Network Working Group W. Kumari
Internet-Draft Google
Intended status: Standards Track E. Hunt
Expires: February 10, 2020 ISC
R. Arends
ICANN
W. Hardaker
USC/ISI
D. Lawrence
Oracle + Dyn
August 09, 2019
Extended DNS Errors
draft-ietf-dnsop-extended-error-07
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.
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
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This Internet-Draft will expire on February 10, 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
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Table of Contents
1. Introduction and background . . . . . . . . . . . . . . . . . 3
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3
2. Extended Error EDNS0 option format . . . . . . . . . . . . . 4
3. Use of the Extended DNS Error option . . . . . . . . . . . . 4
3.1. The INFO-CODE field . . . . . . . . . . . . . . . . . . . 5
3.2. The EXTRA-TEXT field . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . 5
4.3. Extended DNS Error Code 2 - Unsupported
DS Algorithm . . . . . . . . . . . . . . . . . . . . . . 5
4.4. Extended DNS Error Code 3 - Stale Answer . . . . . . . . 5
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 . . . . . . . 6
4.11. Extended DNS Error Code 10 - RRSIGs Missing . . . . . . . 6
4.12. Extended DNS Error Code 11 - No Zone Key Bit Set . . . . 6
4.13. Extended DNS Error Code 12 - NSEC Missing . . . . . . . . 6
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 - Prohibited . . . . . . . . . 7
4.19. Extended DNS Error Code 18 - Stale Answer . . . . . . . . 7
4.20. Extended DNS Error Code 19 - Lame . . . . . . . . . . . . 7
4.21. Extended DNS Error Code 20 - Deprecated . . . . . . . . . 8
4.22. Extended DNS Error Code 21 - No Reachable Authority . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5.1. A New Extended Error Code EDNS Option . . . . . . . . . . 8
5.2. New Double-Index Registry Table for Extended Error Codes 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
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8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
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
a bad hair day?
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 DNSSEC bogus name (using a validating
resolver), the stub resolver receives only a SERVFAIL in response.
Unfortunately, SERVFAIL is used to signal many sorts of DNS errors,
and so the stub resolver simply asks the next configured DNS
resolver. The result of trying the next resolver is one of two
outcomes: either the next resolver also validates, a SERVFAIL is
returned again, and the user gets an (largely) incomprehensible error
message; or the next resolver is not a validating resolver, and the
user is returned a potentially harmful result.
This document specifies a mechanism to extend (or annotate) DNS
errors to provide additional information about the cause of the
error. These extended error codes are specially useful when received
by resolvers, to return to stub resolvers or to downstream resolvers.
Authoritative servers MAY parse and use them, but most error codes
would make no sense for them. Authoritative servers may need to
generate extended error codes though.
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].
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2. Extended 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 (defined in [RFC6891]]), for EDE is TBD.
[RFC Editor: change TBD to the proper code once assigned by IANA.]
o OPTION-LENGTH, 2 octets ((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.
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.
3. Use of the Extended DNS Error option
The Extended DNS Error (EDE) is an EDNS option. It can be included
in any response (SERVFAIL, NXDOMAIN, REFUSED, 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.
The fields of the Extended DNS Error option are defined further in
the following sub-sections.
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3.1. The INFO-CODE field
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 to the "Extended DNS Errors" registry
Section 5.1.
3.2. The EXTRA-TEXT field
The UTF-8-encoded, EXTRA-TEXT field may be zero-length, or may hold
additional information useful to network operators.
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 codes" 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.
4.2. Extended DNS Error Code 1 - Unsupported DNSKEY Algorithm
The resolver attempted to perform DNSSEC validation, but a DNSKEY
RRSET contained only unknown algorithms.
4.3. Extended DNS Error Code 2 - Unsupported DS Algorithm
The resolver attempted to perform DNSSEC validation, but a DS RRSET
contained only unknown algorithms.
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 a previously cached data instead of answering
with an error. This is typically caused by problems on authoritative
side, possibly as result of a DoS attack.
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4.5. Extended DNS Error Code 4 - Forged Answer
For policy reasons (legal obligation, or malware filtering, for
instance), an answer was forged.
4.6. Extended DNS Error Code 5 - DNSSEC Indeterminate
The resolver attempted to perform DNSSEC validation, but validation
ended in the Indeterminate state.
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, a signature in
the validation chain was expired.
4.9. Extended DNS Error Code 8 - Signature Not Yet Valid
The resolver attempted to perform DNSSEC validation, but the
signatures received were not yet valid.
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.
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4.14. Extended DNS Error Code 13 - Cached Error
The resolver has cached SERVFAIL for this query without additional
information.
4.15. Extended DNS Error Code 14 - Not Ready
The server is unable to answer the query as it is not fully up and
functional yet.
4.16. Extended DNS Error Code 15 - Blocked
The resolver attempted to perfom a DNS query but the domain is
blacklisted due to a security policy implemented on the server being
directly talked to.
4.17. Extended DNS Error Code 16 - Censored
The resolver attempted to perfom a DNS query but the domain was
blacklisted by a security policy imposed upon the server being talked
to. Note that how the imposed policy is applied is irrelevant (in-
band DNS somehow, court order, etc).
4.18. Extended DNS Error Code 17 - 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.
4.19. Extended DNS Error Code 18 - Stale Answer
The resolver was unable to resolve answer within its time limits and
decided to answer with a previously cached NXDOMAIN answer instead of
answering with an error. This is typically caused by problems on
authoritative side, possibly as result of a DoS attack.
4.20. Extended DNS Error Code 19 - Lame
An authoritative server that receives a query (with the RD bit clear)
for a domain for which it is not authoritative SHOULD include this
EDE code in the SERVFAIL response. A resolver that receives a query
(with the RD bit clear) SHOULD include this EDE code in the REFUSED
response.
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4.21. Extended DNS Error Code 20 - Deprecated
The requested operation or query is not supported as its use has been
deprecated.
4.22. Extended DNS Error Code 21 - No Reachable Authority
The resolver could not reach any of the authoritative name servers
(or they refused to reply).
5. IANA Considerations
5.1. A New Extended 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 Double-Index Registry Table for Extended Error Codes
This document defines a new double-index 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 each INFO-CODE index is to be broken into 3 ranges:
o 0 - : Specification required.
o 65023 - 65279: First come, first served.
o 65280 - 32767: 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 4.1
INFO-CODE: 1
Purpose: Unsupported DNSKEY Algorithm
Reference: Section 4.2
INFO-CODE: 2
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Purpose: Unsupported DS Algorithm
Reference: Section 4.3
INFO-CODE: 3
Purpose: Answering with stale/cached data
Reference: Section 4.4
INFO-CODE: 4
Purpose: Forged Answer
Reference: Section 4.5
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: No NSEC records could be obtained
Reference: Section 4.13
INFO-CODE: 13
Purpose: The SERVFAIL error comes from the cache
Reference: Section 4.14
INFO-CODE: 14
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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
INFO-CODE: 17
Purpose: Prohibited
Reference: Section 4.18
INFO-CODE: 18
Purpose: Answering with stale/cached NXDOMAIN data
Reference: Section 4.19
INFO-CODE: 19
Purpose: Lame
Reference: Section 4.20
INFO-CODE: 20
Purpose: Deprecated
Reference: Section 4.21
INFO-CODE: 21
Purpose: No Reachable Authority
Reference: Section 4.21
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 is very similar to a kid asking his mother if
he can have another cookie. When the mother says "No, it will ruin
your dinner!", going off and asking his (more permissive) father and
getting a "Yes, sure, have a cookie!".
This information is unauthenticated information, and an attacker (e.g
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
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mechanisms, 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.
7. Acknowledgements
The authors wish to thank Joe Abley, Mark Andrews, Stephane
Bortzmeyer, Vladimir Cunat, Peter DeVries, Peter van Dijk, Donald
Eastlake, Bob Harold, Geoff Huston, Shane Kerr, Edward Lewis, Carlos
M. Martinez, George Michelson, Michael Sheldon, Petr Spacek, Ondrej
Sury, 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.
I also want to thank the band "Infected Mushroom" for providing a
good background soundtrack (and to see if I can get away with this!)
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
[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>.
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
RFC 2671, DOI 10.17487/RFC2671, August 1999,
<https://www.rfc-editor.org/info/rfc2671>.
[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>.
8.2. 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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