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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DNS Extensions (DNSEXT) A. Hubert 3 Internet-Draft Netherlabs Computer Consulting BV. 4 Intended status: Standards Track D. Ulevitch 5 Expires: October 22, 2009 EveryDNS 6 April 20, 2009 8 EDNS Option for performing a data PING 9 draft-hubert-ulevitch-edns-ping-01.txt 11 Status of this Memo 13 This Internet-Draft is submitted to IETF in full conformance with the 14 provisions of BCP 78 and BCP 79. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as "work in progress." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt. 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html. 32 This Internet-Draft will expire on October 22, 2009. 34 Copyright Notice 36 Copyright (c) 2009 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 in effect on the date of 41 publication of this document (http://trustee.ietf.org/license-info). 42 Please review these documents carefully, as they describe your rights 43 and restrictions with respect to this document. 45 Abstract 47 For various reasons, it may be desirable to ask a remote nameserver 48 to add certain data to the response to a query. 50 This document describes an EDNS option that implements such 51 behavioiur. 53 Table of Contents 55 1. Key words . . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 57 3. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 58 3.1. Nameserver Behaviour . . . . . . . . . . . . . . . . . . . 5 59 3.2. Resolver Behaviour . . . . . . . . . . . . . . . . . . . . 5 60 3.3. The PING option . . . . . . . . . . . . . . . . . . . . . 5 61 3.4. Presentation format . . . . . . . . . . . . . . . . . . . 5 62 4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 6 63 4.1. Truncation . . . . . . . . . . . . . . . . . . . . . . . . 6 64 5. Possible Uses and Implementation Guidance . . . . . . . . . . 7 65 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 66 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 67 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 68 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 69 9.1. Normative References . . . . . . . . . . . . . . . . . . . 11 70 9.2. Informative References . . . . . . . . . . . . . . . . . . 11 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 73 1. Key words 75 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 76 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 77 document are to be interpreted as described in [RFC2119]. 79 2. Introduction 81 This document describes an EDNS option that can be used to ask a 82 remote nameserver, be it authoritative or a caching resolver, to copy 83 an opaque string from the query to the response. 85 This string can be used to verify proper transmission of DNS 86 questions and responses of various sizes. 88 Additionally, implementations could utilise EDNS PING as a way to 89 enhance the security of DNS over UDP. 91 3. Protocol 93 This document uses an EDNS [RFC2671] option to signal that the remote 94 nameserver must copy this option, and its payload, from the query to 95 the response, without truncation or modification. 97 3.1. Nameserver Behaviour 99 A name server that understands the PING option and chooses to honor a 100 particular PING request MUST respond by including the opaque payload 101 in a PING option in an EDNS OPT pseudo-RR in the response message. 103 The PING response should be included in addition to the records that 104 would be returned if no PING request were included. 106 An oversized payload MUST be ignored. 108 3.2. Resolver Behaviour 110 Resolvers, including stub resolvers, can signal their desire for an 111 EDNS PING response by adding a PING option in an EDNS OPT pseudo-RR 112 in the question message. 114 The resolver is free to choose a length for the opaque payload of the 115 PING option request, but care should be taken not to exceed 116 acceptable DNS packet size limits. 118 Malformed or truncated responses should be treated as suspicicous. 119 Empty responses, however, may simply indicate a response from a 120 nameserver which does not support EDNS PING responses. 122 3.3. The PING option 124 The OPTION-CODE for the PING option is 5. 126 The OPTION-DATA for the PING option is an opaque byte string, the 127 semantics of which are deliberately left outside of this document. 129 The minimum length of the OPTION-DATA is 4 bytes, the maximum length 130 is 16 bytes. 132 3.4. Presentation format 134 The presentation format of the PING option is left outside the scope 135 of the protocol. It should be observed that the payload of the PING 136 option is completely arbitrary, and need not be null-terminated, and 137 in general will not be. 139 4. Discussion 141 The PING option is modeled on ICMP ECHO-REQUEST and ECHO-RESPONSE 142 packets ([RFC0792]), and can in fact be used in a similar manner to 143 verify connectivity. 145 An example of such verification is to determine the maximum response 146 size that arrives unscathed. 148 In addition, a resolver is free to append a PING option to outgoing 149 queries in order to protect itself from accepting false data by 150 requesting a more clearly marked response. Such a PING-adorned 151 response can clearly be separated from responses sent by third 152 parties. 154 4.1. Truncation 156 In some cases, adding the PING option to a response message may 157 trigger message truncation. This specification does not change the 158 rules for DNS message truncation in any way, but implementers will 159 need to pay attention to this issue. 161 Implementations claiming conformance to this draft, and which are 162 configured to honor PING requests MUST respond to such requests, and 163 must not drop the PING response to prevent truncation. 165 By definition, a resolver that requests PING responses also supports 166 EDNS, so a resolver that requests PING responses can also use the 167 "sender's UDP payload size" field of the OPT pseudo-RR to signal a 168 receive buffer size large enough to make truncation unlikely. 170 5. Possible Uses and Implementation Guidance 172 While this document standardizes how the EDNS PING option can be 173 used, it does not specify how or when it should be used. 175 In this non-normative section, guidance is given how this option 176 might best be used to achieve certain effects. It is expected that 177 this guidance will be supplanted by the experience of implementors 178 over time. 180 In case the EDNS-PING option is used to protect against the spoofing 181 of DNS answers, care must be taken that the payload of the EDNS-PING 182 is sufficiently long and sufficiently unpredictable to serve this 183 purpose. 185 Proper unpredictability can be achieved by employing a high quality 186 (pseudo-)random generator, as described in [RFC4086]. 188 Not all servers support EDNS Options, nor do all servers respond well 189 to EDNS queries per se. Like EDNS in general, care must be taken to 190 determine if a nameserver responds well to EDNS-PING adorned queries. 192 If the state of a remote server's support for EDNS-PING is cached, 193 and EDNS-PING is used to protect against spoofing, it is imperative 194 that such state can not be downgraded within a reasonable timeframe. 196 6. Security Considerations 198 While EDNS PING might be used to enhance the security of query/ 199 response correlation, in and of itself it is not expected to have 200 security implications. 202 7. IANA Considerations 204 IANA is expected and requested to reserve option 5 for EDNS PING. 206 8. Acknowledgments 208 Donald Eastlake first discussed the concept of DNS cookies 209 ([I-D.eastlake-dnsext-cookies]), which are remarkably similar to EDNS 210 PING requests, but cover a wider scope and have a defined purpose. 212 Most of this document was copied almost verbatim from [RFC5001] which 213 implements a very similar EDNS option, used for very different 214 purposes. Thanks are due to Rob Austein and other contributors to 215 the NSID RFC. 217 Although any mistakes remain our own, the authors gratefully 218 acknowledge the help and contributions of: 220 Peter van Dijk, 222 Aki Tuomi 224 9. References 226 9.1. Normative References 228 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 229 RFC 792, September 1981. 231 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 232 STD 13, RFC 1034, November 1987. 234 [RFC1035] Mockapetris, P., "Domain names - implementation and 235 specification", STD 13, RFC 1035, November 1987. 237 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 238 Requirement Levels", BCP 14, RFC 2119, March 1997. 240 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 241 Specification", RFC 2181, July 1997. 243 [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", 244 RFC 2671, August 1999. 246 9.2. Informative References 248 [I-D.eastlake-dnsext-cookies] 249 3rd, D., "Domain Name System (DNS) Cookies", 250 draft-eastlake-dnsext-cookies-03 (work in progress), 251 February 2008. 253 [RFC1123] Braden, R., "Requirements for Internet Hosts - Application 254 and Support", STD 3, RFC 1123, October 1989. 256 [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness 257 Requirements for Security", BCP 106, RFC 4086, June 2005. 259 [RFC5001] Austein, R., "DNS Name Server Identifier (NSID) Option", 260 RFC 5001, August 2007. 262 Authors' Addresses 264 Bert Hubert 265 Netherlabs Computer Consulting BV. 266 Braillelaan 10 267 Rijswijk (ZH) 2289 CM 268 The Netherlands 270 Email: bert.hubert@netherlabs.nl 272 David Ulevitch 273 EveryDNS 274 2601 Greenwich, #4 275 San Francisco, CA 94123 276 United States of America 278 Email: davidu@everydns.net