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Clegg 4 Intended status: Standards Track ISC 5 Expires: September 5, 2019 March 04, 2019 7 DNS EDNS Tags 8 draft-bellis-dnsop-edns-tags-00 10 Abstract 12 This document describes EDNS Tags, a mechanism by which DNS clients 13 and servers can transmit an opaque data field which has no defined 14 semantic meaning other than as previously agreed between the client 15 and server. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at https://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on September 5, 2019. 34 Copyright Notice 36 Copyright (c) 2019 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (https://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 52 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 53 3. Description . . . . . . . . . . . . . . . . . . . . . . . . . 2 54 3.1. Packet Validation Rules . . . . . . . . . . . . . . . . . 3 55 3.2. Error Handling . . . . . . . . . . . . . . . . . . . . . 3 56 3.3. Wire Format . . . . . . . . . . . . . . . . . . . . . . . 3 57 3.3.1. EDNS-Client-Tag . . . . . . . . . . . . . . . . . . . 3 58 3.3.2. EDNS-Server-Tag . . . . . . . . . . . . . . . . . . . 4 59 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 60 5. Implementation status . . . . . . . . . . . . . . . . . . . . 4 61 6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 5 62 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 63 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 64 9. Normative References . . . . . . . . . . . . . . . . . . . . 5 65 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 67 1. Introduction 69 This document describes EDNS Tags, a mechanism by which DNS clients 70 and servers [RFC1034] can transmit an opaque data field which has no 71 defined semantic meaning other than as previously agreed between the 72 client and server operators. 74 The tag is a single 16 bit field stored within the RDATA of an 75 EDNS(0) OPT RR as described in [RFC6891]. 77 Two EDNS options are defined to allow for the detection of servers 78 that incorrectly echo responses verbatim. The EDNS-Client-Tag option 79 may only appear in client requests, and the EDNS-Server-Tag may only 80 appear in responses from servers. 82 2. Terminology 84 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 85 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 86 "OPTIONAL" in this document are to be interpreted as described in BCP 87 14 [RFC2119] [RFC8174] when, and only when, they appear in all 88 capitals, as shown here. 90 3. Description 92 The values of the individual bits within a tag are not defined to 93 have any semantic meaning in this specification. Their 94 interpretation is defined entirely by bi-lateral agreement between 95 client and server operators. The definitions for EDNS-Client-Tag and 96 EDNS-Server-Tag values MAY be different. 98 Operators are free to partition the bits within that field as they 99 see fit; for example it could be used to transmit up to 16 separate 100 boolean flags, or perhaps to transmit a 10 bit numeric value combined 101 a 2 bit value and four boolean flags. 103 Possible use cases for EDNS-Client-Tags include: 105 o client-controlled selection of a DNS-based security filter 107 o marking a packet passing through a proxy with transport-related 108 information 110 Use cases for EDNS-Server-Tags are still to be determined. The 111 option is specified here for symmetry and in anticipation of new use 112 cases being discovered. 114 3.1. Packet Validation Rules 116 The OPT RR in a DNS request packet (QR = 0) MUST NOT contain an EDNS- 117 Server-Tag option. A request packet MUST NOT contain more than one 118 EDNS-Client-Tag option. 120 The OPT RR in a DNS response packet (QR = 1) MUST NOT contain an 121 EDNS-Client-Tag option. A response packet MUST NOT contain more than 122 one EDNS-Server-Tag option. 124 An EDNS-Server-Tag option MUST NOT be sent unless the corresponding 125 client query contained an EDNS-Client-Tag option. 127 3.2. Error Handling 129 Clients MUST discard any response packet that breaches any applicable 130 packet validation rule. 132 Servers MUST respond with a FORMERR in accordance with Section 7 of 133 [RFC6891] on receipt of a request that breaches any applicable packet 134 validation rule. 136 3.3. Wire Format 138 The format of the EDNS options are as follows, to be stored within 139 the RDATA of an OPT RR as specified in [RFC6891]: 141 3.3.1. EDNS-Client-Tag 142 +0 (MSB) +1 (LSB) 143 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 144 0: | OPTION-CODE (TBD1) | 145 +---+---+---+---+---+---+---+---|---+---+---+---+---+---+---+---+ 146 2: | OPTION-LENGTH (2) | 147 +---+---+---+---+---+---+---+---|---+---+---+---+---+---+---+---+ 148 4: | CLIENT-TAG-DATA | 149 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 151 OPTION-CODE: The option code identifier (TBD1). 153 OPTION-LENGTH: Size (in octets) of OPTION-DATA. MUST be 2. 155 CLIENT-TAG-DATA: The tag field sent from client to server. 157 3.3.2. EDNS-Server-Tag 159 +0 (MSB) +1 (LSB) 160 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 161 0: | OPTION-CODE (TBD2) | 162 +---+---+---+---+---+---+---+---|---+---+---+---+---+---+---+---+ 163 2: | OPTION-LENGTH (2) | 164 +---+---+---+---+---+---+---+---|---+---+---+---+---+---+---+---+ 165 4: | SERVER-TAG-DATA | 166 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 168 OPTION-CODE: The option code identifier (TBD2). 170 OPTION-LENGTH: Size (in octets) of OPTION-DATA. MUST be 2. 172 SERVER-TAG-DATA: The tag field sent from server to client. 174 4. Security Considerations 176 Client tags are under the control of the client software and as such 177 (and in the absence of any other mechanism to authenticate the 178 client's identity) this mechanism is not appropriate for applications 179 where the DNS server operator wishes to contractually differentiate 180 service based on the presence (or absence) of any particular tag. 182 5. Implementation status 184 TBC. 186 6. Privacy Considerations 188 Tags are opaque fields that encode only a limited amount of 189 information. The size of the data field in this specification is 190 chosen to offer a compromise between offering sufficient content to 191 be technically useful while also limiting the scope for it to be used 192 to transmit Personally Identifiable Information. 194 7. IANA Considerations 196 IANA has assigned the following EDNS(0) Option Codes: 198 Value Name Status Reference 199 ---------------------------------------------------------- 200 TBD1 EDNS-Client-Tag Standard RFCXXXX 201 TBD2 EDNS-Server-Tag Standard RFCXXXX 203 << Note to IANA - please assign an even value to TBD1, and the next 204 consecutive odd value to TBD2. This allows the least-significant bit 205 of the option value to be compared against the packet's QR bit >> 207 8. Acknowledgements 209 The authors wish to particularly thank Brian Conry, Peter van Dijk 210 and Matthijs Mekking for early review and feedback on this document. 212 9. Normative References 214 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 215 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 216 . 218 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 219 Requirement Levels", BCP 14, RFC 2119, 220 DOI 10.17487/RFC2119, March 1997, 221 . 223 [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms 224 for DNS (EDNS(0))", STD 75, RFC 6891, 225 DOI 10.17487/RFC6891, April 2013, 226 . 228 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 229 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 230 May 2017, . 232 Authors' Addresses 234 Ray Bellis 235 Internet Systems Consortium, Inc. 236 950 Charter Street 237 Redwood City CA 94063 238 USA 240 Phone: +1 650 423 1200 241 Email: ray@isc.org 243 Alan Clegg 244 Internet Systems Consortium, Inc. 245 950 Charter Street 246 Redwood City CA 94063 247 USA 249 Phone: +1 650 423 1200 250 Email: aclegg@isc.org