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Bellis 3 Internet-Draft Nominet UK 4 Intended status: Standards Track March 27, 2012 5 Expires: September 28, 2012 7 Title 8 draft-bellis-dnsext-multi-qtypes-01 10 Abstract 12 This document specifies a method for a DNS client to request 13 additional DNS record types to be delivered alongside the primary 14 record type specified in the question section of a DNS query. 16 Status of this Memo 18 This Internet-Draft is submitted in full conformance with the 19 provisions of BCP 78 and BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF). Note that other groups may also distribute 23 working documents as Internet-Drafts. The list of current Internet- 24 Drafts is at http://datatracker.ietf.org/drafts/current/. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 This Internet-Draft will expire on September 28, 2012. 33 Copyright Notice 35 Copyright (c) 2012 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents 40 (http://trustee.ietf.org/license-info) in effect on the date of 41 publication of this document. Please review these documents 42 carefully, as they describe your rights and restrictions with respect 43 to this document. Code Components extracted from this document must 44 include Simplified BSD License text as described in Section 4.e of 45 the Trust Legal Provisions and are provided without warranty as 46 described in the Simplified BSD License. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 52 2. Terminology used in this document . . . . . . . . . . . . . . . 3 54 3. Description . . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 3.1. Multiple QTYPE EDNS Option Format . . . . . . . . . . . . . 3 56 3.2. Response Generation . . . . . . . . . . . . . . . . . . . . 4 57 3.2.1. Server Side Processing . . . . . . . . . . . . . . . . 4 58 3.2.2. Client Side Processing . . . . . . . . . . . . . . . . 5 59 3.2.3. DNSSEC . . . . . . . . . . . . . . . . . . . . . . . . 5 61 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 63 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 65 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 67 7. Normative References . . . . . . . . . . . . . . . . . . . . . 6 69 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . . 7 71 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7 73 1. Introduction 75 A commonly requested DNS [RFC1035] feature is the ability to receive 76 multiple related resource records (RRs) in a single DNS response. 78 For example, it may be desirable to receive both the A and AAAA 79 records for a domain name together, rather than having to issue 80 multiple queries. 82 The DNS wire protocol in theory supports having multiple questions in 83 a single packet, but in practise this does not work: 85 o Each question consists of the tuple (QNAME, QTYPE, QCLASS). Since 86 each question has its own QNAME field it would be possible for one 87 name to exist and another to not exist, resulting in an 88 inconsistent response code. 89 o The idea that only a single question is allowed is sufficiently 90 entrenched that many DNS servers will simply return an error (or 91 fail to response at all) if they receive a query with a question 92 count (QDCOUNT) of more than one. 94 To resolve both of these issues, this document constraints the 95 problem to those cases where only the QTYPE varies by specifying a 96 new option for the Extension Mechanisms for DNS (EDNS [RFC2671]) that 97 contains an additional list of QTYPE values that the client wishes to 98 receive in addition to that in the primary question. 100 TODO: why not "ANY" ? 102 2. Terminology used in this document 104 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 105 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 106 document are to be interpreted as described in [RFC2119]. 108 3. Description 110 3.1. Multiple QTYPE EDNS Option Format 112 The overall format of an EDNS option is shown for reference below, 113 per [RFC2671], followed by the option specific data: 115 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 116 0: | OPTION-CODE | 117 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 118 2: | OPTION-LENGTH | 119 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 120 4: | | 121 / OPTION-DATA / 122 / / 123 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 125 OPTION-CODE: TBD by IANA 127 OPTION-LENGTH: Size (in octets) of OPTION-DATA. 129 OPTION-DATA: Option specific, as below: 131 +0 (MSB) +1 (LSB) 132 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 133 0: |QTD| reserved | QTCOUNT | QT1 (MSB) | 134 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 135 2: | QT1 (LSB) | ... | 136 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 137 | ... /// QTn (MSB) | 138 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 139 | QTn (LSB) | 140 +---+---+---+---+---+---+---+---+ 142 QTD: this bit indicates the direction of the packet. It MUST be 143 clear (0) in a query and set (1) in a response. 145 QTCOUNT: a 3 bit field with range 0 .. 7 specifying the number of QT 146 fields to follow. 148 QTn: a 2 byte field (MSB first) specifying a DNS RR type. The RR 149 type MUST be for a real resource record, and MUST NOT refer to a 150 pseudo RR type such as "OPT", "IXFR", "TSIG", etc. 152 3.2. Response Generation 154 3.2.1. Server Side Processing 156 A conforming server that receives a Multiple QTYPE Option in a query 157 MUST return a Multiple QTYPE Option in its response. 159 The QTD bit in that response MUST be set (1) as protection against 160 servers which simply echo unknown EDNS options verbatim. If the QTD 161 bit in a response is zero the client MUST treat the response as if 162 this option is unsupported. 164 The server SHOULD attempt to return any resource records known to it 165 that match the additional (QTYPE, QCLASS, QTn) tuples. These records 166 MUST be returned in the Answer Section of the response, but the 167 answer for the primary QTYPE from the Question Section MUST be 168 included first. 170 For any particular QTn in the query, if the server provides addtional 171 answers, or has knowledge that the RR type type does not exist for 172 that QNAME (a "negative answer"), it must include that QTn value in 173 the Multiple QTYPE Option of its response. 175 A negative answer is therefore indicated by the combination of the 176 presence of a QTn value in the Multiple QTYPE Option and the absence 177 of a matching record in the Answer Section. This is necessary (in 178 the absence of DNSSEC) to differentiate between absence of the record 179 from the zone and absence of the record from the response. 181 A server that is authoritative for the specified QNAME on receipt of 182 a Multiple QTYPE Option MUST attempt to return all specified RR types 183 except where that would result in truncation in which case it may 184 omit some (or all) of the records for the additional RR types. Those 185 RR types MUST then also be omitted from the Multiple QTYPE Option in 186 the response. 188 A caching recursive server receiving a Multiple QTYPE Option SHOULD 189 attempt to fill its positive and negative caches with all of the 190 specified RR types before returning its response to the client. 192 TODO: is there a case for mandatory answers, i.e. the client saying I 193 _really_ want all these? 195 3.2.2. Client Side Processing 197 Recursive resolvers MAY use this method to obtain multiple records 198 from an authoritative server. For the purposes of Section 5.4.1 of 199 [RFC2181] any authoritative answers received MUST be ranked the same 200 as the answer for the primary question. 202 3.2.3. DNSSEC 204 If the DNS client sets the "DNSSEC OK" (DO) bit in the query then the 205 server MUST also return the related DNSSEC records that would have 206 been returned in a standalone query for the same QTYPE. 208 A negative answer from a signed zone MUST contain the appropriate 209 authenticated denial of existence records, per [RFC4034] and 210 [RFC5155]. 212 In a signed zone there is a theoretical risk of valid signatures for 213 one RR type and invalid signatures for another. This is the only 214 case known to the author where the response code for any particular 215 QNAME may be inconsistent across different RR types. 217 Should a validating resolver produce NOERROR for some RR types and 218 SERVFAIL for others it MUST omit the RR types that failed to validate 219 from its response and from the QTn fields on the Multiple QTYPE 220 option. The client MAY then initiate standalone queries for those RR 221 types. 223 4. Security Considerations 225 The method documented here does not change any of the security 226 properties of the DNS protocol itself. 228 It should however be noted that this method does increase the 229 potential amplification factor when the DNS protocol is used as a 230 vector for a denial of service attack. 232 5. IANA Considerations 234 IANA is requested to assign a new value in the DNS EDNS0 Options 235 registry. 237 6. Acknowledgements 239 The author wishes to thank the following for their feedback and 240 reviews during the initial development of this document: Michael 241 Graff, Olafur Gudmundsson, Matthijs Mekking, Paul Vixie. 243 7. Normative References 245 [RFC1035] Mockapetris, P., "Domain names - implementation and 246 specification", STD 13, RFC 1035, November 1987. 248 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 249 Requirement Levels", BCP 14, RFC 2119, March 1997. 251 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 252 Specification", RFC 2181, July 1997. 254 [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", 255 RFC 2671, August 1999. 257 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 258 Rose, "Resource Records for the DNS Security Extensions", 259 RFC 4034, March 2005. 261 [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS 262 Security (DNSSEC) Hashed Authenticated Denial of 263 Existence", RFC 5155, March 2008. 265 Appendix A. Change Log 267 NB: to be removed by the RFC Editor before publication. 269 draft-bellis-dnsext-multi-qtypes-00 270 Initial draft 272 Author's Address 274 Ray Bellis 275 Nominet UK 276 Edmund Halley Road 277 Oxford OX4 4DQ 278 United Kingdom 280 Phone: +44 1865 332211 281 Email: ray.bellis@nominet.org.uk 282 URI: http://www.nominet.org.uk/