Network Working Group W. Kumari
Internet-Draft Google
Intended status: Informational E. Hunt
Expires: January 18, 2018 ISC
R. Arends
Nominet
W. Hardaker
USC/ISI
D. Lawrence
Akamai Technologies
July 17, 2017
Extended DNS Errors
draft-wkumari-dnsop-extended-error-02
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 http://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 18, 2018.
Copyright Notice
Copyright (c) 2017 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
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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 . . . . . . . . . . . . . 3
3. Use of the Extended DNS Error option . . . . . . . . . . . . 4
4. Defined Extended DNS Errors . . . . . . . . . . . . . . . . . 5
4.1. Extended DNS Error Code 1 - DNSSEC Bogus . . . . . . . . 5
4.2. Extended DNS Error Code 2 - DNSSEC Indeterminite . . . . 5
4.3. Extended DNS Error Code 3 - Lame . . . . . . . . . . . . 5
4.4. Extended DNS Error Code 4 - Prohibited . . . . . . . . . 5
4.5. Extended DNS Error Code 5 - TooBusy . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Open questions . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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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 there is 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].
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:
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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 | FLAGS |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6: | CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
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 FLAGS, 2 octets.
o CODE, 2 octets.
Currently the only defined flag is the R flag.
R - Retry The R (or Retry) flag provides a hint to the receiver if
it should retry the query, possibly by querying 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 it should not ask another
server.
The remaining bits in the flags field MUST be set to 0 by the sender
and SHOULD be ignored by the receiver.
Code: A code point 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 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
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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.
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.
4.1. 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 be set.
4.2. Extended DNS Error Code 2 - DNSSEC Indeterminite
The resolver attempted to perform DNSSEC validation, but validation
ended in the Indeterminate state.
Usually attached to SERVFAIL messages. The R flag should be set.
4.3. Extended DNS Error Code 3 - 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 not set the R flag in this case (another
nameserver might not be lame).
4.4. Extended DNS Error Code 4 - 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, etc.
Implementations SHOULD allow operators to define what to set the R
flag to in this case.
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4.5. Extended DNS Error Code 5 - TooBusy
[ Ed: This might be a bad idea. It is intended to allow servers
under a DoS (for example a random subdomain attack) to signal to
recursive clients that they are being abusive and should back off.
This may be a bad idea -- it may "complete the attack", it may be
spoofable (by anyone who could also do a MITM style attack), etc. ]
A nameserver which is under excessive load (for example, because it
is experiencing a DoS) may annotate any answer with this code.
It is RECOMMENDED that implementations set the R flag in this case,
but may allow operators to define what to set the R flag to.
[ agreed: bad idea -wjh ]
5. IANA Considerations
[This section under construction, beware. ]
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 ]
Data Tag Name Length Meaning ---- ---- ------ ------- TBD1 FooBar N
FooBar server
The IANA is requested to create and maintain the "Extended DNS Error
codes" registry. The codepoint space is 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.
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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 do 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, cookie!".
8. Acknowledgements
The authors wish to thank Geoff Huston. 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...
9. References
9.1. Normative References
[IANA.AS_Numbers]
IANA, "Autonomous System (AS) Numbers",
<http://www.iana.org/assignments/as-numbers>.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://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.
Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ]
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
Nominet
UK
Email: TBD
Wes Hardaker
USC/ISI
P.O. Box 382
Davis, VA 95617
US
David C Lawrence
Akamai Technologies
150 Broadway
Cambridge, MA 02142-1054
US
Email: tale@akamai.com
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