Network Working Group W. Kumari Internet-Draft Google Intended status: Standards Track E. Hunt Expires: June 20, 2020 ISC R. Arends ICANN W. Hardaker USC/ISI D. Lawrence Oracle + Dyn December 18, 2019 Extended DNS Errors draft-ietf-dnsop-extended-error-13 Abstract This document defines an extensible method to return additional information about the cause of DNS errors. Though created primarily to extend SERVFAIL to provide additional information about the cause of DNS and DNSSEC failures, the Extended DNS Errors option defined in this document allows all response types to contain extended error information. Extended DNS Error information does not change the processing of RCODEs. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on June 20, 2020. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. Kumari, et al. Expires June 20, 2020 [Page 1] Internet-Draft draft-ietf-dnsop-extended-error December 2019 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction and background . . . . . . . . . . . . . . . . . 3 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 4 2. Extended DNS Error EDNS0 option format . . . . . . . . . . . 4 3. Extended DNS Error Processing . . . . . . . . . . . . . . . . 5 4. Defined Extended DNS Errors . . . . . . . . . . . . . . . . . 5 4.1. Extended DNS Error Code 0 - Other . . . . . . . . . . . . 5 4.2. Extended DNS Error Code 1 - Unsupported DNSKEY Algorithm . . . . . . . . . . . . . . 6 4.3. Extended DNS Error Code 2 - Unsupported DS Digest Type . . . . . . . . . . . . . . . . . . . . . . . 6 4.4. Extended DNS Error Code 3 - Stale Answer . . . . . . . . 6 4.5. Extended DNS Error Code 4 - Forged Answer . . . . . . . . 6 4.6. Extended DNS Error Code 5 - DNSSEC Indeterminate . . . . 6 4.7. Extended DNS Error Code 6 - DNSSEC Bogus . . . . . . . . 6 4.8. Extended DNS Error Code 7 - Signature Expired . . . . . . 6 4.9. Extended DNS Error Code 8 - Signature Not Yet Valid . . . 6 4.10. Extended DNS Error Code 9 - DNSKEY Missing . . . . . . . 7 4.11. Extended DNS Error Code 10 - RRSIGs Missing . . . . . . . 7 4.12. Extended DNS Error Code 11 - No Zone Key Bit Set . . . . 7 4.13. Extended DNS Error Code 12 - NSEC Missing . . . . . . . . 7 4.14. Extended DNS Error Code 13 - Cached Error . . . . . . . . 7 4.15. Extended DNS Error Code 14 - Not Ready . . . . . . . . . 7 4.16. Extended DNS Error Code 15 - Blocked . . . . . . . . . . 7 4.17. Extended DNS Error Code 16 - Censored . . . . . . . . . . 7 4.18. Extended DNS Error Code 17 - Filtered . . . . . . . . . . 7 4.19. Extended DNS Error Code 18 - Prohibited . . . . . . . . . 8 4.20. Extended DNS Error Code 19 - Stale NXDOMAIN Answer . . . 8 4.21. Extended DNS Error Code 20 - Not Authoritative . . . . . 8 4.22. Extended DNS Error Code 21 - Not Supported . . . . . . . 8 4.23. Extended DNS Error Code 22 - No Reachable Authority . . . 8 4.24. Extended DNS Error Code 23 - Network Error . . . . . . . 8 4.25. Extended DNS Error Code 24 - Invalid Data . . . . . . . . 8 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 5.1. A New Extended DNS Error Code EDNS Option . . . . . . . . 9 5.2. New Registry Table for Extended DNS Error Codes . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 Kumari, et al. Expires June 20, 2020 [Page 2] Internet-Draft draft-ietf-dnsop-extended-error December 2019 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 8.1. Normative References . . . . . . . . . . . . . . . . . . 12 8.2. Informative References . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 1. Introduction and background There are many reasons that a DNS query may fail, some of them transient, some permanent; some can be resolved by querying another server, some are likely best handled by stopping resolution. Unfortunately, the error signals that a DNS server can return are very limited, and are not very expressive. This means that applications and resolvers often have to "guess" at what the issue is - e.g. was the answer marked REFUSED because of a lame delegation, or because the nameserver is still starting up and loading zones? Is a SERVFAIL a DNSSEC validation issue, or is the nameserver experiencing some other failure? What error messages should be presented to the user or logged under these conditions? A good example of issues that would benefit by additional error information are errors caused by DNSSEC validation issues. When a stub resolver queries a name which is DNSSEC bogus (using a validating resolver), the stub resolver receives only a SERVFAIL in response. Unfortunately, the SERVFAIL Response Code (RCODE) is used to signal many sorts of DNS errors, and so the stub resolvers only option is to ask the next configured DNS resolver. The result of trying the next resolver is one of two outcomes: either the next resolver also validates, and a SERVFAIL is returned again or the next resolver is not a validating resolver, and the user is returned a potentially harmful result. With an Extended DNS Error (EDE) option enclosed in the response message, the resolver is able to return a more descriptive reason as to why any failures happened, or add additional context to a message containing a NOERROR RCODE. This document specifies a mechanism to extend DNS errors to provide additional information about the cause of an error. These extended DNS error codes described in this document and can be used by any system that sends DNS queries and receives a response containing an EDE option. Different codes are useful in different circumstances, and thus different systems (stub resolvers, recursive resolvers, and authoritative resolvers) might receive and use them. This document does not allow or prohibit any particular extended error codes and information to be matched with any particular RCODEs. Some combinations of extended error codes and RCODEs may seem nonsensical (such as resolver-specific extended error codes in responses from authoritative servers), so systems interpreting the Kumari, et al. Expires June 20, 2020 [Page 3] Internet-Draft draft-ietf-dnsop-extended-error December 2019 extended error codes MUST NOT assume that a combination will make sense. Receivers MUST be able to accept EDE codes and EXTRA-TEXT in all messages, including those with a NOERROR RCODE. Applications MUST continue to follow requirements from applicable specs on how to process RCODEs no matter what EDE values is also received. Senders MAY include more than one EDE option and receivers MUST be able to accept (but not necessarily process or act on) multiple EDE options in a DNS message. 1.1. Requirements notation 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]. 2. Extended DNS Error EDNS0 option format This draft uses an EDNS0 ([RFC6891]) option to include Extended DNS Error (EDE) information in DNS messages. The option is structured as follows: 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 0: | OPTION-CODE | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 2: | OPTION-LENGTH | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 4: | INFO-CODE | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 6: / EXTRA-TEXT ... / +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ Field definition details: o OPTION-CODE, 2-octets/16-bits (defined in [RFC6891]]), for EDE is TBD. [RFC Editor: change TBD to the proper code once assigned by IANA.] o OPTION-LENGTH, 2-octets/16-bits ((defined in [RFC6891]]) contains the length of the payload (everything after OPTION-LENGTH) in octets and should be 2 plus the length of the EXTRA-TEXT field (which may be a zero-length string). o INFO-CODE, 16-bits, which is the principal contribution of this document. This 16-bit value, encoded in network (MSB) byte order, provides the additional context for the RESPONSE-CODE of the DNS message. The INFO-CODE serves as an index into the "Extended DNS Errors" registry Section 5.1. Kumari, et al. Expires June 20, 2020 [Page 4] Internet-Draft draft-ietf-dnsop-extended-error December 2019 o EXTRA-TEXT, a variable length, UTF-8 encoded, text field that may hold additional textual information. Note: EXTRA-TEXT may be zero octets in length, indicating there is no EXTRA-TEXT included. Care should be taken not to leak private information that an observer would not otherwise have access to, such as account numbers. The Extended DNS Error (EDE) option can be included in any response (SERVFAIL, NXDOMAIN, REFUSED, and even NOERROR, etc) to a query that includes OPT Pseudo-RR [RFC6891]. This document includes a set of initial codepoints (and requests to the IANA to add them to the registry), but is extensible via the IANA registry to allow additional error and information codes to be defined in the future. 3. Extended DNS Error Processing When the response grows beyond the requestor's UDP payload size [RFC6891], servers SHOULD truncate messages by dropping EDE options before dropping other data from packets. Implementations SHOULD set the truncation bit when dropping EDE options. When a resolver or forwarder receives an EDE option, whether or not (and how) to pass along EDE information on to their original client is implementation dependent. Implementations MAY choose to not forward information, or they MAY choose to create a new EDE option(s) that conveys the information encoded in the received EDE. When doing so, care should be taken to ensure any information is properly attributed since an EDNS0 option received by the original client will be perceived only to have come from the resolver or forwarder sending it. 4. Defined Extended DNS Errors This document defines some initial EDE codes. The mechanism is intended to be extensible, and additional code-points can be registered in the "Extended DNS Errors" registry Section 5.1. The INFO-CODE from the EDE EDNS option is used to serve as an index into the "Extended DNS Error" IANA registry, the initial values for which are defined in the following sub-sections. 4.1. Extended DNS Error Code 0 - Other The error in question falls into a category that does not match known extended error codes. Implementations SHOULD include a EXTRA-TEXT value to augment this error code with additional information. Kumari, et al. Expires June 20, 2020 [Page 5] Internet-Draft draft-ietf-dnsop-extended-error December 2019 4.2. Extended DNS Error Code 1 - Unsupported DNSKEY Algorithm The resolver attempted to perform DNSSEC validation, but a DNSKEY RRSET contained only unsupported DNSSEC algorithms. 4.3. Extended DNS Error Code 2 - Unsupported DS Digest Type The resolver attempted to perform DNSSEC validation, but a DS RRSET contained only unsupported Digest Types. 4.4. Extended DNS Error Code 3 - Stale Answer The resolver was unable to resolve answer within its time limits and decided to answer with previously cached data instead of answering with an error. This is typically caused by problems communicating with an authoritative serever, possibly as result of a DoS attack against another network. 4.5. Extended DNS Error Code 4 - Forged Answer For policy reasons (legal obligation, or malware filtering, for instance), an answer was forged. Note that this should be used when an answer is still provided, not when failure codes are returned instead. See Blocked(15), Censored (16), and Filtered (17) for use when returning other response codes. 4.6. Extended DNS Error Code 5 - DNSSEC Indeterminate The resolver attempted to perform DNSSEC validation, but validation ended in the Indeterminate state [RFC4035]. 4.7. Extended DNS Error Code 6 - DNSSEC Bogus The resolver attempted to perform DNSSEC validation, but validation ended in the Bogus state. 4.8. Extended DNS Error Code 7 - Signature Expired The resolver attempted to perform DNSSEC validation, but no signatures are presently valid and some (often all) are expired. 4.9. Extended DNS Error Code 8 - Signature Not Yet Valid The resolver attempted to perform DNSSEC validation, but but no signatures are presently valid and at least some are not yet valid. Kumari, et al. Expires June 20, 2020 [Page 6] Internet-Draft draft-ietf-dnsop-extended-error December 2019 4.10. Extended DNS Error Code 9 - DNSKEY Missing A DS record existed at a parent, but no supported matching DNSKEY record could be found for the child. 4.11. Extended DNS Error Code 10 - RRSIGs Missing The resolver attempted to perform DNSSEC validation, but no RRSIGs could be found for at least one RRset where RRSIGs were expected. 4.12. Extended DNS Error Code 11 - No Zone Key Bit Set The resolver attempted to perform DNSSEC validation, but no Zone Key Bit was set in a DNSKEY. 4.13. Extended DNS Error Code 12 - NSEC Missing The resolver attempted to perform DNSSEC validation, but the requested data was missing and a covering NSEC or NSEC3 was not provided. 4.14. Extended DNS Error Code 13 - Cached Error The resolver is returning the SERVFAIL RCODE from its cache. 4.15. Extended DNS Error Code 14 - Not Ready The server is unable to answer the query as it is not fully functional (yet). 4.16. Extended DNS Error Code 15 - Blocked The server is unable to respond to the request because the domain is blacklisted due to an internal security policy imposed by the operator of the server being directly talked to. 4.17. Extended DNS Error Code 16 - Censored The server is unable to respond to the request because the domain is blacklisted by a security policy imposed upon the server being talked to by an external requirement. Note that how the imposed policy is applied is irrelevant (in-band DNS filtering, court order, etc). 4.18. Extended DNS Error Code 17 - Filtered The server is unable to respond to the request because the domain is blacklisted as requested by the client. Functionally, this amounts to "you requested that we filter domains like this one." Kumari, et al. Expires June 20, 2020 [Page 7] Internet-Draft draft-ietf-dnsop-extended-error December 2019 4.19. Extended DNS Error Code 18 - Prohibited An authoritative or recursive resolver that receives a query from an "unauthorized" client can annotate its REFUSED message with this code. Examples of "unauthorized" clients are recursive queries from IP addresses outside the network, blacklisted IP addresses, local policy, etc. 4.20. Extended DNS Error Code 19 - Stale NXDOMAIN Answer The resolver was unable to resolve an answer within its configured time limits and decided to answer with a previously cached NXDOMAIN answer instead of answering with an error. This is may be caused, for example, by problems communicating with an authoritative server, possibly as result of a DoS attack against another network. 4.21. Extended DNS Error Code 20 - Not Authoritative An authoritative server that receives a query (with the RD bit clear, or when not configured for recursion) for a domain for which it is not authoritative SHOULD include this EDE code in the REFUSED response. A resolver that receives a query (with the RD bit clear) SHOULD include this EDE code in the REFUSED response. 4.22. Extended DNS Error Code 21 - Not Supported The requested operation or query is not supported as its use has been deprecated. 4.23. Extended DNS Error Code 22 - No Reachable Authority The resolver could not reach any of the authoritative name servers (or they refused to reply). 4.24. Extended DNS Error Code 23 - Network Error An unrecoverable error occurred while communicating with another server. 4.25. Extended DNS Error Code 24 - Invalid Data An authoritative server that cannot answer with data for a zone it is otherwise configured to support. This may occur because its most recent zone is too old, or has expired, for example. Kumari, et al. Expires June 20, 2020 [Page 8] Internet-Draft draft-ietf-dnsop-extended-error December 2019 5. IANA Considerations 5.1. A New Extended DNS Error Code EDNS Option This document defines a new EDNS(0) option, entitled "Extended DNS Error", assigned a value of TBD1 from the "DNS EDNS0 Option Codes (OPT)" registry [to be removed upon publication: [http://www.iana.org/assignments/dns-parameters/dns- parameters.xhtml#dns-parameters-11] Value Name Status Reference ----- ---------------- ------ ------------------ TBD Extended DNS Error TBD [ This document ] 5.2. New Registry Table for Extended DNS Error Codes This document defines a new IANA registry table, where the index value is the INFO-CODE from the "Extended DNS Error" EDNS option defined in this document. The IANA is requested to create and maintain this "Extended DNS Error" codes registry. The code-point space for the INFO-CODE index is to be broken into 2 ranges: o 0 - 49151: First come, first served. o 49152 - 65280: Private use. A starting set of entries, based on the contents of this document, is as follows: INFO-CODE: 0 Purpose: Other Error Reference: Section 4.1 INFO-CODE: 1 Purpose: Unsupported DNSKEY Algorithm Reference: Section 4.2 INFO-CODE: 2 Purpose: Unsupported DS Digest Type Reference: Section 4.3 INFO-CODE: 3 Purpose: Stale Answer Reference: Section 4.4, [I-D.ietf-dnsop-serve-stale] INFO-CODE: 4 Purpose: Forged Answer Reference: Section 4.5 Kumari, et al. Expires June 20, 2020 [Page 9] Internet-Draft draft-ietf-dnsop-extended-error December 2019 INFO-CODE: 5 Purpose: DNSSEC Indeterminate Reference: Section 4.6 INFO-CODE: 6 Purpose: DNSSEC Bogus Reference: Section 4.7 INFO-CODE: 7 Purpose: Signature Expired Reference: Section 4.8 INFO-CODE: 8 Purpose: Signature Not Yet Valid Reference: Section 4.9 INFO-CODE: 9 Purpose: DNSKEY Missing Reference: Section 4.10 INFO-CODE: 10 Purpose: RRSIGs Missing Reference: Section 4.11 INFO-CODE: 11 Purpose: No Zone Key Bit Set Reference: Section 4.12 INFO-CODE: 12 Purpose: NSEC Missing Reference: Section 4.13 INFO-CODE: 13 Purpose: Cached Error Reference: Section 4.14 INFO-CODE: 14 Purpose: Not Ready. Reference: Section 4.15 INFO-CODE: 15 Purpose: Blocked Reference: Section 4.16 INFO-CODE: 16 Purpose: Censored Reference: Section 4.17 Kumari, et al. Expires June 20, 2020 [Page 10] Internet-Draft draft-ietf-dnsop-extended-error December 2019 INFO-CODE: 17 Purpose: Filtered Reference: Section 4.18 INFO-CODE: 18 Purpose: Prohibited Reference: Section 4.19 INFO-CODE: 19 Purpose: Stale NXDomain Answer Reference: Section 4.20 INFO-CODE: 20 Purpose: Not Authoritative Reference: Section 4.21 INFO-CODE: 21 Purpose: Not Supported Reference: Section 4.22 INFO-CODE: 22 Purpose: No Reachable Authority Reference: Section 4.23 INFO-CODE: 23 Purpose: Network Error Reference: Section 4.24 INFO-CODE: 24 Purpose: Invalid Data Reference: Section 4.25 6. Security Considerations Though DNSSEC continues to be deployed, unfortunately a significant number of clients (~11% according to [GeoffValidation]) that receive a SERVFAIL from a validating resolver because of a DNSSEC validaion issue will simply ask the next (potentially non-validating) resolver in their list, and thus don't get any of the protections which DNSSEC should provide. This information is unauthenticated information, and an attacker (e.g a MITM or malicious recursive server) could insert an extended error response into already untrusted data -- ideally clients and resolvers would not trust any unauthenticated information, but until we live in an era where all DNS answers are authenticated via DNSSEC or other mechanisms [RFC2845] [RFC8094], there are some tradeoffs. As an example, an attacker who is able to insert the DNSSEC Bogus Extended Kumari, et al. Expires June 20, 2020 [Page 11] Internet-Draft draft-ietf-dnsop-extended-error December 2019 Error into a packet could instead simply reply with a fictitious address (A or AAAA) record. Note that DNS Response Codes also contain no authentication and can be just as easily manipulated. 7. Acknowledgements The authors wish to thank Joe Abley, Mark Andrews, Tim April, Vittorio Bertola, Stephane Bortzmeyer, Vladimir Cunat, Ralph Dolmans, Peter DeVries, Peter van Dijk, Mats Dufberg, Donald Eastlake, Bob Harold, Paul Hoffman, Geoff Huston, Shane Kerr, Edward Lewis, Carlos M. Martinez, George Michelson, Eric Orth, Michael Sheldon, Puneet Sood, Petr Spacek, Ondrej Sury, John Todd, Loganaden Velvindron, and Paul Vixie. They also vaguely remember discussing this with a number of people over the years, but have forgotten who all they were -- if you were one of them, and are not listed, please let us know and we'll acknowledge you. One author also wants to thank the band "Infected Mushroom" for providing a good background soundtrack (and to see if he can get away with this in an RFC!) Another author would like to thank the band "Mushroom Infectors". This was funny at the time we wrote it, but we cannot remember why... 8. References 8.1. Normative References [I-D.ietf-dnsop-serve-stale] Lawrence, D., Kumari, W., and P. Sood, "Serving Stale Data to Improve DNS Resiliency", draft-ietf-dnsop-serve- stale-10 (work in progress), December 2019. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Protocol Modifications for the DNS Security Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, . [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms for DNS (EDNS(0))", STD 75, RFC 6891, DOI 10.17487/RFC6891, April 2013, . Kumari, et al. Expires June 20, 2020 [Page 12] Internet-Draft draft-ietf-dnsop-extended-error December 2019 8.2. Informative References [GeoffValidation] APNIC, G. H., "A quick review of DNSSEC Validation in today's Internet", June 2016, . [RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B. Wellington, "Secret Key Transaction Authentication for DNS (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000, . [RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram Transport Layer Security (DTLS)", RFC 8094, DOI 10.17487/RFC8094, February 2017, . Authors' Addresses Warren Kumari Google 1600 Amphitheatre Parkway Mountain View, CA 94043 US Email: warren@kumari.net Evan Hunt ISC 950 Charter St Redwood City, CA 94063 US Email: each@isc.org Roy Arends ICANN Email: roy.arends@icann.org Kumari, et al. Expires June 20, 2020 [Page 13] Internet-Draft draft-ietf-dnsop-extended-error December 2019 Wes Hardaker USC/ISI P.O. Box 382 Davis, CA 95617 US Email: ietf@hardakers.net David C Lawrence Oracle + Dyn 150 Dow St Manchester, NH 03101 US Email: tale@dd.org Kumari, et al. Expires June 20, 2020 [Page 14]