draft-ietf-dnsop-extended-error-15.txt   draft-ietf-dnsop-extended-error-16.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: October 26, 2020 ISC Expires: November 6, 2020 ISC
R. Arends R. Arends
ICANN ICANN
W. Hardaker W. Hardaker
USC/ISI USC/ISI
D. Lawrence D. Lawrence
Oracle + Dyn Oracle + Dyn
April 24, 2020 May 05, 2020
Extended DNS Errors Extended DNS Errors
draft-ietf-dnsop-extended-error-15 draft-ietf-dnsop-extended-error-16
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. Extended DNS Error information does not change the information. Extended DNS Error information does not change the
processing of RCODEs. processing of RCODEs.
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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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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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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 October 26, 2020. This Internet-Draft will expire on November 6, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 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 DNS Error EDNS0 option format . . . . . . . . . . . 4 2. Extended DNS Error EDNS0 option format . . . . . . . . . . . 4
3. Extended DNS Error Processing . . . . . . . . . . . . . . . . 5 3. Extended DNS Error Processing . . . . . . . . . . . . . . . . 5
4. Defined Extended DNS Errors . . . . . . . . . . . . . . . . . 5 4. Defined Extended DNS Errors . . . . . . . . . . . . . . . . . 5
4.1. Extended DNS Error Code 0 - Other . . . . . . . . . . . . 6 4.1. Extended DNS Error Code 0 - Other . . . . . . . . . . . . 6
4.2. Extended DNS Error Code 1 - 4.2. Extended DNS Error Code 1 -
Unsupported DNSKEY Algorithm . . . . . . . . . . . . . . 6 Unsupported DNSKEY Algorithm . . . . . . . . . . . . . . 6
4.3. Extended DNS Error Code 2 - Unsupported DS 4.3. Extended DNS Error Code 2 - Unsupported DS
Digest Type . . . . . . . . . . . . . . . . . . . . . . . 6 Digest Type . . . . . . . . . . . . . . . . . . . . . . . 6
4.4. Extended DNS Error Code 3 - Stale Answer . . . . . . . . 6 4.4. Extended DNS Error Code 3 - Stale Answer . . . . . . . . 6
4.5. Extended DNS Error Code 4 - Forged Answer . . . . . . . . 6 4.5. Extended DNS Error Code 4 - Forged Answer . . . . . . . . 6
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because the nameserver is still starting up and loading zones? Is a because the nameserver is still starting up and loading zones? Is a
SERVFAIL a DNSSEC validation issue, or is the nameserver experiencing SERVFAIL a DNSSEC validation issue, or is the nameserver experiencing
some other failure? What error messages should be presented to the some other failure? What error messages should be presented to the
user or logged under these conditions? user or logged under these conditions?
A good example of issues that would benefit from additional error A good example of issues that would benefit from additional error
information are errors caused by DNSSEC validation issues. When a information are errors caused by DNSSEC validation issues. When a
stub resolver queries a name which is DNSSEC bogus [RFC8499] (using a stub resolver queries a name which is DNSSEC bogus [RFC8499] (using a
validating resolver), the stub resolver receives only a SERVFAIL in validating resolver), the stub resolver receives only a SERVFAIL in
response. Unfortunately, the SERVFAIL Response Code (RCODE) is used response. Unfortunately, the SERVFAIL Response Code (RCODE) is used
to signal many sorts of DNS errors, and so the stub resolvers only to signal many sorts of DNS errors, and so the stub resolver's only
option is to ask the next configured DNS resolver. The result of option is to ask the next configured DNS resolver. The result of
trying the next resolver is one of two outcomes: either the next trying the next resolver is one of two outcomes: either the next
resolver also validates, and a SERVFAIL is returned again; or the resolver also validates, and a SERVFAIL is returned again, or the
next resolver is not a validating resolver, and the user is returned next resolver is not a validating resolver, and the user is returned
a potentially harmful result. With an Extended DNS Error (EDE) a potentially harmful result. With an Extended DNS Error (EDE)
option enclosed in the response message, the resolver is able to option enclosed in the response message, the resolver is able to
return a more descriptive reason as to why any failures happened, or return a more descriptive reason as to why any failures happened, or
add additional context to a message containing a NOERROR RCODE. add additional context to a message containing a NOERROR RCODE.
This document specifies a mechanism to extend DNS errors to provide This document specifies a mechanism to extend DNS errors to provide
additional information about the cause of an error. These extended additional information about the cause of an error. These extended
DNS error codes are described in this document and can be used by any DNS error codes are described in this document can be used by any
system that sends DNS queries and receives a response containing an system that sends DNS queries and receives a response containing an
EDE option. Different codes are useful in different circumstances, EDE option. Different codes are useful in different circumstances,
and thus different systems (stub resolvers, recursive resolvers, and and thus different systems (stub resolvers, recursive resolvers, and
authoritative resolvers) might receive and use them. authoritative resolvers) might receive and use them.
This document does not allow or prohibit any particular extended
error codes and information to be matched with any particular RCODEs.
Some combinations of extended error codes and RCODEs may seem
nonsensical (such as resolver-specific extended error codes in
responses from authoritative servers), so systems interpreting the
extended error codes MUST NOT assume that a combination will make
sense. Receivers MUST be able to accept EDE codes and EXTRA-TEXT in
all messages, including those with a NOERROR RCODE, but need not act
on them. Applications MUST continue to follow requirements from
applicable specifications on how to process RCODEs no matter what EDE
values are also received. Senders MAY include more than one EDE
option and receivers MUST be able to accept (but not necessarily
process or act on) multiple EDE options in a DNS message.
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", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. Extended DNS Error EDNS0 option format 2. Extended DNS Error EDNS0 option format
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IANA.] IANA.]
o OPTION-LENGTH, 2-octets/16-bits ((defined in [RFC6891]]) contains o OPTION-LENGTH, 2-octets/16-bits ((defined in [RFC6891]]) contains
the length of the payload (everything after OPTION-LENGTH) in the length of the payload (everything after OPTION-LENGTH) in
octets and should be 2 plus the length of the EXTRA-TEXT field octets and should be 2 plus the length of the EXTRA-TEXT field
(which may be a zero-length string). (which may be a zero-length string).
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. This 16-bit value, encoded in network (MSB) byte order, document. This 16-bit value, encoded in network (MSB) byte order,
provides the additional context for the RESPONSE-CODE of the DNS provides the additional context for the RESPONSE-CODE of the DNS
message. The INFO-CODE serves as an index into the "Extended DNS message. The INFO-CODE serves as an index into the "Extended DNS
Errors" registry defined and created in Section 5.2. Errors" registry defined and created in Section 5.2.
o EXTRA-TEXT, a variable length, UTF-8 encoded, text field that may o EXTRA-TEXT, a variable length, UTF-8 encoded [RFC5198], text field
hold additional textual information. This information is intended that may hold additional textual information. This information is
for human consumption (not automated parsing). The EXTRA-TEXT intended for human consumption (not automated parsing). EDE text
may be null terminated but MUST NOT be assumed to be; the length
MUST be derived from the OPTION-LENGTH field. The EXTRA-TEXT
field may be zero octets in length, indicating that there is no field may be zero octets in length, indicating that there is no
EXTRA-TEXT included. Care should be taken not to include private EXTRA-TEXT included. Care should be taken not to include private
information in the EXTRA-TEXT field that an observer would not information in the EXTRA-TEXT field that an observer would not
otherwise have access to, such as account numbers. otherwise have access to, such as account numbers.
The Extended DNS Error (EDE) option can be included in any response The Extended DNS Error (EDE) option can be included in any response
(SERVFAIL, NXDOMAIN, REFUSED, and even NOERROR, etc) to a query that (SERVFAIL, NXDOMAIN, REFUSED, and even NOERROR, 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, but is extensible via the IANA registry defined initial codepoints, but is extensible via the IANA registry defined
and created in Section 5.2. and created in Section 5.2.
3. Extended DNS Error Processing 3. Extended DNS Error Processing
When the response grows beyond the requestor's UDP payload size When the response grows beyond the requestor's UDP payload size
[RFC6891], servers SHOULD truncate messages by dropping EDE options [RFC6891], servers SHOULD truncate messages by dropping EDE options
before dropping other data from packets. Implementations SHOULD set before dropping other data from packets. Implementations SHOULD set
the truncation bit when dropping EDE options. Because long EXTRA- the truncation bit when dropping EDE options. Because long EXTRA-
TEXT fields may trigger truncation, which is undesirable given the TEXT fields may trigger truncation (which is undesirable given the
supplemental nature of EDE. Implementers and operators creating EDE supplemental nature of EDE) implementers and operators creating EDE
options SHOULD avoid lengthy EXTRA-TEXT contents. options SHOULD avoid lengthy EXTRA-TEXT contents.
When a resolver or forwarder receives an EDE option, whether or not When a resolver or forwarder receives an EDE option, whether or not
(and how) to pass along EDE information on to their original client (and how) to pass along EDE information on to their original client
is implementation dependent. Implementations MAY choose to not is implementation dependent. Implementations MAY choose to not
forward information, or they MAY choose to create a new EDE option(s) forward information, or they MAY choose to create a new EDE option(s)
that conveys the information encoded in the received EDE. When doing that conveys the information encoded in the received EDE. When doing
so, the source of the error SHOULD be attributed in the EXTRA-TEXT so, the source of the error SHOULD be attributed in the EXTRA-TEXT
field, since an EDNS0 option received by the original client will field, since an EDNS0 option received by the original client will
appear to have come from the resolver or forwarder sending it. appear to have come from the resolver or forwarder sending it.
This document does not allow or prohibit any particular extended
error codes and information to be matched with any particular RCODEs.
Some combinations of extended error codes and RCODEs may seem
nonsensical (such as resolver-specific extended error codes in
responses from authoritative servers), so systems interpreting the
extended error codes MUST NOT assume that a combination will make
sense. Receivers MUST be able to accept EDE codes and EXTRA-TEXT in
all messages, including those with a NOERROR RCODE, but need not act
on them. Applications MUST continue to follow requirements from
applicable specifications on how to process RCODEs no matter what EDE
values are also received. Senders MAY include more than one EDE
option and receivers MUST be able to accept (but not necessarily
process or act on) multiple EDE options in a DNS message.
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 Section 5.2. The registered in the "Extended DNS Errors" registry Section 5.2. The
INFO-CODE from the EDE EDNS option is used to serve as an index into INFO-CODE from the EDE EDNS option is used to serve as an index into
the "Extended DNS Error" IANA registry, the initial values for which the "Extended DNS Error" IANA registry, the initial values for which
are defined in the following sub-sections. are defined in the following sub-sections.
4.1. Extended DNS Error Code 0 - Other 4.1. Extended DNS Error Code 0 - Other
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IANA is requested to create and maintain a new registry table called IANA is requested to create and maintain a new registry table called
"Extended DNS Error Codes" on the "Domain Name System (DNS) "Extended DNS Error Codes" on the "Domain Name System (DNS)
Parameters" web page as follows: Parameters" web page as follows:
Registry Name: Extended DNS Error Codes Registry Name: Extended DNS Error Codes
Registration Procedures: Registration Procedures:
o 0 - 49151: First come, first served. o 0 - 49151: First come, first served.
o 49152 - 65280: Private use. o 49152 - 65535: Private use.
Reference: [this document] Reference: [this document]
The Extended DNS Error Codes registry is a table with three columns: The Extended DNS Error Codes registry is a table with three columns:
INFO-CODE, Purpose, and Reference. The initial contents is as below INFO-CODE, Purpose, and Reference. The initial contents is as below
with [this document] added to each reference given. with [this document] added to each reference given.
INFO-CODE: 0 INFO-CODE: 0
Purpose: Other Error Purpose: Other Error
Reference: Section 4.1 Reference: Section 4.1
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INFO-CODE: 23 INFO-CODE: 23
Purpose: Network Error Purpose: Network Error
Reference: Section 4.24 Reference: Section 4.24
INFO-CODE: 24 INFO-CODE: 24
Purpose: Invalid Data Purpose: Invalid Data
Reference: Section 4.25 Reference: Section 4.25
INFO-CODE: 25-65535 INFO-CODE: 25-65535
Purpose: Unasigned Purpose: Unassigned
Reference: Section 5.2 Reference: Section 5.2
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 validation a SERVFAIL from a validating resolver because of a DNSSEC validation
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 the protections which DNSSEC should in their list, and thus don't get the protections which DNSSEC should
provide. provide.
EDE information is unauthenticated information, unless secured by a EDE information is unauthenticated information, unless secured by a
form of secured DNS transaction such as [RFC2845], [RFC2931] or form of secured DNS transaction such as [RFC2845], [RFC2931],
[RFC8094]. An attacker (e.g a MITM or malicious recursive server) [RFC8094] or [RFC8484]. An attacker (e.g a MITM or malicious
could insert an extended error response into untrusted data -- recursive server) could insert an extended error response into
although ideally clients and resolvers would not trust any untrusted data -- although ideally clients and resolvers would not
unauthenticated information. As such, EDE content should be treated trust any unauthenticated information. As such, EDE content should
only as diagnostic information and MUST NOT alter DNS protocol be treated only as diagnostic information and MUST NOT alter DNS
processing. Until all DNS answers are authenticated via DNSSEC or protocol processing. Until all DNS answers are authenticated via
the other mechanisms mentioned above, there are some tradeoffs. As DNSSEC or the other mechanisms mentioned above, there are some
an example, an attacker who is able to insert the DNSSEC Bogus tradeoffs. As an example, an attacker who is able to insert the
Extended Error into a DNS message could instead simply reply with a DNSSEC Bogus Extended Error into a DNS message could instead simply
fictitious address (A or AAAA) record. Note that DNS Response Codes reply with a fictitious address (A or AAAA) record. Note that DNS
(RCODEs) also contain no authentication and can be just as easily Response Codes (RCODEs) also contain no authentication and can be
manipulated. just as easily manipulated.
By design, EDE potentially exposes additional information DNS By design, EDE potentially exposes additional information DNS
resolution processes that may leak information. An example of this resolution processes that may leak information. An example of this
is the Prohibited EDE code (18), which may leak the fact that the is the Prohibited EDE code (18), which may leak the fact that the
name is on a blacklist. name is on a blacklist.
7. Acknowledgements 7. Acknowledgements
The authors wish to thank Joe Abley, Mark Andrews, Tim April, The authors wish to thank Joe Abley, Mark Andrews, Tim April,
Vittorio Bertola, Stephane Bortzmeyer, Vladimir Cunat, Ralph Dolmans, Vittorio Bertola, Stephane Bortzmeyer, Vladimir Cunat, Ralph Dolmans,
skipping to change at page 13, line 19 skipping to change at page 13, line 19
[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, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
<https://www.rfc-editor.org/info/rfc4035>. <https://www.rfc-editor.org/info/rfc4035>.
[RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
<https://www.rfc-editor.org/info/rfc5198>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891, for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013, DOI 10.17487/RFC6891, April 2013,
<https://www.rfc-editor.org/info/rfc6891>. <https://www.rfc-editor.org/info/rfc6891>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS [RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
skipping to change at page 14, line 10 skipping to change at page 14, line 14
[RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures [RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures
( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September ( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September
2000, <https://www.rfc-editor.org/info/rfc2931>. 2000, <https://www.rfc-editor.org/info/rfc2931>.
[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, DOI 10.17487/RFC8094, February 2017,
<https://www.rfc-editor.org/info/rfc8094>. <https://www.rfc-editor.org/info/rfc8094>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.
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
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