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Checking references for intended status: Experimental ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 5077 (Obsoleted by RFC 8446) ** Obsolete normative reference: RFC 6347 (Obsoleted by RFC 9147) ** Obsolete normative reference: RFC 7525 (Obsoleted by RFC 9325) == Outdated reference: A later version (-11) exists of draft-ietf-dprive-dtls-and-tls-profiles-07 == Outdated reference: A later version (-01) exists of draft-rescorla-tls-dtls13-00 -- Obsolete informational reference (is this intentional?): RFC 7626 (Obsoleted by RFC 9076) Summary: 3 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DPRIVE T. Reddy 3 Internet-Draft Cisco 4 Intended status: Experimental D. Wing 5 Expires: June 19, 2017 6 P. Patil 7 Cisco 8 December 16, 2016 10 Specification for DNS over Datagram Transport Layer Security (DTLS) 11 draft-ietf-dprive-dnsodtls-15 13 Abstract 15 DNS queries and responses are visible to network elements on the path 16 between the DNS client and its server. These queries and responses 17 can contain privacy-sensitive information which is valuable to 18 protect. 20 This document proposes the use of Datagram Transport Layer Security 21 (DTLS) for DNS, to protect against passive listeners and certain 22 active attacks. As latency is critical for DNS, this proposal also 23 discusses mechanisms to reduce DTLS round trips and reduce DTLS 24 handshake size. The proposed mechanism runs over port 853. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at http://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on June 19, 2017. 43 Copyright Notice 45 Copyright (c) 2016 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 61 1.1. Relationship to TCP Queries and to DNSSEC . . . . . . . . 3 62 1.2. Document Status . . . . . . . . . . . . . . . . . . . . . 3 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 3. Establishing and Managing DNS-over-DTLS Sessions . . . . . . 4 65 3.1. Session Initiation . . . . . . . . . . . . . . . . . . . 4 66 3.2. DTLS Handshake and Authentication . . . . . . . . . . . . 5 67 3.3. Established Sessions . . . . . . . . . . . . . . . . . . 5 68 4. Performance Considerations . . . . . . . . . . . . . . . . . 6 69 5. PMTU issues . . . . . . . . . . . . . . . . . . . . . . . . . 7 70 6. Anycast . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 71 7. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 72 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 73 9. Security Considerations . . . . . . . . . . . . . . . . . . . 9 74 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 75 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 76 11.1. Normative References . . . . . . . . . . . . . . . . . . 10 77 11.2. Informative References . . . . . . . . . . . . . . . . . 11 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 80 1. Introduction 82 The Domain Name System is specified in [RFC1034] and [RFC1035]. DNS 83 queries and responses are normally exchanged unencrypted and are thus 84 vulnerable to eavesdropping. Such eavesdropping can result in an 85 undesired entity learning domains that a host wishes to access, thus 86 resulting in privacy leakage. The DNS privacy problem is further 87 discussed in [RFC7626]. 89 This document defines DNS over DTLS (DNS-over-DTLS) which provides 90 confidential DNS communication between stub resolvers and recursive 91 resolvers, stub resolvers and forwarders, forwarders and recursive 92 resolvers. DNS-over-DTLS puts an additional computational load on 93 servers. The largest gain for privacy is to protect the 94 communication between the DNS client (the end user's machine) and its 95 caching resolver. DNS-over-DTLS might work equally between recursive 96 clients and authoritative servers, but this application of the 97 protocol is out of scope for the DNS PRIVate Exchange (DPRIVE) 98 Working Group per its current charter. This document does not change 99 the format of DNS messages. 101 The motivations for proposing DNS-over-DTLS are that 103 o TCP suffers from network head-of-line blocking, where the loss of 104 a packet causes all other TCP segments to not be delivered to the 105 application until the lost packet is re-transmitted. DNS-over- 106 DTLS, because it uses UDP, does not suffer from network head-of- 107 line blocking. 109 o DTLS session resumption consumes 1 round trip whereas TLS session 110 resumption can start only after TCP handshake is complete. 111 However, with TCP Fast Open [RFC7413], the implementation can 112 achieve the same RTT efficiency as DTLS. 114 Note: DNS-over-DTLS is an experimental update to DNS, and the 115 experiment will be concluded when the specification is evaluated 116 through implementations and interoperability testing. 118 1.1. Relationship to TCP Queries and to DNSSEC 120 DNS queries can be sent over UDP or TCP. The scope of this document, 121 however, is only UDP. DNS over TCP can be protected with TLS, as 122 described in [RFC7858]. DNS-over-DTLS alone cannot provide privacy 123 for DNS messages in all circumstances, specifically when the DTLS 124 record size is larger than the path MTU. In such situations the DNS 125 server will respond with a truncated response (see Section 5). 126 Therefore DNS clients and servers that implement DNS-over-DTLS MUST 127 also implement DNS-over-TLS in order to provide privacy for clients 128 that desire Strict Privacy as described in 129 [I-D.ietf-dprive-dtls-and-tls-profiles]. 131 DNS Security Extensions (DNSSEC [RFC4033]) provides object integrity 132 of DNS resource records, allowing end-users (or their resolver) to 133 verify legitimacy of responses. However, DNSSEC does not provide 134 privacy for DNS requests or responses. DNS-over-DTLS works in 135 conjunction with DNSSEC, but DNS-over-DTLS does not replace the need 136 or value of DNSSEC. 138 1.2. Document Status 140 This document is an Experimental RFC. One key aspect to judge 141 whether the approach is usable on a large scale is by observing the 142 uptake, usability, and operational behavior of the protocol in large- 143 scale, real-life deployments. 145 This DTLS solution was considered by the DPRIVE working group as an 146 option to use in case the TLS based approach specified in [RFC7858] 147 turns out to have some issues when deployed. At the time of writing, 148 it is expected that [RFC7858] is what will be deployed, and so this 149 specification is mainly intended as a backup. 151 The following guidelines should be considered when performance 152 benchmarking DNS over DTLS: 154 1. DNS over DTLS can recover from packet loss and reordering, and 155 does not suffer from network head-of-line blocking. DNS over 156 DTLS performance in comparison with DNS over TLS may be better in 157 lossy networks. 159 2. The number of round trips to send the first DNS query over DNS 160 over DTLS is less than the number of round trips to send the 161 first DNS query over TLS. Even if TCP Fast Open is used, it only 162 works for subsequent TCP connections between the DNS client and 163 server (Section 3 in [RFC7413]). 165 3. If DTLS 1.3 protocol [I-D.rescorla-tls-dtls13] is used for DNS 166 over DTLS, it provides critical latency improvements for 167 connection establishment over DTLS 1.2. 169 2. Terminology 171 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 172 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 173 "OPTIONAL" in this document are to be interpreted as described in 174 [RFC2119] . 176 3. Establishing and Managing DNS-over-DTLS Sessions 178 3.1. Session Initiation 180 By default, DNS-over-DTLS MUST run over standard UDP port 853 as 181 defined in Section 8, unless the DNS server has mutual agreement with 182 its clients to use a port other than 853 for DNS-over-DTLS. In order 183 to use a port other than 853, both clients and servers would need a 184 configuration option in their software. 186 The DNS client should determine if the DNS server supports DNS-over- 187 DTLS by sending a DTLS ClientHello message to port 853 on the server, 188 unless it has mutual agreement with its server to use a port other 189 than port 853 for DNS-over-DTLS. Such another port MUST NOT be port 190 53 but MAY be from the "first-come, first-served" port range (User 191 Ports [RFC6335], range 1024- 49151) . This recommendation against use 192 of port 53 for DNS-over-DTLS is to avoid complication in selecting 193 use or non-use of DTLS and to reduce risk of downgrade attacks. 195 A DNS server that does not support DNS-over-DTLS will not respond to 196 ClientHello messages sent by the client. If no response is received 197 from that server, and the client has no better round-trip estimate, 198 the client SHOULD retransmit the DTLS ClientHello according to 199 Section 4.2.4.1 of [RFC6347]. After 15 seconds, it SHOULD cease 200 attempts to re-transmit its ClientHello. The client MAY repeat that 201 procedure to discover if DNS-over-DTLS service becomes available from 202 the DNS server, but such probing SHOULD NOT be done more frequently 203 than every 24 hours and MUST NOT be done more frequently than every 204 15 minutes. This mechanism requires no additional signaling between 205 the client and server. 207 DNS clients and servers MUST NOT use port 853 to transport cleartext 208 DNS messages. DNS clients MUST NOT send and DNS servers MUST NOT 209 respond to cleartext DNS messages on any port used for DNS-over-DTLS 210 (including, for example, after a failed DTLS handshake). There are 211 significant security issues in mixing protected and unprotected data, 212 therefore UDP connections on a port designated by a given server for 213 DNS-over-DTLS are reserved purely for encrypted communications. 215 3.2. DTLS Handshake and Authentication 217 DNS client initiates DTLS handshake as described in [RFC6347], 218 following the best practices specified in [RFC7525]. After DTLS 219 negotiation completes, if the DTLS handshake succeeds according to 220 [RFC6347] the connection will be encrypted and is now protected from 221 eavesdropping. 223 DNS privacy requires encrypting the query (and response) from passive 224 attacks. Such encryption typically provides integrity protection as 225 a side-effect, which means on-path attackers cannot simply inject 226 bogus DNS responses. However, to provide stronger protection from 227 active attackers pretending to be the server, the server itself needs 228 to be authenticated. To authenticate the server providing DNS 229 privacy, DNS client MUST use the authenication mechanisms discussed 230 in [I-D.ietf-dprive-dtls-and-tls-profiles]. This document does not 231 propose new ideas for authentication. 233 3.3. Established Sessions 235 In DTLS, all data is protected using the same record encoding and 236 mechanisms. When the mechanism described in this document is in 237 effect, DNS messages are encrypted using the standard DTLS record 238 encoding. When a user of DTLS wishes to send a DNS message, the data 239 is delivered to the DTLS implementation as an ordinary application 240 data write (e.g., SSL_write()). A single DTLS session can be used to 241 send multiple DNS requests and receive multiple DNS responses. 243 To mitigate the risk of unintentional server overload, DNS-over-DTLS 244 clients MUST take care to minimize the number of concurrent DTLS 245 sessions made to any individual server. It is RECOMMENDED that for 246 any given client/server interaction there SHOULD be no more than one 247 DTLS session. Similarly, servers MAY impose limits on the number of 248 concurrent DTLS sessions being handled for any particular client IP 249 address or subnet. These limits SHOULD be much looser than the 250 client guidelines above, because the server does not know, for 251 example, if a client IP address belongs to a single client, is 252 multiple resolvers on a single machine, or is multiple clients behind 253 a device performing Network Address Translation (NAT). 255 In between normal DNS traffic while the communication to the DNS 256 server is quiescent, the DNS client MAY want to probe the server 257 using DTLS heartbeat [RFC6520] to ensure it has maintained 258 cryptographic state. Such probes can also keep alive firewall or NAT 259 bindings. This probing reduces the frequency of needing a new 260 handshake when a DNS query needs to be resolved, improving the user 261 experience at the cost of bandwidth and processing time. 263 A DTLS session is terminated by the receipt of an authenticated 264 message that closes the connection (e.g., a DTLS fatal alert). If 265 the server has lost state, a DTLS handshake needs to be initiated 266 with the server. For the server, to mitigate the risk of 267 unintentional server overload, it is RECOMMENDED that the default 268 DNS-over-DTLS server application-level idle time be set to several 269 seconds and not set to less than a second, but no particular value is 270 specified. When no DNS queries have been received from the client 271 after idle time out, the server MUST send a DTLS fatal alert and then 272 destroy its DTLS state. The DTLS fatal alert packet indicates the 273 server has destroyed its state, signaling to the client if it wants 274 to send a new DTLS message it will need to re-establish cryptographic 275 context with the server (via full DTLS handshake or DTLS session 276 resumption). In practice, the idle period can vary dynamically, and 277 servers MAY allow idle connections to remain open for longer periods 278 as resources permit. 280 4. Performance Considerations 282 DTLS protocol profile for DNS-over-DTLS is discussed in Section 11 of 283 [I-D.ietf-dprive-dtls-and-tls-profiles]. To reduce the number of 284 octets of the DTLS handshake, especially the size of the certificate 285 in the ServerHello (which can be several kilobytes), DNS clients and 286 servers can use raw public keys [RFC7250] or Cached Information 287 Extension [RFC7924]. Cached Information Extension avoids 288 transmitting the server's certificate and certificate chain if the 289 client has cached that information from a previous TLS handshake. 290 TLS False Start [RFC7918] can reduce round-trips by allowing the TLS 291 second flight of messages (ChangeCipherSpec) to also contain the 292 (encrypted) DNS query. 294 It is highly advantageous to avoid server-side DTLS state and reduce 295 the number of new DTLS sessions on the server which can be done with 296 TLS Session Resumption without server state [RFC5077]. This also 297 eliminates a round-trip for subsequent DNS-over-DTLS queries, because 298 with [RFC5077] the DTLS session does not need to be re-established. 300 Since responses within a DTLS session can arrive out of order, 301 clients MUST match responses to outstanding queries on the same DTLS 302 connection using the DNS Message ID. If the response contains a 303 question section, the client MUST match the QNAME, QCLASS, and QTYPE 304 fields. Failure by clients to properly match responses to 305 outstanding queries can have serious consequences for 306 interoperability ( [RFC7766], Section 7). 308 5. PMTU issues 310 Compared to normal DNS, DTLS adds at least 13 octets of header, plus 311 cipher and authentication overhead to every query and every response. 312 This reduces the size of the DNS payload that can be carried. DNS 313 client and server MUST support the EDNS0 option defined in [RFC6891] 314 so that the DNS client can indicate to the DNS server the maximum DNS 315 response size it can reassemble and deliver in the DNS client's 316 network stack. If the DNS client does set the EDNS0 option defined 317 in [RFC6891] then the maximum DNS response size of 512 bytes plus 318 DTLS overhead will be well within the Path MTU. If the Path MTU is 319 not known, an IP MTU of 1280 bytes SHOULD be assumed. The client 320 sets its EDNS0 value as if DTLS is not being used. The DNS server 321 MUST ensure that the DNS response size does not exceed the Path MTU 322 i.e. each DTLS record MUST fit within a single datagram, as required 323 by [RFC6347]. The DNS server must consider the amount of record 324 expansion expected by the DTLS processing when calculating the size 325 of DNS response that fits within the path MTU. Path MTU MUST be 326 greater than or equal to [DNS response size + DTLS overhead of 13 327 octets + padding size ([RFC7830]) + authentication overhead of the 328 negotiated DTLS cipher suite + block padding (Section 4.1.1.1 of 329 [RFC6347]]. If the DNS server's response were to exceed that 330 calculated value, the server MUST send a response that does fit 331 within that value and sets the TC (truncated) bit. Upon receiving a 332 response with the TC bit set and wanting to receive the entire 333 response, the client behaviour is governed by the current Usage 334 profile [I-D.ietf-dprive-dtls-and-tls-profiles]. For Strict Privacy 335 the client MUST only send a new DNS request for the same resource 336 record over an encrypted transport (e.g. DNS-over-TLS [RFC7858]). 337 Clients using Opportunistic Privacy SHOULD try for the best case (an 338 encrypted and authenticated transport) but MAY fallback to 339 intermediate cases and eventually the worst case scenario (clear 340 text) in order to obtain a response. 342 6. Anycast 344 DNS servers are often configured with anycast addresses. While the 345 network is stable, packets transmitted from a particular source to an 346 anycast address will reach the same server that has the cryptographic 347 context from the DNS-over-DTLS handshake. But when the network 348 configuration or routing changes, a DNS-over-DTLS packet can be 349 received by a server that does not have the necessary cryptographic 350 context. Clients using DNS-over-DTLS need to always be prepared to 351 re-initiate DTLS handshake and in the worst case this could even 352 happen immediately after re-initiating a new handshake. To encourage 353 the client to initiate a new DTLS handshake, DNS servers SHOULD 354 generate a DTLS fatal alert message in response to receiving a DTLS 355 packet for which the server does not have any cryptographic context. 356 Upon receipt of an un-authenicated DTLS fatal alert, the DTLS client 357 validates the fatal alert is within the replay window 358 (Section 4.1.2.6 of [RFC6347]). It is difficult for the DTLS client 359 to validate that the DTLS fatal alert was generated by the DTLS 360 server in response to a request or was generated by an on- or off- 361 path attacker. Thus, upon receipt of an in-window DTLS fatal alert, 362 the client SHOULD continue re-transmitting the DTLS packet (in the 363 event the fatal alert was spoofed), and at the same time it SHOULD 364 initiate DTLS session resumption. When the DTLS client receives an 365 authenticated DNS response from one of those DTLS sessions, the other 366 DTLS session should be terminated. 368 7. Usage 370 Two Usage Profiles, Strict and Opportunistic are explained in 371 [I-D.ietf-dprive-dtls-and-tls-profiles]. Using encrypted DNS 372 messages with an authenticated server is most preferred, encrypted 373 DNS messages with an unauthenticated server is next preferred, and 374 plain text DNS messages is least preferred. 376 8. IANA Considerations 378 This specification uses port 853 already allocated in the IANA port 379 number registry as defined in Section 6 of [RFC7858]. 381 9. Security Considerations 383 The interaction between a DNS client and DNS server requires Datagram 384 Transport Layer Security (DTLS) with a ciphersuite offering 385 confidentiality protection. The guidance given in [RFC7525] MUST be 386 followed to avoid attacks on DTLS. The DNS client SHOULD use the TLS 387 Certificate Status Request extension (Section 8 of [RFC6066]), 388 commonly called "OCSP stapling" to check the revocation status of 389 public key certificate of the DNS server. OCSP stapling, unlike OCSP 390 [RFC6960], does not suffer from scale and privacy issues. DNS 391 clients keeping track of servers known to support DTLS enables 392 clients to detect downgrade attacks. To interfere with DNS-over- 393 DTLS, an on- or off-path attacker might send an ICMP message towards 394 the DTLS client or DTLS server. As these ICMP messages cannot be 395 authenticated, all ICMP errors should be treated as soft errors 396 [RFC1122]. If the DNS query was sent over DTLS then the 397 corresponding DNS response MUST only be accepted if it is received 398 over the same DTLS connection. This behavior mitigates all possible 399 attacks described in Measures for Making DNS More Resilient against 400 Forged Answers [RFC5452]. Security considerations in [RFC6347] and 401 [I-D.ietf-dprive-dtls-and-tls-profiles] are to be taken into account. 403 A malicious client might attempt to perform a high number of DTLS 404 handshakes with a server. As the clients are not uniquely identified 405 by the protocol and can be obfuscated with IPv4 address sharing and 406 with IPv6 temporary addresses, a server needs to mitigate the impact 407 of such an attack. Such mitigation might involve rate limiting 408 handshakes from a certain subnet or more advanced DoS/DDoS techniques 409 beyond the scope of this paper. 411 10. Acknowledgements 413 Thanks to Phil Hedrick for his review comments on TCP and to Josh 414 Littlefield for pointing out DNS-over-DTLS load on busy servers (most 415 notably root servers). The authors would like to thank Simon 416 Josefsson, Daniel Kahn Gillmor, Bob Harold, Ilari Liusvaara, Sara 417 Dickinson, Christian Huitema, Stephane Bortzmeyer, Alexander 418 Mayrhofer, Allison Mankin, Jouni Korhonen, Stephen Farrell, Mirja 419 Kuehlewind, Benoit Claise and Geoff Huston for discussions and 420 comments on the design of DNS-over-DTLS. The authors would like to 421 give special thanks to Sara Dickinson for her help. 423 11. References 424 11.1. Normative References 426 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 427 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 428 . 430 [RFC1035] Mockapetris, P., "Domain names - implementation and 431 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 432 November 1987, . 434 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 435 Requirement Levels", BCP 14, RFC 2119, 436 DOI 10.17487/RFC2119, March 1997, 437 . 439 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 440 Rose, "DNS Security Introduction and Requirements", 441 RFC 4033, DOI 10.17487/RFC4033, March 2005, 442 . 444 [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, 445 "Transport Layer Security (TLS) Session Resumption without 446 Server-Side State", RFC 5077, DOI 10.17487/RFC5077, 447 January 2008, . 449 [RFC5452] Hubert, A. and R. van Mook, "Measures for Making DNS More 450 Resilient against Forged Answers", RFC 5452, 451 DOI 10.17487/RFC5452, January 2009, 452 . 454 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 455 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 456 January 2012, . 458 [RFC6520] Seggelmann, R., Tuexen, M., and M. Williams, "Transport 459 Layer Security (TLS) and Datagram Transport Layer Security 460 (DTLS) Heartbeat Extension", RFC 6520, 461 DOI 10.17487/RFC6520, February 2012, 462 . 464 [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms 465 for DNS (EDNS(0))", STD 75, RFC 6891, 466 DOI 10.17487/RFC6891, April 2013, 467 . 469 [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, 470 "Recommendations for Secure Use of Transport Layer 471 Security (TLS) and Datagram Transport Layer Security 472 (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 473 2015, . 475 [RFC7830] Mayrhofer, A., "The EDNS(0) Padding Option", RFC 7830, 476 DOI 10.17487/RFC7830, May 2016, 477 . 479 11.2. Informative References 481 [I-D.ietf-dprive-dtls-and-tls-profiles] 482 Dickinson, S., Gillmor, D., and T. Reddy, "Authentication 483 and (D)TLS Profile for DNS-over-(D)TLS", draft-ietf- 484 dprive-dtls-and-tls-profiles-07 (work in progress), 485 October 2016. 487 [I-D.rescorla-tls-dtls13] 488 Rescorla, E. and H. Tschofenig, "The Datagram Transport 489 Layer Security (DTLS) Protocol Version 1.3", draft- 490 rescorla-tls-dtls13-00 (work in progress), October 2016. 492 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 493 Communication Layers", STD 3, RFC 1122, 494 DOI 10.17487/RFC1122, October 1989, 495 . 497 [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) 498 Extensions: Extension Definitions", RFC 6066, 499 DOI 10.17487/RFC6066, January 2011, 500 . 502 [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. 503 Cheshire, "Internet Assigned Numbers Authority (IANA) 504 Procedures for the Management of the Service Name and 505 Transport Protocol Port Number Registry", BCP 165, 506 RFC 6335, DOI 10.17487/RFC6335, August 2011, 507 . 509 [RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A., 510 Galperin, S., and C. Adams, "X.509 Internet Public Key 511 Infrastructure Online Certificate Status Protocol - OCSP", 512 RFC 6960, DOI 10.17487/RFC6960, June 2013, 513 . 515 [RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J., 516 Weiler, S., and T. Kivinen, "Using Raw Public Keys in 517 Transport Layer Security (TLS) and Datagram Transport 518 Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250, 519 June 2014, . 521 [RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP 522 Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, 523 . 525 [RFC7626] Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626, 526 DOI 10.17487/RFC7626, August 2015, 527 . 529 [RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and 530 D. Wessels, "DNS Transport over TCP - Implementation 531 Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016, 532 . 534 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., 535 and P. Hoffman, "Specification for DNS over Transport 536 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 537 2016, . 539 [RFC7918] Langley, A., Modadugu, N., and B. Moeller, "Transport 540 Layer Security (TLS) False Start", RFC 7918, 541 DOI 10.17487/RFC7918, August 2016, 542 . 544 [RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security 545 (TLS) Cached Information Extension", RFC 7924, 546 DOI 10.17487/RFC7924, July 2016, 547 . 549 Authors' Addresses 551 Tirumaleswar Reddy 552 Cisco Systems, Inc. 553 Cessna Business Park, Varthur Hobli 554 Sarjapur Marathalli Outer Ring Road 555 Bangalore, Karnataka 560103 556 India 558 Email: tireddy@cisco.com 559 Dan Wing 561 Email: dwing-ietf@fuggles.com 563 Prashanth Patil 564 Cisco Systems, Inc. 565 Bangalore 566 India 568 Email: praspati@cisco.com