< draft-ietf-dnsop-extended-error-06.txt   draft-ietf-dnsop-extended-error-07.txt >
Network Working Group W. Kumari Network Working Group W. Kumari
Internet-Draft Google Internet-Draft Google
Intended status: Standards Track E. Hunt Intended status: Standards Track E. Hunt
Expires: January 9, 2020 ISC Expires: February 10, 2020 ISC
R. Arends R. Arends
ICANN ICANN
W. Hardaker W. Hardaker
USC/ISI USC/ISI
D. Lawrence D. Lawrence
Oracle + Dyn Oracle + Dyn
July 08, 2019 August 09, 2019
Extended DNS Errors Extended DNS Errors
draft-ietf-dnsop-extended-error-06 draft-ietf-dnsop-extended-error-07
Abstract Abstract
This document defines an extensible method to return additional This document defines an extensible method to return additional
information about the cause of DNS errors. Though created primarily information about the cause of DNS errors. Though created primarily
to extend SERVFAIL to provide additional information about the cause to extend SERVFAIL to provide additional information about the cause
of DNS and DNSSEC failures, the Extended DNS Errors option defined in of DNS and DNSSEC failures, the Extended DNS Errors option defined in
this document allows all response types to contain extended error this document allows all response types to contain extended error
information. information.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 9, 2020. This Internet-Draft will expire on February 10, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction and background . . . . . . . . . . . . . . . . . 3 1. Introduction and background . . . . . . . . . . . . . . . . . 3
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 4 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3
2. Extended Error EDNS0 option format . . . . . . . . . . . . . 4 2. Extended Error EDNS0 option format . . . . . . . . . . . . . 4
3. Use of the Extended DNS Error option . . . . . . . . . . . . 5 3. Use of the Extended DNS Error option . . . . . . . . . . . . 4
3.1. The R (Retry) flag . . . . . . . . . . . . . . . . . . . 5 3.1. The INFO-CODE field . . . . . . . . . . . . . . . . . . . 5
3.2. The RESPONSE-CODE field . . . . . . . . . . . . . . . . . 5 3.2. The EXTRA-TEXT field . . . . . . . . . . . . . . . . . . 5
3.3. The INFO-CODE field . . . . . . . . . . . . . . . . . . . 6 4. Defined Extended DNS Errors . . . . . . . . . . . . . . . . . 5
3.4. The EXTRA-TEXT field . . . . . . . . . . . . . . . . . . 6 4.1. Extended DNS Error Code 0 - Other . . . . . . . . . . . . 5
4. Defined Extended DNS Errors . . . . . . . . . . . . . . . . . 6 4.2. Extended DNS Error Code 1 -
4.1. INFO-CODEs for use with RESPONSE-CODE: NOERROR(0) . . . . 6 Unsupported DNSKEY Algorithm . . . . . . . . . . . . . . 5
4.1.1. NOERROR Extended DNS Error Code 1 - Unsupported 4.3. Extended DNS Error Code 2 - Unsupported
DNSKEY Algorithm . . . . . . . . . . . . . . . . . . 6 DS Algorithm . . . . . . . . . . . . . . . . . . . . . . 5
4.1.2. NOERROR Extended DNS Error Code 2 - Unsupported 4.4. Extended DNS Error Code 3 - Stale Answer . . . . . . . . 5
DS Algorithm . . . . . . . . . . . . . . . . . . . . 6 4.5. Extended DNS Error Code 4 - Forged Answer . . . . . . . . 6
4.1.3. INFO-CODEs for use with RESPONSE-CODE: NOERROR(3) . . 7 4.6. Extended DNS Error Code 5 - DNSSEC Indeterminate . . . . 6
4.1.4. NOERROR Extended DNS Error Code 4 - Forged answer . . 7 4.7. Extended DNS Error Code 6 - DNSSEC Bogus . . . . . . . . 6
4.1.5. SERVFAIL Extended DNS Error Code 5 - DNSSEC 4.8. Extended DNS Error Code 7 - Signature Expired . . . . . . 6
Indeterminate . . . . . . . . . . . . . . . . . . . . 7 4.9. Extended DNS Error Code 8 - Signature Not Yet Valid . . . 6
4.2. INFO-CODEs for use with RESPONSE-CODE: SERVFAIL(2) . . . 7 4.10. Extended DNS Error Code 9 - DNSKEY Missing . . . . . . . 6
4.2.1. SERVFAIL Extended DNS Error Code 1 - DNSSEC Bogus . . 7 4.11. Extended DNS Error Code 10 - RRSIGs Missing . . . . . . . 6
4.2.2. SERVFAIL Extended DNS Error Code 2 - Signature 4.12. Extended DNS Error Code 11 - No Zone Key Bit Set . . . . 6
Expired . . . . . . . . . . . . . . . . . . . . . . . 7 4.13. Extended DNS Error Code 12 - NSEC Missing . . . . . . . . 6
4.2.3. SERVFAIL Extended DNS Error Code 3 - Signature Not 4.14. Extended DNS Error Code 13 - Cached Error . . . . . . . . 7
Yet Valid . . . . . . . . . . . . . . . . . . . . . . 7 4.15. Extended DNS Error Code 14 - Not Ready . . . . . . . . . 7
4.2.4. SERVFAIL Extended DNS Error Code 4 - DNSKEY missing . 7 4.16. Extended DNS Error Code 15 - Blocked . . . . . . . . . . 7
4.2.5. SERVFAIL Extended DNS Error Code 5 - RRSIGs missing . 8 4.17. Extended DNS Error Code 16 - Censored . . . . . . . . . . 7
4.2.6. SERVFAIL Extended DNS Error Code 6 - No Zone Key Bit 4.18. Extended DNS Error Code 17 - Prohibited . . . . . . . . . 7
Set . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.19. Extended DNS Error Code 18 - Stale Answer . . . . . . . . 7
4.2.7. SERVFAIL Extended DNS Error Code 7 - No 4.20. Extended DNS Error Code 19 - Lame . . . . . . . . . . . . 7
Reachable Authority . . . . . . . . . . . . . . . . . 8 4.21. Extended DNS Error Code 20 - Deprecated . . . . . . . . . 8
4.2.8. SERVFAIL Extended DNS Error Code 8 - NSEC Missing . . 8 4.22. Extended DNS Error Code 21 - No Reachable Authority . . . 8
4.2.9. SERVFAIL Extended DNS Error Code 9 - Cached Error . . 8 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
4.2.10. SERVFAIL Extended DNS Error Code 10 - Not Ready . . . 8 5.1. A New Extended Error Code EDNS Option . . . . . . . . . . 8
4.3. INFO-CODEs for use with RESPONSE-CODE: NOTIMP(4) . . . . 8 5.2. New Double-Index Registry Table for Extended Error Codes 8
4.3.1. NOTIMP Extended DNS Error Code 1 - Deprecated . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
4.4. INFO-CODEs for use with RESPONSE-CODE: REFUSED(5) . . . . 8 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
4.4.1. REFUSED Extended DNS Error Code 1 - Lame . . . . . . 8 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.4.2. REFUSED Extended DNS Error Code 2 - Prohibited . . . 9 8.1. Normative References . . . . . . . . . . . . . . . . . . 11
4.5. INFO-CODEs for use with RESPONSE-CODE: NXDOMAIN(3) . . . 9 8.2. Informative References . . . . . . . . . . . . . . . . . 11
4.5.1. NXDOMAIN Extended DNS Error Code 1 - Blocked . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
4.6. INFO-CODEs for use with RESPONSE-CODE: NXDOMAIN(3) . . . 9
4.6.1. NXDOMAIN Extended DNS Error Code 2 - Censored . . . . 9
4.7. INFO-CODEs for use with RESPONSE-CODE: NXDOMAIN(3) . . . 9
4.7.1. NXDOMAIN Extended DNS Error Code 3 - Stale Answer . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
5.1. A New Extended Error Code EDNS Option . . . . . . . . . . 10
5.2. New Double-Index Registry Table for Extended Error Codes 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . 13
8.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction and background 1. Introduction and background
There are many reasons that a DNS query may fail, some of them There are many reasons that a DNS query may fail, some of them
transient, some permanent; some can be resolved by querying another transient, some permanent; some can be resolved by querying another
server, some are likely best handled by stopping resolution. server, some are likely best handled by stopping resolution.
Unfortunately, the error signals that a DNS server can return are Unfortunately, the error signals that a DNS server can return are
very limited, and are not very expressive. This means that very limited, and are not very expressive. This means that
applications and resolvers often have to "guess" at what the issue is 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 - e.g. was the answer marked REFUSED because of a lame delegation, or
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Unfortunately, SERVFAIL is used to signal many sorts of DNS errors, Unfortunately, SERVFAIL is used to signal many sorts of DNS errors,
and so the stub resolver simply asks the next configured DNS and so the stub resolver simply asks the next configured DNS
resolver. The result of trying the next resolver is one of two resolver. The result of trying the next resolver is one of two
outcomes: either the next resolver also validates, a SERVFAIL is outcomes: either the next resolver also validates, a SERVFAIL is
returned again, and the user gets an (largely) incomprehensible error returned again, and the user gets an (largely) incomprehensible error
message; or the next resolver is not a validating resolver, and the message; or the next resolver is not a validating resolver, and the
user is returned a potentially harmful result. user is returned a potentially harmful result.
This document specifies a mechanism to extend (or annotate) DNS This document specifies a mechanism to extend (or annotate) DNS
errors to provide additional information about the cause of the errors to provide additional information about the cause of the
error. When properly authenticated, this information can be used by error. These extended error codes are specially useful when received
the resolver to make a decision regarding whether or not to retry or by resolvers, to return to stub resolvers or to downstream resolvers.
it can be used or by technical users attempting to debug issues.
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 Authoritative servers MAY parse and use them, but most error codes
would make no sense for them. Authoritative servers may need to would make no sense for them. Authoritative servers may need to
generate extended error codes though. generate extended error codes though.
1.1. Requirements notation 1.1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
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Error (EDE) information in DNS messages. The option is structured as Error (EDE) information in DNS messages. The option is structured as
follows: follows:
1 1 1 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | OPTION-CODE | 0: | OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | OPTION-LENGTH | 2: | OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | RCODE | R | Res | 4: | INFO-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6: | INFO-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6: / EXTRA-TEXT ... / 6: / EXTRA-TEXT ... /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Field definition details: Field definition details:
o OPTION-CODE, 2 octets (defined in [RFC6891]), for EDE is TBD. o OPTION-CODE, 2 octets (defined in [RFC6891]]), for EDE is TBD.
[RFC Editor: change TBD to the proper code once assigned by IANA.] [RFC Editor: change TBD to the proper code once assigned by IANA.]
o OPTION-LENGTH, 2 octets ((defined in [RFC6891]) contains the o OPTION-LENGTH, 2 octets ((defined in [RFC6891]]) contains the
length of the payload (everything after OPTION-LENGTH) in octets length of the payload (everything after OPTION-LENGTH) in octets
and should be 4 plus the length of the EXTRA-TEXT section (which and should be 4 plus the length of the EXTRA-TEXT section (which
may be a zero-length string). may be a zero-length string).
o The RETRY flag, 1 bit; the RETRY bit (R) indicates a flag defined
for use in this specification.
o The RESERVED bits, 4 bits: these bits are reserved for future use,
potentially as additional flags. The RESERVED bits MUST be set to
0 by the sender and MUST be ignored by the receiver.
o RESPONSE-CODE, 12 bits: the concatenation of the upper 8-bits of
the RCODE (stored in the TTL field of the EDNS0 resource record
[RFC2671]) and the 4 bits of the RCODE field of the DNS message.
o INFO-CODE, 16-bits, which is the principal contribution of this o INFO-CODE, 16-bits, which is the principal contribution of this
document. document.
o EXTRA-TEXT, a variable length, UTF-8 encoded, text field that may o EXTRA-TEXT, a variable length, UTF-8 encoded, text field that may
hold additional textual information. Note: EXTRA-TEXT may be zero hold additional textual information. Note: EXTRA-TEXT may be zero
octets in length, indicating there is no EXTRA-TEXT included. octets in length, indicating there is no EXTRA-TEXT included.
3. Use of the Extended DNS Error option 3. Use of the Extended DNS Error option
The Extended DNS Error (EDE) is an EDNS option. It can be included The Extended DNS Error (EDE) is an EDNS option. It can be included
in any response (SERVFAIL, NXDOMAIN, REFUSED, etc) to a query that in any response (SERVFAIL, NXDOMAIN, REFUSED, etc) to a query that
includes OPT Pseudo-RR [RFC6891]. This document includes a set of includes OPT Pseudo-RR [RFC6891]. This document includes a set of
initial codepoints (and requests to the IANA to add them to the initial codepoints (and requests to the IANA to add them to the
registry), but is extensible via the IANA registry to allow registry), but is extensible via the IANA registry to allow
additional error and information codes to be defined in the future. additional error and information codes to be defined in the future.
The fields of the Extended DNS Error option are defined further in The fields of the Extended DNS Error option are defined further in
the following sub-sections. the following sub-sections.
3.1. The R (Retry) flag 3.1. The INFO-CODE field
The R (Retry) flag provides a hint as to what the receiver may want
to do with this annotated error. Specifically, the R (or Retry) flag
provides a hint to the receiver that it should retry the query to
another server. If the R bit is set (1), the sender believes that
retrying the query may provide a successful answer next time; if the
R bit is clear (0), the sender believes that the resolver should not
ask another server.
The mechanism is specifically designed to be extensible, and so
implementations may receive EDE codes that it does not understand.
The R flag allows implementations to make a decision as to what to do
if it receives a response with an unknown code - retry or drop the
query. Note that this flag is only a suggestion. Unless a
protective transport mechanism (like TSIG [RFC2845] or (D)TLS xref
target="RFC7858"/>, [RFC8094]) is used, the bit's value could have
have been altered by a person-in-the-middle. Receivers can choose to
ignore this hint. See the security considerations for additional
considerations.
3.2. The RESPONSE-CODE field
This 12-bit value SHOULD be a copy of the combined RCODE from the
extended RCODE field defined in the EDNS0 optional resource record
(stored in the TTL field of the EDNS0 resource record [RFC2671]) and
the 4 bits of the RCODE field of the DNS message. RESPONSE-CODEs MAY
use a different RCODE to provide additional or better information.
For example, multiple EDNS0/EDE records may be included in the
response and the supplemental EDNS0/EDE records may wish to include
other RESPONSE-CODE values based on communication results with other
DNS servers.
3.3. The INFO-CODE field
This 16-bit value provides the additional context for the RESPONSE-
CODE value. This combination of the RESPONSE-CODE and the INFO-CODE
serve as a joint-index into the IANA "Extended DNS Errors" registry.
Note to implementers: the combination of the RESPONSE-CODE and INFO- This 16-bit value, encoded in network (MSB) byte order, provides the
CODE fits within a 24-bit field, allowing implementers the choice of additional context for the RESPONSE-CODE of the DNS message. The
treating the combination as either two separate values, as defined in INFO-CODE serves as an index to the "Extended DNS Errors" registry
this document, or as a single 24-bit integer as long as the results Section 5.1.
are deterministic.
3.4. The EXTRA-TEXT field 3.2. The EXTRA-TEXT field
The UTF-8-encoded, EXTRA-TEXT field may be zero-length, or may hold The UTF-8-encoded, EXTRA-TEXT field may be zero-length, or may hold
additional information useful to network operators. additional information useful to network operators.
4. Defined Extended DNS Errors 4. Defined Extended DNS Errors
This document defines some initial EDE codes. The mechanism is This document defines some initial EDE codes. The mechanism is
intended to be extensible, and additional code-points can be intended to be extensible, and additional code-points can be
registered in the "Extended DNS Errors" registry. This document registered in the "Extended DNS Errors" registry Section 5.1. The
provides suggestions for the R flag, but the originating server may INFO-CODE from the EDE EDNS option is used to serve as an index into
ignore these recommendations if it knows better. the "Extended DNS Error codes" IANA registry, the initial values for
which are defined in the following sub-sections.
The RESPONSE-CODE and the INFO-CODE from the EDE EDNS option is used 4.1. Extended DNS Error Code 0 - Other
to serve as a double index into the "Extended DNS Error codes" IANA
registry, the initial values for which are defined in the following
sub-sections.
4.1. INFO-CODEs for use with RESPONSE-CODE: NOERROR(0) 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.
4.1.1. NOERROR Extended DNS Error Code 1 - Unsupported DNSKEY Algorithm 4.2. Extended DNS Error Code 1 - Unsupported DNSKEY Algorithm
The resolver attempted to perform DNSSEC validation, but a DNSKEY The resolver attempted to perform DNSSEC validation, but a DNSKEY
RRSET contained only unknown algorithms. The R flag should be set. RRSET contained only unknown algorithms.
4.1.2. NOERROR Extended DNS Error Code 2 - Unsupported DS Algorithm 4.3. Extended DNS Error Code 2 - Unsupported DS Algorithm
The resolver attempted to perform DNSSEC validation, but a DS RRSET The resolver attempted to perform DNSSEC validation, but a DS RRSET
contained only unknown algorithms. The R flag should be set. contained only unknown algorithms.
4.1.3. INFO-CODEs for use with RESPONSE-CODE: NOERROR(3)
4.1.3.1. NOERROR Extended DNS Error Code 3 - Stale Answer 4.4. Extended DNS Error Code 3 - Stale Answer
The resolver was unable to resolve answer within its time limits and The resolver was unable to resolve answer within its time limits and
decided to answer with a previously cached data instead of answering decided to answer with a previously cached data instead of answering
with an error. This is typically caused by problems on authoritative with an error. This is typically caused by problems on authoritative
side, possibly as result of a DoS attack. The R flag should not be side, possibly as result of a DoS attack.
set, since retrying is likely to create additional load without
yielding a more fresh answer.
4.1.4. NOERROR Extended DNS Error Code 4 - Forged answer 4.5. Extended DNS Error Code 4 - Forged Answer
For policy reasons (legal obligation, or malware filtering, for For policy reasons (legal obligation, or malware filtering, for
instance), an answer was forged. The R flag should not be set. instance), an answer was forged.
4.1.5. SERVFAIL Extended DNS Error Code 5 - DNSSEC Indeterminate 4.6. Extended DNS Error Code 5 - DNSSEC Indeterminate
The resolver attempted to perform DNSSEC validation, but validation The resolver attempted to perform DNSSEC validation, but validation
ended in the Indeterminate state. The R flag should not be set. ended in the Indeterminate state.
4.2. INFO-CODEs for use with RESPONSE-CODE: SERVFAIL(2)
4.2.1. SERVFAIL Extended DNS Error Code 1 - DNSSEC Bogus 4.7. Extended DNS Error Code 6 - DNSSEC Bogus
The resolver attempted to perform DNSSEC validation, but validation The resolver attempted to perform DNSSEC validation, but validation
ended in the Bogus state. The R flag should not be set. ended in the Bogus state.
4.2.2. SERVFAIL Extended DNS Error Code 2 - Signature Expired 4.8. Extended DNS Error Code 7 - Signature Expired
The resolver attempted to perform DNSSEC validation, a signature in The resolver attempted to perform DNSSEC validation, a signature in
the validation chain was expired. The R flag should not be set. the validation chain was expired.
4.2.3. SERVFAIL Extended DNS Error Code 3 - Signature Not Yet Valid 4.9. Extended DNS Error Code 8 - Signature Not Yet Valid
The resolver attempted to perform DNSSEC validation, but the The resolver attempted to perform DNSSEC validation, but the
signatures received were not yet valid. The R flag should not be signatures received were not yet valid.
set.
4.2.4. SERVFAIL Extended DNS Error Code 4 - DNSKEY missing 4.10. Extended DNS Error Code 9 - DNSKEY Missing
A DS record existed at a parent, but no supported matching DNSKEY A DS record existed at a parent, but no supported matching DNSKEY
record could be found for the child. The R flag should not be set. record could be found for the child.
4.2.5. SERVFAIL Extended DNS Error Code 5 - RRSIGs missing 4.11. Extended DNS Error Code 10 - RRSIGs Missing
The resolver attempted to perform DNSSEC validation, but no RRSIGs The resolver attempted to perform DNSSEC validation, but no RRSIGs
could be found for at least one RRset where RRSIGs were expected. could be found for at least one RRset where RRSIGs were expected.
4.2.6. SERVFAIL Extended DNS Error Code 6 - No Zone Key Bit Set 4.12. Extended DNS Error Code 11 - No Zone Key Bit Set
The resolver attempted to perform DNSSEC validation, but no Zone Key The resolver attempted to perform DNSSEC validation, but no Zone Key
Bit was set in a DNSKEY. Bit was set in a DNSKEY.
4.2.7. SERVFAIL Extended DNS Error Code 7 - No Reachable Authority 4.13. Extended DNS Error Code 12 - NSEC Missing
The resolver could not reach any of the authoritative name servers
(or they refused to reply). The R flag should be set.
4.2.8. SERVFAIL Extended DNS Error Code 8 - NSEC Missing
The resolver attempted to perform DNSSEC validation, but the The resolver attempted to perform DNSSEC validation, but the
requested data was missing and a covering NSEC or NSEC3 was not requested data was missing and a covering NSEC or NSEC3 was not
provided. The R flag should be set. provided.
4.2.9. SERVFAIL Extended DNS Error Code 9 - Cached Error 4.14. Extended DNS Error Code 13 - Cached Error
The resolver has cached SERVFAIL for this query without additional The resolver has cached SERVFAIL for this query without additional
information. Th R flag should be set. information.
4.2.10. SERVFAIL Extended DNS Error Code 10 - Not Ready 4.15. Extended DNS Error Code 14 - Not Ready
The server is unable to answer the query as it is not fully up and The server is unable to answer the query as it is not fully up and
functional yet. functional yet.
4.3. INFO-CODEs for use with RESPONSE-CODE: NOTIMP(4) 4.16. Extended DNS Error Code 15 - Blocked
4.3.1. NOTIMP Extended DNS Error Code 1 - Deprecated
The requested operation or query is not supported as its use has been
deprecated. Implementations should not set the R flag. (Retrying
request elsewhere is unlikely to yield any other results.)
4.4. INFO-CODEs for use with RESPONSE-CODE: REFUSED(5) 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.
4.4.1. REFUSED Extended DNS Error Code 1 - Lame 4.17. Extended DNS Error Code 16 - Censored
An authoritative server that receives a query (with the RD bit clear) The resolver attempted to perfom a DNS query but the domain was
for a domain for which it is not authoritative SHOULD include this blacklisted by a security policy imposed upon the server being talked
EDE code in the SERVFAIL response. A resolver that receives a query to. Note that how the imposed policy is applied is irrelevant (in-
(with the RD bit clear) SHOULD include this EDE code in the REFUSED band DNS somehow, court order, etc).
response. Implementations should set the R flag in this case
(another nameserver or resolver might not be lame).
4.4.2. REFUSED Extended DNS Error Code 2 - Prohibited 4.18. Extended DNS Error Code 17 - Prohibited
An authoritative or recursive resolver that receives a query from an An authoritative or recursive resolver that receives a query from an
"unauthorized" client can annotate its REFUSED message with this "unauthorized" client can annotate its REFUSED message with this
code. Examples of "unauthorized" clients are recursive queries from code. Examples of "unauthorized" clients are recursive queries from
IP addresses outside the network, blacklisted IP addresses, local IP addresses outside the network, blacklisted IP addresses, local
policy, etc. policy, etc.
Implementations SHOULD allow operators to define what to set the R 4.19. Extended DNS Error Code 18 - Stale Answer
flag to in this case.
4.5. INFO-CODEs for use with RESPONSE-CODE: NXDOMAIN(3)
4.5.1. NXDOMAIN Extended DNS Error Code 1 - Blocked
The resolver attempted to perfom a DNS query but the domain is The resolver was unable to resolve answer within its time limits and
blacklisted due to a security policy implemented on the server being decided to answer with a previously cached NXDOMAIN answer instead of
directly talked to. The R flag should be set. answering with an error. This is typically caused by problems on
authoritative side, possibly as result of a DoS attack.
4.6. INFO-CODEs for use with RESPONSE-CODE: NXDOMAIN(3) 4.20. Extended DNS Error Code 19 - Lame
4.6.1. NXDOMAIN Extended DNS Error Code 2 - Censored 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.
The resolver attempted to perfom a DNS query but the domain was 4.21. Extended DNS Error Code 20 - Deprecated
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). The R flag should be set.
4.7. INFO-CODEs for use with RESPONSE-CODE: NXDOMAIN(3) The requested operation or query is not supported as its use has been
deprecated.
4.7.1. NXDOMAIN Extended DNS Error Code 3 - Stale Answer 4.22. Extended DNS Error Code 21 - No Reachable Authority
The resolver was unable to resolve answer within its time limits and The resolver could not reach any of the authoritative name servers
decided to answer with a previously cached NXDOMAIN answer instead of (or they refused to reply).
answering with an error. This is typically caused by problems on
authoritative side, possibly as result of a DoS attack. The R flag
should not be set, since retrying is likely to create additional load
without yielding a more fresh answer.
5. IANA Considerations 5. IANA Considerations
5.1. A New Extended Error Code EDNS Option 5.1. A New Extended Error Code EDNS Option
This document defines a new EDNS(0) option, entitled "Extended DNS This document defines a new EDNS(0) option, entitled "Extended DNS
Error", assigned a value of TBD1 from the "DNS EDNS0 Option Codes Error", assigned a value of TBD1 from the "DNS EDNS0 Option Codes
(OPT)" registry [to be removed upon publication: (OPT)" registry [to be removed upon publication:
[http://www.iana.org/assignments/dns-parameters/dns- [http://www.iana.org/assignments/dns-parameters/dns-
parameters.xhtml#dns-parameters-11] parameters.xhtml#dns-parameters-11]
Value Name Status Reference Value Name Status Reference
----- ---------------- ------ ------------------ ----- ---------------- ------ ------------------
TBD Extended DNS Error TBD [ This document ] TBD Extended DNS Error TBD [ This document ]
5.2. New Double-Index Registry Table for Extended Error Codes 5.2. New Double-Index Registry Table for Extended Error Codes
This document defines a new double-index IANA registry table, where This document defines a new double-index IANA registry table, where
the first index value is the combined RCODE value (see the the index value is the INFO-CODE from the Extended DNS Error EDNS
Section 3.2 section) and the second index value is the INFO-CODE from option defined in this document. The IANA is requested to create and
the Extended DNS Error EDNS option defined in this document. The maintain this "Extended DNS Error codes" registry. The code-point
IANA is requested to create and maintain this "Extended DNS Error space for each INFO-CODE index is to be broken into 3 ranges:
codes" registry. The codepoint space for each INFO-CODE index is to
be broken into 3 ranges:
o 0 - 65023: Specification required. o 0 - : Specification required.
o 65023 - 65279: First come, first served. o 65023 - 65279: First come, first served.
o 65280 - 65536: Experimental / Private use o 65280 - 32767: Experimental / Private use
A starting set of entries, based on the contents of this document, is A starting set of entries, based on the contents of this document, is
as follows: as follows:
RESPONSE-CODE: 0 (NOERROR) INFO-CODE: 0
Purpose: Other Error
Reference: Section 4.1
INFO-CODE: 1 INFO-CODE: 1
Purpose: Unsupported DNSKEY Purpose: Unsupported DNSKEY Algorithm
Reference: Section 4.1.1 Reference: Section 4.2
RESPONSE-CODE: 0 (NOERROR)
INFO-CODE: 2 INFO-CODE: 2
Purpose: Unsupported DS Algorithm Purpose: Unsupported DS Algorithm
Reference: Section 4.1.2 Reference: Section 4.3
RESPONSE-CODE: 3 (NOERROR)
INFO-CODE: 3 INFO-CODE: 3
Purpose: Answering with stale/cached data Purpose: Answering with stale/cached data
Reference: Section 4.1.3.1 Reference: Section 4.4
RESPONSE-CODE: 0 (NOERROR)
INFO-CODE: 4 INFO-CODE: 4
Purpose: Forged answer Purpose: Forged Answer
Reference: Section 4.1.4 Reference: Section 4.5
RESPONSE-CODE: 0 (NOERROR)
INFO-CODE: 5 INFO-CODE: 5
Purpose: DNSSEC Indeterminate Purpose: DNSSEC Indeterminate
Reference: Section 4.1.5 Reference: Section 4.6
RESPONSE-CODE: 2 (SERVFAIL) INFO-CODE: 6
INFO-CODE: 1
Purpose: DNSSEC Bogus Purpose: DNSSEC Bogus
Reference: Section 4.2.1 Reference: Section 4.7
RESPONSE-CODE: 2 (SERVFAIL) INFO-CODE: 7
INFO-CODE: 2
Purpose: Signature Expired Purpose: Signature Expired
Reference: Section 4.2.2 Reference: Section 4.8
RESPONSE-CODE: 2 (SERVFAIL) INFO-CODE: 8
INFO-CODE: 3
Purpose: Signature Not Yet Valid Purpose: Signature Not Yet Valid
Reference: Section 4.2.3 Reference: Section 4.9
RESPONSE-CODE: 2 (SERVFAIL) INFO-CODE: 9
INFO-CODE: 4 Purpose: DNSKEY Missing
Purpose: DNSKEY missing Reference: Section 4.10
Reference: Section 4.2.4
RESPONSE-CODE: 2 (SERVFAIL) INFO-CODE: 10
INFO-CODE: 5 Purpose: RRSIGs Missing
Purpose: RRSIGs missing Reference: Section 4.11
Reference: Section 4.2.5
RESPONSE-CODE: 2 (SERVFAIL) INFO-CODE: 11
INFO-CODE: 6
Purpose: No Zone Key Bit Set Purpose: No Zone Key Bit Set
Reference: Section 4.2.6 Reference: Section 4.12
RESPONSE-CODE: 2 (SERVFAIL) INFO-CODE: 12
INFO-CODE: 7
Purpose: No NSEC records could be obtained Purpose: No NSEC records could be obtained
Reference: Section 4.2.8 Reference: Section 4.13
RESPONSE-CODE: 2 (SERVFAIL) INFO-CODE: 13
INFO-CODE: 9
Purpose: The SERVFAIL error comes from the cache Purpose: The SERVFAIL error comes from the cache
Reference: Section 4.2.9 Reference: Section 4.14
RESPONSE-CODE: 2 (SERVFAIL) INFO-CODE: 14
INFO-CODE: 10
Purpose: Not Ready. Purpose: Not Ready.
Reference: Section 4.15
Reference: Section 4.2.10 INFO-CODE: 15
RESPONSE-CODE: 3 (NXDOMAIN)
INFO-CODE: 1
Purpose: Blocked Purpose: Blocked
Reference: Section 4.5.1 Reference: Section 4.16
RESPONSE-CODE: 3 (NXDOMAIN) INFO-CODE: 16
INFO-CODE: 2
Purpose: Censored Purpose: Censored
Reference: Section 4.6.1 Reference: Section 4.17
RESPONSE-CODE: 3 (NXDOMAIN) INFO-CODE: 17
INFO-CODE: 3 Purpose: Prohibited
Purpose: Answering with stale/cached NXDOMAIN data Reference: Section 4.18
Reference: Section 4.7.1
RESPONSE-CODE: 4 (NOTIMP) INFO-CODE: 18
INFO-CODE: 1 Purpose: Answering with stale/cached NXDOMAIN data
Purpose: Reference: Section 4.19
Reference: Section 4.4.2
RESPONSE-CODE: 5 (REFUSED) INFO-CODE: 19
INFO-CODE: 1
Purpose: Lame Purpose: Lame
Reference: Section 4.4.1 Reference: Section 4.20
RESPONSE-CODE: 5 (REFUSED) INFO-CODE: 20
INFO-CODE: 2 Purpose: Deprecated
Purpose: Prohibited Reference: Section 4.21
Reference: Section 4.4.2
INFO-CODE: 21
Purpose: No Reachable Authority
Reference: Section 4.21
6. Security Considerations 6. Security Considerations
Though DNSSEC continues to be deployed, unfortunately a significant Though DNSSEC continues to be deployed, unfortunately a significant
number of clients (~11% according to [GeoffValidation]) that receive number of clients (~11% according to [GeoffValidation]) that receive
a SERVFAIL from a validating resolver because of a DNSSEC validaion a SERVFAIL from a validating resolver because of a DNSSEC validaion
issue will simply ask the next (potentially non-validating) resolver issue will simply ask the next (potentially non-validating) resolver
in their list, and thus don't get any of the protections which DNSSEC 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 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 he can have another cookie. When the mother says "No, it will ruin
skipping to change at page 13, line 8 skipping to change at page 11, line 7
getting a "Yes, sure, have a cookie!". getting a "Yes, sure, have a cookie!".
This information is unauthenticated information, and an attacker (e.g This information is unauthenticated information, and an attacker (e.g
MITM or malicious recursive server) could insert an extended error MITM or malicious recursive server) could insert an extended error
response into already untrusted data -- ideally clients and resolvers response into already untrusted data -- ideally clients and resolvers
would not trust any unauthenticated information, but until we live in would not trust any unauthenticated information, but until we live in
an era where all DNS answers are authenticated via DNSSEC or other an era where all DNS answers are authenticated via DNSSEC or other
mechanisms, there are some tradeoffs. As an example, an attacker who mechanisms, there are some tradeoffs. As an example, an attacker who
is able to insert the DNSSEC Bogus Extended Error into a packet could is able to insert the DNSSEC Bogus Extended Error into a packet could
instead simply reply with a fictitious address (A or AAAA) record. instead simply reply with a fictitious address (A or AAAA) record.
The R bit hint and extended error information are informational -
implementations can choose how much to trust this information and
validating resolvers / stubs may choose to put a different weight on
it.
7. Acknowledgements 7. Acknowledgements
The authors wish to thank Joe Abley, Mark Andrews, Stephane The authors wish to thank Joe Abley, Mark Andrews, Stephane
Bortzmeyer, Vladimir Cunat, Peter DeVries, Peter van Dijk, Donald Bortzmeyer, Vladimir Cunat, Peter DeVries, Peter van Dijk, Donald
Eastlake, Bob Harold, Evan Hunt, Geoff Huston, Shane Kerr, Edward Eastlake, Bob Harold, Geoff Huston, Shane Kerr, Edward Lewis, Carlos
Lewis, Carlos M. Martinez, George Michelson, Michael Sheldon, Petr M. Martinez, George Michelson, Michael Sheldon, Petr Spacek, Ondrej
Spacek, Ondrej Sury, Loganaden Velvindron, and Paul Vixie. They also Sury, Loganaden Velvindron, and Paul Vixie. They also vaguely
vaguely remember discussing this with a number of people over the remember discussing this with a number of people over the years, but
years, but have forgotten who all they were -- if you were one of have forgotten who all they were -- if you were one of them, and are
them, and are not listed, please let us know and we'll acknowledge not listed, please let us know and we'll acknowledge you.
you.
I also want to thank the band "Infected Mushroom" for providing a 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!) good background soundtrack (and to see if I can get away with this!)
Another author would like to thank the band "Mushroom Infectors". Another author would like to thank the band "Mushroom Infectors".
This was funny at the time we wrote it, but I cannot remember why... This was funny at the time we wrote it, but we cannot remember why...
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>. editor.org/info/rfc2119>.
skipping to change at page 14, line 22 skipping to change at page 12, line 15
[RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B. [RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
Wellington, "Secret Key Transaction Authentication for DNS Wellington, "Secret Key Transaction Authentication for DNS
(TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000, (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,
<https://www.rfc-editor.org/info/rfc2845>. <https://www.rfc-editor.org/info/rfc2845>.
[RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram [RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
Transport Layer Security (DTLS)", RFC 8094, Transport Layer Security (DTLS)", RFC 8094,
DOI 10.17487/RFC8094, February 2017, <https://www.rfc- DOI 10.17487/RFC8094, February 2017, <https://www.rfc-
editor.org/info/rfc8094>. editor.org/info/rfc8094>.
Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ]
From -00 to -01:
o Address comments from IETF meeting.
o document copying the response code
o mention zero length fields are ok
o clarify lookup procedure
o mention that table isn't done
From -03 to -IETF 00:
o Renamed to draft-ietf-dnsop-extended-error
From -02 to -03:
o Added David Lawrence -- I somehow missed that in last version.
From -00 to -01;
o Fixed up some of the text, minor clarifications.
Authors' Addresses Authors' Addresses
Warren Kumari Warren Kumari
Google Google
1600 Amphitheatre Parkway 1600 Amphitheatre Parkway
Mountain View, CA 94043 Mountain View, CA 94043
US US
Email: warren@kumari.net Email: warren@kumari.net
Evan Hunt Evan Hunt
ISC ISC
 End of changes. 98 change blocks. 
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