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MUST use classic (unencrypted) DNS ...' RFC 2119 keyword, line 152: '... MUST try each indicated authoritati...' (3 more instances...) Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (2 May 2021) is 1089 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for intended status: Experimental ---------------------------------------------------------------------------- == Outdated reference: A later version (-04) exists of draft-schwartz-svcb-dns-03 == Outdated reference: A later version (-12) exists of draft-ietf-dnsop-svcb-https-05 == Outdated reference: A later version (-04) exists of draft-ietf-dprive-unauth-to-authoritative-00 Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 2 comments (--).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: 3 November 2021 ICANN 6 2 May 2021 8 Common Features for Encrypted Recursive to Authoritative DNS 9 draft-pp-dprive-common-features-00 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 3 November 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 in the Parent Zone . . . . . . . . . . . 3 55 3. Processing Discovery Responses . . . . . . . . . . . . . . . 3 56 3.1. Resolver Process as Pseudocode . . . . . . . . . . . . . 4 57 4. TLS Requirements for Encrypting Resolver to Authoritative 58 Server Sessions . . . . . . . . . . . . . . . . . . . . . 5 59 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 60 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 61 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 62 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 63 8.1. Normative References . . . . . . . . . . . . . . . . . . 6 64 8.2. Informative References . . . . . . . . . . . . . . . . . 6 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 * TLS requirements (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 An authoritative server that supports DNS with encryption makes 98 itself discoverable by publishing one or more DNS SVCB records that 99 contain "alpn" parameter keys. SVCB records are defined in [SVCB], 100 and the DNS extension to those records are define in [DNS-SVCB]. 102 A recursive resolver discovers whether an authoritative server 103 supports DNS with encryption by looking for cached SVCB records for 104 the name of the authoritative server with a positive answer. A 105 cached DNS SVCB record with a negative answer indicates that the 106 authoritative server does not support any encrypted transport. 108 If the cache has no positive or negative answers for any DNS SVCB 109 record for any of a zone's authoritative servers, the resolver needs 110 to send queries for the DNS SVCB records for some or all of the 111 zone's authoritative servers. 113 Because some authoritative servers or middleboxes are misconfigured, 114 requests for unknown RRtypes might be ignored by them. Resolvers 115 should be ready to deal with timeouts or other bad responses to their 116 SVCB queries. 118 2.1. DNS SVCB Records in the Parent Zone 120 DNS SVCB records act as advisory information for resolvers about the 121 encrypted protocols that are supported. They can be thought of as 122 similar to NS records on the parent side of a zone cut: advisory 123 enough to act on, but not authoritative. Given this, authoritative 124 servers that know the DNS SCVB records associated with NS records for 125 any child zones MAY include those DNS SCVB records in the Additional 126 section of responses to queries to a parent authoritative server. 128 (( Before this is published for real, it would be useful to check 129 whether any resolvers freak out or fall over when they receive SVCB 130 records in the Additional section. )) 132 3. Processing Discovery Responses 134 After a resolver has DNS SCVB records in its cache (possibly due to 135 having just queried for them), it needs to use those records to try 136 to find an authoritative server that uses DNS with encryption. This 137 section describes how the resolver can make that selection. 139 A resolver MUST NOT attempt encryption for a server that has a 140 negative response in its cache for the associated DNS SVCB record. 142 After sending out all requests for SVCB records for the authoritative 143 servers in the NS RRset for a name, if all of the SVCB records for 144 those authoritative servers in the cache are negative responses, the 145 resolver MUST use classic (unencrypted) DNS instead of encryption. 146 Similarly, if none of the DNS SVCB records for the authoritative 147 servers in the cache have supported "alpn" parameters, the resolver 148 MUST use classic (unencrypted) DNS instead of encryption. 150 If there are any DNS SVCB records in the cache for the authoritative 151 servers for a zone with supported "alpn" parameters, the resolver 152 MUST try each indicated authoritative server using DNS with 153 encryption until it successfully sets up a connection. The resolver 154 only attempts to use the encrypted transports that are in the 155 associated SVCB record for the authoritative server. (( Note that 156 this completely prohibits "simple port 853 probing" even though that 157 is what some operators are currently doing. Does the WG want to be 158 this strict? )) 160 A resolver SHOULD keep a DNS with encryption session to a particular 161 server open if it expects to send additional queries to that server 162 in a short period of time. [DNS-OVER-TCP] says "both clients and 163 servers SHOULD support connection reuse" for TCP connections, and 164 that advice could apply as well for DNS with encryption, especially 165 as DNS with encryption has far greater overhead for re-establishing a 166 connection. If the server closes the DNS with encryption session, 167 the resolver can possibly re-establish a DNS with encryption session 168 using encrypted session resumption. 170 3.1. Resolver Process as Pseudocode 172 This section is meant as an informal clarification of the protocol, 173 and is not normative. The pseudocode here is designed to show the 174 intent of the protocol, so it is not optimized for things like 175 intersection of sets and other shortcuts. 177 In this code, "signal_rrset(name)" means an "SVCB" query for the 178 "'_dns'" prefix of "this_name". The "Query over secure transport 179 until successful" section ignores differences in name server 180 selection and retry behaviour in different resolvers. The pseudocode 181 was written to roughly cover the shared behaviour between [UNAUTH] 182 and [FULL-AUTH]. Specifically, whether an implementation waits for 183 the resolution of "queue a query" would differ between the two. 185 # Inputs 186 ns_names = List of NS Rdatas from the NS RRset for the queried name 187 can_do_secure = List of secure transports supported by resolver 188 secure_names_and_transports = Empty list, filled in below 190 # Fill secure_names_and_transports with (name, transport) tuples 191 for this_name in ns_names: 192 if signal_rrset(this_name) is in the resolver cache: 193 if signal_rrset(this_name) positively does not exist: 194 continue 195 for this_transport in signal_rrset(this_name): 196 if this_transport in can_do_secure: 197 add (this_name, this_transport) to secure_names_and_transports 198 else: # signal_rrset(this_name) is not in the resolver cache 199 queue a query for signal_rrset(this_name) for later caching 201 # Query over secure transport until successful 202 for (this_name, this_transport) tuple in secure_names_and_transports: 203 query using this_transport on this_name 204 if successful: 205 finished 207 # Got here if no this_name/this_transport query was successful 208 # or if secure_names_and_transports was empty 209 query using classic DNS on any/all ns_names; finished 211 4. TLS Requirements for Encrypting Resolver to Authoritative Server 212 Sessions 214 All protocols for DNS with encryption rely on TLS. This section 215 defines requirements for the TLS use of DNS with encryption clients 216 and servers. 218 For any DNS with encryption protocols, TLS version 1.3 [TLS-13] or 219 later MUST be used. 221 (( There are other requirements, surely? )) 223 5. IANA Considerations 225 This document contains no changes to IANA registries. 227 6. Security Considerations 229 (( Talk about requiring TLS 1.3 )) 231 7. Acknowledgements 233 The use of SVCB records for discovering whether an authoritative 234 server supports encryption was first described by the authors of 235 [FULL-AUTH]. 237 8. References 239 8.1. Normative References 241 [DNS-SVCB] Schwartz, B., "Service Binding Mapping for DNS Servers", 242 Work in Progress, Internet-Draft, draft-schwartz-svcb-dns- 243 03, 19 April 2021, . 246 [FULL-AUTH] 247 Pauly, T., Rescorla, E., Schinazi, D., and C. A. Wood, 248 "Signaling Authoritative DNS Encryption", Work in 249 Progress, Internet-Draft, draft-rescorla-dprive-adox- 250 latest-00, 26 February 2021, 251 . 254 [SVCB] Schwartz, B., Bishop, M., and E. Nygren, "Service binding 255 and parameter specification via the DNS (DNS SVCB and 256 HTTPS RRs)", Work in Progress, Internet-Draft, draft-ietf- 257 dnsop-svcb-https-05, 21 April 2021, 258 . 261 [TLS-13] Rescorla, E., "The Transport Layer Security (TLS) Protocol 262 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 263 . 265 [UNAUTH] Hoffman, P. and P. V. Dijk, "Recursive to Authoritative 266 DNS with Unauthenticated Encryption", Work in Progress, 267 Internet-Draft, draft-ietf-dprive-unauth-to-authoritative- 268 00, 12 April 2021, . 271 8.2. Informative References 273 [DNS-OVER-TCP] 274 Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and 275 D. Wessels, "DNS Transport over TCP - Implementation 276 Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016, 277 . 279 Authors' Addresses 281 Peter van Dijk 282 PowerDNS 284 Email: peter.van.dijk@powerdns.com 286 Paul Hoffman 287 ICANN 289 Email: paul.hoffman@icann.org