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Network Working Group W. Kumari
Internet-Draft Google
Intended status: Standards Track E. Hunt
Expires: January 3, 2019 ISC
R. Arends
ICANN
W. Hardaker
USC/ISI
D. Lawrence
Akamai Technologies
July 02, 2018
Extended DNS Errors
draft-ietf-dnsop-extended-error-01
Abstract
This document defines an extensible method to return additional
information about the cause of DNS errors. The primary use case is
to extend SERVFAIL to provide additional information about the cause
of DNS and DNSSEC failures.
[ Open question: The document currently defines a registry for
errors. It has also been suggested that the option also carry human
readable (text) messages, to allow the server admin to provide
additional debugging information (e.g: "example.com pointed their NS
at us. No idea why...", "We don't provide recursive DNS to
192.0.2.0. Please stop asking...", "Have you tried Acme Anvil and
DNS? We do DNS right..." (!). Please let us know if you think text
is needed, or if a 16bit FCFS registry is expressive enough. ]
[ Open question: This document discusses extended *errors*, but it
has been suggested that this could be used to also annotate *non-
error* messages. The authors do not think that this is a good idea,
but could be persuaded otherwise. ]
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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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 3, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction and background . . . . . . . . . . . . . . . . . 3
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3
2. Extended Error EDNS0 option format . . . . . . . . . . . . . 4
3. Use of the Extended DNS Error option . . . . . . . . . . . . 5
4. Defined Extended DNS Errors . . . . . . . . . . . . . . . . . 5
4.1. SERVFAIL(3) extended information codes . . . . . . . . . 6
4.1.1. Extended DNS Error Code 1 - DNSSEC Bogus . . . . . . 6
4.1.2. Extended DNS Error Code 2 - DNSSEC Indeterminate . . 6
4.1.3. Extended DNS Error Code 3 - Signature Expired . . . . 6
4.1.4. Extended DNS Error Code 4 - Signature Not Yet Valid . 6
4.1.5. Extended DNS Error Code 5 - Unsupported
DNSKEY Algorithm . . . . . . . . . . . . . . . . . . 6
4.1.6. Extended DNS Error Code 6 - Unsupported
DS Algorithm . . . . . . . . . . . . . . . . . . . . 6
4.1.7. Extended DNS Error Code 7 - DNSKEY missing . . . . . 6
4.1.8. Extended DNS Error Code 8 - RRSIGs missing . . . . . 6
4.1.9. Extended DNS Error Code 9 - No Zone Key Bit Set . . . 7
4.2. REFUSED(5) extended information codes . . . . . . . . . . 7
4.2.1. Extended DNS Error Code 1 - Lame . . . . . . . . . . 7
4.2.2. Extended DNS Error Code 2 - Prohibited . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5.1. new Extended Error Code EDNS Option . . . . . . . . . . . 7
5.2. new Extended Error Code EDNS Option . . . . . . . . . . . 7
6. Open questions . . . . . . . . . . . . . . . . . . . . . . . 8
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7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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 the answer was marked REFUSED because of a lame delegation, or
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 is an error caused by a DNSSEC validation issue. 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. This information can be used by the resolver to make a
decision regarding whether or not to retry, or by technical users
attempting to debug issues.
Here is a reference to an "external" (non-RFC / draft) thing:
([IANA.AS_Numbers]). And this is a link to an
ID:[I-D.ietf-sidr-iana-objects].
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 error
(ExtError) 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: | R | RESERVED |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6: | RESPONSE-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
8: | INFO-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
A: | EXTRA-TEXT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
o OPTION-CODE, 2 octets (defined in [RFC6891]), for ExtError is TBD.
o OPTION-LENGTH, 2 octets ((defined in [RFC6891]) contains the
length of the payload (everything after OPTION-LENGTH) in octets
and should be 4.
o RESERVED, 2 octets; the first bit (R) indicates a flag defined in
this specification. The remaining bits are reserved for future
use, potentially as additional flags.
o RESPONSE-CODE, 2 octets: this SHOULD be a copy of the RCODE from
the primary DNS packet. When including multiple extended error
EDNS0 records in a response in order to provide additional error
information, the RESPONSE-CODE MAY be a different RCODE.
o INFO-CODE, 2 octets.
o A variable length EXTRA-TEXT field holding additional textual
information. It may be zero length when no additional textual
information is included.
Currently the only defined flag is the R flag.
R - Retry The R (or Retry) flag provides a hint to the receiver that
it should retry the query, probably by querying another server.
If the R bit is set (1), the sender believes that retrying the
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query may provide a successful answer next time; if the R bit is
clear (0), the sender believes that it should not ask another
server.
The remaining bits in the RESERVED field are reserved for future use
and MUST be set to 0 by the sender and SHOULD be ignored by the
receiver.
INFO-CODE: A code point that, when combined with the RCODE from the
DNS packet, serve as a joint-index into the IANA "Extended DNS
Errors" registry.
3. Use of the Extended DNS Error option
The Extended DNS Error (EDE) is an EDNS option. It can be included
in any error response (SERVFAIL, NXDOMAIN, REFUSED, etc) to a query
that includes an EDNS option. 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 R (Retry) flag provides a hint (or suggestion) as to what the
receiver may want to do with this annotated error. 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 or hint. Receivers can choose to
ignore this hint.
The EXTRA-INFO textual 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 codepoints will 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.
The RESPONSE-CODE and the INFO-CODE from the EDE EDNS option is used
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.
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4.1. SERVFAIL(3) extended information codes
4.1.1. Extended DNS Error Code 1 - DNSSEC Bogus
The resolver attempted to perform DNSSEC validation, but validation
ended in the Bogus state. The R flag should not be set.
4.1.2. Extended DNS Error Code 2 - DNSSEC Indeterminate
The resolver attempted to perform DNSSEC validation, but validation
ended in the Indeterminate state. The R flag should not be set.
4.1.3. Extended DNS Error Code 3 - Signature Expired
The resolver attempted to perform DNSSEC validation, but the
signature was expired. The R flag should not be set.
4.1.4. Extended DNS Error Code 4 - 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.
4.1.5. Extended DNS Error Code 5 - Unsupported DNSKEY Algorithm
The resolver attempted to perform DNSSEC validation, but a DNSKEY
RRSET contained only unknown algorithms. The R flag should not be
set.
4.1.6. Extended DNS Error Code 6 - Unsupported DS Algorithm
The resolver attempted to perform DNSSEC validation, but a DS RRSET
contained only unknown algorithms. The R flag should not be set.
4.1.7. Extended DNS Error Code 7 - DNSKEY missing
A DS record existed at a parent, but no DNSKEY record could be found
for the child. The R flag should not be set.
4.1.8. Extended DNS Error Code 8 - RRSIGs missing
The resolver attempted to perform DNSSEC validation, but no RRSIGs
could be found for at least one RRset where RRSIGs were expected.
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4.1.9. Extended DNS Error Code 9 - No Zone Key Bit Set
The resolver attempted to perform DNSSEC validation, but no Zone Key
Bit was set in a DNSKEY.
4.2. REFUSED(5) extended information codes
4.2.1. Extended DNS Error Code 1 - Lame
An authoritative resolver 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 REFUSED response. Implementations should set
the R flag in this case (another nameserver might not be lame).
4.2.2. 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.
5. IANA Considerations
[This section under construction, beware. ]
5.1. 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 Extended Error Code EDNS Option
This document defines a new double-index IANA registry table, where
the first index value is the RCODE value 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
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"Extended DNS Error codes" registry. The codepoint space for each
RCODE index is to be broken into 3 ranges:
o 1 - 16384: Specification required.
o 16385 - 65000: First Come First Served
o 65000 - 65534: Experimental / Private use
The codepoints 0, 65535 are reserved.
A starting table, based on the contents of this document, is as
follows:
| RCODE | EDE-INFO-CODE | Meaning | Ref |
|-------------+-------------------------+---------------------------------------------+------------------------------------------|
| SERVFAIL(2) | DNSSEC_BOGUS(1) | DNSSEC Validation resulted in Bogus | section <xref target="errbogus" /> |
| SERVFAIL(2) | DNSSEC_INDETERMINATE(2) | DNSSEC Validation resulted in Indeterminate | section <xref target="errindeterminate" /> |
[incomplete]
6. Open questions
1 Can this be included in *any* response or only responses to
requests that included an EDNS option? Resolvers are supposed to
ignore additional. EDNS capable ones are supposed to simply
ignore unknown options. I know the spec says you can only include
EDNS0 in a response if in a request -- it is time to reevaluate
this?
2 Can this be applied to *any* response, or only error responses?
3 Should textual information be allowed as well? What if the only
thing allowed is a domain name, e.g to point at where validation
began failing?
7. Security Considerations
DNSSEC is being deployed - unfortunately a significant number of
clients (~11% according to [GeoffValidation]), when receiving a
SERVFAIL from a validating resolver because of a DNSSEC validaion
issue simply ask the next (non-validating) resolver in their list,
and 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
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dinner!", going off and asking his (more permissive) father and
getting a "Yes, sure, cookie!".
8. Acknowledgements
The authors wish to thank Geoff Huston and Bob Harold, Carlos M.
Martinez, Peter DeVries, George Michelson, Mark Andrews, Ondrej Sury,
Edward Lewis, Paul Vixie, Shane Kerr. 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 cannot remember why...
We would like to especially thank Peter van Dijk, who sent GitHub
pull requests.
9. References
9.1. Normative References
[IANA.AS_Numbers]
IANA, "Autonomous System (AS) Numbers",
<http://www.iana.org/assignments/as-numbers>.
[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>.
9.2. 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>.
[I-D.ietf-sidr-iana-objects]
Manderson, T., Vegoda, L., and S. Kent, "RPKI Objects
issued by IANA", draft-ietf-sidr-iana-objects-03 (work in
progress), May 2011.
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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
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Roy Arends
ICANN
Email: roy.arends@icann.org
Wes Hardaker
USC/ISI
P.O. Box 382
Davis, VA 95617
US
Email: ietf@hardakers.net
David C Lawrence
Akamai Technologies
150 Broadway
Cambridge, MA 02142-1054
US
Email: tale@akamai.com
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