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MUST try each indicated authoritati...' RFC 2119 keyword, line 141: '... A resolver SHOULD keep a DNS with e...' (7 more instances...) Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (16 June 2021) is 1044 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. Checking references for intended status: Experimental ---------------------------------------------------------------------------- == Outdated reference: A later version (-04) exists of draft-schwartz-svcb-dns-03 == Outdated reference: A later version (-12) exists of draft-ietf-dnsop-svcb-https-06 == Outdated reference: A later version (-04) exists of draft-ietf-dprive-unauth-to-authoritative-01 Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group P. van Dijk 3 Internet-Draft PowerDNS 4 Intended status: Experimental P. Hoffman 5 Expires: 18 December 2021 ICANN 6 16 June 2021 8 Common Features for Encrypted Recursive to Authoritative DNS 9 draft-pp-dprive-common-features-02 11 Abstract 13 Encryption between recursive and authoritative DNS servers is 14 currently being defined in two modes: unauthenticated and fully- 15 authenticated. These two modes have some features in common, and 16 this document defines those common features so that the documents 17 defining the modes do not need to point to each other. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at https://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on 18 December 2021. 36 Copyright Notice 38 Copyright (c) 2021 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 43 license-info) in effect on the date of publication of this document. 44 Please review these documents carefully, as they describe your rights 45 and restrictions with respect to this document. Code Components 46 extracted from this document must include Simplified BSD License text 47 as described in Section 4.e of the Trust Legal Provisions and are 48 provided without warranty as described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 2. Discovery of Authoritative Server Encryption . . . . . . . . 3 54 2.1. DNS SVCB Records . . . . . . . . . . . . . . . . . . . . 3 55 3. Processing Discovery Responses . . . . . . . . . . . . . . . 3 56 3.1. Resolver Process as Pseudocode . . . . . . . . . . . . . 4 57 4. Serving with Encryption . . . . . . . . . . . . . . . . . . . 5 58 5. Resolvers Reporting Errors to Authoritative Servers . . . . . 6 59 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 60 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 61 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 62 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 63 9.1. Normative References . . . . . . . . . . . . . . . . . . 6 64 9.2. Informative References . . . . . . . . . . . . . . . . . 7 65 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 67 1. Introduction 69 The DPRIVE Working Group in the IETF is working on standardizing 70 methods for encrypted communication between DNS recursive resolvers 71 and authoritative servers. At the time of this writing, [UNAUTH] is 72 a work item in the working group, and [FULL-AUTH] has been widely 73 discussed. The working group expressed a desire that the modes share 74 as much design as possible to simplify the working group's process of 75 evaluating the security and operational aspects of the methods. If 76 the DPRIVE Working Group later adopts other modes, those modes should 77 be considered in this document. 79 This document lists the major technical features that are shared by 80 [UNAUTH] and [FULL-AUTH]. Differences from the common features in 81 this document are listed in the respective method documents. The 82 following are the features in common between and [UNAUTH] and 83 [FULL-AUTH]: 85 * Discovery of an authoritative server's encryption support 86 (Section 2) 88 * Order of processing discovered authoritative servers (Section 3) 90 * Serving with Encryption (Section 4) 92 Other topics might be added as the working group discusses [UNAUTH] 93 and [FULL-AUTH] (and maybe other methods). 95 2. Discovery of Authoritative Server Encryption 97 This section describes methods for resolvers to discover whether an 98 authoritative server supports encryption. At the current time, there 99 is only one method listed. 101 2.1. DNS SVCB Records 103 An authoritative server that supports DNS with encryption makes 104 itself discoverable by publishing one or more DNS SVCB records that 105 contain "alpn" parameter keys. SVCB records are defined in [SVCB], 106 and the DNS extension to those records is defined in [DNS-SVCB]. 108 A recursive resolver discovers whether an authoritative server 109 supports DNS with encryption by looking for cached SVCB records for 110 the name of the authoritative server with a positive answer. A 111 cached DNS SVCB record with a negative answer indicates that the 112 authoritative server does not support any encrypted transport. 114 3. Processing Discovery Responses 116 After a resolver has DNS SCVB records in its cache (possibly due to 117 having just queried for them), it needs to use those records to try 118 to find an authoritative server that uses DNS with encryption. This 119 section describes how the resolver can make that selection. 121 A resolver MUST NOT attempt encryption for a server that has a 122 negative response in its cache for the associated DNS SVCB record. 124 After sending out all requests for SVCB records for the authoritative 125 servers in the NS RRset for a name, if all of the SVCB records for 126 those authoritative servers in the cache are negative responses, the 127 resolver MUST use classic (unencrypted) DNS instead of encryption. 128 Similarly, if none of the DNS SVCB records for the authoritative 129 servers in the cache have supported "alpn" parameters, the resolver 130 MUST use classic (unencrypted) DNS instead of encryption. 132 If there are any DNS SVCB records in the cache for the authoritative 133 servers for a zone with supported "alpn" parameters, the resolver 134 MUST try each indicated authoritative server using DNS with 135 encryption until it successfully sets up a connection. The resolver 136 only attempts to use the encrypted transports that are in the 137 associated SVCB record for the authoritative server. (( Note that 138 this completely prohibits "simple port 853 probing" even though that 139 is what some operators are currently doing. Does the WG want to be 140 this strict? )) 141 A resolver SHOULD keep a DNS with encryption session to a particular 142 server open if it expects to send additional queries to that server 143 in a short period of time. [DNS-OVER-TCP] says "both clients and 144 servers SHOULD support connection reuse" for TCP connections, and 145 that advice could apply as well for DNS with encryption, especially 146 as DNS with encryption has far greater overhead for re-establishing a 147 connection. If the server closes the DNS with encryption session, 148 the resolver can possibly re-establish a DNS with encryption session 149 using encrypted session resumption. 151 For any DNS with encryption protocols, TLS version 1.3 [TLS-13] or 152 later MUST be used. 154 3.1. Resolver Process as Pseudocode 156 This section is meant as an informal clarification of the protocol, 157 and is not normative. The pseudocode here is designed to show the 158 intent of the protocol, so it is not optimized for things like 159 intersection of sets and other shortcuts. 161 In this code, "signal_rrset(this_name)" means an "SVCB" query for the 162 "'_dns'" prefix of "this_name". The "Query over secure transport 163 until successful" section ignores differences in name server 164 selection and retry behaviour in different resolvers. The pseudocode 165 was written to roughly cover the shared behaviour between [UNAUTH] 166 and [FULL-AUTH]. Specifically, whether an implementation waits for 167 the resolution of "queue a query" would differ between the two. 169 # Inputs 170 ns_names = List of NS Rdatas from the NS RRset for the queried name 171 can_do_secure = List of secure transports supported by resolver 172 secure_names_and_transports = Empty list, filled in below 174 # Fill secure_names_and_transports with (name, transport) tuples 175 for this_name in ns_names: 176 if signal_rrset(this_name) is in the resolver cache: 177 if signal_rrset(this_name) positively does not exist: 178 continue 179 for this_transport in signal_rrset(this_name): 180 if this_transport in can_do_secure: 181 add (this_name, this_transport) to secure_names_and_transports 182 else: # signal_rrset(this_name) is not in the resolver cache 183 queue a query for signal_rrset(this_name) for later caching 185 # Query over secure transport until successful 186 for (this_name, this_transport) tuple in secure_names_and_transports: 187 query using this_transport on this_name 188 if successful: 189 finished 191 # Got here if no this_name/this_transport query was successful 192 # or if secure_names_and_transports was empty 193 query using classic DNS on any/all ns_names; finished 195 4. Serving with Encryption 197 An operator of an authoritative server following this protocol SHOULD 198 publish SVCB records as described in Section 2. If they cannot 199 publish such records, the security properties of their authoritative 200 servers will not be found. If an operator wants to test serving 201 using encryption, they can publish SVCB records with short TTLs and 202 then stop serving with encryption after removing the SVCB records and 203 waiting for the TTLs to expire. 205 It is acceptable for an operator of authoritative servers to only 206 offer encryption on some of the named authoritative servers, such as 207 when the operator is determining how far to roll out encrypted 208 service. 210 A server MAY close an encrypted connection at any time. For example, 211 it can close the session if it has not received a DNS query in a 212 defined length of time. The server MAY close an encrypted session 213 after it sends a DNS response; however, it might also want to keep 214 the session open waiting for another DNS query from the resolver. 215 [DNS-OVER-TCP] says "both clients and servers SHOULD support 216 connection reuse" for TCP connections, and that advice could apply as 217 well for DNS with encryption, especially as DNS with encryption has 218 far greater overhead for re-establishing a connection. If the server 219 closes the DNS with encryption session, the resolver can possibly re- 220 establish a DNS with encryption session using encrypted session 221 resumption. 223 For any DNS with encryption protocols, TLS version 1.3 [TLS-13] or 224 later MUST be used. 226 5. Resolvers Reporting Errors to Authoritative Servers 228 Resolvers should have a method of telling authoritative servers that 229 there are problems with the encrypted service they are offering. 230 There is a proposal that the DNSOP Working Group might adopt 231 [ERROR-REPORTING], which would enable such reporting. 233 (( Clearly, more will need to go here. )) 235 6. IANA Considerations 237 (( Update registration for TCP/853 to also include ADoT )) 239 (( Maybe other updates for DoH and DoQ )) 241 7. Security Considerations 243 An authoritative server that wants to only serve data to resolvers 244 that use fully-authenticated encryption as described in [FULL-AUTH] 245 cannot differentiate between those resolvers and resolvers using the 246 mechanisms described in this document. 248 (( Talk about requiring TLS 1.3 )) 250 8. Acknowledgements 252 The use of SVCB records for discovering whether an authoritative 253 server supports encryption was first described by the authors of 254 [FULL-AUTH]. 256 The DPRIVE Working Group has contributed many ideas that keep 257 shifting the focus and content of this document. 259 9. References 261 9.1. Normative References 263 [DNS-SVCB] Schwartz, B., "Service Binding Mapping for DNS Servers", 264 Work in Progress, Internet-Draft, draft-schwartz-svcb-dns- 265 03, 19 April 2021, . 268 [FULL-AUTH] 269 Pauly, T., Rescorla, E., Schinazi, D., and C. A. Wood, 270 "Signaling Authoritative DNS Encryption", Work in 271 Progress, Internet-Draft, draft-rescorla-dprive-adox- 272 latest-00, 26 February 2021, 273 . 276 [SVCB] Schwartz, B., Bishop, M., and E. Nygren, "Service binding 277 and parameter specification via the DNS (DNS SVCB and 278 HTTPS RRs)", Work in Progress, Internet-Draft, draft-ietf- 279 dnsop-svcb-https-06, 16 June 2021, 280 . 283 [TLS-13] Rescorla, E., "The Transport Layer Security (TLS) Protocol 284 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 285 . 287 [UNAUTH] Hoffman, P. and P. V. Dijk, "Recursive to Authoritative 288 DNS with Unauthenticated Encryption", Work in Progress, 289 Internet-Draft, draft-ietf-dprive-unauth-to-authoritative- 290 01, 19 May 2021, . 293 9.2. Informative References 295 [DNS-OVER-TCP] 296 Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and 297 D. Wessels, "DNS Transport over TCP - Implementation 298 Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016, 299 . 301 [ERROR-REPORTING] 302 Arends, R. and M. Larson, "DNS Error Reporting", Work in 303 Progress, Internet-Draft, draft-arends-dns-error- 304 reporting-00, 30 October 2020, 305 . 308 Authors' Addresses 309 Peter van Dijk 310 PowerDNS 312 Email: peter.van.dijk@powerdns.com 314 Paul Hoffman 315 ICANN 317 Email: paul.hoffman@icann.org