< draft-ietf-dnsext-dnssec-bis-updates-18.txt   draft-ietf-dnsext-dnssec-bis-updates-19.txt >
Network Working Group S. Weiler Network Working Group S. Weiler
Internet-Draft SPARTA, Inc. Internet-Draft SPARTA, Inc.
Updates: 4033, 4034, 4035, 5155 D. Blacka Updates: 4033, 4034, 4035, 5155 D. Blacka
(if approved) Verisign, Inc. (if approved) Verisign, Inc.
Intended status: Standards Track April 30, 2012 Intended status: Standards Track July 13, 2012
Expires: November 1, 2012 Expires: January 14, 2013
Clarifications and Implementation Notes for DNSSECbis Clarifications and Implementation Notes for DNSSEC
draft-ietf-dnsext-dnssec-bis-updates-18 draft-ietf-dnsext-dnssec-bis-updates-19
Abstract Abstract
This document is a collection of technical clarifications to the This document is a collection of technical clarifications to the
DNSSECbis document set. It is meant to serve as a resource to DNSSEC document set. It is meant to serve as a resource to
implementors as well as a repository of DNSSECbis errata. implementors as well as a repository of DNSSEC errata.
This document updates the core DNSSECbis documents (RFC4033, RFC4034, This document updates the core DNSSEC documents (RFC4033, RFC4034,
and RFC4035) as well as the NSEC3 specification (RFC5155). It also and RFC4035) as well as the NSEC3 specification (RFC5155). It also
defines NSEC3 and SHA-2 as core parts of the DNSSECbis specification. defines NSEC3 and SHA-2 as core parts of the DNSSEC specification.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
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 November 1, 2012. This Internet-Draft will expire on January 14, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction and Terminology . . . . . . . . . . . . . . . . . 4 1. Introduction and Terminology . . . . . . . . . . . . . . . . . 4
1.1. Structure of this Document . . . . . . . . . . . . . . . . 4 1.1. Structure of this Document . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Important Additions to DNSSSECbis . . . . . . . . . . . . . . 4 2. Important Additions to DNSSEC . . . . . . . . . . . . . . . . 4
2.1. NSEC3 Support . . . . . . . . . . . . . . . . . . . . . . 4 2.1. NSEC3 Support . . . . . . . . . . . . . . . . . . . . . . 4
2.2. SHA-2 Support . . . . . . . . . . . . . . . . . . . . . . 5 2.2. SHA-2 Support . . . . . . . . . . . . . . . . . . . . . . 5
3. Scaling Concerns . . . . . . . . . . . . . . . . . . . . . . . 5 3. Scaling Concerns . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Implement a BAD cache . . . . . . . . . . . . . . . . . . 5 3.1. Implement a BAD cache . . . . . . . . . . . . . . . . . . 5
4. Security Concerns . . . . . . . . . . . . . . . . . . . . . . 5 4. Security Concerns . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Clarifications on Non-Existence Proofs . . . . . . . . . . 5 4.1. Clarifications on Non-Existence Proofs . . . . . . . . . . 5
4.2. Validating Responses to an ANY Query . . . . . . . . . . . 6 4.2. Validating Responses to an ANY Query . . . . . . . . . . . 6
4.3. Check for CNAME . . . . . . . . . . . . . . . . . . . . . 6 4.3. Check for CNAME . . . . . . . . . . . . . . . . . . . . . 6
4.4. Insecure Delegation Proofs . . . . . . . . . . . . . . . . 6 4.4. Insecure Delegation Proofs . . . . . . . . . . . . . . . . 7
5. Interoperability Concerns . . . . . . . . . . . . . . . . . . 7 5. Interoperability Concerns . . . . . . . . . . . . . . . . . . 7
5.1. Errors in Canonical Form Type Code List . . . . . . . . . 7 5.1. Errors in Canonical Form Type Code List . . . . . . . . . 7
5.2. Unknown DS Message Digest Algorithms . . . . . . . . . . . 7 5.2. Unknown DS Message Digest Algorithms . . . . . . . . . . . 7
5.3. Private Algorithms . . . . . . . . . . . . . . . . . . . . 8 5.3. Private Algorithms . . . . . . . . . . . . . . . . . . . . 8
5.4. Caution About Local Policy and Multiple RRSIGs . . . . . . 8 5.4. Caution About Local Policy and Multiple RRSIGs . . . . . . 9
5.5. Key Tag Calculation . . . . . . . . . . . . . . . . . . . 9 5.5. Key Tag Calculation . . . . . . . . . . . . . . . . . . . 9
5.6. Setting the DO Bit on Replies . . . . . . . . . . . . . . 9 5.6. Setting the DO Bit on Replies . . . . . . . . . . . . . . 9
5.7. Setting the AD Bit on Queries . . . . . . . . . . . . . . 9 5.7. Setting the AD Bit on Queries . . . . . . . . . . . . . . 9
5.8. Setting the AD Bit on Replies . . . . . . . . . . . . . . 9 5.8. Setting the AD Bit on Replies . . . . . . . . . . . . . . 10
5.9. Always set the CD bit on Queries . . . . . . . . . . . . . 10 5.9. Always set the CD bit on Queries . . . . . . . . . . . . . 10
5.10. Nested Trust Anchors . . . . . . . . . . . . . . . . . . . 10 5.10. Nested Trust Anchors . . . . . . . . . . . . . . . . . . . 10
5.11. Mandatory Algorithm Rules . . . . . . . . . . . . . . . . 11 5.11. Mandatory Algorithm Rules . . . . . . . . . . . . . . . . 11
5.12. Ignore Extra Signatures From Unknown Keys . . . . . . . . 11 5.12. Ignore Extra Signatures From Unknown Keys . . . . . . . . 12
6. Minor Corrections and Clarifications . . . . . . . . . . . . . 12 6. Minor Corrections and Clarifications . . . . . . . . . . . . . 12
6.1. Finding Zone Cuts . . . . . . . . . . . . . . . . . . . . 12 6.1. Finding Zone Cuts . . . . . . . . . . . . . . . . . . . . 12
6.2. Clarifications on DNSKEY Usage . . . . . . . . . . . . . . 12 6.2. Clarifications on DNSKEY Usage . . . . . . . . . . . . . . 12
6.3. Errors in Examples . . . . . . . . . . . . . . . . . . . . 12 6.3. Errors in Examples . . . . . . . . . . . . . . . . . . . . 13
6.4. Errors in RFC 5155 . . . . . . . . . . . . . . . . . . . . 13 6.4. Errors in RFC 5155 . . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13 8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . . 14 9.1. Normative References . . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . . 14 9.2. Informative References . . . . . . . . . . . . . . . . . . 15
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 15 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 15
Appendix B. Discussion of Setting the CD Bit . . . . . . . . . . 15 Appendix B. Discussion of Setting the CD Bit . . . . . . . . . . 16
Appendix C. Discussion of Trust Anchor Preference Options . . . . 18 Appendix C. Discussion of Trust Anchor Preference Options . . . . 19
C.1. Closest Encloser . . . . . . . . . . . . . . . . . . . . . 18 C.1. Closest Encloser . . . . . . . . . . . . . . . . . . . . . 19
C.2. Accept Any Success . . . . . . . . . . . . . . . . . . . . 19 C.2. Accept Any Success . . . . . . . . . . . . . . . . . . . . 20
C.3. Preference Based on Source . . . . . . . . . . . . . . . . 19 C.3. Preference Based on Source . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction and Terminology 1. Introduction and Terminology
This document lists some additions, clarifications and corrections to This document lists some additions, clarifications and corrections to
the core DNSSECbis specification, as originally described in the core DNSSEC specification, as originally described in [RFC4033],
[RFC4033], [RFC4034], and [RFC4035], and later amended by [RFC5155]. [RFC4034], and [RFC4035], and later amended by [RFC5155]. (See
(See section Section 2 for more recent additions to that core section Section 2 for more recent additions to that core document
document set.) set.)
It is intended to serve as a resource for implementors and as a It is intended to serve as a resource for implementors and as a
repository of items that need to be addressed when advancing the repository of items that need to be addressed when advancing the
DNSSECbis documents from Proposed Standard to Draft Standard. DNSSEC documents along the Standards Track.
1.1. Structure of this Document 1.1. Structure of this Document
The clarifications and changes to DNSSECbis are sorted according to The clarifications and changes to DNSSEC are sorted according to
their importance, starting with ones which could, if ignored, lead to their importance, starting with ones which could, if ignored, lead to
security problems and progressing down to clarifications that are security problems and progressing down to clarifications that are
expected to have little operational impact. expected to have little operational impact.
1.2. Terminology 1.2. Terminology
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 "OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. [RFC2119].
2. Important Additions to DNSSSECbis 2. Important Additions to DNSSEC
This section lists some documents that should be considered core This section lists some documents that are now considered core DNSSEC
DNSSEC protocol documents in addition to those originally specified protocol documents in addition to those originally specified in
in Section 10 of [RFC4033]. Section 10 of [RFC4033].
2.1. NSEC3 Support 2.1. NSEC3 Support
[RFC5155] describes the use and behavior of the NSEC3 and NSEC3PARAM [RFC5155] describes the use and behavior of the NSEC3 and NSEC3PARAM
records for hashed denial of existence. Validator implementations records for hashed denial of existence. Validator implementations
are strongly encouraged to include support for NSEC3 because a number are strongly encouraged to include support for NSEC3 because a number
of highly visible zones use it. Validators that do not support of highly visible zones use it. Validators that do not support
validation of responses using NSEC3 will be hampered in validating validation of responses using NSEC3 will be hampered in validating
large portions of the DNS space. large portions of the DNS space.
[RFC5155] should be considered part of the DNS Security Document [RFC5155] is now considered part of the DNS Security Document Family
Family as described by [RFC4033], Section 10. as described by [RFC4033], Section 10.
Note that the algorithm identifiers defined in RFC5155 (DSA-NSEC3- Note that the algorithm identifiers defined in RFC5155 (DSA-NSEC3-
SHA1 and RSASHA1-NSEC3-SHA1) and RFC5702 (RSASHA256 and RSASHA512) SHA1 and RSASHA1-NSEC3-SHA1) and RFC5702 (RSASHA256 and RSASHA512)
signal that a zone MAY be using NSEC3, rather than NSEC. The zone signal that a zone might be using NSEC3, rather than NSEC. The zone
MAY be using either and validators supporting these algorithms MUST may be using either and validators supporting these algorithms MUST
support both NSEC3 and NSEC responses. support both NSEC3 and NSEC responses.
2.2. SHA-2 Support 2.2. SHA-2 Support
[RFC4509] describes the use of SHA-256 as a digest algorithm in [RFC4509] describes the use of SHA-256 as a digest algorithm in
Delegation Signer (DS) RRs. [RFC5702] describes the use of the Delegation Signer (DS) RRs. [RFC5702] describes the use of the
RSASHA256 and RSASHA512 algorithms in DNSKEY and RRSIG RRs. RSASHA256 and RSASHA512 algorithms in DNSKEY and RRSIG RRs.
Validator implementations are strongly encouraged to include support Validator implementations are strongly encouraged to include support
for these algorithms for DS, DNSKEY, and RRSIG records. for these algorithms for DS, DNSKEY, and RRSIG records.
Both [RFC4509] and [RFC5702] should also be considered part of the Both [RFC4509] and [RFC5702] are now considered part of the DNS
DNS Security Document Family as described by [RFC4033], Section 10. Security Document Family as described by [RFC4033], Section 10.
3. Scaling Concerns 3. Scaling Concerns
3.1. Implement a BAD cache 3.1. Implement a BAD cache
Section 4.7 of RFC4035 permits security-aware resolvers to implement Section 4.7 of RFC4035 permits security-aware resolvers to implement
a BAD cache. Because of scaling concerns not discussed in this a BAD cache. That guidance has changed: security-aware resolvers
document, that guidance has changed: security-aware resolvers SHOULD SHOULD implement a BAD cache as described in RFC4035.
implement a BAD cache as described in RFC4035.
This change in guidance is based on operational experience with
DNSSEC administrative errors leading to significant increases in DNS
traffic, with an accompanying realization that such events are more
likely and more damaging than originally supposed. An example of one
such event is documented in "Roll Over and Die" [Huston].
4. Security Concerns 4. Security Concerns
This section provides clarifications that, if overlooked, could lead This section provides clarifications that, if overlooked, could lead
to security issues. to security issues.
4.1. Clarifications on Non-Existence Proofs 4.1. Clarifications on Non-Existence Proofs
[RFC4035] Section 5.4 under-specifies the algorithm for checking non- [RFC4035] Section 5.4 under-specifies the algorithm for checking non-
existence proofs. In particular, the algorithm as presented would existence proofs. In particular, the algorithm as presented would
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When validating a response to QTYPE=*, all received RRsets that match When validating a response to QTYPE=*, all received RRsets that match
QNAME and QCLASS MUST be validated. If any of those RRsets fail QNAME and QCLASS MUST be validated. If any of those RRsets fail
validation, the answer is considered Bogus. If there are no RRsets validation, the answer is considered Bogus. If there are no RRsets
matching QNAME and QCLASS, that fact MUST be validated according to matching QNAME and QCLASS, that fact MUST be validated according to
the rules in [RFC4035] Section 5.4 (as clarified in this document). the rules in [RFC4035] Section 5.4 (as clarified in this document).
To be clear, a validator must not expect to receive all records at To be clear, a validator must not expect to receive all records at
the QNAME in response to QTYPE=*. the QNAME in response to QTYPE=*.
4.3. Check for CNAME 4.3. Check for CNAME
Section 5 of [RFC4035] says little about validating responses based Section 5 of [RFC4035] says nothing explicit about validating
on (or that should be based on) CNAMEs. When validating a NOERROR/ responses based on (or that should be based on) CNAMEs. When
NODATA response, validators MUST check the CNAME bit in the matching validating a NOERROR/NODATA response, validators MUST check the CNAME
NSEC or NSEC3 RR's type bitmap in addition to the bit for the query bit in the matching NSEC or NSEC3 RR's type bitmap in addition to the
type. bit for the query type.
Without this check, an attacker could successfully transform a Without this check, an attacker could successfully transform a
positive CNAME response into a NOERROR/NODATA response by (e.g.) positive CNAME response into a NOERROR/NODATA response by (e.g.)
simply stripping the CNAME RRset from the response. A naive simply stripping the CNAME RRset from the response. A naive
validator would then note that the QTYPE was not present in the validator would then note that the QTYPE was not present in the
matching NSEC/NSEC3 RR, but fail to notice that the CNAME bit was matching NSEC/NSEC3 RR, but fail to notice that the CNAME bit was
set, and thus the response should have been a positive CNAME set, and thus the response should have been a positive CNAME
response. response.
4.4. Insecure Delegation Proofs 4.4. Insecure Delegation Proofs
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If no private algorithms appear in the DS RRset, or if any supported If no private algorithms appear in the DS RRset, or if any supported
algorithm appears in the DS RRset, no special processing is needed. algorithm appears in the DS RRset, no special processing is needed.
Furthermore, if the validator implementation does not support any Furthermore, if the validator implementation does not support any
private algorithms, or only supports private algorithms using an private algorithms, or only supports private algorithms using an
algorithm number not present in the DS RRset, no special processing algorithm number not present in the DS RRset, no special processing
is needed. is needed.
In the remaining cases, the security status of the zone depends on In the remaining cases, the security status of the zone depends on
whether or not the resolver supports any of the private algorithms in whether or not the resolver supports any of the private algorithms in
use (provided that these DS records use supported hash functions, as use (provided that these DS records use supported message digest
discussed in Section 5.2). In these cases, the resolver MUST algorithms, as discussed in Section 5.2 of this document). In these
retrieve the corresponding DNSKEY for each private algorithm DS cases, the resolver MUST retrieve the corresponding DNSKEY for each
record and examine the public key field to determine the algorithm in private algorithm DS record and examine the public key field to
use. The security-aware resolver MUST ensure that the hash of the determine the algorithm in use. The security-aware resolver MUST
DNSKEY RR's owner name and RDATA matches the digest in the DS RR as ensure that the hash of the DNSKEY RR's owner name and RDATA matches
described in Section 5.2 of [RFC4035], authenticating the DNSKEY. If the digest in the DS RR as described in Section 5.2 of [RFC4035],
all of the retrieved and authenticated DNSKEY RRs use unknown or authenticating the DNSKEY. If all of the retrieved and authenticated
unsupported private algorithms, then the zone is treated as if it DNSKEY RRs use unknown or unsupported private algorithms, then the
were unsigned. zone is treated as if it were unsigned.
Note that if none of the private algorithm DS RRs can be securely Note that if none of the private algorithm DS RRs can be securely
matched to DNSKEY RRs and no other DS establishes that the zone is matched to DNSKEY RRs and no other DS establishes that the zone is
secure, the referral should be considered Bogus data as discussed in secure, the referral should be considered Bogus data as discussed in
[RFC4035]. [RFC4035].
This clarification facilitates the broader use of private algorithms, This clarification facilitates the broader use of private algorithms,
as suggested by [RFC4955]. as suggested by [RFC4955].
5.4. Caution About Local Policy and Multiple RRSIGs 5.4. Caution About Local Policy and Multiple RRSIGs
When multiple RRSIGs cover a given RRset, [RFC4035] Section 5.3.3 When multiple RRSIGs cover a given RRset, [RFC4035] Section 5.3.3
suggests that "the local resolver security policy determines whether suggests that "the local resolver security policy determines whether
the resolver also has to test these RRSIG RRs and how to resolve the resolver also has to test these RRSIG RRs and how to resolve
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[RFC4034] Appendix B.1 incorrectly defines the Key Tag field [RFC4034] Appendix B.1 incorrectly defines the Key Tag field
calculation for algorithm 1. It correctly says that the Key Tag is calculation for algorithm 1. It correctly says that the Key Tag is
the most significant 16 of the least significant 24 bits of the the most significant 16 of the least significant 24 bits of the
public key modulus. However, [RFC4034] then goes on to incorrectly public key modulus. However, [RFC4034] then goes on to incorrectly
say that this is 4th to last and 3rd to last octets of the public key say that this is 4th to last and 3rd to last octets of the public key
modulus. It is, in fact, the 3rd to last and 2nd to last octets. modulus. It is, in fact, the 3rd to last and 2nd to last octets.
5.6. Setting the DO Bit on Replies 5.6. Setting the DO Bit on Replies
As stated in [RFC3225], the DO bit of the query MUST be copied in the As stated in Section 3 of [RFC3225], the DO bit of the query MUST be
response. However, in order to interoperate with implementations copied in the response. However, in order to interoperate with
that ignore this rule on sending, resolvers MUST ignore the DO bit in implementations that ignore this rule on sending, resolvers MUST
responses. ignore the DO bit in responses.
5.7. Setting the AD Bit on Queries 5.7. Setting the AD Bit on Queries
The use of the AD bit in the query was previously undefined. This The semantics of the AD bit in the query were previously undefined.
document defines it as a signal indicating that the requester Section 4.6 of [RFC4035] instructed resolvers to always clear the AD
understands and is interested in the value of the AD bit in the bit when composing queries.
response. This allows a requestor to indicate that it understands
the AD bit without also requesting DNSSEC data via the DO bit. This document defines setting the AD bit in a query as a signal
indicating that the requester understands and is interested in the
value of the AD bit in the response. This allows a requestor to
indicate that it understands the AD bit without also requesting
DNSSEC data via the DO bit.
5.8. Setting the AD Bit on Replies 5.8. Setting the AD Bit on Replies
Section 3.2.3 of [RFC4035] describes under which conditions a Section 3.2.3 of [RFC4035] describes under which conditions a
validating resolver should set or clear the AD bit in a response. In validating resolver should set or clear the AD bit in a response. In
order to interoperate with legacy stub resolvers and middleboxes that order to interoperate with legacy stub resolvers and middleboxes that
neither understand nor ignore the AD bit, validating resolvers SHOULD neither understand nor ignore the AD bit, validating resolvers SHOULD
only set the AD bit when a response both meets the conditions listed only set the AD bit when a response both meets the conditions listed
in RFC 4035, section 3.2.3, and the request contained either a set DO in RFC 4035, section 3.2.3, and the request contained either a set DO
bit or a set AD bit. bit or a set AD bit.
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the CD bit was set on the incoming query or whether it has a trust the CD bit was set on the incoming query or whether it has a trust
anchor at or above the QNAME. anchor at or above the QNAME.
[RFC4035] is ambiguous about what to do when a cached response was [RFC4035] is ambiguous about what to do when a cached response was
obtained with the CD bit unset, a case that only arises when the obtained with the CD bit unset, a case that only arises when the
resolver chooses not to set the CD bit on all upstream queries, as resolver chooses not to set the CD bit on all upstream queries, as
specified above. In the typical case, no new query is required, nor specified above. In the typical case, no new query is required, nor
does the cache need to track the state of the CD bit used to make a does the cache need to track the state of the CD bit used to make a
given query. The problem arises when the cached response is a server given query. The problem arises when the cached response is a server
failure (RCODE 2), which may indicate that the requested data failed failure (RCODE 2), which may indicate that the requested data failed
DNSSEC validation at an upstream validating resolver. (RFC2308 DNSSEC validation at an upstream validating resolver. ([RFC2308]
permits caching of server failures for up to five minutes.) In these permits caching of server failures for up to five minutes.) In these
cases, a new query with the CD bit set is required. cases, a new query with the CD bit set is required.
Appendix B discusses more of the logic behind the recommendation Appendix B discusses more of the logic behind the recommendation
presented in this section. presented in this section.
5.10. Nested Trust Anchors 5.10. Nested Trust Anchors
A DNSSEC validator may be configured such that, for a given response, A DNSSEC validator may be configured such that, for a given response,
more than one trust anchor could be used to validate the chain of more than one trust anchor could be used to validate the chain of
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present in the DNSKEY RRset. It is possible to add algorithms at present in the DNSKEY RRset. It is possible to add algorithms at
the DNSKEY that aren't in the DS record, but not vice-versa. If the DNSKEY that aren't in the DS record, but not vice-versa. If
more than one key of the same algorithm is in the DNSKEY RRset, it more than one key of the same algorithm is in the DNSKEY RRset, it
is sufficient to sign each RRset with any subset of these DNSKEYs. is sufficient to sign each RRset with any subset of these DNSKEYs.
It is acceptable to sign some RRsets with one subset of keys (or It is acceptable to sign some RRsets with one subset of keys (or
key) and other RRsets with a different subset, so long as at least key) and other RRsets with a different subset, so long as at least
one DNSKEY of each algorithm is used to sign each RRset. one DNSKEY of each algorithm is used to sign each RRset.
Likewise, if there are DS records for multiple keys of the same Likewise, if there are DS records for multiple keys of the same
algorithm, any subset of those may appear in the DNSKEY RRset. algorithm, any subset of those may appear in the DNSKEY RRset.
Lastly, note that this a requirement at the server side, not the This requirement applies to servers, not validators. Validators
client side. Validators SHOULD accept any single valid path. They SHOULD accept any single valid path. They SHOULD NOT insist that all
SHOULD NOT insist that all algorithms signaled in the DS RRset work, algorithms signaled in the DS RRset work, and they MUST NOT insist
and they MUST NOT insist that all algorithms signaled in the DNSKEY that all algorithms signaled in the DNSKEY RRset work. A validator
RRset work. A validator MAY have a configuration option to perform a MAY have a configuration option to perform a signature completeness
signature completeness test to support troubleshooting. test to support troubleshooting.
5.12. Ignore Extra Signatures From Unknown Keys 5.12. Ignore Extra Signatures From Unknown Keys
Validating resolvers MUST disregard RRSIGs in a zone that do not Validating resolvers MUST disregard RRSIGs in a zone that do not
(currently) have a corresponding DNSKEY in the zone. Similarly, a (currently) have a corresponding DNSKEY in the zone. Similarly, a
validating resolver MUST disregard RRSIGs with algorithm types that validating resolver MUST disregard RRSIGs with algorithm types that
don't exist in the DNSKEY RRset. don't exist in the DNSKEY RRset.
Good key rollover and algorithm rollover practices, as discussed in Good key rollover and algorithm rollover practices, as discussed in
RFC4641 and its successor documents and as suggested by the rules in RFC4641 and its successor documents and as suggested by the rules in
the previous section, may require that such RRSIGs be present in a the previous section, may require that such RRSIGs be present in a
zone. zone.
6. Minor Corrections and Clarifications 6. Minor Corrections and Clarifications
6.1. Finding Zone Cuts 6.1. Finding Zone Cuts
Appendix C.8 of [RFC4035] discusses sending DS queries to the servers Appendix C.8 of [RFC4035] discusses sending DS queries to the servers
for a parent zone. To do that, a resolver may first need to apply for a parent zone but does not state how to find those servers.
special rules to discover what those servers are. Specific instructions can be found in Section 4.2 of [RFC4035].
As explained in Section 3.1.4.1 of [RFC4035], security-aware name
servers need to apply special processing rules to handle the DS RR,
and in some situations the resolver may also need to apply special
rules to locate the name servers for the parent zone if the resolver
does not already have the parent's NS RRset. Section 4.2 of
[RFC4035] specifies a mechanism for doing that.
6.2. Clarifications on DNSKEY Usage 6.2. Clarifications on DNSKEY Usage
It is possible to use different DNSKEYs to sign different subsets of It is possible to use different DNSKEYs to sign different subsets of
a zone, constrained only by the rules in Section 5.11. It is even a zone, constrained only by the rules in Section 5.11. It is even
possible to use a different DNSKEY for each RRset in a zone, subject possible to use a different DNSKEY for each RRset in a zone, subject
only to practical limits on the size of the DNSKEY RRset and the only to practical limits on the size of the DNSKEY RRset and the
above rules. However, be aware that there is no way to tell above rules. However, be aware that there is no way to tell
resolvers what a particular DNSKEY is supposed to be used for -- any resolvers what a particular DNSKEY is supposed to be used for -- any
DNSKEY in the zone's signed DNSKEY RRset may be used to authenticate DNSKEY in the zone's signed DNSKEY RRset may be used to authenticate
skipping to change at page 14, line 43 skipping to change at page 15, line 7
[RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
Security (DNSSEC) Hashed Authenticated Denial of Security (DNSSEC) Hashed Authenticated Denial of
Existence", RFC 5155, March 2008. Existence", RFC 5155, March 2008.
[RFC5702] Jansen, J., "Use of SHA-2 Algorithms with RSA in DNSKEY [RFC5702] Jansen, J., "Use of SHA-2 Algorithms with RSA in DNSKEY
and RRSIG Resource Records for DNSSEC", RFC 5702, and RRSIG Resource Records for DNSSEC", RFC 5702,
October 2009. October 2009.
9.2. Informative References 9.2. Informative References
[Huston] Michaelson, G., Wallstrom, P., Arends, R., and G. Huston,
"Roll Over and Die?", February 2010.
[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, March 1998.
[RFC3755] Weiler, S., "Legacy Resolver Compatibility for Delegation [RFC3755] Weiler, S., "Legacy Resolver Compatibility for Delegation
Signer (DS)", RFC 3755, May 2004. Signer (DS)", RFC 3755, May 2004.
[RFC4641] Kolkman, O. and R. Gieben, "DNSSEC Operational Practices", [RFC4641] Kolkman, O. and R. Gieben, "DNSSEC Operational Practices",
RFC 4641, September 2006. RFC 4641, September 2006.
[RFC4955] Blacka, D., "DNS Security (DNSSEC) Experiments", RFC 4955, [RFC4955] Blacka, D., "DNS Security (DNSSEC) Experiments", RFC 4955,
July 2007. July 2007.
[RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC) [RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC)
skipping to change at page 15, line 15 skipping to change at page 15, line 34
[RFC5074] Weiler, S., "DNSSEC Lookaside Validation (DLV)", RFC 5074, [RFC5074] Weiler, S., "DNSSEC Lookaside Validation (DLV)", RFC 5074,
November 2007. November 2007.
Appendix A. Acknowledgments Appendix A. Acknowledgments
The editors would like the thank Rob Austein for his previous work as The editors would like the thank Rob Austein for his previous work as
an editor of this document. an editor of this document.
The editors are extremely grateful to those who, in addition to The editors are extremely grateful to those who, in addition to
finding errors and omissions in the DNSSECbis document set, have finding errors and omissions in the DNSSEC document set, have
provided text suitable for inclusion in this document. provided text suitable for inclusion in this document.
The lack of specificity about handling private algorithms, as The lack of specificity about handling private algorithms, as
described in Section 5.3, and the lack of specificity in handling ANY described in Section 5.3, and the lack of specificity in handling ANY
queries, as described in Section 4.2, were discovered by David queries, as described in Section 4.2, were discovered by David
Blacka. Blacka.
The error in algorithm 1 key tag calculation, as described in The error in algorithm 1 key tag calculation, as described in
Section 5.5, was found by Abhijit Hayatnagarkar. Donald Eastlake Section 5.5, was found by Abhijit Hayatnagarkar. Donald Eastlake
contributed text for Section 5.5. contributed text for Section 5.5.
skipping to change at page 15, line 42 skipping to change at page 16, line 14
Text on the mandatory algorithm rules was derived from suggestions by Text on the mandatory algorithm rules was derived from suggestions by
Matthijs Mekking and Ed Lewis. Matthijs Mekking and Ed Lewis.
The CD bit logic was analyzed in depth by David Blacka, Olafur The CD bit logic was analyzed in depth by David Blacka, Olafur
Gudmundsson, Mike St. Johns, and Andrew Sullivan. Gudmundsson, Mike St. Johns, and Andrew Sullivan.
The editors would like to thank Alfred Hoenes, Ed Lewis, Danny Mayer, The editors would like to thank Alfred Hoenes, Ed Lewis, Danny Mayer,
Olafur Gudmundsson, Suzanne Woolf, Rickard Bellgrim, Mike St. Johns, Olafur Gudmundsson, Suzanne Woolf, Rickard Bellgrim, Mike St. Johns,
Mark Andrews, Wouter Wijngaards, Matthijs Mekking, Andrew Sullivan, Mark Andrews, Wouter Wijngaards, Matthijs Mekking, Andrew Sullivan,
and Scott Rose for their substantive comments on the text of this Jeremy Reed, Paul Hoffman, Mohan Parthasarathy, Florian Weimer,
Warren Kumari and Scott Rose for their contributions to this
document. document.
Appendix B. Discussion of Setting the CD Bit Appendix B. Discussion of Setting the CD Bit
RFC 4035 may be read as relying on the implicit assumption that there [RFC4035] may be read as relying on the implicit assumption that
is at most one validating system between the stub resolver and the there is at most one validating system between the stub resolver and
authoritative server for a given zone. It is entirely possible, the authoritative server for a given zone. It is entirely possible,
however, for more than one validator to exist between a stub resolver however, for more than one validator to exist between a stub resolver
and an authoritative server. If these different validators have and an authoritative server. If these different validators have
disjoint trust anchors configured, then it is possible that each disjoint trust anchors configured, then it is possible that each
would be able to validate some portion of the DNS tree but neither is would be able to validate some portion of the DNS tree but neither is
able to validate all of it. Accordingly, it might be argued that it able to validate all of it. Accordingly, it might be argued that it
is desirable not to set the CD bit on upstream queries, because that is desirable not to set the CD bit on upstream queries, because that
allows for maximal validation. allows for maximal validation.
In section Section 5.9 of this document, it is recommended to set the In section Section 5.9 of this document, it is recommended to set the
CD bit on an upstream query even when the incoming query arrives with CD bit on an upstream query even when the incoming query arrives with
skipping to change at page 16, line 40 skipping to change at page 17, line 11
as local policy or from the API in the case of a stub). The second as local policy or from the API in the case of a stub). The second
column indicates whether the query needs to be forwarded for column indicates whether the query needs to be forwarded for
resolution (F) or can be satisfied from a local cache (C). The third resolution (F) or can be satisfied from a local cache (C). The third
column is a line number, so that it can be referred to later in the column is a line number, so that it can be referred to later in the
table. The fourth column indicates any relevant conditions at the table. The fourth column indicates any relevant conditions at the
resolver: whether the resolver has a covering trust anchor and so on. resolver: whether the resolver has a covering trust anchor and so on.
If there are no parameters here, the column is empty. The fifth and If there are no parameters here, the column is empty. The fifth and
final column indicates what action the resolver takes. final column indicates what action the resolver takes.
The tables differentiate between "cached data" and "cached RCODE=2". The tables differentiate between "cached data" and "cached RCODE=2".
This is a shorthand; the point is that one has to treat RCODE=2 as This is a shorthand; the point is that one has to treat RCODE=2
special, because it might indicate a validation failure somewhere (server failure) as special, because it might indicate a validation
upstream. The distinction is really between "cached RCODE=2" and failure somewhere upstream. The distinction is really between
"cached everything else". "cached RCODE=2" and "cached everything else".
The tables are probably easiest to think of in terms of describing The tables are probably easiest to think of in terms of describing
what happens when a stub resolver sends a query to an intermediate what happens when a stub resolver sends a query to an intermediate
resolver, but they are perfectly general and can be applied to any resolver, but they are perfectly general and can be applied to any
validating resolver. validating resolver.
Model 1: "always set" Model 1: "always set"
This model is so named because the validating resolver sets the CD This model is so named because the validating resolver sets the CD
bit on queries it makes regardless of whether it has a covering trust bit on queries it makes regardless of whether it has a covering trust
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