wdiff draft-ietf-dnsop-extended-error-06.txt draft-ietf-dnsop-extended-error-07.txt

Network Working Group W. Kumari
Internet-Draft Google
Intended status: Standards Track E. Hunt
Expires: January 9, February 10, 2020 ISC
R. Arends
ICANN
W. Hardaker
USC/ISI
D. Lawrence
Oracle + Dyn
July 08,
August 09, 2019

Extended DNS Errors
draft-ietf-dnsop-extended-error-06
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
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 January 9, February 10, 2020.

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
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 3
2. Extended Error EDNS0 option format . . . . . . . . . . . . . 4
3. Use of the Extended DNS Error option . . . . . . . . . . . . 5 4
3.1. The R (Retry) flag INFO-CODE field . . . . . . . . . . . . . . . . . . . 5
3.2. The RESPONSE-CODE EXTRA-TEXT field . . . . . . . . . . . . . . . . . . 5
3.3. The INFO-CODE field
4. Defined Extended DNS Errors . . . . . . . . . . . . . . . . . 5
4.1. Extended DNS Error Code 0 - Other . . 6
3.4. The EXTRA-TEXT field . . . . . . . . . . 5
4.2. Extended DNS Error Code 1 -
Unsupported DNSKEY Algorithm . . . . . . . . 6
4. Defined . . . . . . 5
4.3. Extended DNS Errors Error Code 2 - Unsupported
DS Algorithm . . . . . . . . . . . . . . . . . 6
4.1. INFO-CODEs for use with RESPONSE-CODE: NOERROR(0) . . . . 6
4.1.1. NOERROR . 5
4.4. Extended DNS Error Code 1 3 - Unsupported
DNSKEY Algorithm . . Stale Answer . . . . . . . . 5
4.5. Extended DNS Error Code 4 - Forged Answer . . . . . . . . 6
4.1.2. NOERROR
4.6. Extended DNS Error Code 2 5 - Unsupported
DS Algorithm . . DNSSEC Indeterminate . . . . 6
4.7. Extended DNS Error Code 6 - DNSSEC Bogus . . . . . . . . 6
4.8. Extended DNS Error Code 7 - Signature Expired . . . . . . 6
4.1.3. INFO-CODEs for use with RESPONSE-CODE: NOERROR(3) . . 7
4.1.4. NOERROR
4.9. Extended DNS Error Code 4 8 - Forged answer Signature Not Yet Valid . . 7
4.1.5. SERVFAIL . 6
4.10. Extended DNS Error Code 5 9 - DNSSEC
Indeterminate . . . . . . . . . DNSKEY Missing . . . . . . . 6
4.11. Extended DNS Error Code 10 - RRSIGs Missing . . . . 7
4.2. INFO-CODEs for use with RESPONSE-CODE: SERVFAIL(2) . . . 7
4.2.1. SERVFAIL 6
4.12. Extended DNS Error Code 1 11 - DNSSEC Bogus No Zone Key Bit Set . . 7
4.2.2. SERVFAIL . . 6
4.13. Extended DNS Error Code 2 12 - Signature
Expired NSEC Missing . . . . . . . . 6
4.14. Extended DNS Error Code 13 - Cached Error . . . . . . . . 7
4.15. Extended DNS Error Code 14 - Not Ready . . . . . . . . . 7
4.2.3. SERVFAIL
4.16. Extended DNS Error Code 3 15 - Signature Not
Yet Valid . . Blocked . . . . . . . . . . 7
4.17. Extended DNS Error Code 16 - Censored . . . . . . . . . . 7
4.2.4. SERVFAIL
4.18. Extended DNS Error Code 4 17 - DNSKEY missing Prohibited . . . . . . . . . 7
4.2.5. SERVFAIL
4.19. Extended DNS Error Code 5 18 - RRSIGs missing Stale Answer . 8
4.2.6. SERVFAIL Extended DNS Error Code 6 - No Zone Key Bit
Set . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2.7. SERVFAIL Extended DNS Error Code 7 - No
Reachable Authority . . . . . . . . . . . . . . . . . 8
4.2.8. SERVFAIL
4.20. Extended DNS Error Code 8 19 - NSEC Missing Lame . . 8
4.2.9. SERVFAIL Extended DNS Error Code 9 - Cached Error . . 8
4.2.10. SERVFAIL Extended DNS Error Code 10 - Not Ready . . . 8
4.3. INFO-CODEs for use with RESPONSE-CODE: NOTIMP(4) . . . . 8
4.3.1. NOTIMP . 7
4.21. Extended DNS Error Code 1 20 - Deprecated . . . . 8
4.4. INFO-CODEs for use with RESPONSE-CODE: REFUSED(5) . . . . 8
4.4.1. REFUSED Extended DNS Error Code 1 - Lame . . . . . . 8
4.4.2. REFUSED Extended DNS Error Code 2 - Prohibited . . . 9
4.5. INFO-CODEs for use with RESPONSE-CODE: NXDOMAIN(3) . . . 9
4.5.1. NXDOMAIN Extended DNS Error Code 1 - Blocked . . . . 9
4.6. INFO-CODEs for use with RESPONSE-CODE: NXDOMAIN(3) . . . 9
4.6.1. NXDOMAIN
4.22. Extended DNS Error Code 2 21 - Censored . . . . 9
4.7. INFO-CODEs for use with RESPONSE-CODE: NXDOMAIN(3) . . No Reachable Authority . 9
4.7.1. NXDOMAIN Extended DNS Error Code 3 - Stale Answer . . 9 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 8
5.1. A New Extended Error Code EDNS Option . . . . . . . . . . 10 8
5.2. New Double-Index Registry Table for Extended Error Codes 10 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 11
8.1. Normative References . . . . . . . . . . . . . . . . . . 13 11
8.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 14 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 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. When properly authenticated, this information can be used by
the resolver to make a decision regarding whether or not to retry or
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
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].

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: | RCODE | R | Res |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6: | INFO-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6: / EXTRA-TEXT ... /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

Field definition details:

o OPTION-CODE, 2 octets (defined in [RFC6891]), [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]) [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 The RETRY flag, 1 bit; INFO-CODE, 16-bits, which is the RETRY bit (R) indicates a flag defined
for use in principal contribution of 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
document.
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.

3.1. The R (Retry) flag

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 value, encoded in network (MSB) byte order, provides the
additional context for the RESPONSE-
CODE value. This combination of the RESPONSE-CODE and of the DNS message. The
INFO-CODE
serve serves as a joint-index into an index to the IANA "Extended DNS Errors" registry.

Note to implementers: the combination of the RESPONSE-CODE and INFO-
CODE fits within a 24-bit field, allowing implementers the choice of
treating the combination as either two separate values, as defined in
this document, or as a single 24-bit integer as long as the results
are deterministic.

3.4. 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. This document
provides suggestions for the R flag, but the originating server may
ignore these recommendations if it knows better. registry Section 5.1. The RESPONSE-CODE and the
INFO-CODE from the EDE EDNS option is used to serve as a double an 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 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 RESPONSE-CODE: NOERROR(0)

4.1.1. NOERROR 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. The R flag should be set.

4.1.2. NOERROR

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. The R flag should be set.

4.1.3. INFO-CODEs for use with RESPONSE-CODE: NOERROR(3)

4.1.3.1. NOERROR

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. The R flag should not be
set, since retrying is likely to create additional load without
yielding a more fresh answer.

4.1.4. NOERROR

4.5. Extended DNS Error Code 4 - Forged answer Answer

For policy reasons (legal obligation, or malware filtering, for
instance), an answer was forged. The R flag should not be set.

4.1.5. SERVFAIL

4.6. Extended DNS Error Code 5 - DNSSEC Indeterminate

The resolver attempted to perform DNSSEC validation, but validation
ended in the Indeterminate state. The R flag should not be set.

4.2. INFO-CODEs for use with RESPONSE-CODE: SERVFAIL(2)

4.2.1. SERVFAIL

4.7. Extended DNS Error Code 1 6 - DNSSEC Bogus

The resolver attempted to perform DNSSEC validation, but validation
ended in the Bogus state. The R flag should not be set.

4.2.2. SERVFAIL

4.8. Extended DNS Error Code 2 7 - Signature Expired

The resolver attempted to perform DNSSEC validation, a signature in
the validation chain was expired. The R flag should not be set.

4.2.3. SERVFAIL

4.9. Extended DNS Error Code 3 8 - Signature Not Yet Valid

The resolver attempted to perform DNSSEC validation, but the
signatures received were not yet valid. The R flag should not be
set.

4.2.4. SERVFAIL

4.10. Extended DNS Error Code 4 9 - DNSKEY missing Missing

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.

4.2.5. SERVFAIL

4.11. Extended DNS Error Code 5 10 - RRSIGs missing Missing

The resolver attempted to perform DNSSEC validation, but no RRSIGs
could be found for at least one RRset where RRSIGs were expected.

4.2.6. SERVFAIL

4.12. Extended DNS Error Code 6 11 - No Zone Key Bit Set

The resolver attempted to perform DNSSEC validation, but no Zone Key
Bit was set in a DNSKEY.

4.2.7. SERVFAIL Extended DNS Error Code 7 - No Reachable Authority

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 resolver attempted to perform DNSSEC validation, but no Zone Key
Bit was set in a DNSKEY.

4.13. Extended DNS Error Code 8 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. The R flag should be set.

4.2.9. SERVFAIL

4.14. Extended DNS Error Code 9 13 - Cached Error

The resolver has cached SERVFAIL for this query without additional
information. Th R flag should be set.

4.2.10. SERVFAIL

4.15. Extended DNS Error Code 10 14 - Not Ready

The server is unable to answer the query as it is not fully up and
functional yet.

4.3. INFO-CODEs for use with RESPONSE-CODE: NOTIMP(4)

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)

4.4.1. REFUSED Extended DNS Error Code 1 - 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. 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

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.

Implementations SHOULD allow operators to define what to set the R
flag to in this case.

4.5. INFO-CODEs for use with RESPONSE-CODE: NXDOMAIN(3)

4.5.1. NXDOMAIN

4.16. Extended DNS Error Code 1 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. The R flag should be set.

4.6. INFO-CODEs for use with RESPONSE-CODE: NXDOMAIN(3)

4.6.1. NXDOMAIN

4.17. Extended DNS Error Code 2 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). The R flag should be set.

4.7. INFO-CODEs for use

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 RESPONSE-CODE: NXDOMAIN(3)

4.7.1. NXDOMAIN 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 3 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. The R flag
should

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 be set, since retrying 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.

4.21. Extended DNS Error Code 20 - Deprecated

The requested operation or query is likely 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 create additional load
without yielding a more fresh answer. 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 first index value is the combined RCODE value (see the
Section 3.2 section) and the second 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 codepoint code-point
space for each INFO-CODE index is to be broken into 3 ranges:

o 0 - 65023: : Specification required.
o 65023 - 65279: First come, first served.
o 65280 - 65536: 32767: Experimental / Private use

A starting set of entries, based on the contents of this document, is
as follows:

RESPONSE-CODE:

INFO-CODE: 0 (NOERROR)
Purpose: Other Error
Reference: Section 4.1

INFO-CODE: 1
Purpose: Unsupported DNSKEY Algorithm
Reference: Section 4.1.1

RESPONSE-CODE: 0 (NOERROR) 4.2

INFO-CODE: 2
Purpose: Unsupported DS Algorithm
Reference: Section 4.1.2

RESPONSE-CODE: 3 (NOERROR) 4.3

INFO-CODE: 3
Purpose: Answering with stale/cached data
Reference: Section 4.1.3.1

RESPONSE-CODE: 0 (NOERROR) 4.4

INFO-CODE: 4
Purpose: Forged answer Answer
Reference: Section 4.1.4
RESPONSE-CODE: 0 (NOERROR) 4.5

INFO-CODE: 5
Purpose: DNSSEC Indeterminate
Reference: Section 4.1.5

RESPONSE-CODE: 2 (SERVFAIL) 4.6

INFO-CODE: 1 6
Purpose: DNSSEC Bogus
Reference: Section 4.2.1

RESPONSE-CODE: 2 (SERVFAIL) 4.7

INFO-CODE: 2 7
Purpose: Signature Expired
Reference: Section 4.2.2

RESPONSE-CODE: 2 (SERVFAIL) 4.8

INFO-CODE: 3 8
Purpose: Signature Not Yet Valid
Reference: Section 4.2.3

RESPONSE-CODE: 2 (SERVFAIL) 4.9

INFO-CODE: 4 9
Purpose: DNSKEY missing Missing
Reference: Section 4.2.4

RESPONSE-CODE: 2 (SERVFAIL) 4.10

INFO-CODE: 5 10
Purpose: RRSIGs missing Missing
Reference: Section 4.2.5

RESPONSE-CODE: 2 (SERVFAIL) 4.11

INFO-CODE: 6 11
Purpose: No Zone Key Bit Set
Reference: Section 4.2.6

RESPONSE-CODE: 2 (SERVFAIL) 4.12

INFO-CODE: 7 12
Purpose: No NSEC records could be obtained
Reference: Section 4.2.8

RESPONSE-CODE: 2 (SERVFAIL) 4.13

INFO-CODE: 9 13
Purpose: The SERVFAIL error comes from the cache
Reference: Section 4.2.9

RESPONSE-CODE: 2 (SERVFAIL) 4.14

INFO-CODE: 10 14
Purpose: Not Ready.
Reference: Section 4.2.10

RESPONSE-CODE: 3 (NXDOMAIN) 4.15

INFO-CODE: 1 15
Purpose: Blocked
Reference: Section 4.5.1

RESPONSE-CODE: 3 (NXDOMAIN) 4.16

INFO-CODE: 2 16
Purpose: Censored
Reference: Section 4.6.1

RESPONSE-CODE: 3 (NXDOMAIN) 4.17

INFO-CODE: 3 17
Purpose: Prohibited
Reference: Section 4.18

INFO-CODE: 18
Purpose: Answering with stale/cached NXDOMAIN data
Reference: Section 4.7.1

RESPONSE-CODE: 4 (NOTIMP) 4.19

INFO-CODE: 1 19
Purpose: Lame
Reference: Section 4.4.2

RESPONSE-CODE: 5 (REFUSED) 4.20

INFO-CODE: 1 20
Purpose: Lame Deprecated
Reference: Section 4.4.1

RESPONSE-CODE: 5 (REFUSED) 4.21

INFO-CODE: 2 21
Purpose: Prohibited No Reachable Authority
Reference: Section 4.4.2 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
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.
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

The authors wish to thank Joe Abley, Mark Andrews, Stephane
Bortzmeyer, Vladimir Cunat, Peter DeVries, Peter van Dijk, Donald
Eastlake, Bob Harold, Evan Hunt, 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 I 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>.

[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>.

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

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
David C Lawrence
Oracle + Dyn
150 Dow St
Manchester, NH 03101
US

Email: tale@dd.org