be (and often 239 is not) the typical TCP port 53 used for conventional DNS. 241 1. The client begins the discovery by sending a DNS query to the 242 local resolver with record type SOA [RFC1035] for the name of the 243 record it wishes to subscribe. 245 2. If the SOA record exists, it MUST be returned in the Answer 246 Section of the reply. If not, the server SHOULD include the SOA 247 record for the zone of the requested name in the Authority 248 Section. 250 3. If no SOA record is returned, the client then strips off the 251 leading label from the requested name. If the resulting name has 252 at least one label in it, the client sends a new SOA query and 253 processing continues at step 2 above. If the resulting name is 254 empty (the root label) then this is a network configuration error 255 and the client gives up. The client MAY retry the operation at a 256 later time. 258 4. Once the SOA is known, the client sends a DNS query with type SRV 259 [RFC2782] for the record name "_dns-push._tcp.", where 260 is the owner name of the discovered SOA record. 262 5. If the zone in question does not offer DNS Push Notifications 263 then SRV record MUST NOT exist and the SRV query will return a 264 negative answer. 266 6. If the zone in question is set up to offer DNS Push Notifications 267 then this SRV record MUST exist. The SRV "target" contains the 268 name of the server providing DNS Push Notifications for the zone. 269 The port number on which to contact the server is in the SRV 270 record "port" field. The address(es) of the target host MAY be 271 included in the Additional Section, however, the address records 272 SHOULD be authenticated before use as described below in 273 Section 9.2 [RFC7673]. 275 7. More than one SRV record may be returned. In this case, the 276 "priority" and "weight" values in the returned SRV records are 277 used to determine the order in which to contact the servers for 278 subscription requests. As described in the SRV specification 279 [RFC2782], the server with the lowest "priority" is first 280 contacted. If more than one server has the same "priority", the 281 "weight" is indicates the weighted probability that the client 282 should contact that server. Higher weights have higher 283 probabilities of being selected. If a server is not reachable or 284 is not willing to accept a subscription request, then a 285 subsequent server is to be contacted. 287 If a server closes a DNS Push Notification subscription connection, 288 the client SHOULD repeat the discovery process in order to determine 289 the preferred DNS server for subscriptions at that time. 291 6.2. DNS Push Notification SUBSCRIBE 293 A DNS Push Notification client indicates its desire to receive DNS 294 Push Notifications for a given domain name by sending a SUBSCRIBE 295 request over the established TCP connection to the server. A 296 SUBSCRIBE request is formatted identically to a conventional DNS 297 QUERY request [RFC1035], except that the opcode is SUBSCRIBE (6) 298 instead of QUERY (0). If neither QTYPE nor QCLASS are ANY (255) then 299 this is a specific subscription to changes for the given name, type 300 and class. If one or both of QTYPE or QCLASS are ANY (255) then this 301 subscription matches any type and/or any class, as appropriate. 303 In a SUBSCRIBE request the DNS Header QR bit MUST be zero. 304 If the QR bit is not zero the message is not a SUBSCRIBE request. 306 The AA, TC, RD, RA, Z, AD, and CD bits, the ID field, and the RCODE 307 field, MUST be zero on transmission, and MUST be silently ignored on 308 reception. 310 Like a DNS QUERY request, a SUBSCRIBE request MUST contain exactly 311 one question. Since SUBSCRIBE requests are sent over TCP, multiple 312 SUBSCRIBE requests can be concatenated in a single TCP stream and 313 packed efficiently into TCP segments, so the ability to pack multiple 314 SUBSCRIBE operations into a single DNS message within that TCP stream 315 would add extra complexity for little benefit. 317 ANCOUNT MUST be zero, and the Answer Section MUST be empty. 318 Any records in the Answer Section MUST be silently ignored. 320 NSCOUNT MUST be zero, and the Authority Section MUST be empty. 321 Any records in the Authority Section MUST be silently ignored. 323 ARCOUNT MUST be zero, and the Additional Section MUST be empty. 324 Any records in the Additional Section MUST be silently ignored. 326 Each SUBSCRIBE request generates exactly one SUBSCRIBE response from 327 the server. 329 In the SUBSCRIBE response the RCODE indicates whether or not the 330 subscription was accepted. Supported RCODEs are as follows: 332 +----------+-------+------------------------------------------------+ 333 | Mnemonic | Value | Description | 334 +----------+-------+------------------------------------------------+ 335 | NOERROR | 0 | SUBSCRIBE successful | 336 | FORMERR | 1 | Server failed to process request due to a | 337 | | | malformed request | 338 | SERVFAIL | 2 | Server failed to process request due to | 339 | | | resource exhaustion | 340 | NOTIMP | 4 | Server does not implement DNS Push | 341 | | | Notifications | 342 | REFUSED | 5 | Server refuses to process request for policy | 343 | | | or security reasons | 344 +----------+-------+------------------------------------------------+ 346 Table 1: Response codes 348 In a SUBSCRIBE response the DNS Header QR bit MUST be one. 349 If the QR bit is not one the message is not a SUBSCRIBE response. 351 The AA, TC, RD, RA, Z, AD, and CD bits, and the ID field, MUST be 352 zero on transmission, and MUST be silently ignored on reception. 354 The Question Section MUST echo back the values provided by the client 355 in the SUBSCRIBE request that generated this SUBSCRIBE response. 357 ANCOUNT MUST be zero, and the Answer Section MUST be empty. 358 Any records in the Answer Section MUST be silently ignored. 359 If the subscription was accepted and there are positive answers for 360 the requested name, type and class, then these positive answers MUST 361 be communicated to the client in an immediately following Push 362 Notification Update, not in the Answer Section of the SUBSCRIBE 363 response. This simplifying requirement is made so that there is only 364 a single way that information is communicated to a DNS Push 365 Notification client. Since a DNS Push Notification client has to 366 parse information received via Push Notification Updates anyway, it 367 is simpler if it does not also have to parse information received via 368 the Answer Section of a SUBSCRIBE response. 370 NSCOUNT MUST be zero, and the Authority Section MUST be empty. 371 Any records in the Authority Section MUST be silently ignored. 373 ARCOUNT MUST be zero, and the Additional Section MUST be empty. 375 Any records in the Additional Section MUST be silently ignored. 377 If accepted, the subscription will stay in effect until the client 378 revokes the subscription or until the connection between the client 379 and the server is closed. 381 A client MUST not send a SUBSCRIBE message that duplicates the name, 382 type and class of an existing active subscription. For the purpose 383 of this matching, the established DNS case-insensitivity for US-ASCII 384 letters applies (e.g., "foo.com" and "Foo.com" are the same). If a 385 server receives such a duplicate SUBSCRIBE message this is an error 386 and the server MUST immediately close the TCP connection. 388 DNS wildcarding is not supported. That is, a wildcard ("*") in a 389 SUBSCRIBE message matches only a wildcard ("*") in the zone, and 390 nothing else. 392 Aliasing is not supported. That is, a CNAME in a SUBSCRIBE message 393 matches only a CNAME in the zone, and nothing else. 395 A client may SUBSCRIBE to records that are unknown to the server at 396 the time of the request and this is not an error. The server MUST 397 accept these requests and send Push Notifications if and when matches 398 are found in the future. 400 6.3. DNS Push Notification UNSUBSCRIBE 402 To cancel an individual subscription without closing the entire 403 connection, the client sends an UNSUBSCRIBE message over the 404 established TCP connection to the server. The UNSUBSCRIBE message is 405 formatted identically to the SUBSCRIBE message which created the 406 subscription, with the exact same name, type and class, except that 407 the opcode is UNSUBSCRIBE (7) instead of SUBSCRIBE (6). 409 A client MUST not send an UNSUBSCRIBE message that does not exactly 410 match the name, type and class of an existing active subscription. 411 If a server receives such an UNSUBSCRIBE message this is an error and 412 the server MUST immediately close the TCP connection. 414 No response message is generated as a result of processing an 415 UNSUBSCRIBE message. 417 Having being successfully revoked with a correctly-formatted 418 UNSUBSCRIBE message, the previously referenced subscription is no 419 longer active and the server MAY discard the state associated with it 420 immediately, or later, at the server's discretion. 422 6.4. DNS Push Notification Update Messages 424 Once a subscription has been successfully established, the server 425 generates Push Notification Updates to send to the client as 426 appropriate. An initial Push Notification Update will be sent 427 immediately in the case that the answer set was non-empty at the 428 moment the subscription was established. Subsequent changes to the 429 answer set are then communicated to the client in subsequent Push 430 Notification Updates. 432 The format of Push Notification Updates borrows from the existing DNS 433 Update [RFC2136] protocol, with some simplifications. 435 The following figure shows the existing DNS Update header format: 437 1 1 1 1 1 1 438 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 439 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 440 | ID | 441 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 442 |QR| Opcode | Z | RCODE | 443 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 444 | ZOCOUNT | 445 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 446 | PRCOUNT | 447 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 448 | UPCOUNT | 449 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 450 | ADCOUNT | 451 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 453 Figure 1 455 For DNS Push Notifications the following rules apply: 457 The QR bit MUST be zero, and the Opcode MUST be UPDATE (5). 458 Messages received where this is not true are not Push Notification 459 Update Messages and should be silently ignored for the purposes of 460 Push Notification Update Message handling. 462 ID, the Z bits, and RCODE MUST be zero on transmission, 463 and MUST be silently ignored on reception. 465 ZOCOUNT MUST be zero, and the Zone Section MUST be empty. 466 Any records in the Zone Section MUST be silently ignored. 468 PRCOUNT MUST be zero, and the Prerequisite Section MUST be empty. 469 Any records in the Prerequisite Section MUST be silently ignored. 471 ADCOUNT MUST be zero, and the Additional Data Section MUST be empty. 472 Any records in the Additional Data Section MUST be silently ignored. 474 The Update Section contains the relevant change information for the 475 client, formatted identically to a DNS Update [RFC2136]. To recap: 477 Delete all RRsets from a name: 478 TTL=0, CLASS=ANY, RDLENGTH=0, TYPE=ANY. 480 Delete an RRset from a name: 481 TTL=0, CLASS=ANY, RDLENGTH=0; 482 TYPE specifies the RRset being deleted. 484 Delete an individual RR from a name: 485 TTL=0, CLASS=NONE; 486 TYPE, RDLENGTH and RDATA specifies the RR being deleted. 488 Add an individual RR to a name: 489 TTL, CLASS, TYPE, RDLENGTH and RDATA specifies the RR being added. 491 Upon reception of a Push Notification Update Message, the client 492 receiving the message MUST validate that the records being added or 493 deleted correspond with at least one currently active subscription on 494 that connection. Specifically, the record name MUST match the name 495 given in the SUBSCRIBE request, subject to the usual established DNS 496 case-insensitivity for US-ASCII letters. If the QTYPE was not ANY 497 (255) then the TYPE of the record must match the QTYPE given in the 498 SUBSCRIBE request. If the QCLASS was not ANY (255) then the CLASS of 499 the record must match the QCLASS given in the SUBSCRIBE request. If 500 a matching active subscription on that connection is not found, then 501 that individual record addition/deletion is silently ignored. 502 Processing of other additions and deletions in this message is not 503 affected. The TCP connection is not closed. This is to allow for 504 the race condition where a client sends an outbound UNSUBSCRIBE while 505 inbound Push Notification Updates for that subscription from the 506 server are still in flight. 508 In the case where a single change affects more than one active 509 subscription, only one update is sent. For example, an update adding 510 a given record may match both a SUBSCRIBE request with the same QTYPE 511 and a different SUBSCRIBE request with QTYPE=ANY. It is not the case 512 that two updates are sent because the new record matches two active 513 subscriptions. 515 The server SHOULD encode change notifications in the most efficient 516 manner possible. For example, when three AAAA records are deleted 517 from a given name, and no other AAAA records exist for that name, the 518 server SHOULD send a "delete an RRset from a name" update, not three 519 separate "delete an individual RR from a name" updates. Similarly, 520 when both an SRV and a TXT record are deleted from a given name, and 521 no other records of any kind exist for that name, the server SHOULD 522 send a "delete all RRsets from a name" update, not two separate 523 "delete an RRset from a name" updates. 525 Reception of a Push Notification Update Message results in no 526 response back to the server. 528 The TTL of an added record is stored by the client and decremented as 529 time passes, with the caveat that for as long as a relevant 530 subscription is active, the TTL does not decrement below 1 second. 531 For as long as a relevant subscription remains active, the client 532 SHOULD assume that when a record goes away the server will notify it 533 of that fact. Consequently, a client does not have to poll to verify 534 that the record is still there. Once a subscription is cancelled 535 (individually, or as a result of the TCP connection being closed) 536 record aging resumes and records are removed from the local cache 537 when their TTL reaches zero. 539 7. Acknowledgements 541 The authors would like to thank Kiren Sekar and Marc Krochmal for 542 previous work completed in this field. This draft has been improved 543 due to comments from Ran Atkinson. 545 8. IANA Considerations 547 This document defines the service name: "_dns-push._tcp". 548 It is only applicable for the TCP protocol. 549 This name is to be published in the IANA Service Name Registry. 551 This document defines two DNS OpCodes: SUBSCRIBE with (tentative) 552 value 6 and UNSUBSCRIBE with (tentative) value 7. 554 9. Security Considerations 556 TLS support is mandatory in DNS Push Notifications. There is no 557 provision for opportunistic encryption using a mechanism like 558 "STARTTLS". 560 9.1. Security Services 562 It is the goal of using TLS to provide the following security 563 services: 565 Confidentiality All application-layer communication is encrypted 566 with the goal that no party should be able to decrypt it except 567 the intended receiver. 569 Data integrity protection Any changes made to the communication in 570 transit are detectable by the receiver. 572 Authentication An end-point of the TLS communication is 573 authenticated as the intended entity to communicate with. 575 Deployment recommendations on the appropriate key lengths and cypher 576 suites are beyond the scope of this document. Please refer to TLS 577 Recommendations [RFC7525] for the best current practices. Keep in 578 mind that best practices only exist for a snapshot in time and 579 recommendations will continue to change. Updated versions or errata 580 may exist for these recommendations. 582 9.2. TLS Name Authentication 584 As described in Section 6.1, the client discovers the DNS Push 585 Notification server using an SRV lookup for the record name "_dns- 586 push._tcp.". The server connection endpoint SHOULD then be 587 authenticated using DANE TLSA records for the associated SRV record. 588 This associates the target's name and port number with a trusted TLS 589 certificate [RFC7673]. This procedure uses the TLS Sever Name 590 Indication (SNI) extension [RFC6066] to inform the server of the name 591 the client has authenticated through the use of TLSA records. 592 Therefore, if the SRV record passes DNSSEC validation and a TLSA 593 record matching the target name is useable, an SNI extension MUST be 594 used for the target name to ensure the client is connecting to the 595 server it has authenticated. If the target name does not have a 596 usable TLSA record, then the use of the SNI extension is optional. 598 9.3. TLS Compression 600 In order to reduce the chances of compression related attacks, TLS- 601 level compression SHOULD be disabled when using TLS versions 1.2 and 602 earlier. In the draft version of TLS 1.3 [I-D.ietf-tls-tls13], TLS- 603 level compression has been removed completely. 605 9.4. TLS Session Resumption 607 TLS Session Resumption is permissible on DNS Push Notification 608 servers. The server may keep TLS state with Session IDs [RFC5246] or 609 operate in stateless mode by sending a Session Ticket [RFC5077] to 610 the client for it to store. However, once the connection is closed, 611 any existing subscriptions will be dropped. When the TLS session is 612 resumed, the DNS Push Notification server will not have any 613 subscription state and will proceed as with any other new connection. 615 10. References 617 10.1. Normative References 619 [I-D.ietf-tls-tls13] 620 Rescorla, E., "The Transport Layer Security (TLS) Protocol 621 Version 1.3", draft-ietf-tls-tls13-10 (work in progress), 622 October 2015. 624 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 625 DOI 10.17487/RFC0768, August 1980, 626 . 628 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 629 RFC 793, DOI 10.17487/RFC0793, September 1981, 630 . 632 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 633 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 634 . 636 [RFC1035] Mockapetris, P., "Domain names - implementation and 637 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 638 November 1987, . 640 [RFC1123] Braden, R., Ed., "Requirements for Internet Hosts - 641 Application and Support", STD 3, RFC 1123, 642 DOI 10.17487/RFC1123, October 1989, 643 . 645 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 646 Requirement Levels", BCP 14, RFC 2119, 647 DOI 10.17487/RFC2119, March 1997, 648 . 650 [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, 651 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 652 RFC 2136, DOI 10.17487/RFC2136, April 1997, 653 . 655 [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for 656 specifying the location of services (DNS SRV)", RFC 2782, 657 DOI 10.17487/RFC2782, February 2000, 658 . 660 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 661 (TLS) Protocol Version 1.2", RFC 5246, 662 DOI 10.17487/RFC5246, August 2008, 663 . 665 [RFC5966] Bellis, R., "DNS Transport over TCP - Implementation 666 Requirements", RFC 5966, DOI 10.17487/RFC5966, August 667 2010, . 669 [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) 670 Extensions: Extension Definitions", RFC 6066, 671 DOI 10.17487/RFC6066, January 2011, 672 . 674 [RFC6195] Eastlake 3rd, D., "Domain Name System (DNS) IANA 675 Considerations", RFC 6195, DOI 10.17487/RFC6195, March 676 2011, . 678 [RFC7673] Finch, T., Miller, M., and P. Saint-Andre, "Using DNS- 679 Based Authentication of Named Entities (DANE) TLSA Records 680 with SRV Records", RFC 7673, DOI 10.17487/RFC7673, October 681 2015, . 683 10.2. Informative References 685 [I-D.ietf-dnssd-hybrid] 686 Cheshire, S., "Hybrid Unicast/Multicast DNS-Based Service 687 Discovery", draft-ietf-dnssd-hybrid-00 (work in progress), 688 November 2014. 690 [I-D.sekar-dns-llq] 691 Sekar, K., "DNS Long-Lived Queries", draft-sekar-dns- 692 llq-01 (work in progress), August 2006. 694 [IPJ.9-4-TCPSYN] 695 Eddy, W., "Defenses Against TCP SYN Flooding Attacks", The 696 Internet Protocol Journal, Cisco Systems, Volume 9, 697 Number 4, December 2006. 699 [RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone 700 Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996, 701 August 1996, . 703 [RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom 704 Syndication Format", RFC 4287, DOI 10.17487/RFC4287, 705 December 2005, . 707 [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, 708 "Transport Layer Security (TLS) Session Resumption without 709 Server-Side State", RFC 5077, DOI 10.17487/RFC5077, 710 January 2008, . 712 [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, 713 DOI 10.17487/RFC6762, February 2013, 714 . 716 [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service 717 Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, 718 . 720 [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, 721 "Recommendations for Secure Use of Transport Layer 722 Security (TLS) and Datagram Transport Layer Security 723 (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 724 2015, . 726 [XEP-0060] 727 Millard, P., Saint-Andre, P., and R. Meijer, "Publish- 728 Subscribe", XSF XEP 0060, July 2010. 730 Authors' Addresses 732 Tom Pusateri 733 Seeking affiliation 734 Hilton Head Island, SC 735 USA 737 Phone: +1 843 473 7394 738 Email: pusateri@bangj.com 739 Stuart Cheshire 740 Apple Inc. 741 1 Infinite Loop 742 Cupertino, CA 95014 743 USA 745 Phone: +1 408 974 3207 746 Email: cheshire@apple.com