Network Working Group W. Kumari
Internet-Draft Google
Intended status: Standards Track E. Hunt
Expires: April 3, 2020 ISC
R. Arends
ICANN
W. Hardaker
USC/ISI
D. Lawrence
Oracle + Dyn
October 01, 2019
Extended DNS Errors
draft-ietf-dnsop-extended-error-12
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 http://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 April 3, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://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
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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. Defined Extended DNS Errors . . . . . . . . . . . . . . . . . 5
3.1. Extended DNS Error Code 0 - Other . . . . . . . . . . . . 5
3.2. Extended DNS Error Code 1 -
Unsupported DNSKEY Algorithm . . . . . . . . . . . . . . 5
3.3. Extended DNS Error Code 2 - Unsupported DS
Digest Type . . . . . . . . . . . . . . . . . . . . . . . 5
3.4. Extended DNS Error Code 3 - Stale Answer . . . . . . . . 5
3.5. Extended DNS Error Code 4 - Forged Answer . . . . . . . . 6
3.6. Extended DNS Error Code 5 - DNSSEC Indeterminate . . . . 6
3.7. Extended DNS Error Code 6 - DNSSEC Bogus . . . . . . . . 6
3.8. Extended DNS Error Code 7 - Signature Expired . . . . . . 6
3.9. Extended DNS Error Code 8 - Signature Not Yet Valid . . . 6
3.10. Extended DNS Error Code 9 - DNSKEY Missing . . . . . . . 6
3.11. Extended DNS Error Code 10 - RRSIGs Missing . . . . . . . 6
3.12. Extended DNS Error Code 11 - No Zone Key Bit Set . . . . 6
3.13. Extended DNS Error Code 12 - NSEC Missing . . . . . . . . 6
3.14. Extended DNS Error Code 13 - Cached Error . . . . . . . . 7
3.15. Extended DNS Error Code 14 - Not Ready . . . . . . . . . 7
3.16. Extended DNS Error Code 15 - Blocked . . . . . . . . . . 7
3.17. Extended DNS Error Code 16 - Censored . . . . . . . . . . 7
3.18. Extended DNS Error Code 17 - Filtered . . . . . . . . . . 7
3.19. Extended DNS Error Code 18 - Prohibited . . . . . . . . . 7
3.20. Extended DNS Error Code 19 - Stale NXDOMAIN Answer . . . 7
3.21. Extended DNS Error Code 20 - Not Authoritative . . . . . 8
3.22. Extended DNS Error Code 21 - Not Supported . . . . . . . 8
3.23. Extended DNS Error Code 22 - No Reachable Authority . . . 8
3.24. Extended DNS Error Code 23 - Network Error . . . . . . . 8
3.25. Extended DNS Error Code 24 - Invalid Data . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
4.1. A New Extended DNS Error Code EDNS Option . . . . . . . . 8
4.2. New Registry Table for Extended DNS Error Codes . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
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7. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . 12
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
extended error codes MUST NOT assume that a combination will make
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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 ([RFC2671]) 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 4 plus the length of the EXTRA-TEXT section
(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 4.1.
o EXTRA-TEXT, a variable length, UTF-8 encoded, text field that may
hold additional textual information. Note: EXTRA-TEXT may be zero
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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. 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 4.1. 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.
3.1. 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.
3.2. Extended DNS Error Code 1 - Unsupported DNSKEY Algorithm
The resolver attempted to perform DNSSEC validation, but a DNSKEY
RRSET contained only unsupported DNSSEC algorithms.
3.3. 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.
3.4. 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.
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3.5. 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.
3.6. Extended DNS Error Code 5 - DNSSEC Indeterminate
The resolver attempted to perform DNSSEC validation, but validation
ended in the Indeterminate state [RFC4035].
3.7. Extended DNS Error Code 6 - DNSSEC Bogus
The resolver attempted to perform DNSSEC validation, but validation
ended in the Bogus state.
3.8. 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.
3.9. 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.
3.10. 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.
3.11. 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.
3.12. 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.
3.13. 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.
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3.14. Extended DNS Error Code 13 - Cached Error
The resolver is returning the SERVFAIL RCODE from its cache.
3.15. Extended DNS Error Code 14 - Not Ready
The server is unable to answer the query as it is not fully
functional (yet).
3.16. 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.
3.17. 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).
3.18. 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."
3.19. 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.
3.20. 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.
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3.21. 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.
3.22. Extended DNS Error Code 21 - Not Supported
The requested operation or query is not supported as its use has been
deprecated.
3.23. Extended DNS Error Code 22 - No Reachable Authority
The resolver could not reach any of the authoritative name servers
(or they refused to reply).
3.24. Extended DNS Error Code 23 - Network Error
An unrecoverable error occurred while communicating with another
server.
3.25. 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.
4. IANA Considerations
4.1. 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 ]
4.2. 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
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maintain this "Extended DNS Error" codes registry. The code-point
space for the INFO-CODE index is to be broken into 3 ranges:
o 0 - 32767: Expert Review [RFC2434].
o 32768 - 49151: First come, first served.
o 49152 - 65535: Experimental / 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 3.1
INFO-CODE: 1
Purpose: Unsupported DNSKEY Algorithm
Reference: Section 3.2
INFO-CODE: 2
Purpose: Unsupported DS Digest Type
Reference: Section 3.3
INFO-CODE: 3
Purpose: Stale Answer
Reference: Section 3.4, [I-D.ietf-dnsop-serve-stale]
INFO-CODE: 4
Purpose: Forged Answer
Reference: Section 3.5
INFO-CODE: 5
Purpose: DNSSEC Indeterminate
Reference: Section 3.6
INFO-CODE: 6
Purpose: DNSSEC Bogus
Reference: Section 3.7
INFO-CODE: 7
Purpose: Signature Expired
Reference: Section 3.8
INFO-CODE: 8
Purpose: Signature Not Yet Valid
Reference: Section 3.9
INFO-CODE: 9
Purpose: DNSKEY Missing
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Reference: Section 3.10
INFO-CODE: 10
Purpose: RRSIGs Missing
Reference: Section 3.11
INFO-CODE: 11
Purpose: No Zone Key Bit Set
Reference: Section 3.12
INFO-CODE: 12
Purpose: NSEC Missing
Reference: Section 3.13
INFO-CODE: 13
Purpose: Cached Error
Reference: Section 3.14
INFO-CODE: 14
Purpose: Not Ready.
Reference: Section 3.15
INFO-CODE: 15
Purpose: Blocked
Reference: Section 3.16
INFO-CODE: 16
Purpose: Censored
Reference: Section 3.17
INFO-CODE: 17
Purpose: Filtered
Reference: Section 3.18
INFO-CODE: 18
Purpose: Prohibited
Reference: Section 3.19
INFO-CODE: 19
Purpose: Stale NXDomain Answer
Reference: Section 3.20
INFO-CODE: 20
Purpose: Not Authoritative
Reference: Section 3.21
INFO-CODE: 21
Purpose: Not Supported
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Reference: Section 3.22
INFO-CODE: 22
Purpose: No Reachable Authority
Reference: Section 3.23
INFO-CODE: 23
Purpose: Network Error
Reference: Section 3.24
INFO-CODE: 24
Purpose: Invalid Data
Reference: Section 3.25
5. 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
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.
6. 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.
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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...
7. References
7.1. 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-08 (work in progress), September 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 2434,
DOI 10.17487/RFC2434, October 1998, <https://www.rfc-
editor.org/info/rfc2434>.
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
RFC 2671, DOI 10.17487/RFC2671, August 1999,
<https://www.rfc-editor.org/info/rfc2671>.
[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,
<https://www.rfc-editor.org/info/rfc4035>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013, <https://www.rfc-
editor.org/info/rfc6891>.
7.2. Informative References
[GeoffValidation]
IANA, "A quick review of DNSSEC Validation in today's
Internet", June 2016, <http://www.potaroo.net/
presentations/2016-06-27-dnssec.pdf>.
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[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,
<https://www.rfc-editor.org/info/rfc2845>.
[RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
Transport Layer Security (DTLS)", RFC 8094,
DOI 10.17487/RFC8094, February 2017, <https://www.rfc-
editor.org/info/rfc8094>.
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
Wes Hardaker
USC/ISI
P.O. Box 382
Davis, CA 95617
US
Email: ietf@hardakers.net
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David C Lawrence
Oracle + Dyn
150 Dow St
Manchester, NH 03101
US
Email: tale@dd.org
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