DNS Extensions (DNSEXT) A. Hubert Internet-Draft Netherlabs Computer Consulting BV. Intended status: Standards Track D. Ulevitch Expires: October 22, 2009 EveryDNS April 20, 2009 EDNS Option for performing a data PING draft-hubert-ulevitch-edns-ping-01.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on October 22, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Hubert & Ulevitch Expires October 22, 2009 [Page 1] Internet-Draft EDNS Option for performing a data PING April 2009 Abstract For various reasons, it may be desirable to ask a remote nameserver to add certain data to the response to a query. This document describes an EDNS option that implements such behavioiur. Table of Contents 1. Key words . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Nameserver Behaviour . . . . . . . . . . . . . . . . . . . 5 3.2. Resolver Behaviour . . . . . . . . . . . . . . . . . . . . 5 3.3. The PING option . . . . . . . . . . . . . . . . . . . . . 5 3.4. Presentation format . . . . . . . . . . . . . . . . . . . 5 4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4.1. Truncation . . . . . . . . . . . . . . . . . . . . . . . . 6 5. Possible Uses and Implementation Guidance . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 9.1. Normative References . . . . . . . . . . . . . . . . . . . 11 9.2. Informative References . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 Hubert & Ulevitch Expires October 22, 2009 [Page 2] Internet-Draft EDNS Option for performing a data PING April 2009 1. Key words The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Hubert & Ulevitch Expires October 22, 2009 [Page 3] Internet-Draft EDNS Option for performing a data PING April 2009 2. Introduction This document describes an EDNS option that can be used to ask a remote nameserver, be it authoritative or a caching resolver, to copy an opaque string from the query to the response. This string can be used to verify proper transmission of DNS questions and responses of various sizes. Additionally, implementations could utilise EDNS PING as a way to enhance the security of DNS over UDP. Hubert & Ulevitch Expires October 22, 2009 [Page 4] Internet-Draft EDNS Option for performing a data PING April 2009 3. Protocol This document uses an EDNS [RFC2671] option to signal that the remote nameserver must copy this option, and its payload, from the query to the response, without truncation or modification. 3.1. Nameserver Behaviour A name server that understands the PING option and chooses to honor a particular PING request MUST respond by including the opaque payload in a PING option in an EDNS OPT pseudo-RR in the response message. The PING response should be included in addition to the records that would be returned if no PING request were included. An oversized payload MUST be ignored. 3.2. Resolver Behaviour Resolvers, including stub resolvers, can signal their desire for an EDNS PING response by adding a PING option in an EDNS OPT pseudo-RR in the question message. The resolver is free to choose a length for the opaque payload of the PING option request, but care should be taken not to exceed acceptable DNS packet size limits. Malformed or truncated responses should be treated as suspicicous. Empty responses, however, may simply indicate a response from a nameserver which does not support EDNS PING responses. 3.3. The PING option The OPTION-CODE for the PING option is 5. The OPTION-DATA for the PING option is an opaque byte string, the semantics of which are deliberately left outside of this document. The minimum length of the OPTION-DATA is 4 bytes, the maximum length is 16 bytes. 3.4. Presentation format The presentation format of the PING option is left outside the scope of the protocol. It should be observed that the payload of the PING option is completely arbitrary, and need not be null-terminated, and in general will not be. Hubert & Ulevitch Expires October 22, 2009 [Page 5] Internet-Draft EDNS Option for performing a data PING April 2009 4. Discussion The PING option is modeled on ICMP ECHO-REQUEST and ECHO-RESPONSE packets ([RFC0792]), and can in fact be used in a similar manner to verify connectivity. An example of such verification is to determine the maximum response size that arrives unscathed. In addition, a resolver is free to append a PING option to outgoing queries in order to protect itself from accepting false data by requesting a more clearly marked response. Such a PING-adorned response can clearly be separated from responses sent by third parties. 4.1. Truncation In some cases, adding the PING option to a response message may trigger message truncation. This specification does not change the rules for DNS message truncation in any way, but implementers will need to pay attention to this issue. Implementations claiming conformance to this draft, and which are configured to honor PING requests MUST respond to such requests, and must not drop the PING response to prevent truncation. By definition, a resolver that requests PING responses also supports EDNS, so a resolver that requests PING responses can also use the "sender's UDP payload size" field of the OPT pseudo-RR to signal a receive buffer size large enough to make truncation unlikely. Hubert & Ulevitch Expires October 22, 2009 [Page 6] Internet-Draft EDNS Option for performing a data PING April 2009 5. Possible Uses and Implementation Guidance While this document standardizes how the EDNS PING option can be used, it does not specify how or when it should be used. In this non-normative section, guidance is given how this option might best be used to achieve certain effects. It is expected that this guidance will be supplanted by the experience of implementors over time. In case the EDNS-PING option is used to protect against the spoofing of DNS answers, care must be taken that the payload of the EDNS-PING is sufficiently long and sufficiently unpredictable to serve this purpose. Proper unpredictability can be achieved by employing a high quality (pseudo-)random generator, as described in [RFC4086]. Not all servers support EDNS Options, nor do all servers respond well to EDNS queries per se. Like EDNS in general, care must be taken to determine if a nameserver responds well to EDNS-PING adorned queries. If the state of a remote server's support for EDNS-PING is cached, and EDNS-PING is used to protect against spoofing, it is imperative that such state can not be downgraded within a reasonable timeframe. Hubert & Ulevitch Expires October 22, 2009 [Page 7] Internet-Draft EDNS Option for performing a data PING April 2009 6. Security Considerations While EDNS PING might be used to enhance the security of query/ response correlation, in and of itself it is not expected to have security implications. Hubert & Ulevitch Expires October 22, 2009 [Page 8] Internet-Draft EDNS Option for performing a data PING April 2009 7. IANA Considerations IANA is expected and requested to reserve option 5 for EDNS PING. Hubert & Ulevitch Expires October 22, 2009 [Page 9] Internet-Draft EDNS Option for performing a data PING April 2009 8. Acknowledgments Donald Eastlake first discussed the concept of DNS cookies ([I-D.eastlake-dnsext-cookies]), which are remarkably similar to EDNS PING requests, but cover a wider scope and have a defined purpose. Most of this document was copied almost verbatim from [RFC5001] which implements a very similar EDNS option, used for very different purposes. Thanks are due to Rob Austein and other contributors to the NSID RFC. Although any mistakes remain our own, the authors gratefully acknowledge the help and contributions of: Peter van Dijk, Aki Tuomi Hubert & Ulevitch Expires October 22, 2009 [Page 10] Internet-Draft EDNS Option for performing a data PING April 2009 9. References 9.1. Normative References [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, September 1981. [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, November 1987. [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS Specification", RFC 2181, July 1997. [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671, August 1999. 9.2. Informative References [I-D.eastlake-dnsext-cookies] 3rd, D., "Domain Name System (DNS) Cookies", draft-eastlake-dnsext-cookies-03 (work in progress), February 2008. [RFC1123] Braden, R., "Requirements for Internet Hosts - Application and Support", STD 3, RFC 1123, October 1989. [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005. [RFC5001] Austein, R., "DNS Name Server Identifier (NSID) Option", RFC 5001, August 2007. Hubert & Ulevitch Expires October 22, 2009 [Page 11] Internet-Draft EDNS Option for performing a data PING April 2009 Authors' Addresses Bert Hubert Netherlabs Computer Consulting BV. Braillelaan 10 Rijswijk (ZH) 2289 CM The Netherlands Email: bert.hubert@netherlabs.nl David Ulevitch EveryDNS 2601 Greenwich, #4 San Francisco, CA 94123 United States of America Email: davidu@everydns.net Hubert & Ulevitch Expires October 22, 2009 [Page 12]